English 中文   Site Map

Earth Evolution
Earth Materials
Earth Evolution
Geological History
Solar System
Archean Proterozoic Early
Late Paleozoic Mesozoic Cenozoic

Habitable Earth - What allows Planet Earth to support life?
Earth is not too big:
The gravity associated with a large planet that is too big to support life would retain too many light elements (gases) in its atmosphere and become a gas giant like Jupiter.
Earth is not too small:
Small planets may cool relatively quickly and not have enough heat to sustain geodynamic activities. Examples are Mars and our Moon.
The larger size of the Earth ensured slow cooling and differentiation into a core, mantle and crust, which meant that volcanic activity cound take place through plate tectonic processes. Volcanic activity in turn has generated an atmosphere with greenhouse gases that strip away harmful UV radiation. They also maintain a warm, near constant temperature on the planet's surface.
Earth is not too close to the sun:
Planet Earth lies in the habitable zone of our solar system. This zone is the region that lies at a suitable distance from the sun where a planet is able to sustain liquid water, being neither too close for it all to be vaporized into a thick and heavy atmosphere (such as Venus), nor too distant so that it all freezes and the atmosphere becomes thin (such as Mars).
Earth is not too small:
A planet that is relatively small would not have sufficient gravity to be able to sustain an atmosphere with oxygen and nitrogen. Only heavier gases (argon) would be retained such as on Mars.