Over Earth's history, most of the original crust has recycled by sinking into the planet's hot interior, melting, and heading back toward the surface. However, a few pieces of the ancient crust never sank.
The oldest such area is the Greenland formation known as the Isua supracrustal belt, with rocks from 3.7 to 3.8 billion years old. It's "by far the oldest material on the planet that is structurally coherent, [but] people had never really found these telltale signs of oceanic spreading," says study coauthor Hubert Staudigel of the Scripps Institution of Oceanography in La Jolla, Calif.
Staudigel and his colleagues recently observed ancient outcrops of oceanic crust marked by long, parallel cracks filled with volcanic rock. Tension caused this ancient piece of seafloor to split, the researchers propose, allowing magma from the hot interior to rise and seal the cracks. Those physical characteristics, along with the chemical signature of oceanic magma, indicate that the rock was part of a spreading oceanic plate—a sure sign of tectonic activity.
"It's a marvelous case of solving a jigsaw puzzle, and a very difficult one because these rocks are all very old and have been badly mangled," comments Gustaf Arrhenius, also of Scripps.
- Science News
Hard to judge this without reading the original article, but it sounds interesting.
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