Origin and evolution of earth


Beginning of the Universe started about 13.6 billion years ago,when the Big Bang created the universe from a point source.
During this process, light elements, like H, He, Li, B, and Be formed. From this point in time, the universe began to expand and has been expanding ever since.
Concentrations of gas and dust within the universe eventually became galaxies consisting of millions of stars.
Within the larger stars, nuclear fusion processes eventually created heavier elements, like C, Si, Ca, Mg, K, and Fe.
Stars eventually collapse and explode during an event called a supernova. During a supernova, heavier elements, from Fe to U, are formed. (See figure 1.9 in your text).
Throughout galaxies clusters of gas attracted by gravity start to rotate and accrete to form stars and solar systems. For our solar system this occurred about 4.6 billion years ago.
The ball at the center grows dense and hot, eventually nuclear fusion reactions start and a star is born (in our case, the sun).
Rings of gas and dust orbiting around the sun eventually condenses into small particles. These particles are attracted to one another and larger bodies called planetismals begin to form.
Planetesimals accumulate into a larger mass. An irregularly-shaped proto-Earth develops.
The interior heats and becomes soft. Gravity shapes the Earth into a sphere. The interior differentiates into a nickel-iron core, and a stony (silicate) mantle.
Soon, a small planetoid collides with Earth. Debris forms a ring around the Earth.The debris coalesces and forms the Moon.
The atmosphere develops from volcanic gases. When the Earth becomes cool enough, moisture condenses and accumulates, and the oceans are born.

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