Current Science has developed many disciplines to assess Earth history. Obviously, this is based on the Universe, Solar and Earth genesys models, with all possible hypothesis, starting with the Big Bang theory, the solar nebulae accretion, and the earth generation from planetoides accretion and collisions. What is of some value is the consistancy between many observations and models like baryogenesis and the quantity and diversity of elements in the universe and on the earth. It gives some credibility to it. The purpose of this post is to give the scientific understanding in regard with earth history and life genesis vs time in order to compare with the traditions time-lines. It comes from Geology, and it is called the stratigraphic scale.
4 major eras have been identified (numbers are in million of years) : Precambrian (4,600 M to 550 M), Paleozoic (550 M to 250 M), Mesozoic (250 M to 65 M), and Cenozoic (65 M to now).
They are divided in sub-periods which may be of some interests in our search, in regard with life development on earth. They will be listed together with the sequence of events.
According to lastest findings and models :
– Earth accretion process started 4,600 M years ago. Accretion started when the protosolar cloud temperature decreased, triggering materials condensation. Then the combined energy of gravitational collapse and radioactive elements disintegration generated the fusion process, melting the compound of materials. The final cooling phase creates the different layers of the earth. The complete process is supposed to have lasted for 100 M years. (to be compared to the 300 M years from the SD)
– Life emerged first on earth between 4,600M and 3,500M years ago (blue-green algae) – The SD says that first appearance of “humanity” on planetary chain was 1,664 M years ago.
– Invertebrates and lower vegetals started 2,500 M years ago
– First vertebrate (fish) appeared during Cambrian era ( 550 M years ago )
– First batracian = Carboniferous era, 350 M years ago
– First reptiles = Permian era, 280 M years ago
– First mammal = Trias era, 235 M years ago
– First birds = Jurassic era, 200 M years ago
– Oldest man discovered = Pleistocene era, 1.8 M years ago. The S.D says that the human period, up, to year 1887 lasted for 18.6 M years.