The Evolution of Life

Topics: Extinction event, Dinosaur, Fossil Pages: 30 (11667 words) Published: May 12, 2011
The Evolution of Life
This section provides information about the evolution of life on Earth. For reasons of simplicity some important events and life forms were selected for each geological time span. However this should not give the impression that the evolution of life on Earth is or was a sequential event. Many life forms that were not mentioned in this text were very successful and have evolved or in some cases maintained a very successful life strategy. Prokaryotes, for example are the most successful and abundant organisms on Earth, in both numbers and biomass and still make up to 90% of the total weight of living things. For further information on each geological period or special life forms mentioned, there are links to other websites about this time. The evolution of life is organized into 20 sections referring to their biological and geological significance. You will find a list of useful reference websites at the very end of the sections * Birth of Earth - approximately 4600 million years ago - The Hadean Period (4600 m.y. -3800 m.y.) * The earliest cells and stromatolites - The Archaean Period (3800 m.y. - 2500m.y.) * The first algae - 1200 million years ago - The Proterozoic Era (2500 m.y. - 544 m.y.) * The Vendian animals - 570 million years ago - The Vendian Period (650 m.y. - 544 m.y) * The Cambrian Explosion - The Cambrian Period (544m.y.- 505 m.y.) * The Rise of the fish - The Ordovician Period (505 m.y.-440 m.y.) * Venturing on land - the Silurian Period (440 m.y. - 410 m.y.) * Invasion of the land - the Devonian period (410m.y. - 360m.y.) * Reptiles and Conifers - the Carboniferous Period (360m.y. - 286m.y.) * Pangea - the Permian period (286m.y.- 248m.y.)

* Mammals and dinosaurs - the Triassic period (248m.y.-213m.y.) * Dinosaurs and birds - the Jurassic period (213 m.y. - 145 m.y.) * The final season of the dinosaurs - The Cretaceaous period (145m.y.-65m.y.) * Archaic mammals and early primates - the Palaeocene epoch (65m.y.- 55.5m.y.) * Whales and horses - The Eocene epoch (55.5 m.y. - 33.7m.y.) * Grasses and primates - the Oligocene epoch (33.7m.y. - 23.8m.y.) * Kelp forests and horses - the Miocene epoch (23.8 m.y. - 5.3m.y.) * The first hominids - the Pliocene epoch (5.3 m.y. - 1.8 m.y.) * Glaciation, the Moa and Homo sapiens - the Pleistocene epoch (1.8 m.y. - 10,000 y.) * The Age of Humans - the Holocene epoch (8,000 years - present) * Reference Websites

Birth of Earth - approximately 4600 million years ago - The Hadean Period (4600 m.y. - 3800 m.y.) Scientists estimate that our planet, Earth, formed around 4600 million years ago. The oldest rocks dated so far are from the Acasta Gneiss Complex near Great Slave Lake, Canada with an age of about 4030 million years. The Isua Supracrustal rocks in West Greenland are dated at about 3700 to 3800 million years old. The best age estimate for the Earth's final formation is about 4540 million years ago, based on data from the Canyon Diablo meteorite. In addition, mineral grains called zircon from sedimentary rocks from west-central Australia have recently been reported with an age of about 4400 million years. While we don't know exactly how the Earth was formed, we have some really good evidence to support the following hypothesis: The Earth began as part of the accretion of thesolar system. The formation of the planets (including Earth), asteroids, meteors, comets and the central sun - formed through the tendency of matter to clump together, until finally there were substantial bodies, the planets and their moons, sweeping up all the 'left-over' bits in their orbits. Studies of the Moon's surface show that in its early history it was subjected to bombardment by giant meteorites. Earth's early history must have been even more violent because of the greater gravitational forces involved. None of those early bombardments can be seen today, as they have been transformed by Earth's erosional...
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