19 janvier 2016

Évolution des continents...

Extraits du fascinant article:

Already, Mueller’s team, working with collaborators at the University of Oslo and Caltech, has completed a stunningly detailed digital reconstruction of 410 million years of earthly history, going back to the collision of then-existing continents that created Pangaea. In January, they plan to release version 2.0 of GPlates, an open-source software model that anyone can use to go back in time to the early days of Earth. Next, they are preparing for peer review of an extension of the model to 1 billion years ago—the era of Pangaea’s ancestor, a supercontinent called Rodinia. Then they will lunge again—to 2 billion years, yet another supercontinent, and the evolution of the first multicellular life.

(...) After Pangaea was accepted, scientists had excited a new stir by assembling geological evidence of prior supercontinents: first Kenorland, which would have broken up some 2.4 billion years ago, then Nuna, and after that, about 1 billion years ago, Rodinia. By this stage, multicellular organisms had appeared in the oceans, but the land would still have been bare of anything but bacteria and some algae. Rodinia begat Pangaea, which has hosted all of the complex plant and animal history with which we are familiar.

(...) Mueller and his collaborators set out to change that—to produce a model anchored in tectonic geometry, showing the boundaries and seamless motion of the dozen or so major plates, without gaps between them, fully integrated with the convecting mantle, and including a more rigorous appraisal of the correct longitude. It would be what he called a virtual time machine that would allow anyone to pick almost any point in the long-ago geological eras on Earth, and return there.

(...) Mueller named his team EarthByte, and the system he created with Gurnis and Torsvik is now called GPlates.

“We don’t just want to make inferences about what happened in the past,” Mueller said. “We actually want to travel into the geological past, and understand what the planet looked like, not only at the surface, but also at depth, in fact all the way to the core.”

(...) Another key advance in Matthews’ combined model is in unifying the surface with the deep Earth all the way to the core. Distinct from competing animations, which feature only the land masses on the surface of the globe, the GPlates model reveals the moving, roiling Earth underneath, in addition to the tell-tale appearance of the reversing magnetic lines on a spreading Atlantic Ocean.

But while thrilling, that would be almost an anti-climax if Mueller’s team stopped there—if they did not now set out to extend the GPlates model to Rodinia and beyond. Which is what came next.

(...) Last year, with Pangaea out of the way, Mueller assigned a PhD student (...) to start work on extending the GPlates model to Rodinia. But how? The further back in time you went, the fewer and fewer rocks you encountered—the evidence required to make any accurate picture. The plates themselves were different—some had been swallowed up into the Earth’s mantle; many had broken into pieces; most were different shapes. The oldest verified crusts—in Australia and Canada—are about 3.8 or 4 billion years old, but they are extremely lucky to have escaped destruction.

(...) The resulting model would aim to be the likeliest facsimile. It would be the first that knitted together the post-Rodinian plates, and presented the period from 1 billion to 410 million years ago not as fragmented snapshots, but as a single piece, all anchored in the tectonic rules. 

(...) How far back into the history of Earth can you go?

Mike Tetley, a high-school-dropout, former rock bassist, and one of Mueller’s top PhD students, said that paleogeologically speaking, you can go back in time 3 billion years. Before that, there aren’t enough rocks or correlating data to reach any conclusions. At least, not right now.

Le programme GPlates peut être téléchargé ici.

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