Fast Growing Mountains Could Affect Evolution... And the Climate

Image from USGS/NASA

Who knew mountains, like awkward teens, could have sudden growth spurts? According to a new study published in Science (sub. required), the Andes mountains may have doubled their height in as few as 2 - 4 million years -- suggesting that the latest plate tectonics science may need some revision. Conventional thinking had it that mountain ranges tended to rise gradually over a period of several million years. Indeed, most geologists had pegged the Andes mountain range's "age" at roughly 40 million years and had attributed its formation to plate tectonics.

Carmala Garzione's research, however, seemed to indicate otherwise. Garzione, a professor of geology at the University of Rochester, and her colleagues examined the sediment record and found that the Andes had slowly grown for tens of millions of years before suddenly spiking between 10 and 6 million years ago -- a process they call "delamination":

Conventional theory says that movement of the fluid mantle deep in the Earth slowly erodes this heavy root, allowing mountains to rise gradually . . . She argues that instead of eroding slowly away, the root heats up and oozes downward like a drop of thick syrup, abruptly breaking free and sinking into the hot mantle. The mountains above, suddenly free of the root, then spring up.

How might this affect the then prevalent climate and evolution? Well, the Andes' sudden growth would have required the ambient wildlife to adapt to the pressure/elevation change through natural selection -- potentially leading to some species extinctions -- and may have resulted in the introduction of new species. As for the climate, Garzione and her colleagues are still investigating; this last part of the Science article might provide some indication:

Crustal compression doesn't happen that fast, but Garzione and her colleagues say an indirect effect can explain the rapid rise. Compression thickens not only the crust but also the cold, dense mantle rock immediately beneath. The central Andes seem to have lost this so-called mantle lithosphere, the group says, removing a weight from the lighter crust. Without that ballast, the crust could rise. The timing and style of volcanism in the central Andes suggest that the mantle lithosphere fell away suddenly--as a huge drop dripping off the crust or as a layer peeling away--just when the isotopic data indicate a punctuated uplift, the group writes.

The Andean paleo-elevation data all but clinch the case for that scenario, says tectonophysicist David Rowley of the University of Chicago in Illinois. But first the paleo-elevation data need to be tested further, says Todd Ehlers of the University of Michigan, Ann Arbor. Garzione and colleagues state that the climate under which new minerals recorded elevation change resembled the modern climate, he says, "but they've never tested it." Ehlers reported at last December's American Geophysical Union meeting that in a climate model, the rise of the Andes themselves alters climate--for example, by changing the source and therefore the isotopic composition of precipitation. That could give a false paleo-elevation, he says. He would like to see more work with models rather than in the field.

Via ::Reuters: Mountains could have growth spurts (news website)

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