Development
After its creation via accretion, the protoplanet Earth was molten. Chemical reactions between various compounds both inside the protoplanet and in its atmosphere. This page will attempt to explain how land, the oceans and the atmosphere developed in to a resemblance of what we see today.
Land Formation
As explained on the Creation page, the earth was originally formed when many small amounts of solid matter collided, eventually forming a protoplanet. Due to the heat of these collisions, only the most dense elements, such as iron, were allowed to exist in solid form.
As the collisions lessened and the protoplanet began to cool, these molten materials separated themselves in order of density. Heavy elements, such as iron and nickel, formed the core. Further out was a mixture of less heavy elements compressed in to what we call the mantle. Finally, a crust of light, silicon-rich rock formed the outer crust.[1]
Further Reading: Continental Shifts.
This website shows various illustrations of what Earth's landmasses may have looked like over the past billion years due to shifts in tectonic plates.
Oceans and Atmosphere
The Earth, like the other solid planets, originally had an atmosphere of hydrogen and helium. This atmosphere was 'blown off' due to collision with high energy particles in the solar wind. Left behind was a thin atmosphere of hydrogen rich compounds, ammonia (NH4), water (H2O and methane (CH4), and nitrogen/silicon based compounds released from volcanoes.
3.8 billion years ago, light from the sun caused the methane, ammonia and water to break down in to their component atoms, hydrogen, oxygen, nitrogen and carbon. Trace amounts of the original gasses were also left. Since Hydrogen is so light, Earth's gravity was unable to contain it and most of it escaped in to space. The remaining material reacted, forming compounds like carbon dioxide (CO2) and ozone (O3).
Ozone is an especially important compound. It formed a layer high in the atmosphere, protecting anything beneath it from the suns ultraviolet radiation. This radiation is converted in to the infrared spectrum, providing heat. This development led to the evolution of the first photosynthesising organisms, whose importance will be explained on the Life page.[2]
Alongside this process, volcanoes released gaseous forms of various compounds and elements, such as water vapour, carbon dioxide, nitrogen, sulphur, argon and chlorine. These gasses condensed in to liquids and rained down on the planet. Since the rocky crust was uneven, formed with highlands of light rock such as granite surrounnded by low lying beds of heavy rock like basalt, the rains formed the oceans.[3]
Further Reading: Ozone.
This PDF document, from the University of Columbia, New York, explains the complex reactions of ozone with ultraviolet light.
Bibliography.
- [1]: Earth - The Formation of Earth, sciece.jrank.org. Accessed 24 April 2010.
- [2]: Development of the Atmosphere, mmscrusaders.com. Accessed 24 April 2010.
- [3]: Development of the Oceans and Atmosphere, zebu.oregon.edu. Accessed 24 April 2010.