Origin of the Earth

Nebular Theory of Earth’s Origin We call the area between the stars is the “vacuum” of space. A vacuum is a space with no material. However, even though we call the area between stars a vacuum there is some material present. Dispersed dust and gases inhabit the areas between the stars. A cloud of dispersed gases is called a Nebula. A nebula generally consists of 92% hydrogen, 7% helium and >1% of the remaining heavier elements. As gravitational forces pull on the particles they begin to contract and rotate slowly around a center mass. As they contract further they begin to rotate faster (think of a skater spinning and pulling their arms in to spin faster).

Nebular Theory of Earth’s Origin Studies of nebulae have led to the theory or the origin of our Solar system. According to the nebular theory, the Sun and planets formed from a rotating disk of dust and gases.

Planetary Evolution and History As the speed of rotation increased, the center of the disk began to flatten out. Matter became more concentrated in the center where the Sun eventually formed.

Planetesimals The growth of the planets of our Solar system began as solid bits of matter began to collide and clump together through a process known as accretion. The colliding materials clumped together to form planetesimals. As more collisions occurred they grew large enough to exert a gravitational pull on surrounding objects, adding more mass and eventually becoming true planets.

Planetary Evolution and History In the inner Solar system temperatures were so hot that only metals and silicate materials could form solid grains. It was to hot for ices of water, carbon dioxide or methane to form. For this reason Earth grew mainly from materials with high melting points.