Meteorites are among the oldest objects we know about - formed about 4. But how do scientists know this? This article describes the principles and methods used to make that determination.
What are the oldest rocks on Earth, and how did they form? The material that holds the greatest insight into these fundamental questions, because it can contain a record of some of the earliest history of the Earth, is a mineral named zircon. For example, a few grains of zircon found in the early s in a sandstone from western Australia dates back 4.
Radiometric dating of rocks and minerals using naturally occurring, long-lived radioactive isotopes is troublesome for young-earth creationists because the techniques have provided overwhelming evidence of the antiquity of the earth and life. Some so-called creation scientists have attempted to show that radiometric dating does not work on theoretical grounds for example, Arndts and Overn ; Gill but such attempts invariably have fatal flaws see Dalrymple ; York and Dalrymple Other creationists have focused on instances in which radiometric dating seems to yield incorrect results.
Petrology Tulane University Prof. Stephen A. Nelson Radiometric Dating Prior to the best and most accepted age of the Earth was that proposed by Lord Kelvin based on the amount of time necessary for the Earth to cool to its present temperature from a completely liquid state. Although we now recognize lots of problems with that calculation, the age of 25 my was accepted by most physicists, but considered too short by most geologists.
Radiometric dating calculates an age in years for geologic materials by measuring the presence of a short-life radioactive element, e. The term applies to all methods of age determination based on nuclear decay of naturally occurring radioactive isotopes. Bates and Jackson To determine the ages in years of Earth materials and the timing of geologic events such as exhumation and subduction, geologists utilize the process of radiometric decay.
When a rock cools from the molten to the solid state, its radioactive isotopes are immobilized in mineral crystal lattices and then decay in place. Knowing the rate of decay of one nuclear species nuclide into another, scientists can, in…. The elements uranium and thorium gradually decay into lead, different isotopes of lead arising from the various isotopes of uranium and thorium; some isotopes of lead are, however, not produced by any radioactive decay process.
The age of the Earth is estimated to be 4. Following the development of radiometric age-dating in the early 20th century, measurements of lead in uranium-rich minerals showed that some were in excess of a billion years old. It is hypothesised that the accretion of Earth began soon after the formation of the calcium-aluminium-rich inclusions and the meteorites. Because the time this accretion process took is not yet known, and predictions from different accretion models range from a few million up to about million years, the difference between the age of Earth and of the oldest rocks is difficult to determine.
Modern geologistsbased on extensive and detailed scientific evidence, consider the age of the Earth to be around 4. This age represents a compromise between the oldest-known terrestrial minerals — small crystals of zircon from the Jack Hills of Western Australia — and astronomers ' and planetologists' determinations of the age of the solar system based in part on radiometric age dating of meteorite material and lunar samples. The radiometric age dating evidence from the zircons suggests that the Earth is at least 4.