GEOLOGY

Detailed explanation-1: -The earliest life forms we know of were microscopic organisms (microbes) that left signals of their presence in rocks about 3.7 billion years old.

Detailed explanation-2: -During the earliest evolution on earth, life probably resembled one big genetic jumble. At some time, presumably around 3.8 to 3.5 billion years before today, the very first biological species appeared – the ancestor of all life forms that developed via Darwinian evolution.

Detailed explanation-3: -These are the Hadean (4.6 billion to 4 billion years ago), the Archean (4 billion to 2.5 billion years ago), the Proterozoic (2.5 billion to 541 million years ago), and the Phanerozoic (541 million years ago to the present).

Detailed explanation-4: -These include major geologic events, climate changes, radiation of organisms into new habitats, changes in ecosystems, changes in continental positions, and major extinctions.