The Earth is thought to have been formed about 4.6 billion years ago by collisions in the giant disc-shaped cloud of material that also formed the Sun. Gravity slowly gathered this gas and dust together into clumps that became asteroids and small early planets called planetesimals. These objects collided repeatedly and gradually got bigger, building up the planets in the Solar System, including the Earth.
The details of how the Earth formed are still being worked out. Scientists study meteorites and the oldest rocks on Earth to understand what happened in these earliest times in the Solar System. They also observe other solar systems in our galaxy, the Milky Way.
Image: Artwork showing the early Earth (credit: Walter Myers/SPL)
Volcanoes and comets bring water to the Earth.
Dr Iain Stewart explains the theory that steam from volcanoes and water from comets filled the Earth's oceans.
Our planet develops its inner heat.
Dr Iain Stewart explains how the Earth developed its inner heat during a time known as the Hadean eon, about 4.5 billion years ago.
How did Lord Kelvin estimate the age of the Earth?
Lord Kelvin, the eminent 19th and early 20th century scientist, was determined to work out the age of the Earth. A simple experiment with molten rock gave him figures for his calculations. (This experiment should only be carried out under controlled conditions and with professional supervision.)
The history of the Earth concerns the development of the planet Earth from its formation to the present day. Nearly all branches of natural science have contributed to the understanding of the main events of the Earth's past. The age of Earth is approximately one-third of the age of the universe. An immense amount of biological and geological change has occurred in that time span.
Earth formed around 4.54 billion (4.54×109) years ago by accretion from the solar nebula. Volcanic outgassing probably created the primordial atmosphere, but it contained almost no oxygen and would have been toxic to humans and most modern life. Much of the Earth was molten because of extreme volcanism and frequent collisions with other bodies. One very large collision is thought to have been responsible for tilting the Earth at an angle and forming the Moon. Over time, the planet cooled and formed a solid crust, allowing liquid water to exist on the surface. The first life forms appeared between 3.8 and 3.5 billion years ago. Photosynthetic life appeared around 2 billion years ago, enriching the atmosphere with oxygen. Life remained mostly small and microscopic until about 580 million years ago, when complex multicellular life arose. During the Cambrian period it experienced a rapid diversification into most major phyla.
Geological change has been constantly occurring on our planet since the time of its formation and biological change since the first appearance of life. Species continuously evolve, taking on new forms, splitting into daughter species, or going extinct in response to an ever-changing planet. The process of plate tectonics has played a major role in the shaping of Earth's oceans and continents, as well as the life they harbor. The biosphere, in turn, has had a significant effect on the atmosphere and other abiotic conditions on the planet, such as the formation of the ozone layer, the proliferation of oxygen, and the creation of soil.
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