While human beings have been trying to explain the origin and workings of the Earth since ancient times, it was not until the 19th century that geology became a respectable science.
Ancient Myths and Legends
Ancient human beings explained the creation of the Earth and all its natural occurrences through stories - myths and legends - of giant beasts or powerful gods.
According to the ancient Greeks, volcanoes erupted due to the activities of Hephaestus, the blacksmith god of the underworld, lighting his forge. The ancient Greeks also thought that Pluto, the king of the underworld, and his three-headed dog, Cerberus, guarded the mineral wealth within the Earth.
Many other civilizations had their own ideas about how the Earth functions.
The Romans adopted many of the Greek gods, and renamed them. Hephaestus became the Roman god Vulcan, from whom the word volcano originates.
The Indians had Devi, a god with a dual role of both mother Earth (protector) and the dark forces of the Earth (destroyer).
In Scandinavian mythology, dwarfs were the owners of the mineral wealth in the ground. Celtic legend claims that a giant created Lough Neagh in Ireland when he pulled out a piece of the Earth. He flung it into the sea and created the Isle of Man.
A Young Earth
A great flood occurs in many legends, from people as widely separated as the Assyrians and Babylonians of southwestern Asia and the Incas of South America.
The Biblical story of Noah tells of such a flood
In the Middle Ages, beliefs in a great flood developed into a theory that the Earth's features, such as mountains and valleys, formed during sudden, violent catastrophes.
This theory was called catastrophism.
In 1654, the Irish Archbishop James Ussher (1581-1656) worked out, from Biblical history, that the Earth had been created at 9 am on October 26, 4004 BC (BCE).
An Old Earth
Others believed that the Earth was much older.
An Arab scholar, Avicenna (980-1037), claimed that the action of running water had slowly changed the Earth's surface.
In the 1400s, most Europeans believed that the rocks covering the Earth had been formed during the Flood.
However, Leonardo da Vinci, an Italian artist and scientist, believed that these rocks had been formed in several calm episodes.
Da Vinci suggested that fossils in rocks were the remains of ancient animals and plants.
He observed that fossils often occurred in several rock layers, which were separated by barren layers.
This led him to believe that the rocks had been formed at different times, rather than all at once.
How the Earth Was Formed
In the late 1700s, a debate began concerning the origin of rocks. A German professor, Abraham Werner, suggested that rocks were formed from chemicals in the oceans.
His followers were known as Neptunists, after the Roman god of the sea.
However, a Scottish geologist, James Hutton, thought that some common rocks, such as granite, were formed from hot, molten material called magma.
His supporters were known as Plutonists.
Hutton thought that natural forces, such as running water, were constantly wearing away the land and that some rocks were formed from the worn material.
These natural forces work so slowly that Hutton concluded that the Earth must be extremely old.
After Hutton died, Charles Lyell, who was also Scottish, championed his ideas.
By the 1830s, most scientists had accepted the theories of Hutton and Lyell.
Their breakthrough opened the way for Charles Darwin to advance his theories about evolution in 1859.
Modern Geology
The first geological society was set up in London in 1807.
A British surveyor and engineer, William Smith, realized that, in rocks that have not been disturbed, the more recent rocks always overlay the older rocks. Smith was also interested in the fossils in the rocks. Some fossils appeared in several layers but some, called index or zone fossils, occurred in only one layer.
This meant that if rocks, many miles apart, contain the same index fossils, then, they must have been formed at the same time. Applying these principles, Smith produced a geological map of southern England, the first of its kind, in 1815.
Geological mapping continued and geologists identified and named rocks according to their relative ages.
Geologists eventually divided the history of the Earth into a few long eras. They divided these eras into periods, and divided some of the periods into epochs.
In the 1800s, geologists made various estimates of the Earth's age. For example, British physicist Lord Kelvin (1824-1907) believed that the Earth must be between 20 and 30 million years old.
When radioactivity was discovered in the early 1900s, scientists were able to find the absolute ages of rocks and accurately estimate the age of the Earth.