EVERYDAY SCIENCE

Detailed explanation-1: -Life on Earth began at the end of this period called the late heavy bombardment, some 3.8 billion years ago. The earliest known fossils on Earth date from 3.5 billion years ago and there is evidence that biological activity took place even earlier-just at the end of the period of late heavy bombardment.

Detailed explanation-2: -The oldest known fossils, in fact, are cyanobacteria from Archaean rocks of western Australia, dated 3.5 billion years old. This may be somewhat surprising, since the oldest rocks are only a little older: 3.8 billion years old! Cyanobacteria are among the easiest microfossils to recognize.

Detailed explanation-3: -But the oldest known rocks on Earth are in Greenland, where a formation known as the Isua supracrustal belt (ISB) dates to between 3.7 billion and 3.8 billion years old.

Detailed explanation-4: -Evidence of microbes was also preserved in the hard structures (“stromatolites”) they made, which date to 3.5 billion years ago. Stromatolites are created as sticky mats of microbes trap and bind sediments into layers. Minerals precipitate inside the layers, creating durable structures even as the microbes die off.