Science today knows that the Earth is 4.54 billion years old, in addition to many details from different periods of this long history. But how is it possible for scientists to measure these ages so far from our present?
The secret to figuring out the Earth’s age lies within it: in its rocks. Becky Flowers, a geologist at the University of Colorado at Boulder, United States, says in an interview for the LiveScience portal that, when a researcher in the area looks at a rock, “it is as if it has a story that you can try to decipher.”
Minerals formed from the lava of volcanoes often have traces of radioactive elements such as uranium. Over time, these elements decay — that is, emitting particles from their nuclei until they reach more stable forms. An important time stamp of this process is the so-called half-life, the time required for the mass of an element to be reduced by half.
The half-life of uranium-238, a common variety of this element capable of emitting radiation, has a half-life period of over four billion years, which allows it to be used to date objects to very remote times. Seeing in the rocks the proportion between the original element and the element resulting from atomic decay, it is possible to calculate how much time has passed since its origin.
This technique is called radiometric dating and is performed mainly on the mineral zirconite, whose uranium content is relatively high. It is possible, however, to perform it with several other elements — such as carbon, whose half-life of thousands of years is useful in dating organic matter. Through these methods, geologists have managed to find minerals up to 4.4 billion years old — which still leaves about 100 million years out.
To explain this extra period, it is necessary to go beyond the Earth: the oldest minerals may have already undergone erosion or melting, returning to the state of the raw material that gave rise to them. On the other hand, meteorites that hit Earth date back as far as more than 4.56 billion years, while rocks from Mars and the Moon also show similar ages.
Knowing these intervals, the researchers were able to build a timeline that determines the formation of the rocky bodies that make up the solar system — and even the system as a whole. In any case, knowledge about the age of the Earth will never have an exact year, but an era in which our planet may have emerged.
Source: LiveScience
