How old is the earth according to Scientists | Everyday Science

How old is the Earth?

how old is the earth

How old is the earth? Planet earth does not have a certification to record its origination. Researchers and scientists spend hundreds of years to calculate the real age of the earth.

With current data, it is estimated that the age of planet Earth is 4.543 billion years. In addition, this estimate has a margin of error of 1%, which makes it quite accurate.

How do you know the age of the earth?

The Earth’s age is calculated using several techniques, such as the study of meteorites and ancient rocks. The most accurate method today is the radiometric dating of these materials.

Among the ancient rocks used, the Acasta Gneiss, in northern Canada, probably the oldest rocks that can be found in the earth’s crust.

How old is the earth? Acasta Gneiss

Radiometric dating of the earth age

Radiometric dating is a method used to date rocks and other objects based on the known decay rate of radioactive isotopes. Radioactivity is a natural phenomenon present in rock elements. Different methods of radioactive dating can be used to estimate a variety of natural or man-made materials. This radiation provides heat and this extra heat made clear the calculations of Thomson and other scientists who were based on cooling and terrestrial geothermal gradient.

Radioactivity is a phenomenon whereby the nucleus of an unstable atom emits radiation spontaneously. When emitting radiation, this unstable nucleus will become a more stable one (a process known as decay). In this way, due to radioactive decay, elements may appear that were not there before.

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Mineral rocks are naturally formed by certain elements but elements that initially were not present by the phenomenon of radioactive decay.

If the initial concentration of the original radioactive element is known, the current concentration of the stable element produced by radioactive decay is measured and the speed with which this decay occurs is measured, the age of a given rock can easily be calculated.

The most commonly used decay chain for radiometric rock dating is the uranium-lead chain.

With these techniques, rocks of more than 4 billion years have been dated, specifically, the Acasta Gneiss considered the oldest conglomerate rocky found on the earth’s surface and is dated 4.03 billion years old.  

Meteorites in Earth dating

The dating of mineral rocks by radiometric dating has a drawback. Many of the stable products produced by decay can escape from the rock or redistribute, especially if the rock melts, as in the fluid mantle of the planet.

Because of this, rock dating is considered as the lower limit of the earth’s age, that is, knowing the age of the oldest rock on Earth, it could be said that the Earth is at least the age of that rock, but it could not be denied outright that it is older.

In addition, the dating of rocks to calculate the age of the Earth would mean that the rock has remained a closed system but in reality, it has undergone a complex process of mixing and redistribution through plate tectonics, erosion and hydrothermal circulation.

Meteorites are another invaluable source of information about the age of the planet. If the radiometric dating of rocks can give us the lower limit of the terrestrial age, the radiometric dating of meteorites can give us the upper limit.

Clair Cameron Patterson, an American geochemist, published his calculations of the Earth’s age in 1956. He concluded that the Earth was 4.6 billion years by radiometric dating of various meteorites, including the famous Canyon Diablo meteorite (fragment of the asteroid that hit the Barringer crater, Arizona, United States).

Some scientific observations, studies of the Solar System and numerous radiometric dates of various meteorites confirm that some of these meteorites represent original material from which the solar disk was formed and the planets that revolve around it and that, in addition, have behaved as a system closed for some isotopes (a hypothesis much more robust than that of supposing a rock has remained a closed system on planet Earth).

Both ages, that of 4.555 billion years of meteor dating and 4.540 billion years of the rocks of the Acasta Gneiss is currently the two most accepted figures. In addition, comparing the luminosity and volume of the Sun with that of other stars, it is believed that the Solar System could not exceed these ages.

The upper level of the Earth’s age can be found at 4.567 billion years, which is the age calculated for the oldest meteorites in the Solar System (this would be the approximate age of the Solar System and, therefore, the maximum age of the planet Earth).

History of Earth Age Calculation

The first figures of the age of the Earth of some importance were calculated by the Ireland Archbishop James Ussher based on the story told in the Bible.

He estimated that the creation of the world on the night of October 23, 4004 BC. (Although the exact day seems to be a later inclusion of another author and the time given by Ussher 3 is not very clear).

The first scientific-based calculation of a certain draft was made by the Count of Buffon (Georges Louis Leclerc). In his book Histoire Naturelle (1778) he published his estimate of the earth’s age in 50 thousand years based on the study of iron ores.

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He had to retract this information by the judgment of the Catholic Church. Years later he would publish his new calculation of 75,000 years without fear of the Church.

Buffon was in favor of a much older Earth age based on fossil records but could not specify a figure. The scientist Kant, at the same time of Buffon, already spoke of an age of the planet of millions of years but without specifying.

William Thomson, an English physicist, deduced that the Earth formed a mass of molten rock and calculated the cooling time until it reached current temperatures. Thus, he deduced an age of the planet that would be between 24 and 400 million years, calculations he published in 1862.

He had been preceded by the calculations of the German physicist Hermann von Helmholtz, 22 million years old, and the Canadian astronomer Simon Newcomb, 18 million years old, both based on the evolution of the Sun, all calculations that did not contradict, but supported, the Thomson data. 

All these data seemed too small for geologists and biologists throughout the 19th century. Even the highest age so far, 4 billion years calculated by William Thomson, was little for Darwin’s natural selection theory.

However, Thomson was supported by research from scientists around the world, including George H. Darwin (a Cambridge University astronomer and son of Darwin), estimated the earth age at 56 million years using a tidal friction model.

Thomson had further clarified his calculations using a model of terrestrial geothermal gradient and cooling rate, and he also set it at 100 million.

But Thomson (named Lord Kelvin in 1892 for his scientific achievements) did not take into account that the Earth had a thick, very viscous liquid layer.

If John Perry took it into account, who in 1895, using a terrestrial model with a convective mantle and thin crust, calculated an age of the Earth that would be between 2000 and 3 billion years.

The next big jump in the calculation of the earth age was the invention of radiometric dating. The discovery of radioactivity in 1896 by the French chemist A. Henri Becquerel brought a powerful new tool for calculating the age of planet Earth, the most reliable today.

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