Register for an account

X

Enter your name and email address below.

Your email address is used to log in and will not be shared or sold. Read our privacy policy.

X

Website access code

Enter your access code into the form field below.

If you are a Zinio, Nook, Kindle, Apple, or Google Play subscriber, you can enter your website access code to gain subscriber access. Your website access code is located in the upper right corner of the Table of Contents page of your digital edition.

Environment

72. Crust Formed Early In Earth’s History

By Anne SassoJanuary 14, 2008 6:00 AM

Newsletter

Sign up for our email newsletter for the latest science news

Geologists took a new look at a sequence of old rocks in southwest Greenland and discovered the earliest example yet of plate tectonics. Until March, when the findings were published in Science, researchers thought that continents began to solidify on Earth around 2.5 billion years ago. The new discovery shows that the process started much sooner, closer to when the planet formed.

Earth scientists have been crawling over the intensely baked and contorted rocks of the 3.8-billion-year-old Isua Supra­crustal Belt for decades. But when Harald Furnes, a geologist at the University of Bergen in Norway, and his colleagues walked over the Greenland outcrops, bells went off. They saw sheeted dikes—thinly banded rocks composed almost entirely of a shiny, green-black mineral called amphibole. Previously, researchers had found nearby pillow lavas, bulbous lava flows that form ­under water. The combination of the two rock types, along with other geologic clues, could mean only one thing: They were standing on an ancient piece of the ocean floor.

Furnes says the significance of the find hit them immediately: It meant that the ocean floor was forming, and plate tec­tonics was active, nearly 1.3 billion years earlier than previously thought. It’s rare for such ocean rocks to survive so long, and finding them isn’t easy. “It depends on the experience of the observer and if you keep your eyes open when you do field work,” says Furnes.

Go to the next article: 73. Parasite Invades Its Host’s DNA

2 Free Articles Left

Want it all? Get unlimited access when you subscribe.

Subscribe

Already a subscriber? Register or Log In

Want unlimited access?

Subscribe today and save 70%

Subscribe

Already a subscriber? Register or Log In