TABLE OF CONTENTS Section Editor: Michael J. Rycroft
Michael J. Rycroft
The Universe began with the Big Bang, about 14 billion years ago. About 4.6 billion years ago, the Sun formed during the gravitational collapse of an enormous cloud of gas and dust. Rotating around the Sun was a disk of material out of which the planets grew. These planets now orbit the Sun in the ecliptic plane. Our Earth is the third planet away from the Sun.
The different materials within the Earth gradually separated, with the densest (iron) forming an electrically conductive core. Dynamo action in the core generates the geomagnetic field. Above is the mantle, a region which convects very slowly. The Earth has a relatively thin crust, a few tens of kilometres thick, compared with the Earth's equatorial radius of 6,378 km. The crust and uppermost mantle are made up of 12 tectonic plates, hundreds of kilometers or so thick, which move relative to each other at up to one centimeter per year.
The Earth's atmosphere has evolved through outgassing from the interior via volcanoes. Oxygen was generated by dissociation of water vapor; the hydrogen that was also formed gravitationally escaped into space. Oxygen is also generated via photosynthesis by plants.
The Earth's hydrosphere (oceans), atmosphere, biosphere and solid surface interact with each other in many complex ways. This area of science is now termed Earth Systems Science (Ernst 2000).
This...
