Learning Objectives

There are many ideas for the origin of the Earth, atmosphere and the oceans,  this is the popular scientific view.

It is thought that the solar system began as a nebula, a swirling mass of dust and gas.  Gravitational attraction between atoms and molecules caused this nebula to collapse into clumps of matter.  The larger the clumps of matter the more mass they contained and the more mass that they contained the more gravity they exerted.  The increase in gravity lead to an increase in attraction and hence an increase in mass ect.  Eventually a dense central area collapsed in on itself so tightly that nuclear fusion reactions could occur and the Sun was born.

Circling this new Sun were other distinct clumps of matter.  These would eventually form the planets.  Earth is thought to have formed through either cold or hot accretion.  In both models material is added to the planet through gravitational attraction.  In the cold accretion model the Earth was cold at formation and subsequently heated due to meteor impacts and then slowly cooled.  The hot accretion model suggests the Earth was hot at formation and slowly cooled.

The newly formed Earth was an inhospitable place.  The surface was molten rock.  The atmosphere  contained methane, carbon dioxide, nitrogen, hydrogen, helium and ammonia.  (NO OXYGEN)  Outgassing from the surface added water vapor to the atmosphere.  Over time the surface eventually cooled and solid rock formed.  As the atmosphere cooled liquid water began to form but flashed to steam as it struck the surface.  Eventually however the surface cooled sufficiently for liquid water to exist and it collected as oceans.  The atmosphere did not become oxygenated until photosynthetic organisms appeared two billion years later.