The Evolutionary Biology Lecture of the Week for June 19, 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 fifth lecture in a summer-long series on the new science of
astrobiology.

=====================================

June 19, 2006

Part V: Astrobiology

Sympathy for the Devil: The Case for Life on Venus

David Grinspoon, Southwest Research Institute, Boulder
33 min.

"Venus favors the bold."

-- Ovid (43 BC - 17 AD)

The next four lectures will ask the question: "Why did things go so right for
life on Earth?" To answer that question, we ask, "Why did things go so badly on
Earth's nearest neighbors, Venus and Mars?"

Mars is half the size of Earth, but Venus is nearly Earth's identical twin. All
three planets likely had substantial oceans, but Venus and Mars lost their
oceans some time ago. Mars' oceans apparently evaporated almost immediately,
but Venus may have kept its oceans for 600 million years, as estimated by Jim
Kasting of Penn State in 1988, or for as long as two billion years, as
suggested by David Grinspoon in this week's lecture.

For all of its history, Mars has lain outside the "habitable zone," where
planetary temperatures make long-term surface liquid water possible. Worse,
because of Mars' small size, the internal heat engine of Mars sputtered off
sometime ago, thus the world stopped evolving geologically, no longer
replenishing its atmospheric gases.

Venus, on the other hand, lies interior to the habitable zone and has received
too much solar flux. While its oceans were evaporating, UV radiation was
dissociating its water into its constituent components, providing sufficient
energy for the escape of hydrogen into space. For a bit of time, perhaps a
billion years, Venus may had water oceans overlain by an oxygen-rich atmosphere
before any other planet. But that's not Venus today.

Venus' present may well be Earth's future. As the Sun continues to brighten, it
is expected that the Earth will also lose its oceans in 500 million to one
billion years, thus in appproximately the same short period of time that it has
taken life on Earth to progress from trilobite to astronaut, life will come to
an end on Earth as well — at least on its surface.