Answer to Question #101756 in Evolution for Nibedita Rudra

Question

Give an account of geological record.

Answer 1

The geological records refer to the antiquity of the earth as chronicled in the rocks that make its shells known as strata. From when the earth was formed, rocks have continuously formed and worn away.

The strata and their fossils arrangement gave geologists a breakthrough on how the earth was like in the ancient times.

While studying the earth, geologists came up with a standard time scale that splits the earth’s history into four subsets. These subsets are eons and their subdivisions; eras, periods, and epochs.

Hadean, known to be the first eon, lasted from the origin of the earth between 4.6 to 4 billion years ago. During that time, the earth was very hot and partially molten surface.

Archean is noted to be the second eon, which came at the period that the earth had cooled enough (4 to 2.5 billion years ago). At this period, rocks and continental plates could form, although it had some toxic gases that could not support life. Only prokaryotic cells could survive then.

Proterozoic, eon is the third. It started at about 2.5 billion years ago and ended at around 542 million ago. This eon, according to geologists, could support life due to increased atmospheric oxygen concentration; thus, eukaryotic cells could survive.

Phanerozoic eon, which is the fourth eon, lasted 542 million years ago. This eon is subdivided into three eras; the Paleozoic, Mesozoic, and Cenozoic, with each lasting roughly 100 million years.