Register for an account


Enter your name and email address below.

Your email address is used to log in and will not be shared or sold. Read our privacy policy.


Website access code

Enter your access code into the form field below.

If you are a Zinio, Nook, Kindle, Apple, or Google Play subscriber, you can enter your website access code to gain subscriber access. Your website access code is located in the upper right corner of the Table of Contents page of your digital edition.


Early Breath of Fresh Air

By Lauren GravitzApril 1, 2002 6:00 AM


Sign up for our email newsletter for the latest science news

Scientists have long believed that Earth's atmosphere contained little free oxygen until 2.3 billion years ago, when the first photosynthetic bacteria evolved. Neil Phillips, a geologist at the Commonwealth Scientific and Industrial Research Organization in Australia, began to doubt the conventional wisdom while studying gold deposits in South Africa. He uncovered what appear to be pisoliths, pellets of iron oxide (above) thought to arise only in the presence of oxygen. But these pisoliths date from 2.8 billion years ago, long before the rise of oxygen-spewing microbes.

Phillips argues that Earth probably had an oxygen atmosphere from the beginning of geologic history. If so, ideas about how life evolved during the first 2 billion years could be wrong. But some of his colleagues propose that the pisoliths could have formed under anoxic conditions, pointing to geologic and experimental evidence against early oxygen. "To my mind, this issue has been solved for 30 years," says James Kasting, a geoscientist at Pennsylvania State University.


Photograph courtesy of Csiro Exploration and Mining


    3 Free Articles Left

    Want it all? Get unlimited access when you subscribe.


    Already a subscriber? Register or Log In

    Want unlimited access?

    Subscribe today and save 50%


    Already a subscriber? Register or Log In