The Channel 4 production, Catastrophes, is currently running on SBS in Australia. The final episode is scheduled for next Wednesday.
There is some hype and melodrama but the catastrophe theme of evolutionary development is backed up by reasonable, although one sided, scientific comment. When you research it you find there are opposing theories. Nevertheless, this series is good for a discussion IMO.
The evidence for the destruction of the dinosaurs and 70 percent of other species 65 million years ago by an asteroid the size of Mount Everest was well presented. From the  iridium, shocked quartz and soot in the Cretaceous-Tertiary boundary layer we learn that this giant asteroid collided at Mexico’s Yucatan peninsula. The crater was discovered by an oil company so I guess there are unexpected benefits arising from oil exploration 🙂
I was less clear about the reasons for the end of snowball earth 650 million years ago. How come those volcanoes that released CO2 into the atmosphere weren’t sufficiently active earlier. This wasn’t clear to me at least.
The general theme, that evolution proceeds in part through a series of catastrophes is one that resonates with me. The challenge is to present this theme in a more thoroughly scientific manner.
The torrent is available: Catastrophe_complete_series
Rock (slowly) absorbs CO2 over time. It is called the CO2 silicate weathering thermostat. Rock covered with ice cannot absorb CO2. The end of the snowball earth episode is not due to volcanoes suddenly becoming active, but due to ice preventing rock from absorbing the CO2, enabling it to build up. (See also this Richard Alley talk.)
ok, thanks Ilewelly, here is my summary.
Rock weathering takes CO2 out of the atmosphere
calcium silicate+water+CO2 –> Ca ions+Silicic acid+bicarbonate ions
This is then converted into shells – calcium carbonate
The rate of rock weathering depends on the temperature, faster when warmer, slower when colder
Volcanoes put CO2 into the atmosphere – the shells are subducted so it’s the same CO2 being put back in a cycle – but this is more steady state, not dependent on temperature
So, the whole system works like a thermostat. As temperature increases then there is more rock weathering and atmospheric CO2 declines and the earth cools, which may even lead to a snowball earth. As temperature decreases then there is less rock weathering and atmospheric CO2 increases and we get greenhouse warming.
I liked Richard Alley’s enthusiasm for science. I guess Channel 4 didn’t explain this very well, they were more into making a melodrama.