DEEP TIME unearthed a record of geological time that is buried thousands of kilometres deep. The seafloor that covers two-thirds of the earth's surface is a tiny fraction of all seafloor created during the earth’s history – the rest has sunk back into the viscous mantle, where it originated. Slabs of subducted seafloor carry a record of surface history: how continents and oceans were configured over time and where their tectonic plate boundaries lay. DEEP TIME followed former surface oceans as far back in time as the convecting mantle system allowed, by imaging subducted slabs down to the core with cutting-edge seismological techniques. Previous tectonic plate reconstructions incorporated little if any of this deep structural information, which reaches back to at least 300 million years; these reconstructions are mostly based on present-day seafloor, which constrains only the past 100-150 million years. For earlier times, paleo-oceanic areas in these reconstructions become an unconstrained as the backside of the moon used to be, and even the continental hemisphere (“Pangea”) is subject to large quantitative uncertainties.
The spatial configuration of continents, oceans and plate boundaries (and their changes over time) sets boundary conditions for almost every physical, chemical and biological process at the surface. It determines how ocean currents develop and therefore climate; where physical barriers inhibit or enhance the evolution and dispersal of biota; and where the natural resources form that have supported every human society. Thus there is a fundamental interest in paleo-geographic reconstructions that are reliable, quantifiable and testable. The state of the knowledge is particularly lacking for paleo-oceanic areas, which tend to self-destroy the records of their existence, except if one succeeds in imaging their remains deep in the earth’s mantle.
