It was the first underground movement in our planet's history: Primitive bacteria that lived 2.75 billion years ago built themselves caves to live in, according to a new study. Today, the traces they left behind are stoking hopes that similar life forms could exist on Mars.
Early Earth was a rough place to live — there was no oxygen in the atmosphere, or ozone layer to protect the surface from harmful ultraviolet radiation. Most life at the time protected itself by living in the oceans, or excreting thin films of material that acted as biological shields.
Early Earth was a rough place to live — there was no oxygen in the atmosphere, or ozone layer to protect the surface from harmful ultraviolet radiation. Most life at the time protected itself by living in the oceans, or excreting thin films of material that acted as biological shields.
