Early Earth and the coevolution of Earth and life

Early Earth grew by accretion, as colliding planetesimals released heat; together with heat from radioactive decay, this left the young planet largely molten, so dense iron and nickel sank to form the core while lighter materials rose to form the mantle and crust, a process called differentiation. Gases released by volcanoes, called outgassing, mostly water vapor, carbon dioxide, and nitrogen, formed an early atmosphere with almost no free oxygen, and as Earth cooled, water vapor condensed into oceans; comets and asteroids may have delivered some of the water. Life appeared in the oceans by at least about 3.5 billion years ago, and scientists are still testing hypotheses about how it first arose from nonliving chemistry, for example at deep-sea hydrothermal vents. Since then, Earth's systems and life have changed each other, which is called coevolution. Photosynthetic cyanobacteria released oxygen, which first reacted with iron dissolved in seawater, forming banded iron formations, and then began building up in the air during the Great Oxidation Event about 2.4 billion years ago. Oxygen allowed an ozone layer to form that blocks much of the Sun's ultraviolet radiation, making life on land possible, and it made larger, more complex organisms possible. In turn, plants that spread onto land sped up rock weathering and built soils, and corals and shelled organisms have locked huge amounts of carbon into limestone.

This explanation is AI-generated and can occasionally be wrong. 🚩 Report