Monday, October 11, 2010

Geological Timeline

If the evolution of life on Earth seems to go back a long way, it may be put into a geological context by comparing the age of the planet with the life time of a person now 47 years old. Fossils only tell us about life since the Pre Cambrian era began 600 million years ago, but by then our person would have already celebrated their 40th birthday. Soon after, multi cellular life in the sea diversified into thousands of species. Two years later on the human timescale, planets and insects emerged onto land followed by amphibious animals. Then things began to speed up. It is only a year since the age of the dinosaurs, a week since that last ice age and a mere four hours since our own species, Homo sapiens, first walked on the planet.
During the Earth’s life time, the Solar System has moved around the galactic centre about 25 times. The ocean crust has been recycled 50 times. The continents have accumulated, crashed into each other and broken apart. Landscapes have been eroded and weathered. And the atmosphere has been altered by life forms. Now the globe is being transformed by humans.  Judging from the evolutionary path of the Sun, the Earth has five billion years to go.
 The first living things were microscopic bacteria and protozoa. The first visible sign of life was probably a film of algae. Some algae or filamentous bacteria grew in large mats in shallow after near the tide line, binding sand among them to form layered mounds. Still found growing in warm seas today, fossil stromatolites from the oldest macroscopic fossils in 3,500 million years old deposits in Australia.