Denis Diderot explicitly regarded his Encyclopédie, published between 1751 and 1772, as a safe repository of human knowledge, preserving it for posterity in case of a cataclysm that snuffs our civilization as the ancient cultures of the Egyptians, Greeks, and Romans had all been lost, leaving behind only random surviving fragments of their writing.

Some of the clues to our past, our ancestry, lie buried deep underground. They may never be discovered. They may already have disintegrated, merging with the soil, dissolving into groundwater, rendered into fragments of molecules, before anyone ever had the chance to catch them. Others have been prised out of the earth, though. The bones of ordinar

After years of patient work around the globe, volcanologists and climate modelers are now sure: in the years 536 and 539/540, there occurred at least two volcanic eruptions of almost unprecedented magnitude. The first of them may have been somewhere in the tropics, although the location has not yet been pinned down conclusively. The second was at L