The history of the Earth is imprinted on its stones. In places such as the Grand Canyon, the water that destroys its walls exposes the layers of rock from which these walls formed.
Since the old layers lie beneath the new ones, geologists can get some idea of how the crust formed. But knowing that deep layers are older does not tell us what their absolute age is, that is, how old they are.
How did you calculate the age of the earth?
Scientists of the 19th century tried to calculate the age of the Earth, based on the timing of rock formations in modern times. But they could only guess. According to their results, the age of our planet ranges from 3 million years to 1.5 billion years. The spread is 500 times, such a result cannot, of course, be called accurate. Naturally, a different method was required. Scientists wanted to find such watches that, if wound up at the time of creation, would continue to go on until our time. Looking at such a clock, one could accurately indicate the age of the Earth.
With what can you accurately calculate the age of the Earth?
And it turned out that such watches exist: in rocks, trees and in the oceanic depths. These natural clocks are radioactive elements that decay over time to form other elements. Determining the age of rocks or fossils using radioactive elements is called radiometric dating.In a unit of time, a strictly defined part of the radioactive material decays. This fraction does not depend on the mass of the original radioactive substance.
Radiocarbon method
Take the radiocarbon method as an example. It is based on the fact that living organisms absorb both ordinary carbon-12 and its radioactive isotope carbon-14 from air and water. Assume that the ratio of these two isotopes in water and air remains constant.
It is in this ratio that carbon isotopes are found in living organisms. When the body ceases to be perishable, after many years, the amount of ordinary carbon in its remains remains the same as it was at the time of death, and the radioactive isotope decays (carbon-14). This isotope decays in half within 5730 years. So, by measuring the ratio of two carbon isotopes in the remains of a once-living organism, scientists can determine the age of these remains.
Interesting fact: Radioactive elements can serve as a natural clock, because radioactive decay obeys strict temporal patterns.
Checking Results
Of course, none of the dating methods can be considered completely reliable. Therefore, geologists for fidelity investigate several radioactive elements, such as uranium or thorium in addition to carbon-14. Scientists verify their results by conducting duplicate tests with different radioactive isotopes on the same material. Sometimes two methods give different results.For example, geologists took samples of a coral reef off the coast of Barbados to study.
We measured the carbon content, as well as uranium and thorium. If the coral is “young”, that is, not older than 9000 years, then all methods give the same results. But if the coral turned out to be older, then the results may not be clear. The uranium-thorium method established the age of the coral as 20,000 years, and the carbon one only 17,000 years. What is the reason for such a big difference? And which method is more accurate? Scientists believe that the uranium-thorium method is more accurate, because the radiocarbon method has previously yielded ambiguous or even dubious results.
Reliability of age measurement methods
The radiometric dating method is not completely reliable. Therefore, scientists are exploring two different radioactive elements of the same material. The reason may be that, for example, in recent years, the carbon-14 content in the atmosphere has increased, which means that it could change in one direction or another in the past. If the ratio of carbon-14 to carbon-12 changed, the radiocarbon method cannot reliably determine the age of the remains of ancient organisms, since it is based on the fact that the content of radioactive carbon in the atmosphere and water remains unchanged.
Age of the Earth, Moon and Solar System
The half-life of uranium is 4.5 billion years. Measurements of the age of some rocks of the Earth by the uranium-thorium method showed that they are about 3.8 billion years old. How to find out how early our planet formed? Exploring lunar soil samples,delivered by astronauts from the lunar expedition, scientists found that their age is about 4.6 billion years, as well as the age of meteorites that arrived on Earth from closely lying regions of the solar system. Therefore, scientists believe that the entire solar system, including the moon and the sun, formed about 4.6 billion years ago.
