Plate Tectonics: Earth's Lucky Geology

Jan. 11, 2008 -- Four decades after the rise of the great, unifying theory of plate tectonics, geologists are still scratching their heads over a lot of the details.

Unanswered, for instance, are basic questions like how the shifting and colliding of plates got started, what keeps plates moving, why other planets in our solar system lack plate tectonics, and how important all the geological turmoil might be to the evolution of life.

"We didn't get it all right the first time, so let's ask the questions," said geologist Vicki Hansen of the University of Minnesota at Duluth, referring to the fact that despite decades of work, many mysteries remain.

Hansen recently stirred the pot with a controversial hypothesis published in last month's issue of the journal Geology. Meteorite impacts early in Earth's history, she suggested, created the first rifts in the crust, jump-starting plate tectonics.

Prior to the 1960s, geologists were hard pressed to explain such basic things as how most mountain ranges formed and why volcanic regions and earthquakes were clustered in certain parts of the planet. Plate tectonics put these phenomena, and many others, into a single, unified framework.

That framework is an Earth with a rocky crust divided into plates that are moving, rifting, colliding and overrunning each other. It finally made sense of a previously nonsensical geography and is now recognized as one of the greatest scientific breakthroughs of the 20th century.

Energizer Bunny Tectonics?

Another iconoclastic hypothesis just out last week goes after the question of whether plate tectonics ever stops. Has it ever done so? Geologist Paul Silver of the Carnegie Institution of Washington thinks it's possible.

"It's an implicit assumption that plate tectonics never shuts down," Silver told Discovery News. "But it's nowhere stated in plate tectonics theory."

Silver and his colleague Mark Behn proposed in the Jan. 4 issue of Science that all it takes to stop plate tectonics is the devouring of the crustal plate under the Pacific Ocean. And that's not as far-fetched as it sounds.

The Pacific Plate is surrounded by most of Earth's overriding (subducting) crust collision zones, so it's getting smaller all the time. Eventually, roughly 350 million years from now, the surrounding adjacent continents will collide.