The method used is called radioactive dating, it is based on the phenomenon of radioactivity and was discovered at the end of the 19th century. Radioactivity causes atoms to lose particles (protons or neutrons) in the form of radiation, causing a change in their mass number or atomic number. In the case of fossils of living beings, it is customary to use carbon 14 (with six protons and eight neutrons) for dating. Carbon 14 emits radiation, losing two neutrons and turning into carbon 12. In 5,730 years, a certain amount of carbon 14 will be reduced by half, with the other half being transformed into carbon 12. Therefore, this time is called half -life. The half-life of carbon 14 is so short that it can only be used to measure the remains of organisms that lived up to 70,000 years ago. For older organisms, the same process is used – but it becomes necessary to use another radioactive element, with a longer half-life, as a reference.
In addition to carbon 14, potassium 40 – with a half-life of 1.25 billion years – or uranium 238 – with 4.47 billion years – can be used, in addition to many other radioactive elements. To measure, in fossils, the amount of these elements and those they originate by radiation, scientists use a device called a mass spectrometer, which makes it possible to discover the atomic mass of the chemical elements present. This technique, however, should not work correctly in the future, within a few million years – this is because, from the 1940s, the explosion of atomic bombs, the performance of nuclear tests and accidents in atomic power plants caused changes in radioactivity. of the planet that will make this dating method lose its base reference.
Did you like the lizard? It is a resin reconstruction of the dinosaur Santanaraptor placidus – which would have lived in Ceará 110 million years ago -, made from the fossils below
1. Combined with oxygen in the air, radioactive carbon 14 forms carbon dioxide
2. Carbon 14 – like carbon 12 – is absorbed by plants through photosynthesis
3. Animals feed on plants, making carbon 14 enter the food chain
4. The proportion of carbon 12 and 14 in living beings remains constant throughout their lives
5. After death, however, this proportion begins to be altered by radioactivity
6. Every 5,730 years, half of the carbon 14 present in the remains becomes carbon 12. This period of time – called half-life – serves as a reference to determine the age of the fossil
7. Once discovered, fossils have to be taken to a laboratory, where the masses of carbon 12 and 14 can be precisely identified and used in the final calculation.
8. The device that detects the exact atomic mass of each chemical element found in the fossil is the mass spectrometer. With these numbers in hand, it is easy to calculate the age