It is accepted that the ancient Sun was considerably cooler than our local star is today, so much so that Earth a few billion years ago should have been a lifeless frozen ball. But scientists have also shown that the planet was not frozen—shallow seas warmer than any modern ocean abounded with microbial life.
A recent study, detailed in the journal Nature, is a good example of the sometimes convoluted, even improbable reasoning is used to get a handle on earthly climates during eons long vanished. Using the fossilized impact dimples from rain drops that fell 2.7 billion years ago, researchers have calculated new limits on the density of Earth’s atmosphere. This, in turn, has implications on the development of the ancient atmosphere and what role greenhouse gases may have played in warming the young Earth.