Geological dating techniques of earth

They have clearly fallen to Earth from outside, often gouging out huge craters such as that called New Québec (61°17´ N, 73° 41' W).

Using the uranium-lead technique they dated zircon crystals from the gneiss (located southeast of Great Bear Lake in the NWT) and showed that it was formed almost 4 billion years ago.

Therefore it is clear that the Earth is over 4 billion years old.

The remaining number of radioactive atoms is halved every half-life.

Radioactive elements of use in geological dating have relatively long half-lives.

They were found, however, in much younger sediment and it is not known where these zircons originated.

The second approach, which is more indirect but gives an answer currently believed correct, involves a comparison of the Earth with meteorites.Only the tiniest fraction of the Earth, the crust, is accessible.Those rocks available for analysis (ie, the oldest ones) have been heated and squeezed many times in their GEOLOGICAL HISTORY, because for billions of years continents have been drifting over the Earth's surface, colliding and producing mountains and new ocean floors.This uniformity demonstrates that the principle is reliable.When disturbed rocks are studied, the different techniques may give different readings, and much research has been carried out on how to interpret such results.The other key dating techniques involve uranium-235 transforming to lead-207 at a rate of one-half every 713 million years, uranium-238 becoming lead-206 at one-half every 4.5 billion years, potassium changing to argon (and calcium) at one-half every 1.3 billion years and samarium-147 becoming neodymium-143 at one-half every 106 billion years.

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