List the stages in the evolution of the earth and explain each stage in brief.
The evolution of the earth occurred through several distinct stages over a period beginning 4,600 million years ago.
In the initial stage, the earth was a barren, rocky, and hot object with a thin atmosphere consisting of hydrogen and helium. This was far from the present-day picture of the earth with its water and life-supporting atmosphere.
In the next stage, the gas cloud started getting condensed. The matter around the core developed into small-rounded objects which, through the process of cohesion, developed into what are called planetesimals. Larger bodies started forming by collision, and gravitational attraction caused the material to stick together. Planetesimals were a large number of smaller bodies.
In the final stage of planetary formation, these large numbers of small planetesimals accreted to form fewer large bodies in the form of planets.
The last phase in the evolution of the earth relates to the origin and evolution of life. Initially, the earth and its atmosphere were not conducive for life. Life began to evolve sometime around 3,800 million years ago through chemical reactions that generated complex organic molecules capable of duplicating themselves.
Explanation
The textbook describes the evolution of earth in stages: (1) initial barren, rocky, hot state with hydrogen-helium atmosphere, (2) formation of planetesimals through condensation and cohesion, (3) accretion of planetesimals into planets, and (4) origin of life around 3,800 million years ago. The answer follows this sequence using only information from the provided context.