Life on Earth
- Pp. 21-39 (19)Arnold Hanslmeier
This chapter reviews the origin and evolution of life on Earth. The collapse of an interstellar cloud into a protostar surrounded by a protoplanetary disk is reviewed. The early Earth was extreme hostile to life and first signs of life data from the time 3.8 billion years ago. Abiogenesis is discussed and it is highlighted that the process of evolution was not linear but it came about in several big steps. The idea of panspermia is reviewed. The famous Urey Miller experiment and other experiments are reviewed. Most probably life has started in deep undersea geysers called black smokers. During the last 500 million years, at least five times mass extinction has occurred. Possible astrophysical explanation for this extinction is given. The main message of this chapter is that we still do not completely understand abiogenesis though different possibilities are being discussed such as the synthesis of amino acids in Urey-Miller like environments, or near deep underwater geysers etc.