National Geographic



Editor’s note: On March 26, 2012, James Cameron made a record-breaking solo dive to the Earth’s deepest point, successfully piloting the DEEPSEA CHALLENGER nearly 7 seven miles (11 kilometers) to the Challenger Deep in the Mariana Trench. DEEPSEA CHALLENGE is now in its second phase—scientific analysis of the expedition’s findings. 

Descending to the deepest point of the Mariana Trench gave scientists an up-close look at an area where two tectonic plates meet.

Image: Illustration of plate tectonics

Illustration courtesy National Geographic
Infographic of tectonic plates

When James Cameron descended nearly 7 miles (11 kilometers) into the Challenger Deep, he found a world that seemed very, very still. Living things barely stirred. When he skimmed the sediment on the bottom, powder erupted as if he were entering a basement where dust had been collecting for centuries.

Yet for all its eerie stillness, geologists say there’s an incredible amount of activity happening in the deepest parts of the world. These seemingly quiet places can spawn earthquakes and volcanoes. And they might even provide clues to the origins of life. Now that Cameron has returned with images, scientists are getting to work.


One reason the ocean floor seems so smooth at the Challenger Deep, said expedition geologist Patricia Fryer, is because the earth there is always moving. Since the 1960s hundreds of quakes ranging from 4.5 to 8 on the Richter scale have been recorded in the deepest parts of the world’s oceans. Each time they occur, a fresh layer of sediment blankets the seafloor—much like a fresh snowfall—and covers any mounds or tracks that living things may have created.

Tectonic activity at plate boundaries in the ocean can also lead to tsunamis. Fryer is planning to take a close look at the 3-D footage Cameron captured at the Challenger Deep. Studying the features on the seafloor and comparing them to features seen in trenches that have produced tsunamis (such as the Japan tsunami in 2011), could eventually reveal clues that help us predict the devastating giant waves.


In the New Britain Trench off the coast of Papua New Guinea Cameron encountered an unexpected set of pillow lavas. The mounds of lava, each produced by a small pulse from an underwater eruption, resemble giant squeezes of toothpaste and are the deepest ever found. Their location surprised Fryer.

“Incoming oceanic plates generally don’t expose beautiful sections of pillow lavas like that,” she said.  “Usually any rocks exposed there are very altered and covered with sediment.”

But indeed, rather than finding the gentle, sediment-covered slope that Fryer would have normally expected on this oceanic plate, Cameron encountered a slope covered with the smooth formations that almost look comfortable enough to sleep on.

But while they may be fascinating to look at, it’s the potential to study what the pillow lavas are made of that has geologists like Fryer most intrigued. Examining how the composition of the lava has changed over time alongside the distance from its origin could provide clues about how magma formation may be controlled beneath the ocean plate. This means scientists may have the potential to learn more about the history and development of the plate and even its relationship to the formation of volcanic island chains and tectonic processes at its edges that have happened over tens of millions of years.

“Looking at the nature of the ocean crust in that area is going to help us understand the types of processes that might be related to the generation of earthquakes at the plate margins and the generation of tsunamis,” said Fryer.


The expedition provided more opportunity for Fryer to study serpentinization, a process that can occur when plates collide in subduction zones like the Mariana Trench.

Photograph courtesy NERC CHESSO Consortium
These openings in the Earth’s crust, called black smoker chimneys, can spew mineral-rich water as hot as 720°F (382°C).

In subduction, one plate grinds its way under another. Serpentinization occurs when the down-dragged plate is warmed and squeezed and any water trapped in it—often water is locked into the crystal structure of the rock—is forced up through the plate and toward the ocean floor, causing upper mantle rock to transform along the way. The process releases hydrogen and methane at springs on the seafloor, and some scientists think those gases could have fueled the first life-forms. Serpentinization also creates conditions in the water that help organic molecules stay stable, further evidence, some scientists say, that such a zone might have harbored early life.

So, expedition scientists were thrilled to discover what they call microbial mats in an area where they suspect serpentinization is occurring in the Sirena Deep, a zone east of the Challenger Deep in the Mariana Trench. These 35,100-foot-deep (10,700-meter-deep) clumps of microbes may resemble some of the earliest forms of life. There’s much more research to be done, but already biologists have confirmed that these single-celled organisms have genes indicating they can fix carbon dioxide in the dark and feed off of reduced sulfur.

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Pictures: Deepest Ocean Vents Swarm With Heat-Vision Shrimp?

Science Partners

  • Additional major support provided by The Alfred P. Sloan Foundation
  • NASA Jet Propulsion Laboratory
  • Scripps Institution of Oceanography, UC San Diego
  • University of Hawaii at Manoa
  • University of Guam