Crust (geology)

50 years ago, continental drift began to gain acceptance

map of Earth
FULL OF PLATES Earth’s outer crust is composed of more than a dozen large pieces, known as tectonic plates, which bump or slide against each other.
Science News cover from April 29, 1967

Drifting theories shake up geology

Continental drift, a theory often considered amusing but rarely important, seems about to become the focus of a revolution in geology. At the least, it has already split the geological community into those who find the evidence…

Is Zealandia a continent?

New Zealand
New Zealand

Lurking beneath New Zealand is a long-hidden continent, geologists now propose. They call it Zealandia. Don’t expect it to soon end up on a map on your classroom wall, though. Nobody is in charge of officially designating a new continent. Scientists will have to judge for themselves if Zealandia should be added to the ranks of continents.

A team of geologists pitched the scientific case for judging this a new continent in the March/April issue of GSA Today. Zealandia is a continuous expanse of continental crust. It covers some 4.9 million square kilometers (1.9 million square miles). That’s about the size of the Indian subcontinent. But it would be the smallest of the world’s continents. And unlike the others, around 94 percent of Zealandia hides beneath the ocean. Only New Zealand, New Caledonia and a few small islands peek above the waves over it.

“If we could pull the plug on the world’s oceans, it would be quite clear that Zealandia stands out,” says study coauthor Nick Mortimer. He is a geologist at GNS Science in Dunedin, New Zealand. Zealandia rises about 3,000 meters (9,800 feet) above the surrounding ocean crust, he notes. “If it wasn’t for the ocean level,” he says, “long ago we’d have recognized Zealandia for what it was — a continent.”

Story continues below map

continents map
A landmass called Zealandia (gray region) deserves to join the ranks of continents, some geologists now propose. Only 4 percent of Zealandia rises above sea level (dark gray), including New Zealand. But swaths of other continents also are submerged along their margins (light-shaded regions).

This landmass, directly east of Australia, will face an uphill battle for continent status. New planets and slices of geologic time have international panels that can officially name them. But there is no such group to officially validate new continents. The current number of continents is already vague. Most everyone agrees on five of them: Africa, Antarctica, Australia and North and South America. Some people, however, combine the last two — Europe and Asia — into one huge Eurasia. There’s no formal way to add Zealandia to this mix. Proponents will just have to start using the term and hope it catches on, Mortimer says.

This odd path forward stems from the simple fact that nobody expected another continent would ever need to be added, says Keith Klepeis. He is a structural geologist…

Earth’s mantle may be hotter than thought

Earth's mantle
HOT STUFF Temperatures in Earth’s mantle are higher than previously thought, results from a new experiment suggest.

Temperatures across Earth’s mantle are about 60 degrees Celsius higher than previously thought, a new experiment suggests. Such toasty temperatures would make the mantle runnier than earlier research suggested, a development that could help explain the details of how tectonic plates glide on top of the mantle, geophysicists report in the March 3 Science.

“Scientists have been arguing over the mantle temperature for decades,” says study coauthor Emily Sarafian, a geophysicist at the Woods Hole Oceanographic Institution in Massachusetts and at MIT. “Scientists will argue over 10 degree changes, so changing it by 60 degrees is quite a large jump.”

The mostly solid mantle sits between Earth’s crust and core and makes up around 84 percent of Earth’s volume. Heat from the mantle fuels volcanic eruptions and drives plate tectonics, but taking the mantle’s temperature is trickier than dropping a thermometer down a hole.

Scientists know from the paths of earthquake waves and from measures of how electrical charge moves through Earth that a boundary in the mantle exists a few dozen kilometers below Earth’s surface. Above that boundary, mantle rock can begin melting on its way up to the surface. By mimicking the extreme conditions in the deep Earth — squeezing and heating bits of mantle that erupt from undersea volcanoes or similar rocks synthesized in the lab — scientist can also determine the melting temperature of mantle rock. Using these two facts, scientists have estimated that temperatures at the boundary depth below Earth’s oceans are around 1314° C to…