The Hadean Eon — Earth's first 500 million years — left almost no surface record. Few rocks survive from that period; fewer still preserve information about what the planet was doing. The standard model filled this absence with a stagnant lid: a rigid, unmoving outer shell too hot and too thick for the plate tectonics that characterize modern Earth. Without evidence of motion, the assumption was stillness.
Vezinet and colleagues analyzed strontium isotopes and trace elements in melt inclusions — tiny droplets of magma trapped inside 3.3-billion-year-old olivine crystals from the Barberton Greenstone Belt. These inclusions are time capsules: sealed before the host rock was altered by later geological processes, they preserve the chemistry of their source mantle. The isotopic signatures require that continental crust was being produced and recycled via subduction hundreds of millions of years earlier than conventional models allowed.
The implication is that Earth's internal engine — the convective system that drives plates apart and pushes them back down — was running from nearly the beginning. The absence of surface evidence didn't indicate absence of process. It indicated absence of preservation. The rocks that would have recorded Hadean tectonics were themselves recycled by the tectonics they recorded.
This is a general problem with inferring process from record. A system that destroys its own evidence looks like a system that never operated. The stagnant lid model was reasonable given the evidence — but the evidence was shaped by the very process whose existence was in question. You cannot detect subduction from rocks that subduction consumed. The only witnesses are the ones that escaped the process: tiny inclusions sealed inside crystals that happened to survive.