By comparison, Mars is a cold planet with desert landscapes under a thin atmosphere, and Venus has a hot, oppressive and poisonous atmosphere but no water. Some Basic Facts about Earth and her Neighbours 1. The atmospheres of Venus and Mars are nearly pure carbon dioxide, whereas Earth's is almost entirely nitrogen and oxygen. The CO2 on Earth is found dissolved in the oceans and chemically bound in rocks such as limestone. Life on earth consumes CO2 and produces an oxygen-rich atmosphere.
Life thrives on Earth's surface, shielded from harmful ultraviolet radiation by the ozone layer.
Earth's twin, Venus, has about the same diameter, average density and surface gravity. But it is also very different. It is closer to the Sun and so is forbiddingly hot. Beneath its carbon-dioxide atmosphere, a Soviet spacecraft in 1970 measured a surface temperature of 750K and a pressure 90 times that on Earth. This is caused by the so-called greenhouse effect , the thick Venusian clouds trapping heat powerfully and maintaining high surface temperatures.