Astrocast #220 (Mass Extinction Events)

Worth two observation hours, per Mr. Percival

In this podcast, Fraser and Pamela talk about the different times in the past where the majority of the life on Earth died, how they died, and how we finally found out about it.  The most recent one, the asteroid that hit the Yucan peninsula, killed most of its victims either from the initial impact, the shock wave directly resulting from the initial impact, or the years of skies darkened by dust thrown up into low Earth orbit (where anything that had been living after the impact and shock wave that had been carried up there died) by the shock wave from the initial impact.  This caused many plants to die, causing many herbivores to starve, resulting in first-level carnivores to slowly die off.  This wave of one trophic level mostly dying off causing another to die off quickly found its way to the highest levels, where it had the most impact because the animals on top have the biggest appetites, and the fewest resources.

In the KT event, the most famous one, where over 70% of the land population and over 95% of the aquatic population died, it is believed that it was the result of a meteor that hit the Earth so hard at just the right angle that the shock wave built up on the opposite side of the world and either created a volcano of its own or pushed the volcanoes already there into overdrive, effectively kicking the populations back down as soon as they tried to rise up out of the rubble.

For the prior events, it gets exponentially harder to research the events because the Earth recycles its crust, so the older impact craters or volcanic debris either has already been recycled or is on the verge of being recycled.  This means that we mostly have to rely on how many died following each event (because it is more likely for fossils to be available from that time period somewhere in the world than it is for one specific point to still be analyzable).