ELISABETTA PIERAZZO
Lunar & Planetary Laboratory
U. of Arizona

Talk:   Wed., 21 February
        1:00 pm
        375 LeConte
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"Impacts and the Evolution of Planetary Biospheres"

ABSTRACT

It is becoming increasingly clear that impacts affected the evolution
of the Earth's biosphere, ranging from impact annihilation of life to
panspermia. A large amount of evidence points to the possibility that a
large impact was responsible for the mass extinction (including the
demise of the dinosaurs) at the end of the Cretaceous. Impact events
may also have played a role in the origin of life. While it is hard to
test the possibility of a strict connection between origin of life and
impact events, the suggestion that asteroid and comet impacts may have
delivered a substantial fraction of the Earth's prebiotic inventory of
organic is nearly a century old.  This talk summarizes how hydrocode
modeling of impact cratering has been used to better understanding: 1)
the end-Cretaceous impact event and its effects on the environment, and
2) the possibility of survival of organic material (amino acids) in
large impact events on the Earth and other bodies of the Solar System.

The end-Cretaceous impact event produced the Chicxulub structure, in
the Yucatan Peninsula, Mexico. I modeled the Chicxulub impact event with
a series of high-resolution two- and three-dimensional hydrocode
simulations covering both asteroid and comet impacts. The main goal of
this work has been to estimate the amounts of climatically active
gases, namely S-bearing gases, CO2, and water vapor, released into the
atmosphere by the impact event. These estimates are then used to
investigate the climate forcing associated to the impact, and,
eventually, its connection to the environmental catastrophe of the
end-Cretaceous.

About a decade ago Chyba et al (1990) concluded that most organics
would be entirely destroyed in large comet and asteroid impacts on the
early Earth. The problem has been reexamined through new,
high-resolution hydrocode simulations of asteroids and comet impacts
coupled with recent experimental data for amino acid pyrolysis in the
solid phase. The results indicate that organic material does survive
the shock heating of large (km-radius) cometary impacts. In particular,
at the time of the origin of life on Earth, the steady-state oceanic
concentration of certain amino acids delivered by comets could have
equaled or substantially exceeded that due to Miller-Urey synthesis in
a CO2-rich atmosphere. The possibility of impact delivery of organic
material to other planetary surfaces is also investigated.