More details on the Red Beds and Banded Iron Formations are found at the Columbia's website on the Early Evolution of Earth . Today's Atmosphere Our current atmosphere consists of about 79% nitrogen, 20% oxygen and tiny amounts of water vapor, carbon dioxide, ozone and argon. The atmosphere reaches about 150 km above our planet. It also thins as elevation increases, humans have a difficult time breathing and functioning at high elevations without oxygen support. The overall composition of the earth's atmosphere is summarized below along with a comparison to the atmospheres on Venus and Mars - our closest neighbors. Atmospheric Comparison Venus Earth Mars Titan Surface Pressures 100,000 mb 1,000 mb 6 mb 1,500 mb composition composition composition carbon dioxide &gt;98% 0.03% 96% molecular nitrogen 1% 78% 2.5% 90% argon 1% 1% 1.5% 6% oxygen 0.0% 21% 2.5% water vapor 0.0% 0.1% 0-0.1% Why is the atmosphere of Venus (Earth's sister) so different from Earth? On Earth, CO2 is absorbed in the oceans and rocks. If the absorbed CO2 on Earth were released into the atmosphere, 98% would be CO2 and the atmospheric pressure would be 70x what it is now. So, except for the O2 and water, Earth's atmosphere would be similar to Venus' if the CO2 has not gotten absorbed. The oxygen on Earth is a product of life, the result of photosynthetic splitting of water into O2 and H+ ions that are used to drive the future synthesis of ATP and Glucose. The water on Venus