Tuesday, June 5, 2012
There's Rare and then there's Rare
Last night, June 5, 2012, we saw the planet Venus transit our Sun. This event is considered rare, because it happened last in 1882 and will not happen again until 2117. But “rare” is relative, in this case relative to the life span of most humans. But we are in the midst of another far, far rarer event, a mass extinction; the sixth in the history of the earth.
The last mass extinction occurred 65 million years ago (Mya), and obliterated more than half the world’s terrestrial and marine life, including those spellbinding behemoths of prehistory, the dinosaurs -- a species that had dominated earth for 135 million years. Global temperature was up to 40°F warmer than present, and seas over 900 feet higher than today swept over the land and in a flood of truly biblical extent covered 40% of the continents.
There have been five mass extinction events in the earth’s history; at the end of the Ordovician period, 434 Mya; late in the Devonian, 354 Mya: the end of the Permian, 251 Mya, when a staggering 80-90 percent of all marine species went extinct; and the end of the Triassic, when half of all marine invertebrates, and 80% of all land quadrupeds went extinct.
What caused these mass extinctions? The first modern human species appeared only some 2.2 Mya, so we stand blameless for these first five extinctions. That is not the case for the sixth. In coming posts we’ll examine what paleontologists and other scientists tell us about the causes of these events, and why these same scientists tell us we are in the midst of another mass extinction.
Stay tuned. We’ll get to this before Venus next transits the sun.