Simulations track melted Hadean crust to deep mantle

melted Hadean – New physics-based modeling suggests Earth’s early crust didn’t just get pounded—it was melted, recycled, and drained back into the mantle down to at least 600 kilometers. As impacts declined between 3.9 and 3.5 billion years ago, the crust thickened to about 3

Earth’s earliest crust may have vanished not because it never formed, but because it couldn’t survive the planet’s own violence.

In simulations that zoomed in on the localized effects of individual large impacts. researchers found something more sweeping happening beneath the surface: the impacts didn’t merely weaken or destroy fragments. They drove wholesale recycling of crust back into the mantle. with melted material dripping down to depths of at least 600 kilometers.

Johnson argues that this recycling helps explain why so little Hadean crust remains preserved to the present day. It also, in his view, accounts for the near-total absence of shock-deformed Hadean zircons in the geological record. If vast amounts of melt were present at shallow depths. the researchers suggest it would have absorbed and scattered shock waves before those waves could leave lasting deformation in crystals that might otherwise be preserved.

That picture changes when the planet’s bombardment slows. The impact flux didn’t stay high forever; it declined more or less exponentially. Between 3.9 and 3.5 billion years ago. it dropped enough that internal heat sources took over as the dominant influence on the crust. As impact heating faded, the upper mantle cooled, and the once-thin basaltic crust thickened.

The team’s modeling suggests that crustal thickness reached around 30 kilometers by the early Archean—the era that came after the Hadean. With a thicker, cooler, more rigid crust, the planet could finally support plate tectonics. Around this same time, the first continental rocks show up in the geological record.

“As soon as you can create thick crust and you can create a mantle lithosphere underneath, you can start building continents,” Johnson said.

The researchers are clear about the trade-off behind the story. Much of their argument rests on physics-based modeling rather than rock samples. That’s not a detail they brush past—they treat it as a problem with a demandingly simple answer. Johnson says reliance on modeling is justified in the absence of geological evidence.

“We need to start taking seriously the outputs of these models rather than just say, well, we can’t find any rocks, so let’s give up,” he said.

Still, the paper leaves room for a turnaround driven by discovery. Johnson pointed to efforts that could chip away at the silence in the record. “In Nuvvuagittuq Greenstone Belt in Canada. a team of North American researchers has recently dated a dark. mafic rock as 4.2 billion years old. ” he said. He also said he knows of another group that has found a rock which is possibly even older. adding: “Hopefully you will be able to read about it in the next couple of months.”.

At the heart of the study is a sobering reminder: Earth is extremely good at covering up its own past. But it isn’t perfect.

Hadean crust Earth early impacts crustal recycling mantle depths shock-deformed zircons Hadean zircons Archean crust thickness plate tectonics continental rocks Nuvvuagittuq Greenstone Belt 4.2 billion years old