Another God and natural life bookmark
Earth 2.7 billion years ago was very different from the planet we know today.
It spun much faster, the Moon was closer and the Sun was much weaker. And there were no animals or plants in existence back then; the air was simply not breathable.
"There was probably quite a bit of nitrogen in the atmosphere, like today, but there was no oxygen," explained Sanjoy Som from Nasa's Ames Research Center.
"The oxygen was likely replaced by greenhouse gases such as carbon dioxide and methane.
"My palaeobarometry work cannot tell you precisely what the gases were, but it will assist modellers of atmospheric composition by giving them a constraint," he told BBC News.
Dr Som told the AGU meeting - the largest annual gathering of Earth scientists - that the "fossil raindrops" were discovered in Ventersdorp in the North West Province of South Africa in the 1980s.
Jonathan Amos BBC Science and Environment December 5 2012
Fossil raindrops probe ancient atmosphere
