•Extinction 3-known as the Late Devonian Extinction-happened about 364 million years B.C. The bio marker of this event is the great die off of the agnathan or jawless fishes that filled the Devonian seas. But there was land life, too, with the first primitive forests (the Gilboa, N.Y., tree fossils mentioned here a few weeks ago), insects and lungfishes. Again, everything from cosmic impact to climate change are blamed, but there's no definitive smoking gun.
Next week: Extinctions 4 and 5 and cosmic agents of change.
What's in the Sky: On Aug. 10, the Moon is at perigee, the point where our natural satellite's orbit is closest to Earth.
Lou Varricchio, M.Sc., was a science writer at the NASA Ames Research Center. He is a NASA-JPL Solar System Ambassador in Vermont and is the recipient of the U.S. Civil Air Patrol's Brigadier General Charles E. "Chuck" Yeager Aerospace Education Achievement Award. His second book, "Seeing Stars", an illustrated collection of his newspaper columns, will be published next year.