Geology and Placental Reproduction

Oceanographer Paul Falkowski of Rutgers University in New Jersey and his colleagues have come up with the idea that amount of oxygen in the Earth's atmosphere was responsible for the appearance of large placental mammals, around 50 million years ago. They have found that the amount of oxygen in the Earth's atmosphere 200 million years ago was only about half what it is today. And the appearance of large placental mammals, around 50 million years ago, happened at the same time as the oxygen level more or less doubled. The Atlantic Ocean opened up and a super continent split into the Americas, Africa and Eurasia, creating the ocean between them. This created thousands of kilometers of coastline that helped to wash organic carbon into the sea, locking it away from the process of decay. Such carbon escapes chemical processes that would turn it into carbon dioxide. As carbon is washed away, more oxygen remains in the atmosphere. The work highlights the intimate connections between geology and biological evolution.