Astrobiology Science Conference 2015
sess101.pdf
Monday, June 15, 2015
PLENARY SESSION:
THE DEEP HISTORY OF A CARBON ATOM
8:00 a.m. Grand Ballroom
8:00 a.m.
Opening Remarks
8:10 a.m.
The Deep History of a Carbon Atom
Moderator:
Jamie Elsila
Panel Members:
Karen Meech
Andrew Steele
Michael Callahan
Primo Levi’s short story, “The Story of a Carbon Atom,” tracked the path of a carbon atom. The story begins, “Our
character lies for hundreds of millions of years, bound to three atoms of oxygen and one of calcium, in the form of
limestone: it already has a very long cosmic history behind it, but we shall ignore it.” This session will tell the long
cosmic history of that atom, beginning with the formation of carbon in a star, and ending with the atom involved in
prebiotic chemical reactions on Earth.
PLENARY SESSION:
SUSTAINED HABITABILITY ON A DYNAMIC EARLY EARTH
9:15 a.m. Grand Ballroom
Speaker:
James Kasting
Panel:
Timothy Lyons, Noah Planavsky, and Chris Reinhard
We know something about the habitability of early Earth, but many questions remain. Convincing evidence for life
dates back to only 3.5 Ga, whereas Earth itself is a billion years older. Despite the faintness of the young Sun,
conditions near Earth’s surface may have been too hot for life for hundreds of millions of years, either sporadically
as a consequence of impact or more generally as a consequence of high atmospheric CO2 levels. The Archean
(2.5–3.8 Ga) was more clement, but the discrepancy between oxygen isotope data from cherts, which suggest high
surface temperatures, and evidence for repeated glaciations has not been satisfactorily resolved. Climate may have
been stabilized during this time by a combination of feedback loops involving both CO2 and CH4. Like now, methane
was mostly biological in origin, so the climate control system could be described as being “Gaian.” The rise of
atmospheric O2 near 2.4 Ga probably triggered the glaciations that occurred at that time, although some authors
have argued that this causality was reversed. The resulting Proterozoic climate was less stable and “boring” than
previously thought, as glaciations have now been reported at ~1.8 Ga and ~1.2 Ga, in addition to the well-known
Snowball Earth events of the Neoproterozoic. Better empirical constraints on surface temperature and on
atmospheric O2 and CO2 are needed to reach consensus on what the early Earth environment was really like.
A 40-minute presentation by J. Kasting will be followed by 20 minutes of Q and A and open discussion with the
speaker and panel.
10:15 a.m.
BREAK