Mammals grew due to the increase in the amount of oxygen in the air

The mammals that were once small creatures running around on the forest floor grew in size as the amount of oxygen in the air increased over millions of years. This is according to a new study. Today's mammals ranging from mice, dogs and cats to elephants, dolphins and humans rule the planet.

Paul Falkowski of Rutgers University says this success story was helped by the more than doubling of oxygen in the air over the past 205 million years. This is what he wrote in the Friday edition of the journal Science.

The researchers examined samples of material that sank to the bottom of the sea millions of years ago. By measuring the amount of carbon 13 in the samples they were able to estimate the amount of oxygen in the atmosphere at the particular time when the land sank in that area.

They found that the air contained only 10 percent oxygen during the time of the dinosaurs. 50 million years ago the oxygen level grew to 17 percent and 40 million years ago it reached 23 percent. Today its level has decreased slightly and stands at 21 percent.
The increase in the oxygen level almost certainly caused the evolution of the large mammals," the researchers wrote. The oxygen needed by mammals and birds is 6 times greater than that of reptiles. The asteroid impact 65 million years ago contributed to the extinction of the dinosaurs. This extinction also created an opportunity for the rise of the mammals.

There was an increase in the size of small and medium-sized mammals in the first million years after the end of the age of dinosaurs. the researchers said. Another increase, from medium to large, was seen between 50 million and 40 million years before our time. They reported.
The research was funded by the National Science Foundation