Provide time frames (in millions or billions of years ago) for when each events occurred in the history of life on earth based on the fossil record and other scientific techniques.

Fossils are the dead decay of plants and organisms that were buried about millions of years ago, under certain conditions. These fossils belong to different time periods in geological history. Some of the major events that occurred in the geological past, based on the fossil evidence are as follows-

(1) The earliest fossil was found in the rocks of Western Australia that were about 3.4-3.5 billion years old.

(2) The 'great oxidation event' took place almost 2.4 billion years back during which the oxygen started to form in the atmosphere. This led to the occurrence of first photosynthetic bacteria.  

(3) The first eukaryotic and multicellular organisms came into the picture by about 2 billion years and 900 million years back respectively.

(4) The corals were initially formed about 580 million years back.

(5) Then the trilobites first appeared during the Cambrian period (about 540 million years back) and they were the most dominating species during that time.

(6) The dinosaurs were the giant, dominated species that first appeared in the Triassic age about 240 million years back.

(7) The first human fossil dated back to about 4 million years.

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