By Age of the Earth is understood the total time since the earth has existed in its present physical state as a planet. In Geology, this problem has always been found as one of the most complicated and controversial topics. Many conclusions were suggested on different lines but were rejected by equally strong objections. It was only with the discovery of radioactivity that a new method giving an approximate age, with comparatively less chances of error were found. Presently, by any discussion on the problem of age of the Earth is understood a discussion of radioactive methods alone since all the other methods are highly speculative and already stand discarded. They are mentioned below only to show the curiosity among the scientists about the topic.
Radioactive Carbon Dating
Absolute Ages of Rocks | Earth Science
The ability to precisely date, or identify the age of an object, can teach us when Earth formed, help reveal past climates and tell us how early humans lived. So how do scientists do it? Radiocarbon dating is the most common method by far, according to experts. This method involves measuring quantities of carbon, a radioactive carbon isotope — or version of an atom with a different number of neutrons. Carbon is ubiquitous in the environment. After it forms high up in the atmosphere, plants breathe it in and animals breathe it out, said Thomas Higham, an archaeologist and radiocarbon dating specialist at the University of Oxford in England.
Age of Earth
In this section we will explore the use of carbon dating to determine the age of fossil remains. Carbon is a key element in biologically important molecules. During the lifetime of an organism, carbon is brought into the cell from the environment in the form of either carbon dioxide or carbon-based food molecules such as glucose; then used to build biologically important molecules such as sugars, proteins, fats, and nucleic acids. These molecules are subsequently incorporated into the cells and tissues that make up living things. Therefore, organisms from a single-celled bacteria to the largest of the dinosaurs leave behind carbon-based remains.
Many independent measurements have established that the Earth and the universe are billions of years old. Geologists have found annual layers in ice that are easily counted to multiple tens of thousands of years, and when combined with radio isotope dating, we find hundreds of thousands of years of ice layers. Using the known rate of change in radio-active elements radiometric dating , some Earth rocks have been shown to be billions of years old, while the oldest solar system rocks are dated at 4. Astronomers use the distance to galaxies and the speed of light to calculate that the light has been traveling for billions of years.