According to radiometric dating of meteorites how old is earth

The oldest known rocks—the faux amphibolites of the Nuvvuagittuq greenstone belt in Quebec, Canada—however, have an isotopic age of 4.28 billion years.There is in effect a stretch of approximately 300 million years for which no geologic record for rocks exists, and the evolution of this pregeologic period of time is, not surprisingly, the subject of much speculation.Such intense bombardment would have covered most of Earth’s surface, with the impacts causing considerable destruction of the terrestrial crust up to 4 billion years ago.An exciting discovery was made in 1983 by zircon grains that were 4.18 billion years old.Its component gases, however, were most likely very different from those emitted by modern volcanoes.Accordingly, the composition of the early secondary atmosphere was quite distinct from that of today’s atmosphere.

according to radiometric dating of meteorites how old is earth-67

Meanwhile, heavier liquids rich in iron, nickel, and perhaps sulfur separated out and sank under gravity, giving rise to the core at the centre of the growing planet; and the lightest volatile elements were able to rise and escape by outgassing, which may have been associated with surface volcanic activity, to form the secondary atmosphere and the oceans.When the evolution of the isotopes of lead deposits of different age on Earth, including oceanic sediments that represent a homogenized sample of Earth’s lead, the growth curve of terrestrial lead can be calculated, and, when this is extrapolated back in time, it is found to coincide with the age of about 4.6 billion years measured on lead isotopes in meteorites.Earth and the meteorites thus have had similar lead isotope histories, and so it is concluded that over a period of about 30 million years they condensed or accreted as solid bodies from a primeval cloud of interstellar gas and dust—the so-called solar nebula from which the entire solar system is thought to have formed—at about the same time.Research has shown that Earth, with a greater attractive mass than the Moon, must have undergone more extensive meteorite bombardment. Smith, a minimum of 500 to 1,000 impact basins were formed on Earth within a period of about 100 to 200 million years prior to 3.95 billion years ago.Moreover, plausible calculations suggest that this estimate represents merely the tail end of an interval of declining meteorite bombardment and that about 20 times as many basins were formed in the preceding 300 million years.

Leave a Reply