Modern scientists estimate that the earth is 5 to 6 billion years old. By comparison, most of the evolution of human like creatures has taken place in a very short time – the first mammals began to evolve from reptiles perhaps 200 million years ago, and the first placental mammals (i.e., that give birth to live young.
The earth as it may have appeared early in its history after the initial crust had started to form. Prior to about 4.6 billion years ago the proto-earth formed from the coalescence of variously sized ‘planetesimals’ or small bodies of rock and frozen gases that condensed in the plane of the ecliptic, the flat regions of space in which human planets orbit.
Rabbits, cacti, bumblebees, jellyfish, penguins, sunflowers – all living things on the earth are the descendents of simple, single-celled organisms that loved more than 3.5 billion years ago.
The claim based on fossils, not just chemical signals. Filamentous forms in agate-like rock dated to be around 3.5 billions years in age were discovered by American paleontologist William Schopf.
The first human like animals appeared some 3 million years ago, around the beginning of the epoch known as the Pleistocene. This was the time of the great ice ages, when drastic changes in climate affected life throughout the world.
This climate change may account for more rapid evolution that produced modern human beings in such a short period; that is the pace of natural selection may have been quickened because of environmental changes and the resulting pressures on our ancestors.
The evolution of life on earth
