If you are curious about Earth's periodic mass extinction events
such as the sudden demise of the dinosaurs 65 million years ago,
you might consider crashing asteroids and sky-darkening super
volcanoes as culprits. But a new study, published June 15, 2008,
in the journal Nature, suggests that it is the ocean, and in
particular the epic ebbs and flows of sea level and sediment
over the course of geologic time, that is the primary cause of
the world's periodic mass extinctions over the past 500 million
years. "The expansions and contractions of those environments
have pretty profound effects on life on Earth," says Shanan
Peters, a University of Wisconsin-Madison assistant professor of
geology and geophysics and the author of the new Nature report.
In short, according to Peters, changes in ocean environments
related to sea level exert a driving influence on rates of
extinction, which animals and plants survive or vanish, and
generally determine the composition of life in the oceans. Since
the advent of life on