Mother Nature's 2 billion-year-old nuclear reactor

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We tend to think that humans are the only possible source of complex machinery on Earth. Leaving aside the exquisite complexity of biologically evolved organisms, it does seem to be true that the Earth creates less complexity than its human inhabitants. Yet, in the 1970s, nuclear excavators discovered a form of natural technology that not only humbled nuclear scientists with its simplicity, but which actually predated their achievements by several billion years. The startling discovery has supported decades of research, but its depths are still producing lessons for US regulators.

The objects in question are called the Oklo reactors, naturally occurring nuclear reactors named for the West African region of Gabon in which they reside. They've been dead for a very long time, probably over 1.5 billion years, but the evidence of their prior action is unmistakable. Sometime a bit less than 2 billion years ago, and lasting for about 300,000 years, the Oklo reactors held a series of stable nuclear fission reactions. Upon their discovery, the central question about these reactors was simply: How could they possibly work? One early hypothesis was that the fundamental physical constants that restrict nuclear reactions today may have been different 2 billion years ago. Analysis of the wastes at Oklo, running all the way up to this very month, suggest that the physical constants have indeed been constant all along. That means the reactor would have needed a fissionable isotope in the same concentrations we require today.