Sunday 30 July 2017

Fireball meteor over Washington State.

The American Meteor Society has received reports of a bright fireball meteor being seen over Washington State, slightly before 10.00 am, Eastern Daylight Time, (slightly before 4.00 am GMT) on Saturday 29 July 2017. The majority of the sightings came from Washington State, though reports have come from Oregon and British Colombia too. A fireball is defined as a meteor (shooting star) brighter than the planet Venus. These are typically caused by pieces of rock burning up in the atmosphere, but can be the result of man-made space-junk burning up on re-entry.

 The 29 July 2017 fireball meteor seen from Lake Tapps in Pierce County, Washington. Marianne Scott Lincoln/King 5.

The meteor was seen to move from southeast to northwest, apparently terminating over the town of Pilchuck in Snohomish County, Washington (such meteors typically terminate many kilometres above the ground in an explosion caused by friction with the Earth's atmosphere). It has been described as greenish in colour with an orange tip to its tail, and burned for about five seconds.

 Map showing areas where sightings of the meteorite were reported, and the route of the object (blue arrow). American Meteor Society.

Objects of this size probably enter the Earth's atmosphere several times a year, though unless they do so over populated areas they are unlikely to be noticed. They are officially described as fireballs if they produce a light brighter than the planet Venus. It is possible, though unlikely, that this object will have produced meteorites that reached the surface (an object visible in the sky is a meteor, a rock that falls from the sky and can be physically held and examined is a meteorite), though most meteorites come from larger objects that penetrate further into the atmosphere before exploding, and therefore have a better chance of producing fragments that reach the surface.

Witness reports can help astronomers to understand these events. If you witnessed this fireball you can report it to the American Meteor Society here.  

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Magnitude 5.3 Earthquake beneath Lake Edward, Central Africa.

The United States Geological Survey Recorded a Magnitude 5.3. Earthquake at a depth of 10 km beneath northeast Lake Edward, which forms the border between Uganda to the east and the Democratic Republic of Congo to the west, slightly after 10.00 am local time (slightly after 7.00 am GMT) on Sunday 30 July 2017. There are no reports of any damage or casualties associated with this event at this time, but it was felt across much of southwest Uganda, Rwanda and in parts of northeastern Tanzania.

The approximate location of the 30 July 2017 Northern Province Earthquake. USGS.

Lake Edward lies within the the of the Great Rift Valley, which is slowly splitting the African Plate in two along a line from the Red Sea through Ethiopia, and which includes the great lakes and volcanoes of east-central Africa. This has the potential to open into a new ocean over the next few tens of millions of years, splitting Africa into two new, smaller, continents; Nubia to the west and Somalia to the east.

 Movement on the African Rift Valley, with associated volcanoes. Rob Gamesby/Cool Geography.

Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. The international non-profit organisation Earthquake Report is interested in hearing from people who may have felt this event; if you felt this quake then you can report it to Earthquake Report here.
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Saturday 29 July 2017

Australopithecus africanus: Deciphering the osteopathology of a Plio-Pleistocene Hominin.

The Sterkfontein Caves site, part of the wider ‘Cradle of Humankind’ complex in Gauteng State, South Africa, has yielded the largest known collection of specimens assigned to the Plio-Pleistocene Hominin species Australopithecus africanus. The site comprises a series of karstic caves (i.e. caves created by the action of water percolating through soft limestone) that would have been encountered by the Hominins both as cave openings at the surface that could provide potential shelter and as potholes into which they could fall. Specimen StW 431 is a partial Australopithecus africanus skeleton discovered at Sterkfontein in 1987. This specimen's lumbar vertebrae showa number of deformaties, with both bone overgrowth and erosion. This has been diagnosed variously as brucellosis, spondylosis deformans, osteophytic formation,and  osteoarthritis of the facet joints.

In a paper published in the South African Journal of Science on 30 January 2017, Edward Odes of the School of Anatomical Sciences at the University of the Witwatersrand, Alexander Parkinson of the Evolutionary Studies Institute, also at the University of the Witwatersrand, Patrick Randolph-Quinney, also of the School of Anatomical Sciences and Evolutionary Studies Institute at the University of the Witwatersrand, and of the School of Forensic and Applied Sciences at the University of Central Lancashire, Bernhard Zipfel, agian of the Evolutionary Studies Institute, and of the School of Geosciences at the University of the Witwatersrand, Kudakwashe Jakata, again of the Evolutionary Studies Institute at the University of the Witwatersrand, Heather Bonney of the Department of Earth Sciences at the Natural History Museum and Lee Berger, once again of the Evolutionary Studies Institute at the University of the Witwatersrand, re-examine skeleton StW 431, and draw new conclusions about its taphonamy and osteopathology. 

StW 431 – a partial skeleton of Australopithecus africanus discovered at Sterkfontein Caves in 1987. Stw 431 represented only the third partial skeleton attributed at the time to Australopithecus africanus, and represents the only probable male skeleton attributed to this taxon to date. Odes et al. (2017).

Odes et al. examined the fourth and fifth vertebrae of StW 431, using micro computed tomography to examine the internal structures of the bone. They were able to identify areas of both erosion and deposition of bone, though unlike previous studies, which had examined only the exterior of the bones, they conclude that, while the excess bone deposition cleary happened while the individual was alive, the bone erosion was almost certainly post-mortem, and is consistent with damage caused by  Insects, such as Southern African Termite, Trinervitermes trinervoides, or Dermestid Beetle, Dermestes maculatus.

Micro-CT orthoslice views of the L4 vertebra of StW 431: (a) transverse superior, (b) sagittal midline, (c) transverse inferior and (d) anterior. Note the bilateral osteophytic formation and two zones of erosion evident on the inferior endplate surface of the L4 in (c). There is no evidence of sclerosis or new bone formation around the margins of the cavities (c). Also note areas of new bone formation ranging from open woven (c) to sclerotic (d). Odes et al. (2017).

Based upon this Odes et al. conclude that the individual was suffering from osseous proliferation (osteophytosis), cosistant with a degenerative spinal joint disease. Such osseous proliferation is a fairly common condition, typically caused by erosion of the cartilage, which can lead to bone rubbing against bone, leading to bone damage which the body tries to heal through new growth,

Micro-CT orthoslice views of the L5 vertebra of StW 431: (a,b) transverse to the midline (close to surface), (c) transverse to inferior, (d) coronal midline, (e) sagittal superior to bottom. Note new bone formation on the anterior wall (e) and major osteophytic formation at the antero-superior margin indicating remodelling of the cortex, revealing a sclerotic margin, and as crenulated buttresses of porous bone devoid of internal trabeculae (a,b). There is no evidence of sclerosis or reactive bone formation around the cavity margins (a). The inferior endplate (c) exhibits an osteophytic formation as a thin ordered sclerotic rim around inferior circumference with no presence of buttressing. Notice the channel interpreted as invertebrate damage in (e). Odes et al. (2017).

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Asteroid 2017 OL1 passes the Earth.

Asteroid 2017 OL1 passed by the Earth at a distance of about 5 697 000 km (14.8 times the average distance between the Earth and the Moon, or 3.81% of the distance between the Earth and the Sun), at about 2.20 am GMT on Sunday 23 July 2017. There was no danger of the asteroid hitting us, though were it to do so it would have presented a significant threat. 2017 OL1 has an estimated equivalent diameter of 82-270 m (i.e. it is estimated that a spherical object with the same volume would be 82-270 m in diameter), and an object at the upper end of this size range would be predicted to be capable of passing through the Earth's atmosphere relatively intact, impacting the ground directly with an explosion that would be 60 000 times as powerful as the Hiroshima bomb. Such an impact would result in an impact crater about 4 km in diameter and devastation on a global scale, as well as climatic effects that would last decades or even centuries.

 The calculated orbit of 2017 OL1. Minor Planet Center.

2017 OL1 was discovered on 21 July 2017 (two days before its closest approach to the Earth) by the Atlas MLO Telescope at Mauna Loa Observatory in Hawaii. The designation 2017 OL1 implies that the asteroid was the 36th object (object L1) discovered in the second half of July 2017 (period 2017 O). 

2017 OL1 has a 1418 day orbital period and an eccentric orbit tilted at an angle of 1.33° to the plane of the Solar System, which takes it from 0.95 AU from the Sun (i.e. 95% of he average distance at which the Earth orbits the Sun) to 3.99 AU from the Sun (i.e. 399% of the average distance at which the Earth orbits the Sun, and almost three times as distant from the Sun as the planet Mars). It is therefore classed as an Apollo Group Asteroid (an asteroid that is on average further from the Sun than the Earth, but which does get closer). As an asteroid probably larger than 150 m in diameter that occasionally comes within 0.05 AU  (7 480 000 km) of the Earth, 2017 MB1 is also classified as a Potentially Hazardous Asteroid.

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Worker killed at Arizona copper mine.

A worker has died at the Ascaro-operated Mission Mine near Sahuarita in Pima County, Arizona, following a vehicle collision at about 9.30 am on Thursday 27 July 2017.  Gabriel Benitez, 41 was reportedly sitting in a Ford 550 truck when it was crushed by a much larger mine vehicle. The driver of the other vehicle has tested clean for drugs and alcohol, and the incident is being investigated by the Mine Safety and Health Administration and the Arizona State Mine Inspector’s Office.

Mine vehicles at the Mission Mine in Pima County, Arizona. Ascaro.

The Mission Mine consists of a complex of open pits covering an area roughly 4 km by 2.4 km, and about 365 m deep, located about 30 km to the south of Tuscon. The copper is extracted from a porphyry deposit (large grained igneous rock formed by the slow cooling of magma, usually in magma chambers beneath volcanoes on subductive plate margins) that also produces small amounts of zinc, lead and molybdenum minerals. This is intruded into a folded complex of Triassic sedimentary rocks and Palaeozoic limestones, and is associated with the Laramide Orogeny, a period of mountain building along the western margin of North America from Mexico to Canada, associated with the subduction of the Kulla and Fallaron Plates beneath the North American Plate, between about 80 and 35 million years ago.

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Parachemmis julioblancoi: A new species of Corinnine Spider from the Sierra Nevada de Santa Marta of Colombia.

Corinnine Spiders of the genus Parachemmis are distinguished from related genera by the presence of spines on their first pair of legs. To date three species have been described, one from Brazil, one from Guyana and one from Panama, however since this range covers one of the most biodiverse regions on the planet, it is thought highly likely that there are many more undiscovered species in this genus.

In a paper published in the journal ZooKeys on 8 June 2017, Leonel Martinez, Eduardo Villarreal and Neis Martinez of the Grupo de Investigación ECOSIN and Grupo de Investigación Biodiversidad del Caribe colombiano at the Universidad del Atlántico, describe a new species of Parachemmis from San Pedro de la Sierra in the Sierra Nevada de Santa Marta of Magdalena Department in Colombia.

The new species is named Parachemmis julioblancoi, in honour of Julio Enrique Blanco, the founder of the Universidad del Atlántico, for his many contributions to art and education in Colombia. The species is described from four male and six female specimens, collected from leaf litter in a wet mountain forest at an altitude of 2104 m. The females are larger than the males, with one specimen measured at 11.0 mm, compared to 7.7 mm for a male. Both are grey and yellow in colour. 

Parachemmis julioblancoi, (A) male, scale bar is 2mm, (B) female, scale bar is 5 mm. Martinez et al. (2017).

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Magnitude 5.1 Earthquake off the coast of northern California.

The United States Geological Survey recorded a Magnitude 5.1 Earthquake at a depth of about 26.5 km roughly 74 km offshore of the city of Ferndale in Humboldt County, California, slightly after midnight on 5.00 pm on Friday 28 July 2017, local time (slightly after midnight on Saturday 29 July local time). There are no reports of any damage or injuries relating to this quake, but people have reported feeling it across much of northwest California and parts of southwest Oregon.

The approximate location of the 28 July 2017  Californian offshore Earthquake. USGS.

California is extremely prone to Earthquakes due to the presence of the San Andreas Fault, a tectonic plate margin that effectively bisects the state. The west of California, including Santa Barbara and Los Angeles, is located on the Pacific Plate, and is moving to the northwest. The east of California, including Fresno and Bakersfield is on the North American Plate, and is moving to the southeast. The plates do not move smoothly past one-another, but constantly stick together then break apart as the pressure builds up. This has led to a network of smaller faults that criss-cross the state, so that Earthquakes can effectively occur anywhere.

However the  28 July 2017 Earthquake happened on the southern part of the Cascadia Subduction Zone, a northward extension of the San Andreas Fault, where the Gorda Plate is being subducted beneath the North American Plate. Along this boundary the rocks of the two plates continuously stick together, then become stressed as the motion of the two plates draws them apart. This stress builds up until the rocks are forcibly snapped apart, which we experience as Earthquakes.

Map showing the progress of the San Andreas Fault to the north, where it becomes the Gorda Plate subduction zone. Humbolt State University.

 The Gorda Plate, along with the Explorer and Juan de Fuca Plates are remnants of an ancient oceanic plate, the Fallaron Plate which has almost completely disappeared beneath North America. The Fallaron Plate formerly diverged from the Pacific Plate along the Fallaron Ridge, but as the plate has been subducted both it and the ridge have broken up. The remnants of the plate are now the Explorer Plate in the north, then the Juan de Fuca Plate, then the Gorda Plate in the south. This borders onto the Pacific Plate along the Mendocino Fracture Zone, which extends on land as the San Andreas Fault. 

 North of California the San Andreas Fault becomes the Mendocino Fracture Zone. USGS.

Witness accounts of quakes can help geologists to understand these events and the rock structures that cause them. If you felt this quake (or if you were in the area but did not, which is also useful information) you can report it to the USGS here.

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