Sometimes it just seems that the Earth is out to get life. Often, in discussions of what makes a planet habitable - nice liquid water oceans, mild temperatures, gentle seasonal changes - I think we can forget that even a good planet for life may also show an extraordinarily hostile side. I was reminded of this in reading a short piece about an ocean drilling program in the Pacific that may help with our understanding of so-called 'supervolcanoes' (like Yellowstone). Supervolcanoes are a breed apart as volcanoes go - and are possibly due to the buildup of huge amounts of magma that doesn't manage to leak through the Earth's crust politely, and instead goes 'bang' in a big way. The vast amounts of material, in particular gases, that a supervolcano can release have long been considered as a sure fire way to cause mass extinctions and drastic variations to the Earth's climate and environments.
carbon-silicate cycle helps maintain atmospheric CO2 at a level that keeps surface temperatures in the liquid water range, and is critically dependent on geophysical cycles. It also seems likely that the Earth's geophysical magnetic field helps prevent atmospheric loss (and in particular the loss of hydrogen, which comes from dissociated water molecules, and therefore results in the 'drying out' of a planet). Some research even argues that planets somewhat more massive than the Earth, so-called super-earths, may therefore be more amenable to life because all this geophysical activity is more guaranteed than it is on a smaller world.
There's a grand process at play here. While we as a species like stability, the larger phenomenon of life definitely requires planets that are still kicking - geophysically that is. Not only that, but the very process of evolution itself, the natural selection of traits, nature's endless experimentation, seems to ultimately benefit from the occasional disaster. Mass extinctions are bad news for the species getting the pink slip, but terrific news for the thousands of new species that will emerge at a later time. So, supervolcanoes; to use an old adage, can't live with them, can't live without them.