Evidence for subduction-related metamorphism on the coast of Scotland during the Mesoarchean-to-Neoarchean transition.

Plate tectonics are a fundamental part of the Earth's geological system, providing a means by which the planet is able to shed heat from its interior. Under this system crustal deformation and magmatism are generally confined to the margins of the lithospheric plates, with the otherwise stiff plates are weakened, softened, and recycled into the the Earth's mantle along subduction zones, while new crustal material is formed at seafloor spreading zones. As far as we know, plate tectonics are only found on Earth, which has led to speculation that the process may have been essential for the creation of conditions for life, or at least complex life. As such when and how the plate tectonics came about is of great interest to scientists. 

Potential dates for the origin of plate tectonics range from the Hadean Eon, more than four billion years ago, to the early Neoproterozoic, less than one billion years ago. However, finding evidence to support such hypotheses has proven difficult. The ideal geological evidence for plate tectonics would be metamorphic structures such as eclogites (associated with the shallow subduction of oceanic crust) or blueschists (associated with the deep subduction of crustal material) formed under a low temperature/pressure (thermobaric) regime, ideally less than 375 °C/GPa (apparently similar rocks formed under higher tthermobaric regimes are presumed to have formed due to different conditions). The oldest known ecglogites are found in Cameroon and the Democratic Republic of Congo, and are about 2.1 billion years old, while the oldest known blueschists are found in China, and are only 750-800 million years old.

Thus if plate tectonics was occurring during the Archaean (between 4 and 2.5 billion years ago), then there is a surprising lack of evidence for it.

In a paper published in the journal Geology on 1 January 2026, Meiyun Huang of the State Key Laboratory of Lithospheric and Environmental Coevolution at the Institute of Geology and Geophysics of the Chinese Academy of Sciences, and the College of Earth and Planetary Sciences at the University of the Chinese Academy of Sciences, Shujuan Jiao, also of the State Key Laboratory of Lithospheric and Environmental Coevolution at the Institute of Geology and Geophysics of the Chinese Academy of Sciences, Tim Johnson, Chris Clark, and Jie Yu, of the Curtin Frontiers Institute for Geoscience Solutions at Curtin University, Guangyu Huang, again of the State Key Laboratory of Lithospheric and Environmental Coevolution at the Institute of Geology and Geophysics of the Chinese Academy of Sciences, and Jinghui Guo, once again of the State Key Laboratory of Lithospheric and Environmental Coevolution at the Institute of Geology and Geophysics of the Chinese Academy of Sciences, and the College of Earth and Planetary Sciences at the University of the Chinese Academy of Sciences, present of a study of a section of the Lewisian Gneiss Complex on the northwest coast of Scotland, which they date to about 2.8 billion years ago, and which they suggest was formed under temperature and pressure conditions consistent with a subductive plate margin setting.

Gneisses are course-grained metamorphic rocks which show distinct banding, but which do not tend to cleave along those bands. They typically form at temperatures in excess of 300°C and pressures of between 0.2 and 1.5 GPa, and can be derived from both igneous and sedimentary source rocks. The Lewisian Gneiss Complex is a grey gneiss terrane which has yielded magmatic ages of between 3.1 and 2.8 billion years. This includes layers of ultramafic–mafic rock interlayered with a layered garnet-biotite rock known as the brown gneiss, which is thought to have originally been of sedimentary or volcanosedimentary origin.

Rocks from the Lewisian Gneiss Complex on the Scottish mainland have previously been shown to date from the Neoarchean (2.8-2.5 billion years ago) and to have been formed at temperatures in excess of 900°C, although the pressure at which these rocks formed has been harder to determine, with estimates for peak pressure ranging from about 0.8 GPa to more than 1.5 GPa. There are also two proposed interpretations on the timeline over which these rocks formed, with one proposing two distinct metamorphic episodes, one between 2.8 and 2.7 billion years ago, and the other at about 2.5 billion years ago, and the other proposing a single extended metamorphic event lasting about 200 million years. 

(A) Simplified geological map of the Lewisian Gneiss Complex in northwest Scotland. Inset shows location of the Complex. (B) Geological map of the Scourie area in the Assynt terrane showing the location of the studied sample. (C) Outcrop of the studied sample (SC18-02; migmatitic aluminosilicate-bearing metasedimentary rock; 58°21′45″N, 5°09′49″W). Huang et al. (2026).

One possible interpretation is that the Garnet-rich fragments found within the ultramafic–mafic bodies represent retrogressed eclogites (metamorphic rocks which have recrystallised into their current form in response to the lowering of the temperature and pressure from the conditions in which they originally formed) which may have been heated to temperatures as high as 1040–1060°C and exposed to pressures as high as 2.2-2.4 GPa around 2.5 billion years ago, which would imply deep subduction during the late Neoarchaean. An alternative possibility is that they represent xenoliths, fragments of pre-existing rock which became incorporated into  surrounding rock during the emplacement of a volcanic basalt or gabro.

Huang et al. analysed samples taken from a migmatitic aluminosilicate-bearing metasedimentary rock within the Lewisian Gneiss Complex, looking at the mineral phases formed by oxides of sodium, calcium, potassium, iron, magnesium, aluminium, silicon and titanium, all of which from different minerals under different temperature and pressure conditions, as well as examining the whole rock composition, occurrence of zirconium within the mineral rutile (which is temperature dependent), and the silica content of the mineral phengite, which is dependent on the pressure at which it formed.

The specimen is a migmatic 'brown gneiss' comprising brown layers rich in garnet and biotite, and white layers which are composed largely of feldspar. Examined in thin section, the material is about 50% plagioclase by volume, with about 18% garnet, 10% biotite, 10% alumminosilicates, 8% potassium feldspar, and small amounts of corundum, spinel, white mica, zircon, rutile, ilmenite, and pyrite.

(A) Distribution of minerals in the sample SC18-02 from the Lewisian Gneiss Complex in northwest Scotland. Alm, almandine; Pyr, pyrope. (B) Detailed Tescan Integrated Mineral Analyzer image showing mineral inclusions in garnet. Rt, rutile; Py, pyrite; Ky, kyanite; Phn, phengite; Crn, corundum; Spl, spinel. (C) Phengite, rutile, and kyanite inclusions within garnet (Grt). (D) Quartz and kyanite inclusions in garnet cores. (E) Spinel, corundum, and kyanite surrounded by biotite (Bt) in garnet. (F) Kyanite, pyrite, and biotite in the garnet. Pl, plagioclase. (G) Kyanite inclusions in garnet cores and sillimanite (Sil) inclusions in garnet rims. (H) An inclusion in corundum showing rutile replaced by ilmenite (Ilm). Huang et al. (2026).

Garnet grains within the sample were up to 12 mm in diameter, and rich in inclusions, including isolated and polymineralic spinel, white mica, corundum, rutile, ilmenite, plagioclase, potassium-feldspar, quartz, biotite, and/or aluminosilicate. White mica, which was largely confined to inclusions within garnet, had a high silicon content, with most grains being classifiable as phengite (high silicone mica). Kyanite occured as isolated inclusions or together with corundum, rutile, spinel, and/or biotite in poly￾mineralic inclusions concentrated within garnet cores. Sillimanite was found in both the rims of garnets and the surrounding matrix, with no preferential orientation. Rare quartz grains were found within the cores of garnets, although they were otherwise largely absent. Corundum primarily occurs in the matrix in contact with sillimanite, spinel, and rutile, where it is commonly replaced at its margins by biotite, and rarely as polymineralic inclusions with spinel and kyanite within garnet. Rutile is present both as inclusions and within the matrix.Rarely, rutile inclusions are partially replaced by ilmenite.

Biotite found as inclusions within garnets has a different composition from biotite within the surrounding matrix, containing a lower proportion of both magnesium and titanium oxide. Spinel grains within the matrix contain slightly more zinc than those within garnet inclusions. Within garnet grains, these spinel inclusions tend to be associated with kyanite and corundum, and many are partially replaced by biotite. Spinel grains in the matrix are typically in contact with corundum and are commonly surrounded by sillimanite or biotite. However, the high zinc content of these spinel grains makes it hard to assess the temperature and pressure under which they formed, so they were excluded from the remainder of the study.

The presence of isolated inclusions of phengite, kyanite, rutile, quartz, and polymineralic inclusions including corundum, spinel, kyanite, rutile, phengite, and/or biotite within garnets is considered by Huang et al. as indicative of two phases of high-pressure metamorphism, with minerals formed by the first phase partially overwritten by the second. The presence of inclusions of sillimanite and plagioclase within the rims of garnet grains, as well as within the matrix assemblage, are taken as evidence for two later phases of high temperature metamorphism.

In order to determine the temperature and pressure conditions during the first phase of metamorphism, Huang et al. attempted to develop a phase equilibrium model for the whole rock. The presence of phengite, kyanite, and rutile within a quartz matrix suggests high pressure/low temperature conditions, with the silicon content of the phengites suggesting a pressure in excess of 2.4 GPa. Huang et al. estimate that during this first phase, temperatures reached 580-660°C and pressures between 1.5 and 2.5 GPa, giving a thermobaric ratio of between 230 °C/GPa (580 °C/2.5 GPa) and 440 °C/GPa (660 °C/1.5 GPa).

A second phase is deduced from the presence of an association of the minerals corundum, kyanite, biotite, plagioclase, and rutile/ilmenite. This association can only form at temperatures of between 830 and 880°C and pressures of between 1.1 and 1.7 GPa, consistent with the temperature deduced from the concentration of zirconium in rutile, approximately 740–960°C. This would correspond to a thermobaric ratio of between 490°C/GPa (830°C/1.7 GPa) and 800°C/GPa (880°C/1.1 GPa).

Another association present, comprising corundum, mesoperthite/antiperthite, and rutile, suggests a phase with higher temperatures but lower pressure. This association probably formed at a temperature of between 880 and 1000°C, but at a pressure of only 0.9.1.4 GPa. This is corroborated by zirconium-in-rutile data for this association, which suggests a formation temperature of about 800 to 1000°C. This would correspond to a thermobaric ratio of between 630°C/GPa (880°C/1.4 GPa) and 1110°C/GPa (1000°C/0.9 GPa). 

Huang et al. were able to obtain a lutetium–hafnium from a garnet within the sample associated with the high pressure phase of 2.81 billion years (the  isotope lutetium¹⁷⁶ decays to hafnium¹⁷⁶ at a predictable rate, with a half life of 37.1 billion years, enabling this system to be used for dating minerals which would not have contained hafnium at their time of formation).

Previous studies of the Lewisian Gneiss Complex have suggested formation under high pressure conditions, but not a precise age for the rocks nor any insight into the pressure-temperature relationship under which it formed. Huang et al. identify a low temperature/pressure event at about 2.8 billion years ago, associated with the formation of phengite, rutile, kyanite, and quartz inclusions within garnet. During this phase, temperatures reached 580–660°C and pressures reached 1.5–2.5 GPa, corresponding to thermobaric ratios of 230–440°C/GPa. This is consistent with the conditions associated with recent subductive margins where rock metamorphism occurs, but lower than is typical for Archean metamorphic terranes, which generally have thermobaric ratios of over 500°C/GPa.

A second phase is identified based upon the kyanite, biotite, and corundum inclusion complex, thought to have formed under conditions where the pressure had fallen by about 0.7 GPa, but the temperature had risen by about 200°C. This is consistent with the orogenic relaxation stage of a collisional cycle, where the horizontal movement of one plate into another has caused an episode of uplift, but that this horizontal movement has now stopped, causing the pressure within the rocks to slowly relax. This differs from the predominant system within Archean metamorphic environments, where the temperatures and pressures appear to have continued to climb, reaching levels far higher than seen in recent settings.

The low thermobaric ratios reported by Huang et al. are the lowest recorded for any Archean setting, and the only known example of low temperature/pressure metamorphism from the Archean. They propose the rocks or the Lewisian Gneiss Complex may preserve a record of a transition from a pre-plate tectonic regime to one in which subduction is beginning to occur, in a process that would eventually develop into plate tectonics. It has previously been suggested that this transition may have occurred during the Mesoarchean (between about 3.2 and 2.8 billion years ago) on the margins of the North Atlantic craton, as a result of the thickening and strengthening of the lithosphere, and long-term cooling of the mantle.

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Reassessing the contribution of the Deccan Traps volcanism to the End Cretaceous Extinction.

During the Phanerozoic Eon the Earth has suffered a series of major extinction events almost all of which are considered to have been triggered by continental flood basalt emplacement episodes, which released vast amounts of toxic gasses into the atmosphere. The exception to this is the End Cretaceous Extinction, which is largely considered to have been triggered by the impact of an extra-terrestrial object into what is now the Yucatán Peninsula of Mexico. 

While this is a compelling story, it has faced a number of challenges from rival theories, the most notable of which is that there was a significant outpouring of flood basalts at the End of the Cretaceous, leading to the emplacement of the Deccan Traps Igneous Province in India, This, combined with the fact that we have now identified a number of other large impacts in the Phanerozoic rock record, none of which seem to have been associated with extinction events, presents a serious challenge to the Chicxulub Impact Theory. However, studies of the Deccan Traps Igneous Province have suggested that the majority of the basalt-emplacement happened slightly after the extinction event, implying that it cannot have been the cause. 

In a paper published in the journal GSA Bulletin on 5 November 2025, Vivek Kale of the Advanced Center for Water Resources Development and Management, Devdutt Upasani and Madhu Rajput of the Department of Geology at Fergusson College, Gauri Dole of the Department of Environmental Science at Savitribai Phule Pune University, and Shilpa Patil Pillai of the Department of Earth and Climate Science at the Indian Institute of Science Education and Research Pune, present a re-evaluation of the contribution of the Deccan Traps volcanism to the End Cretaceous Extinction, based upon new geochronological studies of the Deccan Traps Igneous Province.

The Deccan Traps Igneous Province covers about 50 000 km² of Western and Central India, and extends westward beneath the Arabian Sea, where it is thought to cover a further area of about 38 000 km². It was produced by shield-volcano-like eruptions, which produced a series of radially overstepping basalt formations. Studies carried out in the 1980s suggested that the onset of the Deccan Traps volcanism coincided with the End Cretaceous Extinction Event, leading the majority of the geological community to conclude that it could not be responsible for the event, and even some suggestions that the volcanism might have been caused in some way by the Chicxulub Impact.

Geographic sectors of the present-day exposures of Deccan volcanic deposits of central and western India (shaded green) on the backdrop of different cratonic blocks (in shades of pink and named in red) of the Indian Peninsular Shield. The named alignments of deep-crustal tectonic zones from this shield, with Precambrian heritage and late Mesozoic to Cenozoic reactivation are depicted with parallel hatching in their respective strike directions.  Locations of sampled offshore basaltic flows with affinities to the Reunion hotspot are shown with green dots in the offshore areas, along with key ocean floor features of the Arabian Sea off the western coast of India. The locations of Late Cretaceous magmatic activity in the Indian Peninsula (early magmatics) are shown as red stars. The maximum projected extent of the Deccan continental flood basalt is shown with a green dotted line. Kale et al. (2025).

However, much of this earlier work was based upon chemostratigraphic correlation between different parts of the Deccan Traps, something which is now considered unreliable as it has been demonstrated that the Traps are in fact made up of a series of subprovinces, the Western, Satpura, Central, Malwa, Mandla, and Saurashtra, each with their own distinct volcanic history. Thus the work carried out in the 1980s appears to have been valid for parts of the Western Subprovince, but not necessarily for any of the other subprovinces.

Kale et al. combined chemostratigraphic methods with palaeomagnetism and studies of key fossils from sedimentary beds interspaced with the volcanic layers, with the aim of understanding the timing and eruptive history of each subprovince of the Deccan Traps. To achieve a high level of confidence, they carried out extensive fieldwork, preparing more than eighty stratigraphic logs. 

Subprovinces of the Deccan Volcanic Province of India (in different shades of green) and the indicative locations of geochronological sections and fossil-bearing intertrappean sediments used in the age assignments of different stratigraphic units in this study. Abbreviation: KPgB, Cretaceous-Paleogene boundary. Kale et al. (2025).

Kale et al. recognised three phases of volcanic activity within the Deccan Traps deposits, phases which were consistently recovered using chemostratigraphic and palaeomagnetic methods. These were the Early Magmatic Phase, the Main Flood Basalt Eruptions, and the Late Volcanic Phase. Deposits associated with the Early Magmatic Phase outcrops in the Saurashtra Subprovince, along the Narmada Son Lineament Zone between the Bastar and Dharwar cratons, and comprises mixed mantle-derived volcanic sediments more than 67.0 million years old. The Late Volcanic Phase comprises intrusive volcanic material inserted into the main deposits after they had been emplaced. These outcrop in a small coastal strip around Mumbai, and have also been found offshore in the Laxmi Basin of the Arabian Sea. This Late Volcanic Phase material is about 63.0 million years old, making them coeval with the separation of the Seychelles from the Western Margin of the Indian Plate. There may also be some material associated with the Late Volcanic Phase at the top of the Amarkantak Group.

The Main phase therefore accounts for about 90% of the material which makes up the Deccan Traps Igneous Province. Furthermore, most of this material appears to have been produced within a period of less than 1 million years within Chron C29r, a period between two reversals of the Earth's magnetic field, which lasted from about 66.43 million years ago to about 65.8 million years ago (therefore spanning the current accepted boundary between the Cretaceous and the Tertiary, at 66.04 million years ago), and the following Chron C29n, which lasted from about 65.8 million years ago to about 64.745 million years ago.

The Western Subprovince hosts the thickest and (probably the) most continuous deposits of the Deccan Traps, as well as the largest single outcrop, at Kalsubai Peak, where a 1642 m continuous stack of basalts is exposed, and continues some way beneath the ground. These deposits are assigned to the Sahyadri Group, which is divided into the Wai, Lonavala and Kalsubai subgroups, with about 3000 m depth of basalt produced within chrons C29r and C29n. These deposits show few fossiliferous sedimentary layers, with scattered 'interflow horizons' (horizons marking time-gaps between episodes of basalt-deposition) of limited lateral extent, suggesting that gaps between eruptive episodes were localised and brief.

Kale et al.'s revised study places the boundary between chrons C29r and C29n at the base of the Mahabaleshwar Formation from the Wai Subgroup of the Sahyadri Group. This is marked by the widespread presence of giant-phenocryst basalt. The Purandargarh Formation, which underlies the Mahabaleshwar Formation, is calculated to date from the earliest part of the Danian Stage of the Palaeocene, i.e. immediately after the Cretaceous-Tertiary boundary. 

The Poladpur Lavas, which underlie the Purandargarh Formation, have been suggested to be of latest Cretaceous origin, on the basis of dates obtained from zircons, but Kale et al. reject this, on the basis that zircons can survive at very high temperatures and are often reworked within volcanic deposits, and also classify the Poladpur Lavas as earliest Danian. Based upon a sediment layer with key Mammalian fossils exposed at Naskal in Telangana State, Kale et al. estimate that the lowest 50 m of the Poladpur Lavas were erupted within 100 000 years of the Cretaceous-Tertiary boundary. The underlying Lonavala and Kalsubai subgroups, therefore, must have erupted entirely within the Latest Cretaceous. 

The Satpura Subprovince forms the second deepest sequence of the Deccan Traps, and has been divided into six formations, with two of these formations containing giant-phenocryst basalts, something which has led to the correlation of the entire subprovince with the Wei Subgroup of the Sahyadri Group. Kale et al. reject this analysis, assigning the entire sequence to the Maastrichtian (Latest Cretaceous) on the basis of fossil inclusions within sedimentary layers.

The Central Subprovince forms the northeastern part of the Deccan Plateau, with a diffuse boundary with the Western subprovince. The lavas of this the Mahur Formation, which form the base of this sequence, also contain a distinctive giant-phenocryst basalt layer, which had led to them being comparied to the Wei Subgroup, but Kale et al. again reject this, assigning this formation to the Maastrichtian on the basis of fossil inclusions. Instead, they place the Cretaceous-Tertiary boundary at the top of the Ajanta Formation, which overlies the Mahur Formation, on the basis of palynological evidence (fossil pollen). This places the final three formations of the Central Subprovince, the Chikhil, the Buldhana, and the Karanja, within the Early Danian.

The Malwa Subprovince sequence has also previously been assigned to the Wei Subgroup, although in this case because it contains a normal-reverse-normal palaeomagnetic sequence, which was thought to mark the Danian chrons C29r and C29n. However, a revised dating sequence suggests that this sequence contains some of the oldest rocks of the Deccan Traps, with only the final, Singachori Formation being Danian in age, while all the lower formations are Maastrichtian, based upon fossil evidence. 

The Mandla Subprovince has proven much harder to establish a chronological sequence for, but appears to contain both some of the oldest and some of the youngest lavas of the Deccan Traps. However, the lowermost Mandla Formation and unclassified underlying beds contain sedimentary layers which produce fossils of Maastrichtian age, while the higher beds of the Multai, Amarwara, Khamla/Khampla, and Kuleru formations contain magnetic reversals and fossils of Palaeocene origin.

Stratigraphic logs of the subprovinces of Deccan Volcanic Province of India depicting dominant morphological types with the approximate position of the 66.05 million-year-old Cretaceous-Palaeogene boundary (red dashed line). In the Sahyadri Group, the cumulative stratigraphic thickness is used, as there is a well-demonstrated southward and southeastward overstepping of the older formations by younger ones. All other logs are plotted for maximum thickness. The available palaeomagnetic orientations (dark, normal; grey, mixed; and white, reverse) are depicted. Abbreviations: BMBY, Bombay Subgroup; LNVL, Lonavala Subgroup; GPB, giant phenocryst basalt. Kale et al. (2025).

The Saurashtra Subprovince is the only part of the Deccan Traps where an iridium layer has been discovered within the Anjur Section, and used as an identifier for the Cretaceous-Tertiary boundary. However, the deposits which host this layer have been shown to belong to Magnetochron C28r, making them too young to be related to the End of the Cretaceous. Other deposits, from layers beneath those exposed at Anjur, have produced Dinosaur bones and nests, as well as other clearly Cretaceous fossils, indicating a Maastrichtian origin. These deposits are also cut through by a series of dykes which have yielded ages of between 66.06 and 62.4 million years. Given the lack of a clear chronological sequence for this group, Kale et al. do not attempt to calculate its full sequence, but for the sake of modelling assume that it contains 5% of the total volume of the Deccan Traps lavas, and that this can be divided equally between the Danian and the Maastrichtian.

Kale et al. also assume that 75% of the Deccan Traps basalts were erupted on land, with about 25% offshore. This gives a total volume of about 1.8 million km² of erupted lava (higher than any previous estimate) with the terrestrial deposits produced during the Maastrichtian and the Danian, while the offshore deposits are assumed to be entirely Danian in origin.

While Kale et al. produce a higher total volume estimate for the Deccan Traps Volcanism than previous studies, this is not a major increase, with most previous estimates being of a similar order of magnitude. However, by separating the Deccan Traps into a number of subprovinces and studying those individually, they do significantly re-estimate the amount of volcanism that occurred before the Cretaceous-Tertiary boundary.

Kale et al. estimate that early magmatism associated with the Deccan Traps were widely spaced across India in the Late Cretaceous, and probably associated with the Reunion Hotspot passing under part of the Indian Plate. Cainozoic Late Phase Magmatism occurred largely on the spreading western edge of the Indian Plate, and the associated shallow submarine shelf, with much of the material produced probably being better viewed as ocean/island basalt rather than continental flood basalt.

Between these two events, the Main Flood Basalt Eruptions produced about 1.2 million cubic kilometres of continental flood basalt (i.e. about 70% of the total volume of the Deccan Traps) within the last 300 000 years of the Cretaceous. This equates to an eruption rate of about 1000 km³ per year of basalt being produced during the Cretaceous portion of Chron C29r, falling to about 300 km³ per year during the Palaeocene portion of the chron. 

The lethal impacts of flood basalts themselves are rather limited, with most Animals able to out-walk all but the fastest lava flows. Ash clouds associated with such eruptions are more dangerous, potentially smothering plant life far from the source. However, the real threat comes from the gasses such events produce, with large volumes of carbon dioxide, carbon monoxide, gaseous sulphur, chlorine, fluorine, mercury, and other potent toxins into the atmosphere. 

Kale et al. estimate that the Main Flood Basalt Eruptions of the Deccan Traps would have produced over 6000 gigatonnes of carbon emissions, less than that produced by the Siberian Traps Basalts (associated with the End Permian Extinction) or the Central Atlantic Magmatic Province (associated with the End Triassic Extinction). However, around 4200 gigatonnes of this would have been produced within the last 300 000 years of the Maastrichtian (i.e. immediately before the Cretaceous-Tertiary boundary) with the remaining 1800 gigatonnes released over a longer period of time.

Fuethermore, Kale et al. conservatively estimate that 1300 gigatonnes of sulphur was released into the atmosphere during the Maastrichtian portion of Chron C29r, with about 200 gigatonnes being released during the Danian portion. 

High mercury levels have been observed around the world towards the end of the Maastrichtian, something which has previously been linked to the onset of the Deccan Traps Volcanism, although why mercury should peak at this point was unclear. Kale et al.'s results suggest that this spike did in fact coincide with the main phase of Deccan Traps volcanism, although they do not attempt to calculate the volumes of mercury produced. Estimates of the volumes of chlorine and fluorine produced by the eruptions were also beyond the scope of the study, although these are also likely to have been substantial.

Emissions of carbon dioxide from volcanic sources are typically enriched in the isotope carbon¹³ compared to other sources, something which is often used to track volcanic activity in the sediment record. Kale et al. examined the ratios of carbon¹³ in terminal Cretaceous sequences from the South Atlantic, North Atlantic, and Spain (areas which would have been far from India at the time), and found a significant spike in carbon¹³ levels immediately before the Cretaceous-Tertiary boundary, something they do not believe is coincidental. They also not fluctuations in other isotopic proxies which begin 600 000-800 000 years before the boundary, approximately the time frame for the onset of the Satpura, Malwa, and Mandla subprovince eruptions.

Based upon this, Kale et al. conclude that the majority of the Deccan Traps Flood Basalts were produced in a short period of time in the terminal Cretaceous, causing an environmental collapse which was the main driver of the End Cretaceous Extinction. The Chicxulub Impact could potentially have caused a single large mortality event against this backdrop, but is unlikely to have been the main cause of the extinction. The delayed recovery of the biosphere seen in the Early Danian is unlikely to have been caused by a 'nuclear winter' triggered by the impact, but instead probably relates to the ongoing, albeit reduced, volcanic emissions coming from the Deccan Traps at this time.

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Looking for a relationship between Australasian tektites and BeLaU spherules.

On 8 January 2014, an object later known as CNEOS 2014-01-08 impacted the Earth off the north coast of Papua New Guinea. Based upon the speed and trajectory of this object, it was suggested by some planetary scientists that its original trajectory had been incompatible with a Solar System object, and that therefore it may have originated outside our Solar System. While this was never universally accepted, the potential for scientists to gain direct access to fragments of an extra-Solar object was sufficient that in 2023 an expedition was sent to the area to collect samples.

The calculated impact site of object CNEOS 2014-01-08. Loeb (2022).

This expedition recovered over 800 particles of potential extraterrestrial origin, about 80% of which were subsequently identified as pieces of S-type, I-type, and G-type chondritic meteorite (such particles are not unusual in deep-marine sediments, where the absence of much input from land means that the tiny amounts of meteoric material which fall all over the Earth can build up over time to form a detectable portion of local sediments). The remaining particles appeared to belong to an entirely new type of meteoric material, which were named D-type particles, which had an unusually low ration of magnesium to iron compared to other meteoric material. Within these D-type particles, a small subset was identified which were also enriched in the elements barium, lanthanum, and uranium, a highly unusual combination of elements, furthering speculation that these objects were of genuinely unique origin.

Back-scattered Electron Microscope images of differentiated spherules from each of the differentiated (D-type) spherule classifications: (a) D-type low strontium, high silicone (IS11M2–2; porphyritic) (b) D-type high strontium, high silicone (IS19M-14) (c) D-type, high silicone (17NMAG-5; vitric) (d) D-type, low strontium, low lilicone (IS21–4; cryptocrystalline) (e) D-type high strontium, low silicone (IS14M-2; cryptocrystalline) and (f) D-type, low silicone (S21 or IS14-SPH1; vitric) groups. The images (c) and (f) are also classified as 'BeLaU'-type spherules. The scale bar is 100 μm. Loeb et al. (2024).

However,  the area where CNEOS 2014-01-08 impacted the Earth also lies within the Australasian Tektite Strewn Field, an area which covers about 15% of the planet's surface, from Southeast Asia through the western Pacific to Australia and Antarctica. This field is thought to have formed by the impact of an extraterrestrial object about 790 000 years ago, probably somewhere in Southest Asia (although the impact site has never been found). Across this area tektites and microtektites (spherical particles formed when rock vaporised during an impact recondenses in the atmosphere) with a distinctive high copper, nickel, and chromium profile are found. These tektites are thought to be comprised largely of terrestrial surface mater vaporised during the impact, with the additional cobalt, nickel, and chromium potentially coming from the impacting object). However, a full-spectrum analysis, comparing the elemental make-up of the Australasian Tektites to the BeLaU spherules has not previously been made.

In a paper published on the arXiv pre-print archive at Cornell University on 15 October 2025, Eugenia Hyung, Emma Levy, Loralei Cook, and Stein Jacobsen of the Department of Earth and Planetary Science at Harvard University, Abraham Loeb of the Department of Astronomy at Harvard University, and Jayden Squire and Juraj Farkas of the Department of Earth Sciences at the University of Adelaide, present the results of a study in which the chemistry of BeLaU spherules was compared to that of Australasian Tektites.

Hyung et al. used four Australasian Tektites from the collection of the Tate Museum in Adelaide, two from Florieton in South Australia, one from Charlotte Waters in the Northern Territory, and one from Kalgoorlie in Western Australia. Between 50 and 100 mg of material was taken from each sample, crushed in a pestle and mortar, then dissolved in a mixture of hydrofluoric acid and nitric acid, dried down, then redissolved in hydrochloric acid. A sample of the resultant solution was then analysed for 55 elements using a ThermoFisher Scientific iCAP TQ triple quadrupole ICP mass spectrometer. The results from this analysis were then compared to previous analyses of BeLaU spherules, as well as the average upper continental crust, and previous results for Australasian Strewn Field deep-sea microtektites.

Panel (a) Primitive-mantle normalized elemental compositions of Australasian tektites compared to the average upper continental crust  arranged in order of most incompatible to most compatible elements. Panel (b): The average upper continental crust normalized elemental patterns of the individual tektites (red, green, blue, and orange) and the average of the four specimens (white symbols, black line). The number '1' represents the average upper continental crust (dark symbols), plotted alongside the average BeLaU abundance pattern (white symbols, grey line) normalized with respect to the average upper continental crust. Panel (c): Australasian-tektite normalized elemental compositions of BeLaU (white circles) and microtektites (grey squares). Here, the number '1' (black circles) represents the average of the Australasian tektites measured in this study. Hyung et al. (2025).

The four tektite samples were all similar to one another (there was some variant in calcium content. as well as being similar to the microtektite samples. Compared to the average upper continental crust, they were slightly enriched in rare earth elements, but depleted in copper, zinc, arsenic, molybdenum, antimony, thallium, lead, and bismuth. Australasian tektites have previously been observed to be depleted in thallium, lead, and bismuth, something which has been attributed to loss of volatile fractions during the impact event. 

While the Australasian tektites were depleted in molybdenum, BeLaU spherules are enriched in this element. BeLaU spherules are also notably more enriched in the heavier rare earth elements. Where the BeLaU spherules are enriched in beryllium and uranium, no such enrichment could be seen in the Australasian tektites. Based upon this, Hyung et al. conclude that these are in fact to different classes of objects, with different origins.

See also...

Using strontium isotope ratios to try to determine the origin of victims of the transAtlantic slave trade.

Between the fifteenth to nineteenth centuries, at least 12.5 million people were abducted from sub-Saharan Africa and taken as slaves to the Americas, and to a lesser extent Europe, the largest forced migration in Human history. This has had a profound impact on the demographics, economics, and politics of both Africa and the Americas, and while is some ways the process was well-documented (we have, for example, documented records of the voyages of at least 30 079 vessels which were involved in the slave trade, including records of ports they visited and the number of captives they transported), we know very little about the identities of the individuals involved and their actual points of origin.

Recent studies have used genetic information from archaeological remains from the Caribbean, Brazil, North America, St Helena, and South Africa, have had some success in determining the populations from which individuals descended, this cannot tell us where they a person was born or brought up.

Strontium isotopes (specifically the ratio between the isotopes strontium⁸⁷ and strontium⁸⁶) in water are largely determined by bedrock, as well as rainfall and geomorphology, and is taken up and incorporated into biomineralized tissues, such as tooth and bone. Importantly, these ratios remain stable over archaeological timescales, enabling archaeologists to use them to determine the origin of Human and Animal remains, as long as a geological reference map, with the isotope ratios present in appropriate locations, is available. 

In sub-Saharan Africa, strontium isotope ratios have been used to trace the migration routes of large Mammals, and to determine the origin of ivory seized from smugglers, as well as to analyse landscape use by early Hominins, but has been under-used in other spheres, such as historical archaeology, largely because data on strontium isotope ratios are not available for large areas of the continent, and in particular much of West and West-Central Africa, the areas from which the overwhelming majority of slaves were taken to the New World. This is in part due to the high cost associated with carrying out strontium isotope testing over large areas, with the added complication that some parts of the continent are plagued by ongoing conflicts and political instability, making the necessary fieldwork difficult and dangerous.

In a paper published in the journal Nature Communications on 30 December 2024, a team of scientists led by Xueye Wang of the Center for Archaeological Science at Sichuan University and the Anthropology Department at the University of California Santa Cruz, present strontium isotope ratios from 778 new environmental studies from 24 African countries, mostly in West and West-Central Africa, which they combine with 1488 previously published strontium isotope ratios from other studies, to build a more detailed map of strontium isotope ratios across sub-Saharan Africa. These are then compared to ratios obtained from Human remains at two cemeteries in the Americas associated with African slaves, the Anson Street African Burial Ground in Charleston, South Carolina, and the Pretos Novos Cemetery in Rio de Janeiro, Brazil.

Strontium⁸⁷/strontium⁸⁶ ratios in Africa range from 0.70381 to 0.87810, a far higher range than is known from any other continent studied. Some areas have a high proportion of radiogenic strontium⁸⁷, notably those areas with an underlying Archaean bedrock, such as Angola, Zimbabwe, Zambia, western Tanzania, northern South Africa, Côte d'Ivoire, Liberia, Sierra Leone, and southwestern Mali. Other areas have a very low level of strontium⁸⁷, particularly areas of East Africa covered by Mesozoic-Cainozoic volcanic rocks, and areas of South Africa covered by flood basalts, as these tend to generate soils with a high cation exchange capacity and clay content. Strontium ratios are also affected by precipitation levels and elevation, both of which impact the weathering rate of silicate rocks.

Geological map and sampling locations. (a) Simplified geological map. (b) Map showing the environmental sampling locations from this study and previously published work. The sampling locations focused on filling gaps in West Africa, West-Central Africa, and parts of South Africa, covering all major geological units across the African continent south of the Sahara. Wang et al. (2024).

Strontium isotope ratios were analysed for five individuals from the Anson Street African Burial Ground for which genetic analysis had been used to determine a population-of-origin, and five individuals from the Pretos Novos Cemetery, for which this data was not available, but oxygen isotope ratios, which can be used to determine diet, were.

Two of the Anson Street African Burial Ground individuals had previously been determined to be of West-Central African origin, both of which produced strontium isotope ratios consistent with an origin in eastern-central Angola. The remaining three individuals were all determined to be from West Africa by genetic analysis. The first of these produced a strontium isotope ratio which indicates that they could have originated from a wide area, including large regions of Liberia, Côte d’Ivoire, Guinea, Sierra Leone, and Mali. The remaining two individuals showed much higher levels of radiogenic strontium, consistent with having come from either a 100 km stretch of the coast of southern Côte d’Ivoire and Ghana, or from the eastern part of Guinea.

Four of the five individuals from the Pretos Novos Cemetery produced strontium isotope ratios consistent with having come from different regions of Angola or South-East Africa, while the fifth produced a result consistent with having come from parts of Guinea, Nigeria, Cameroon, or South Africa. 

Oxygen isotope ratios suggest that this individual grew up in a region where the main crops were C₄ Plants. This would exclude the 'Rice Coast' of West Africa, which runs from Guinea Bissau through Guinea into western Côte d’Ivoire, or the vegecultural zone of southern West Africa, where the predominant crops are Manioc, Yams, and other C₃ root vegetables, but would include parts of central Nigeria where the main crops are Sorghum and Millet, and parts of northern Cameroon where different areas would have grown Sorghum and Millet or Maize (itself introduced from the Americas by European traders). Potentially, a South African could have also had a diet dominated by C₄ Plants, which are easily grown in many places there, but Wang et al. consider this less likely, given the much larger number of slaves taken from West Africa to Brazil.

The four other individuals from Pretos Novos Cemetery are hypothesized to have come from different parts of Angola based upon strontium isotope ratios. This was supported by the oxygen isotope analysis, which suggests they did not share common dietary habits in early life. This is consistent with the known agricultural practices in Angola at the time, with different regions emphasizing the cultivation of manioc and other root crops, or maize and millet.

Wang et al. are confident that improved groundwater sampling from a wider area of Africa would have the potential to greatly improve our ability to determine the origin of African remains from the New World. With the limited sampling available, they were able to provide approximate locations of origin for ten individuals from two well-studied burial grounds, one in the United States and the other in Brazil, and while their answers cannot be taken as 100% reliable at this stage, none of them contradict data from previous studies, nor do they suggest improbable points of origin for the individuals examined.

There are still some notable gaps in the strontium ratio maps used by Wang et al. most notably Namibia and the Sahel Region. Wang et al. identify these regions as being sparsely populated, and therefore unlikely to have been heavily targeted by slavers. This is probably true for Namibia, where the most habitable areas are separated from the coat be large areas of desert, but certainly isn't true for the Sahel Region, which was home to powerful states such as the Mali Empire, and where travellers such as Mungo Park recorded extensive activity by slavers. Sampling is also limited for Mozambique, from where historical records show that at least half a million people were taken as slaves in the first half of the nineteenth century. The method is further limited in that it can only trace the origins of people born and raised in Africa, anyone raised in the Americas will have a strontium isotope signal from there, no matter where their parents came from.

Wang et al. also note that an improved isotope map for Africa, particularly if it includes other elements, such as oxygen, hydrogen, sulphur, and carbon, has the potential to improve not just our ability to identify the origins of Human remains from archaeological contexts, but also items such as smuggled wildlife and timber. It also has the ability to improve our understanding of wildlife migrations, or historic dispersals, including those of species extinct today. Moreover, it also has the ability to help identify the thousands of African migrants who perish in the Mediterranean Sea during their passage to southern Europe, something which has been described as potentially the greatest humanitarian disaster in Europe since the Second World War.

See also...

Assessing the importance of plate tectonic for the development of complex life.

Over the past three decades, research has shown that the overwhelming majority of stars in our galaxy have planets. Logically, a proportion of those planets will have the conditions for life, and life will actually arise on some proportion of the planets which can support it. Furthermore, a small proportion of the planets with life are likely to produce intelligent life, capable of radio communication and other activities which we might be able to detect. This works out at a very small proportion of stars hosting civilizations, but a very small proportion of hundreds of billions still works out at a very large number. We have, nevertheless, never detected any sign of intelligent life (of life at all) beyond our own planet, leaving us, as far as we know the only civilization in the universe, something referred to as the Fermi Paradox. A number of possible explanations have been offered for this paradox, most of which revolve around the idea that while life is probably quite common in the galaxy, complex life is probably much rarer. A variety of reasons why this might be the case have also been proposed, with a link to the other phenomenon also as far as well know unique to our planet, plate tectonics, frequently being proposed.

In a paper published in the journal Scientific Reports on 12 April 2024, Robert Stern of the Department of Sustainable Earth Systems Science at the University of Texas at Dallas, and Taras Gerya of the Department of Earth Sciences at ETH-Zurich, re-examine the biological and geological history of the Earth, looking for connections between key stages in the development of life on Earth and changes in the Earth's geological activity.

Life is generally accepted to have first appeared on Earth more than 3800 million years ago, but the first Animals did not appear until less than 1000 million years ago. Various possible explanations have been proposed for this, including lower oxygen levels on the early Earth and a possible lack of key biological innovations until more recent times. The fact that Animals, Plants, and even multicellular Algae did not appear until quite late in the Neoproterozoic suggests that some profound change in the Earth or its biology led to this development, and Stern and Gerva suggest that this change was a shift from single lid to plate tectonics, and the subsequent profound shifts in the Earth's atmospheric oxygen levels.

The timing of the onset of plate tectonics is still a matter of debate among Earth Scientists, with two broad camps, one which argues that plate tectonics began during the Archean, while the other argues that the current plate tectonic regime began in the Neoproterozoic (although there may-or-may-not have been earlier phases of plate tectonics on Earth). The processes of seafloor spreading, subduction, and continental collision lead to the formation of a distinctive set of minerals, rocks, and rock assemblages, some of which appear to be absent before the onset of the Neoproterozoic, although it has been argued that these differences are due to higher mantle temperatures on the early Earth. Similarly, it is possible to track the movements of continents over the Neoproterozoic and Phanerozoic through the traces of magnetic fields left in some types of rocks when they form, but in rocks older than about 1200 million years this method is not reliable, leaving us uncertain about the movement of the continents that long ago. 

In previous work, Robert Stern divided indicators of plate tectonics into three groups, (1) indicators of seafloor spreading and subduction initiation, (2) subduction indicators, and (3) plate collision indicators. All of these indicators are present in rocks from Neoproterozoic and Phanerozoic times, but their presence in older rocks is far less clear. 

In order for plate tectonics to operate, it is necessary for oceanic lithosphere to be subducted at plate margins, and it is likely that this oceanic lithosphere was not sufficiently strong and dense enough for this to happen in a coherent way until the upper mantle had cooled to between 100°C and 150°C above current temperatures, again something which is predicted to have happened in the Neoproterozoic.

If plate tectonics did indeed start, then it is unlikely to have started all over the world at once, but instead should have started in one place, then taken hundreds of millions of years to spread around the globe. This would result in a gradual increase in the presence of Stern's three indicators for the presence of plate tectonics, something which can again be seen in the Neoproterozoic rock record. The first ophiolites, which are indicators of subduction initiation, appear about 870 million years ago, with the first indicators of actual subduction zones appearing about 750 million years ago, and the first indicators of continental collision appearing about 600 million years ago. 

As far as we understand, an active silicate body can have either a single lid or plate tectonic system. This being the case, for plate tectonics to have initiated in the Neoproterozoic, the Earth must have had a single lid system in the Mesoproterozoic. Stern's previous work also identified three potential indicators for single lid systems. These are (1) an elevated thermal regime, (2) an abundance of unusual dry magmas such as A-type granites and anorthosites, and (3) a lack of new continental margins. The Mesoproterozoic shows an absence of Stern's indicators for plate tectonics, but is rich in the three indicators for single lid tectonics. Curiously, indicators for plate tectonics do appear to be present in the Palaeoproterozoic.

Evolution of Earth’s tectonic regime over the past 1.6 billion years; (a) single lid tectonic indicators, (b) plate tectonic indicators cumulative plot, (c) simplified climate history, (d) Simplified biological evolution. Stern & Gerva (2024).

There is a similar shift in the formation of mineral deposits between the Mesoproterozoic and Neoproterozoic, with orogenic gold and porphyry copper deposits, all associated with an active tectonic regime, being common in Neoproterozoic strata but absent in the Mesoproterozoic, while iron oxide copper gold  deposits and iron-titanium-vanadium-phosphorus deposits, both of which are associated with anorthosites are common in the Mesozoic but rare in the Neoproterozoic.

Finally, the palaeomagnetic record does not show any significant movement of continental landmasses during the Mesoproterozoic, while this is common in younger rocks. Particularly noteworthy is the supercontinent of Nuna (or Colombia), which assembled during the Palaeoproterozoic, then appears to have persisted relatively unchanged throughout the Mesoproterozoic.

Plate tectonics requires a global mosaic of plates, which it could be reasonably expected would take hundreds of millions of years to form a a single lid system. Theoretically, following the formation of an initial subduction zone with associated transform systems and divergent plate boundary margins, the system could slowly propagate to form a global mosaic. The rate at which such a system could form would be governed by the rate at which new subduction zones can form and lengthen. In Cretaceous and younger rocks, subductive trenches appear to be able to lengthen at rates of between 100 and 600 km per million years, which would require between 92 and 550 million years to develop a global network of about 55 000 km of convergent margins.

The last 1.6 billion years of Earth’s tectonic history. Stern & Gerva (2024).

The Neoproterozoic is also known to have had major carbon isotope excursions (changes in the proportions of different carbon isotopes laid down in sedimentary deposits) as well as several glacial interludes, major disruptions to the Earth's environment which we associate with plate tectonics. The most notable of these is the Neoproterozoic Snowball Earth, a prolonged phase of near-global glaciation, which may have been triggered by a huge increase in volcanic activity or true polar wander.  The first major carbon isotope event in the Neoproterozoic is the Bitter Springs Event, at about 811 million years before the present, while the youngest is the Shuram Event, about 570 million years ago. If these events bracket a change from a single lid to a plate tectonic system, then that change took about 241 million years, with the Neoproterozoic Snowball Earth, which started at about 720 million years ago and ended about 580 million years ago, in the middle. If the beginning and end of the Snowball Earth mark the transition period then it is shorter, at about 140 million years. The fact that both the carbon isotope excursions and the glaciation events were sporadic suggests that this process was not smooth, bur occurred in a series of episodes. The Palaeoproterozoic is also noted for several isotope excursions, as well as glacial events, and the Great Oxidation Event, during which the Earth first developed an oxygenated atmosphere. All of these events occurred between about 2.50 and 2.05 billion years ago, with a proposed interval of plate tectonics between 2.05 and 1.80 billion years ago, giving an apparent different relationship between these geochemical events and plate tectonics. This Palaeoproterozoic tectonic interval appears to have ended with the formation of the Supercontinent of Nuna, although these ancient events are not well understood and would merit significant further investigation.

Life first appeared on Earth more than 3.8 billion years ago, but appears to have remained fairly simple for the next three billion years, with all terrestrial ecosystems dominated by Prokaryotes (Bacteria and Archaea), simple organisms which lack cell nuclei organelles. All complex multicellular life on Earth is Eukaryotic (i.e. has cells with nuclei and organelles), so Eukaryotic life had to appear before multicellular life-forms. The fossil record shows what appear to be Eukaryotic single-celled organisms dating back to at least the Palaeoproterozoic, suggesting a link between the emergence of the first Eukaryotes and the Great Oxygenation Event, the first case of co-evolution between the evolution of the atmosphere and Eukaryotic life.

The Mesoproterozoic lacks any such major events, making it impossible to split it into any subdivisions, and making its beginning and end points somewhat arbitrary. The interval between 1800 and 800 million years ago (roughly the Mesoproterozoic) has been referred to as the 'Boring Billion' because of this lack of events, with oxygen levels staying roughly constant, geobiological systems apparently remaining unchanged, and constant carbon isotope ratios throughout. The period, which lasted for about 20% of Earth's history, also saw stability in the proportion of sulphur molybdenum, chromium, and strontium isotopes trapped in sediments throughout, and a prolonged low nutrient system.

In contrast, the Neoproterozoic is a period of both climatic instability and rapid biological evolution, during which the Snowball Earth occurred, as well as major shifts in the carbon cycle, the ocean's oxygen content, a major diversification in microscopic Eukaryotes, and the appearance of Metazoans. The era can be split into three periods based upon clear geological differences, the longer and somewhat uneventful Tonian, between 1000 and 720 million years before the present, the Snowball Earth Cryogenian, and the Ediacaran, which saw the first widespread Metazoan fossils. Molecular clocks suggest that the first multicellular organisms appeared during the Tonian, the bilaterian body plan appeared in the Cryogenian, and that the majority of Metazoan phyla diversified during the Late Ediacaran, between 560 and 540 million years ago. All known Animal phyla are believed to have arisen during the Neoproterozoic.

Five conditions are thought to have been needed for this biological shift to have occurred; an increased nutrient supply, increased oxygen levels in both the atmosphere and oceans, an improved climate, an increased rate of habitat formation and destruction, and a sustained evolutionary pressure caused by such shifting environments.

Summary diagram showing how plate tectonics stimulates life and evolution whereas a single lid tectonic style retards life and evolution. Stern & Gerva (2024).

Nutrients are essential for life, and in particular organic carbon (i.e. compounds with bio-available carbon - we cannot, for example, eat diamonds), ammonium (which provides bio-available nitrogen), ferrous iron (again, bio-available iron) and phosphates (bio-available phosphorus). Phosphorus, in particular, plays vital role in biogeochemistry and is considered a global limiting nutrient. A shortage of phosphorus is thought to have been one of the major restrictions on the Mesoproterozoic biosphere. Phosphorus typically becomes available through the erosion of rocks, and its subsequent delivery to the oceans via rivers. This makes it likely that rock weathering was much reduced during the Mesoproterozoic. In the modern world, fresh rocks are constantly exposed at the surface due to tectonic processes, providing new sources of phosphorus and other nutrients, while soil formation covers rocks, inhibiting this supply. The Earth has gone through phases of enhanced nutrient supply associated with major uplift events, such as the Pan-African Orogeny, the Transgondwanan Supermountain Orogeny, and the Circum-Gondwanan Orogens, which all occurred on convergent plate boundaries associated with tectonic transitions. These events greatly increased the rate of erosion, and therefore the delivery of phosphorus into the oceans, with the microbial enhancement of carbon and sulphate acid weathering being an important part of this delivery process. Rising oxygen levels in the atmosphere would have increased the role of microbes in weathering, which in turn would have increased the rates at which organic carbon was buried and phosphorus was delivered to the oceans, resulting in depleted phosphorus depletion in palaeosols (preserved terrestrial soils), something observed during both the Neoproterozoic Oxygenation Event and the Palaeoproterozoic Great Oxygenation Event.

Further evidence for a major onset of uplift, erosion, and weathering during the Ediacaran can be seen in a rise in the proportion of the isotope strontium⁸⁷ within marine sediments. Strontium⁸⁷ is radiogenic, formed by the decay of rubidium within rocks, and can enter the water column either by the erosion of rocks in which this decay has occurred, or by the erosion of older marine sediments. The proportion of this isotope began to rise during the Tonian, and continued to do so throughout the Neoproterozoic, with a significant increase during the Ediacaran, and the highest values recorded in Earth's rock record being found in the Early Palaeozoic. This Neoproterozoic increase in the proportion of strontium⁸⁷ is thought to have been associated with the Pan-African uplifts and the formation of the Transgondwanan Supermountains. These events were caused by continental collisions, with no similar events having apparently happened during the Mesoproterozoic. Thus the low strontium⁸⁷ levels seen in the Mesoproterozoic are another line of evidence supporting a phase of single lid tectonics during this era. The production of phosphorus, iron, and other nutrients by erosion broke the Mesoproterozoic nutrient drought, stimulating biological evolution. 

Free oxygen levels in both the atmosphere and oceans are likely to have been caused by a proliferation of photosynthetic Cyanobacteria, Prokaryotes which have been around since at least the Palaeoproterozoic, combined with a more efficient burial of organic carbon (which will tend to react with free oxygen). This increased oxygen availability enabled the evolution of larger more complicated organisms, such as Animals, something impossible under the low-oxygen conditions of the Mesoproterozoic. Larger, more complicated Animals need higher oxygen levels than smaller, simpler ones, with oxygen levels during the Cambrian thought to have been much lower than today, but Mesoproterozoic oxygen levels are thought to have been lower still, incapable of supporting even simple Animal life. A range of isotopic proxies indicate a significant oxygenation event during the Neoproterozoic, leading to oxygen levels capable of supporting Animal life in most marine ecosystems by the end of the Cryogenian. 

The most likely explanation for this increase in oxygen is that an increase in nutrient supply led to a boom in phytoplankton growth, converting more carbon dioxide into organic matter. This would have allowed the development of more sophisticated Algae with increased photosynthetic abilities, something thought to have happened in the Late Cryogenian. This in turn further boosted oxygen production, as well as transforming the base of the food chain and providing novel food sources for the first Animals. An alternative explanation is increased weathering on land, leading to more nutrients flowing into the oceans, provoking a surge in Cyanobacterial and Algal production, which caused oxygen levels to rise. The common element to all hypothesis is that more phytoplankton were dying and being buried, increasing the  amount of organic carbon sequestered at the same time as sedimentation rates increased in the new rift basins and continental margins of the changing world.

A stable climate is important for Metazoan life. Prokaryotes can thrive at temperatures between 0°C and about 120°C, but most Animal life needs a temperature between about 5°C and about 35°C. Single lid and plate tectonics will provide different climatic regimes. Under a plate tectonic system, the regular release of volcanic gasses can have either a warming or cooling effect; notably mid-ocean ridges produce large amounts of carbon dioxide, tending to warm the climate, while volcanoes on convergent margins produce lots of sulphur dioxide, tending to cool the environment. 

The presence of oceans on the Earth's surface tends to modulate the overall temperature, due to the thermal inertia of water (it takes a lot more energy to warm water than air). This means that the Earth has a more temperate climate when a higher proportion of its surface is covered by water, and a harsher climate when the proportion of the surface covered by water is lower. This means that during a plate tectonic regime, the climate will go through cycles, with a warm greenhouse phase typically arising about 100 million years after a continental breakup event as the oceans widen. It is unclear how the depth and extent of the oceans would have varied under a single lid tectonic system, but it is likely that any change would have been considerably less significant than under a plate tectonic regime.

The process of weathering silicate rocks uses carbon dioxide. This means that the continual exposure and weathering of new silicate rocks, as happens under a plate tectonic system, will consume more carbon dioxide, leading to a reduction in the proportion of this greenhouse gas in the atmosphere, cooling the climate. Thus the enhanced erosion and weathering under a plate tectonic regime will not only release more nutrients, leading to more photosynthesis in the oceans and a subsequent rise in the burial of organic carbon in marine sediments, it also directly removes carbon dioxide from the atmosphere. Under a single lid system, the amount of uplift occurring should be close to zero, leading to a much lower nutrient flux and a lower exposure of silicate rocks to weathering by carbon dioxide.

Plate tectonics also removes large amounts of marine carbonate rocks and buried organic carbon from the Earth's surface systems as they are drawn down into the Earth at subduction zones, further reducing the amount of carbon dioxide in the atmosphere, and leading to further cooling. 

The carbon cycle on planets with single lid tectonic cycles is not well understood, and that of the Mesoproterozoic Earth less so. Two planets in the modern Solar System have single lid tectonic systems, Venus and Mars, and both of these have atmospheres which are more than 95% carbon dioxide, suggesting a poor ability to cycle this gas. However, models of the early Earth suggest that it might have been possible to recycle carbon dioxide reasonably efficiently if volcanic activity was sufficiently high, through the weathering, burial, sinking and delamination of carbonated crust. This fits with the observation that the Mesoproterozoic Earth had a relatively warm climate without any glacial phases, despite the Sun being 5-20% dimmer than today, presumably due to the contribution of greenhouse gasses.

The constant formation and then destruction of new ecosystems is a feature of an active plate tectonic system. This is also something required for the efficient evolution of biological organisms, but is unclear to what extent this would happen under a single lid tectonic system, possibly leading to a system of biological stasis.

The continuous environmental change of a plate tectonic system should present a constant need for biological innovation, with constantly changing nutrient fluxes, topographies, climates, and habitats. This is particularly true along active plate margins, in shallow marine ecosystems which appear to have been hotspots for biological innovation throughout the Earth's recent history. In these environments plate tectonics produces shifting habitats with abundant nutrient and sediment supplies, as well as strong currents and tides, which will tend to distribute these nutrients. 

The switch a plate tectonic system appears to have stimulated the rapid diversification of life, something which may not have been possible at all under a single lid system. The most dramatic environmental shifts encountered under a single lid system are likely to have been mantle plumes, which would cause global warming when they first appeared, due to the production of carbon dioxide, followed by a period of cooling as weathering of basalts leads to carbon oxide levels lowering again. Under this system the oceans would also likely suffer from conditions of anoxia, acidification, and toxic metal-input.

Without the driving force of plate tectonics, the evolution of biological life appears to be an extremely slow process. Under a plate tectonic regime, the evolution and demise of new organisms, groups of organisms, and whole global ecosystems, appears to follow the opening and closing of oceans. This makes it extremely unlikely that complex life would have arisen on Earth without the development of a plate tectonic system.

We know that life appeared in Earth's oceans more than 3.8 billion years ago, and remained within the oceans for more than 3 billion years. Despite this, it is generally accepted that the presence of dry land on Earth was needed for both the origin and evolution of life, since without this all nutrients would eventually be lost from surface systems. It is possible that the first life originated in ancient palaeosols (or more accurately, regalith), but seawater appears to have been a vital environment for much of the history of life, providing a nutrient bath in which primitive organisms could absorb nutrients through their cell membranes, as well as protection from the Sun's harmful ultraviolet radiation. All complex life on Earth is Eukaryotic, and it is generally accepted that Eukaryotic cells first evolved in the sea, where water would provide structural support for these larger cells until they evolved it themselves. This structural support would also have been needed for the first Metazoans, which appear to have been the soft-bodied organisms recorded in the Ediacaran Biotas.

Stern and Gerva reason that while primitive life must evolve in the sea, advanced civilizations need to evolve on dry land. Changing terrestrial ecosystems provide even more varied habitats than the oceans, providing an additional stimulus for biological evolution, and areas around the margins of continental plates tend to produce particularly varied habitats, as can be seen in the circum-Mediterranean, Mesoamerica, Madagascar and Southeast Asia today. The harsher terrestrial environment also stimulates life to produce specialist water retention and gas exchange structures, reproduction by internal fertilization, and movement systems which do not rely on the support of water, all of which lead organisms to become increasingly sophisticated and complex. 

This biological complexity is one of the prerequisites to developing a system for organisms to transfer experiences and knowledge to one-another, which in turn has the potential to lead to abstract thinking, and the development of language, technology, and science.  In particular, an advanced civilization would require the organisms building it to develop a familiarity with both fire and electricity, something more-or-less impossible if they are restricted to water. Thus the development of an advanced civilization on a planet would require the presence of a plate tectonic system, which Stern and Gerva suggest should be added to the Drake Equation.

The Drake Equation, as envisaged by astrobiologist Frank Drake, proposed that the number of potentially detectable  advanced civilizations in the Galaxy would be equal to the average rate of star formation, multiplied by the fraction of stars which host planets, multiplied by the fraction of planets which hold the conditions for life, multiplied by the fraction of planets which hold the conditions for life which actuallt develop life, multiplied by the proportion of planets with life which develop civilizations, multiplied by the proportion of civilizations which produce detectable signals (such as radiowaves etc.), multiplied by the lifetime of such civilizations. 

Based upon this, Drake made an 'educated guess' that between 200 and 50 000 000 detectable civilizations might exist in the Galaxy, with subsequent estimates by other scientists producing figures from below a hundred to several million. Stern and Gerva suggest that the proportion of planets with life that go on to develop civilizations should be considerably lower than in most estimates, due to the additional requirement for these planets to develop plate tectonic systems which operate for several hundred million years.

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