Saturday, November 23, 2019
Precambrian - The Timeline of Biological History
Precambrian - The Timeline of Biological History The Precambrian (4500 to 543 million years ago) is a vast period of time, nearly 4,000 million years long, that began with the formation of the Earth and culminated with the Cambrian Explosion. The Precambrian accounts for seven-eighths of our planets history. Numerous important milestones in the development of our planet and the evolution of life occurred during the Precambrian. The first life arose during the Precambrian. The tectonic plates formed and began shifting across the surface of the Earth. Eukaryotic cells evolved and the oxygen these eary organisms exhaled collected in the atmosphere. The Precambrian drew to a close just as the first multicellular organisms evolved. For the most part, considering the immense length of time encompassed by the Precambrian, the fossil record is sparse for that time period. The oldest evidence of life is encased in rocks from islands off of western Greenland. Theses fossils are 3.8 billion years old. Bacteria that is more than 3.46 billion years old was discovered in Western Australia. Stromatolite fossils have been discovered that date back 2,700 million years. The most detailed fossils from the Precambrian are known as the Ediacara biota, an assortment of tubular and frond-shaped creatures that lived between 635 and 543 million years ago. The Ediacara fossils represent the earliest known evidence of multicellular life and most of these ancient organisms appear to have vanished at the end of the Precambrian. Although the term Precambrian is somewhat outdated, it is still widely used. Modern terminology disposes of the term Precambrian and instead divides the time before the Cambrian Period into three units, the Hadean (4,500 - 3,800 million years ago), the Archean (3,800 - 2,500 million years ago), and the Proterozoic (2,500 - 543 million years ago).