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Earth Planet Time Line History


Nature creation on Earth ::-- Earth Ocean's||Earth Volcano's|| Earth River's||Earth Mountain's||Earth Waterfall's|| Earth Desert's||Earth Wonder's||Earth Moon||Earth Rainbow||


Age of the Earth

The age of the Earth is 4.54 billion years (4.54 × 109 years ± 1%). This age is based on evidence from radiometric age dating of meteorite material and is consistent with the ages of the oldest-known terrestrial and lunar samples. Following the scientific revolution and the development of radiometric age dating, measurements of lead in uranium-rich minerals showed that some were in excess of a billion years old.
The oldest such minerals analyzed to date – small crystals of zircon from the Jack Hills of Western Australia – are at least 4.404 billion years old. Comparing the mass and luminosity of the Sun to the multitudes of other stars, it appears that the solar system cannot be much older than those rocks. Ca-Al-rich inclusions (inclusions rich in calcium and aluminium) – the oldest known solid constituents within meteorites that are formed within the solar system – are 4.567 billion years old, giving an age for the solar system and an upper limit for the age of Earth.
It is hypothesised that the accretion of Earth began soon after the formation of the Ca-Al-rich inclusions and the meteorites. Because the exact accretion time of Earth is not yet known, and the predictions from different accretion models range from a few millions up to about 100 million years, the exact age of Earth is difficult to determine. It is also difficult to determine the exact age of the oldest rocks on Earth, exposed at the surface, as they are aggregates of minerals of possibly different ages.



Basic timeline Earth planet

The basic timeline of a 4.5 billion year old Earth, with approximate dates:

  • 3.8 billion years of simple cells (prokaryotes),
  • 3 billion years of photosynthesis,
  • 2 billion years of complex cells (eukaryotes),
  • 1 billion years of multicellular life,
  • 600 million years of simple animals,
  • 570 million years of arthropods (ancestors of insects, arachnids and crustaceans),
  • 550 million years of complex animals,
  • 500 million years of fish and proto-amphibians,
  • 475 million years of land plants,
  • 400 million years of insects and seeds,
  • 360 million years of amphibians,
  • 300 million years of reptiles,
  • 200 million years of mammals,
  • 150 million years of birds,
  • 130 million years of flowers,
  • 65 million years since the non-avian dinosaurs died out,
  • 2.5 million years since the appearance of the genus Homo,
  • 200,000 years of anatomically modern humans,
  • 25,000 years since the disappearance of Neanderthal traits from the fossil record.
  • 13,000 years since the disappearance of Homo floresiensis from the fossil record.


Development of modern geologic concepts

Studies of strata, the layering of rocks and earth, gave naturalists an appreciation that Earth may have been through many changes during its existence. These layers often contained fossilized remains of unknown creatures, leading some to interpret a progression of organisms from layer to layer.
Nicolas Steno (17th century) was one of the first Western naturalists to appreciate the connection between fossil remains and strata. His observations led him to formulate important stratigraphic concepts (i.e., the "law of superposition" and the "principle of original horizontality"). In the 1790s, the British naturalist William Smith hypothesized that if two layers of rock at widely differing locations contained similar fossils, then it was very plausible that the layers were the same age. William Smith's nephew and student, John Phillips, later calculated by such means that Earth was about 96 million years old.
The naturalist Mikhail Lomonosov, regarded as the founder of Russian science, suggested in the mid-18th century that Earth had been created separately from the rest of the universe, several hundred thousand years before. Lomonosov's ideas were mostly speculative, but in 1779, the French naturalist the Comte du Buffon tried to obtain a value for the age of Earth using an experiment: He created a small globe that resembled Earth in composition and then measured its rate of cooling. This led him to estimate that Earth was about 75,000 years old.
Other naturalists used these hypotheses to construct a history of Earth, though their timelines were inexact as they did not know how long it took to lay down stratigraphic layers. In 1830, the geologist Charles Lyell, developing ideas found in Scottish natural philosopher James Hutton, popularized the concept that the features of Earth were in perpetual change, eroding and reforming continuously, and the rate of this change was roughly constant. This was a challenge to the traditional view, which saw the history of Earth as static, with changes brought about by intermittent catastrophes. Many naturalists were influenced by Lyell to become "uniformitarians" who believed that changes were constant and uniform.


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