Good show. As opposed to the biological back and forth of the first of todays evolutionary documentaries it showed the scientific back and forth over the cause of the largest mass extinction in history. From decades of fruitless research to a multitude of theories as methods of analysis and new sites were investigated.

The first suspect was massive volcanic eruptions in Siberia but the CO2 estimates from the estimated amount of lava were enough only for a 4 or 5 degree rise. Enough for only a minor mass extinction.

Data was uncovered suggesting a very rapid extinction which lead scientists in the direction of a massive impact, but no crater could be found of the proper age. Then new simulations indicated the impact may have been big enough to cause a lava flow burying the crater. However none of the other indicators of the KT impact could be found at all or at sufficient levels.

A new site was found in Greenland with a far larger terminal layer than anywhere else. It indicated a three phase extinction. A slow gradual extinction on land over tens of thousands of years. A very rapid marine extinction followed by a die off of most of the rest of land life. This pretty much ruled out a singular impact as the cause and the documentary dismissed it all together. Aside from the time scale another clue from Greenland was a huge spike in C12 concentration.

Independent fuel research led to the discovery of methane hydrates in the ocean and evaluation of its properties. It was found that a rise of 4 to 5 degrees would release methane into the atmosphere in an amount capable of increasing the temperature another 4 or 5 degrees giving the total temperature rise scientists estimated would be required to cause a mass extinction of the Permian level. The conclusion a two step Global Warming process initiated by massive volcanic eruptions and CO2 release followed by methane releases causing even more.

The programs final note: Only one of the previously dominant mammal like reptiles is known to have survived the Permian extinction. A cow sized animal with pig like habits. Once again the human ancestral line almost ended.

My take away comments

Don't be blase about global warming.
Don't assume mankind's evolution was an expected outcome of evolution.
The top of the food chain is always the most vulnerable during mass extinctions
DSC often does a good job portraying the back and forth nature of real science
1 hour is two short to tie up all loose ends such as

The buckey ball evidence for a Permian ending impact.
Does the impact evidence play any part in the drama?
Why other sites showed the permian extinction was rapid.
How methane hydrates build up in the ocean.
Could an impact have cause the massive eruptions of the Siberian traps?

I'm dissappointed both shows are not planned for rerun any time soon. They both counter two common misconceptions of science among the general public. That evolution has a direction and that science is some kind of PC monolith unwilling to change.

Regards,
Mark