BILLIONS of years ago, a weaker sun should have made the Earth a chilly place – so why was it balmy instead?
The sun that shone on the early Earth was around 25 per cent dimmer than today, so atmospheric temperatures should have been colder by around 25 °C. But ancient rocks show that liquid water existed, proving that temperatures must have been above freezing.
This can be explained if greenhouse gases acted as an insulator – but modelling has showed that carbon dioxide in the atmosphere would need to have had an implausibly high partial pressure of over 50 millibars…
