Various:
Cosmologist
Adrian
Melott has been researching for some time mass extinctions
in the Earth's fossil records and linking them to astrophysical
events.Recently,
Melott and Brian
Thomas looked at the
Ordovician
extinction, which occurred 450 million years ago and
resulted in the loss of 60% of marine invertebrates.According
to computer simulations and matched with the fossil record,
they find that their data suggests that photons from a
gamma-ray burst approximately over the South Pole (and no
further than -75 degrees) caused the atmosphere's chemistry to
change, doubling the level of ultraviolet-B solar radiation
reaching the surface.In this scenario parts of north China,
Laurentia, and New Guinea—which lay north of the
equator—should be a refuge from the ultraviolet effects,
and show a different pattern of extinction in the "first
strike" of the end-Ordovician extinction, if it was induced by
such a radiation event.Melott cautions that gamma-rays or
x-rays may not be the main cause for extinction events but
could be the trigger for tipping an already stressed
environment into a catastrophic event.
Related Link
Late Ordovician
Geographic Patterns Of Extinction Compared With Simulations Of
Astrophysical Ionizing Radiation DamageIn a broader article
in SEED magazine
Melott
talks about his earlier research on cyclic mass
extinctions.There are at least 20 mass extinctions throughout
the fossil record that fit a 62-million year cycle. Sometime
ago Melott suggested that the solar-system's orbit around the
Milky Way's
center—which oscillates through the galactic plane
with a period of around 65 million years, is the key—the
galactic magnetic field protects the solar-system from
extragalactic cosmic rays.As the solar system "bobs" out of the
galactic plane it becomes exposed to these
cosmic
rays which can cause enhanced cloud formation and depletion
of the ozone layer, killing off many small organisms at the
base of the food chain and potentially leading to a population
crash.
Related Links
The
Extinction Oscillator
Do Extragalactic
Cosmic Rays Induce Cycles in Fossil Diversity?
Related Physics Today article
Recent Nearby
Supernovae May Have Left Their Marks on Earth May
2002
