Lyall Watson – Heaven’s Breath

Then it belched.  The hot breath of the young planet bubbled up through cracks and fissures in the crust, breaking out in the form of geysers, fumaroles and explosive volcanic eruptions.  Methane, ammonia and water vapour – and possibly large quantities of carbon dioxide – were released from combination with hot rocks and thrown almost at random into a mechanical mixture that formed the first atmospheric blanket.  This acted like the glass in a green house, cutting down on the amount of heat radiated back from Earth’s surface and keeping it reasonably warm, probably somewhere between 15 and 30 degrees centigrade.  Warm enough for life to begin.

Once living things appeared on Earth, they started to feed on the atmosphere, nibbling away at the blanket that protected them.  By rights, the planet should soon have become icebound and lifeless, stripped bare as the guardian gases boiled away under the increased radiation from an ever more active Sun.  But neither of these things happened.

Somehow, despite drastic changes in the composition of the early atmosphere, and a large increase in the mean solar flux, the temperature of Earth’s surface has been kept within astonishingly narrow limits for many hundreds of millions of years.  And these limits are precisely the ones that life requires.