What triggered a massive ice age on Earth 480 million years ago? Scientists have a surprising answer: the humble moss.
The simple plants' interactions with rocks are believed to be the cause.
"The humble moss has created the climate which we enjoy today, from which the life we see all around us evolved," said Prof Tim Lenton of Exeter University, one of the lead researchers.
Carbon dioxide insulates the planet, rather like a duvet wrapped around it: the higher the concentration of CO2, the higher the average global temperature.
Atmospheric levels of the gas 480 million years ago are thought to have been 16 times higher than they are now, and average global temperatures are thought to have been 25C, around 10C higher than they are now.
But by 460 million years ago, CO2 levels had fallen by half and the planet began to cool, allowing the formation of the polar ice caps.
The question is: what caused the drop in CO2 levels? The answer, according to an experiment by Prof Lenton and his colleague Prof Liam Dolan of Oxford University is "moss".