[MUSIC]
So looking at our three Goldilocks planets, Venus, Earth, and Mars.
Venus, suffered a runaway greenhouse effect, you already know.
And so the water in the oceans boiled,
goes into the upper atmosphere where the ultraviolet light breaks it apart.
You lose the hydrogen to space, the water's gone, that's it forever.
Well now the nail in the coffin is, if you have no water,
you can't have any weathering.
And so, you have broken the thermostat.
All of the carbon gets cooked and put into the atmosphere,
that's why the atmosphere of Venus has 70 bars of CO2.
That's why all of Venus's carbon is in the atmosphere, rather than on Earth where
almost all of our carbon is in calcium carbonate or other sedimentary rocks.
On Earth, the thermostat will eventually clean up the fossil fuel CO2,
but it takes a very long time.
And the other thing you should know is that there are ways in which the geometry
of the geology can change to sort of alter the set point of the thermostat.
The thermostat regulates the temperature the way a thermostat of a house can
regulate the furnace and regulate a house's temperature.
But it takes a long time to get there.
But you can also slowly change the dial on the thermostat by changing the geometry
of where the land and ocean are and mountain building
and how fast the CO2 is coming out of the Earth by degassing and things like that.
So Earth has tended to drift back and forth between sort of hothouse
climates where there's basically no ice on Earth at all.
And then climates like today.
We call this an Ice Age climate even though.