Martin Kennedy Oxygen Quotations

NASA is interested in what conditions to look for on other planets that might lead to the arrival of life. What are the processes? Using earth as our most detailed study site, what are the necessary steps a planet needs to go through to enable complex animal life to arise? If oxygen is the metabolic pathway, then we need to know what conditions have to allow for that to happen. The geologic record provides us with a record of these steps that occurred on Earth.

One of the things we least understand is why animals evolved so late in Earth history. Why did animals wait until the 11th hour, whereas evidence for more primitive life dates back billions of years? One of the best bets to explain the difference is an increase in oxygen concentration in the atmosphere.