The Forewarned: A Warning Written in Fire. The Foretold, #1

Something struck the Earth 12, 900 years ago - not once, but in a swarm, delivering the force of hundreds of nuclear weapons across multiple continents in the span of hours. There is no crater. There didn't need to be. The evidence survives instead in a thin dark line of scorched earth found from Patagonia to Greenland, in glass melted at temperatures no wildfire or volcano can produce, in the bones of an ecosystem - mammoths, camels, saber-toothed cats - that disappeared almost overnight.
The catastrophe didn't end there. A wall of meltwater collapsed the world's climate engine, plunging the Northern Hemisphere into twelve centuries of cold. A sophisticated, continent-spanning Stone Age culture vanished from the archaeological record, leaving only fragments behind. Civilization itself was pushed to the edge of extinction. And yet, within a single human lifetime of the world beginning to recover, someone built the oldest monumental structure on Earth - a feat of engineering and organization that shouldn't have been possible for a population just emerging from catastrophe.
Its carvings, according to one physicist's controversial analysis, may encode the exact date the sky fell. The Forewarned traces the physical, geological, and mythological evidence for humanity's forgotten catastrophe - and argues that the universal, ancient fear of the sky found in cultures with no contact and no common language isn't superstition. It's memory. This is Book One of The Foretold, a four-part investigation into what was lost 12, 900 years ago, what survived, and why the oldest surviving instruction in human history is the same one, repeated in language after language, across every inhabited continent on Earth:Watch the sky.