For hundreds of millions of years, Earth's climate has remained on a fairly even keel, with some dramatic exceptions: Around 80 million years ago, the planet's temperature plummeted, along with carbon dioxide levels in the atmosphere. The Earth eventually recovered, only to swing back into the present-day ice age 50 million years ago. Now geologists at MIT have identified the likely cause of both ice ages, as well as a natural mechanism for carbon sequestration. Just prior to both periods, massive tectonic collisions took place near the Earth's equator — a tropical zone where rocks undergo heavy weathering due to frequent rain and other environmental conditions. This weathering involves chemical reactions that absorb a large amount of carbon dioxide from the atmosphere. The dramatic drawdown of carbon dioxide cooled the atmosphere, the new study suggests, and set the planet up for two ice ages, 80 million and 50 million years ago.  

After dropping more than 20 spots this year in one ranking that measures how well countries are working to protect the environment, the United States is taking steps to improve its environmental impact. The 2010 Environmental Performance Index (EPI) ranks 163 countries based on 10 indicators of environmental protection, such as levels of air pollution, marine protection laws, water quality, and their rate of planting new trees. The EPI is composed biannually by a team of environmental experts at Yale University and Columbia University.