Age of the Earth: How Old Is Our Planet and How Do Scientists Know?

Humans have likely pondered on the age of the Earth since we first developed a sense of time. Since no evidence directly reveals the exact age of the Earth, experts use various methods to determine how old our planet is.

Early Ideas About the Age of the Earth

Before the age of scientific thinking, most ancient cultures attempted to explain the origin of the Earth through their creation myths based on religious texts or oral traditions. Early estimates of the age of the Earth were relatively short, usually just a few thousand years.

During the time of the Greek philosophers, Aristotle proposed that the Earth existed eternally. Meanwhile, Roman poet Lucretius, intellectual heir to the Greek atomists, believed that the formation of our planet must have been relatively recent.

For a long time in the Western world, ancient people used to derive the history of the Earth and the species on it from the Christian Bible. In 1642, English clergyman John Lightfoot calculated the exact date of the creation of the universe, which he claimed to be September 17, 3928 B.C. He arrived at this date by counting backward through the genealogies in the Scriptures.

In the late 18th century, James Hutton, the father of modern geology, proposed that geological forces acted continuously over long periods. His ideas laid the foundation for the concept that our planet must be older than previously thought.

In 1862, Irish physicist and mathematician William Thomson estimated that Earth was between 20 and 400 million years old. He based this theory on calculating how long Earth would have taken to cool off if it had started as a molten mass. This estimate, however, did not consider the effects of convection in the Earth's mantle.

In 1895, Irish mathematician and engineer John Perry used a model that included a convective mantle and a thin crust. He estimated that the Earth is around 2 to 3 million years old from this model.

Another Irish physicist and geologist, John Joly, theorized that our planet is at least 80 to 100 million years old. He based his conclusion on the rate of appearance of salt in the ocean due to the process of erosion.

Dating the Earth Using Isotopes

Although many people have come up with ideas about the age of the Earth, science has finally given a definitive answer. The first accurate estimates of the age of the Earth came from radiometric dating, which was discovered in the 20th century. This method uses the decay rate of radioactive elements in dating rocks and minerals. Scientists date the age of meteorites using radiometric dating, and since these meteorites formed around the same time as Earth, they offer a reasonable estimate of our planet's age.

In 1953, geochemist Clair Cameron Patterson from the California Institute of Technology measured the ratios of lead isotopes in the Canyon Diablo meteorite, which put a tight constraint on the age of the Earth. The meteorite samples show a spread from 4.53 to 4.58 billion years. Experts interpret this range as the time it took for the evolution of the Solar System, which happened over approximately 50 million years.

Scientists used the rocks on Earth and the information collected about its celestial neighbors. From these observations, experts have placed the Earth's age at approximately 4.54 billion years old, give or take 50 million years. This means that our planet is under half the age of the Milky Way Galaxy (1 to 13 billion years old) and around one-third of the age of the Universe (10 to 15 billion years old).