In the early days there were probably many fields like the Kalahari, but for reasons that are unclear, most were destroyed by subsequent geologic events. Kalahari was left preserved under a layer of volcanic basalt until humans began mining it 2.4 billion years later. But the story takes yet another turn. Too much oxygen in the atmosphere isn't necessarily a good thing. Molecular oxygen in the form of free radicals can damage DNA, the blueprint for all living organisms.
Free radicals are unstable elements that can break down chemical compounds.
Kirschvink theorizes that the origin of that enzyme could date back to the end of the snowball Earth, when even primitive organisms needed some protection from an atmosphere rich in free radicals. And that, he suggests, altered the course of evolution by paving the way for more complex organisms to develop, protected from free radicals that could otherwise destroy them. They had to do it quickly, paving the way for all kinds of organisms to evolve. And we thought we had problems with global warming. A former science writer for the Los Angeles Times , he now lives in Juneau, Alaska.