UKansas: Distance at Which Supernova Would Spark Mass Extinctions Increased

[bystander]

Research increases distance at which supernova would spark mass extinctions on Earth
University of Kansas | 2017 May 11

In 2016, researchers published “slam dunk” evidence, based on iron-60 isotopes in ancient seabed, that supernovae buffeted the Earth — one of them about 2.6 million years ago. University of Kansas researcher Adrian Melott, professor of physics and astronomy, supported those findings in Nature with an associated letter, titled “Supernovae in the neighborhood.”

Melott has followed up since those findings with an examination of the effects of the supernovae on Earth’s biology. In new research to appear in Astrophysical Journal, the KU researcher and colleagues argue the estimated distance of the supernova thought to have occurred roughly 2.6 million years ago should be cut in half.

“There’s even more evidence of that supernova now,” he said. “The timing estimates are still not exact, but the thing that changed to cause us to write this paper is the distance. We did this computation because other people did work that made a revised distance estimate, which cut the distance in half. But now, our distance estimate is more like 150 light years.”

A supernova exploding at such a range probably wouldn’t touch off mass extinctions on Earth, Melott said. ...

A supernova at 50 pc: Effects on the Earth's atmosphere and biota - A.L. Melott et al

• arXiv.org > astro-ph > arXiv:1702.04365 > 14 Feb 2017 (v1), 07 Apr 2017 (v2)

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[b][color=#0000FF]Homo habilis: Forensic facial approximation[/color][/b]

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<<Homo habilis was a species of the tribe Hominini, during the Gelasian and early Calabrian stages of the Pleistocene period, which lived between roughly 2.1 and 1.5 million years ago. Homo habilis is thought to have mastered the Lower Paleolithic Olduwan tool set which used stone flakes. H. habilis used these stones to butcher animals and to skin the animals. These stone flakes were more advanced than any tools previously used, and gave H. habilis the edge it needed to prosper in hostile environments previously too formidable for primates. Whether H. habilis was the first hominid to master stone tool technology remains controversial, as Australopithecus garhi, dated to 2.6 million years ago, has been found along with stone tool implements.

H. habilis' brain capacity of around 640 cm³ was on average 50% larger than australopithecines, but considerably smaller than the 1350 to 1450 cm³ range of modern Homo sapiens. These hominins were smaller than modern humans, on average standing no more than 1.3 m tall. Most experts assume the intelligence and social organization of H. habilis were more sophisticated than typical australopithecines or chimpanzees. H. habilis used tools primarily for scavenging, such as cleaving meat off carrion, rather than defense or hunting. Yet despite tool usage, H. habilis was not the master hunter its sister species (or descendants) proved to be, as ample fossil evidence indicates H. habilis was a staple in the diet of large predatory animals, such as Dinofelis, a large scimitar-toothed predatory cat the size of a jaguar.

Homo habilis coexisted with other Homo-like bipedal primates, such as Paranthropus boisei, some of which prospered for many millennia. However, H. habilis, possibly because of its early tool innovation and a less specialized diet, became the precursor of an entire line of new species, whereas Paranthropus boisei and its robust relatives disappeared from the fossil record. H. habilis may also have coexisted with H. erectus in Africa for a period of 500,000 years.>>

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A Supernova 2.6 Million Years Ago Could Have Wiped Out the Ocean’s Large Animals
Universe Today, December 12, 2018 by Evan Gough

<<About 2.6 million years ago, one or more supernovae exploded about 50 parsecs, or about 160 light years, away from Earth. At that same time, there was also an extinction event on Earth, called the Pliocene marine megafauna extinction. Up to a third of the large marine species on Earth were wiped out at the time, most of them living in shallow coastal waters. A new paper from Adrian Melott, professor emeritus of physics and astronomy at the University of Kansas, and co-authors at the Universidade Federal de São Carlos, in Brazil draws a link between the supernovae and the extinction, and suggests that muons were the guilty parties.>>

<<SLIT-ROBO Rho GTPase-activating protein 2 (srGAP2) also known as formin-binding protein 2 (FNBP2) is a protein that in humans is encoded by the SRGAP2 gene. SRGAP2 is involved in neuronal migration and neuronal differentiation. SRGAP2 also plays a critical role in synaptic development. Downregulation of srGAP2 inhibits cell-cell repulsion and enhances cell-cell contact duration. This gene is one of the 23 genes that are duplicated in humans but not in other primates.

This protein in humans has been duplicated three times in the human genome in the past 3.4 million years: one duplication 3.4 million years ago (mya) called SRGAP2B, a second duplication 2.4 mya (called SRGAP2C), and one final duplication ~1 mya (SRGAP2D). The ancestral gene SRGAP2 is found in all mammals and the human copy has been renamed SRGAP2A.

SRGAP2C slows maturation of some neurons and increases neuronal spine density. The 2.4 million year-old duplication (SRGAP2C) expresses a shortened version that 100% of humans possess. This shortened version SRGAP2C inhibits the function of the ancestral copy SRGAP2A and (1) allows faster migration of neurons by interfering with filopodia production and (2) slows the rate of synaptic maturation and increases the density of synapses in the cerebral cortex.>>