The Evolutionary Biology Lecture of the Week for August 28, 2006 is now
available at:
http://aics-research.com/lotw/
The talks center primarily around evolutionary biology, in all of its
aspects: cosmology, astronomy, planetology, geology, astrobiology,
ecology, ethology, biogeography, phylogenetics and evolutionary biology
itself, and are presented at a professional level, that of one
scientist talking to another. All of the talks were recorded live at
conferences.
This is the fifteenth lecture in a summer-long series on the new
science of astrobiology.
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August 28, 2006
Part XV: Astrobiology
Life and Death on Ice-Covered Worlds
Jere Lipps
University of California, Berkeley
24 min.
"Three feet of ice does not result from one day of cold weather."
- Chinese proverb
The notion that the sciences of paleontology and astrobiology would be
somehow linked seems quite jarring at first, but it only takes a
moment's thought to see the logic in the connection.
Water appears to be the sine qua non of life. Where liquid water
disappears, the life we know similarly disappears. Although water is
now rare on the inner planets of our solar system, it wasn't when the
system was young. Mars and Venus have since lost their oceans, and the
Earth is destined to do so as well. But there are places where water
should persist for as long as the Sun exists.
In our search for life in the solar system, we're certainly going to
look for the signs of ancient life in the former ocean basins of the
inner planets, and thus paleontologists are likely to become a
preeminent part of the astrobiological community.
There are however other bodies in the solar system that appear to have
large extant oceans of water, such as the icy moons of Jupiter and
Saturn, although they are covered by kilometers of ice. While life
could never exist on the surface of these small worlds, here too - at
least initially - we're going to have to rely on standard
paleontological processes while surveying the surfaces to detect any
life that may exist in the interior oceans.
Earth, both now and in the past, has created an analog for these icy
worlds. The idea of "Snowball Earth" proposes an Earth so cold that its
oceans froze over completely, with only interior planetary heat
allowing liquid water to persist below the ice. Two of these Snowball
Earth episodes are apparent in the geological record, and both are
coincident with significant, sudden increases in oxygen in the Earth's
atmosphere, as explained by David Catling in an earlier lecture.
In this talk, Jere Lipps argues that ice-covered worlds are no barriers
to life. These worlds provide the three things life requires - the
chemicals of life, energy to drive it, and the habitats to support it.
But death also occurs on these worlds, resulting in the potential
preservation of life forms and products as fossils that may tell a
story of the origin and evolution of life there, thus the necessity of
a paleontological approach.
On Earth's current and past icy worlds, life abounds. It lives in
close association with ice-shelves and sea ice in Antarctica and the
Arctic. Here life lives easily in a wide variety of sub-ice, inter-ice,
and surficial ice habitats. Earth's fossil record shows that life
similarly endured the Neoproterozoic Snowball Earth, when the planet
was covered entirely or substantially by ice. Life seems to have no
problem with ice, so long as liquid water exists below it.
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