However, rocks and other objects in nature do not give off such obvious clues about how long they have been around.So, we rely on radiometric dating to calculate their ages.

radiometric dating through the earth-85

Our planet was pegged at a youthful few thousand years old by Bible readers (by counting all the "begats" since Adam) as late as the end of the 19th century, with physicist Lord Kelvin providing another nascent estimate of 100 million years.

Kelvin defended this calculation throughout his life, even disputing Darwin's explanations of evolution as impossible in that time period.

Radiometric dating, or radioactive dating as it is sometimes called, is a method used to date rocks and other objects based on the known decay rate of radioactive isotopes.

Different methods of radiometric dating can be used to estimate the age of a variety of natural and even man-made materials.

So, we start out with two isotopes of uranium that are unstable and radioactive.

They release radiation until they eventually become stable isotopes of lead.

In a report of his findings published in 1913 in the journal , Holmes expressed the less-than-ecstatic reception his findings received: "The geologist who ten years ago was embarrassed by the shortness of time allowed to him for the evolution of the Earth’s crust , is still more embarrassed with the superabundance with which he is now confronted." The Earth's age continued to be hotly debated for decades afterward. In the 1920s, Earth's age crept up toward 3 billion years, making it for a time even older than the universe, which was then estimated to be about 1.8 billion years old.

The best estimate for Earth's age is based on radiometric dating of fragments from the Canyon Diablo iron meteorite.

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