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. Click here for news about the historic dive, an exclusive postdive interview with Cameron, and information about the next phase of the expedition.
Descending to the deepest point of the Mariana Trench will give scientists an up-close look at an area where two tectonic plates meet.
Study of the seafloor landscape and retrieval of rocks along the edge of the trench could give scientists insights into earthquakes, tsunamis, and even conditions that might have helped life emerge billions of years ago.
Illustration courtesy National Geographic
Infographic of tectonic plates
When the pilot lands in the trench, he might see large sediment ponds—essentially big flat areas filled with soft, talcum-powder-like particles. Sediment collected on rock exposures or ridges in the deep might look like light dustings of snow.
As he gets closer to the slope of the trench, he might see boulders of varying sizes, which could have fallen just like a rock slides down a mountainside. Everything the pilot sees and films will help give scientists a better idea of what’s down there.
EARTHQUAKES AND TSUNAMIS
Investigating deep-ocean trenches may help scientists better understand tsunamis, including the one that devastated Japan in March 2011.
Tsunamis have been generated in many bodies of water, including the Atlantic and Indian Oceans, the Mediterranean, and the Caribbean, although they have been recorded most frequently in the Pacific, where tectonic activity is the greatest.
Much of the Pacific is surrounded by active tectonic plate boundaries, the so-called Ring of Fire. Sudden lurches of those plates can release enormous pulses of seismic energy—earthquakes—that create giant waves that can wreak destruction on coastal areas.
Earthquakes in subduction zones—where one tectonic plate slides beneath another—cause most tsunamis. Ocean trenches such as the Mariana Trench form at the boundary of these plates. The descending plate releases fluids as pressure and temperatures rise deep in the subduction zone. These fluids reduce the melting point of the mantle of the overlying plate where it contacts the subduction plate and magma can form. If enough magma forms as a result, it can rise to the surface and form a volcano—a prominent feature around much of the Ring of Fire. In the Mariana subduction zone, the older, colder Pacific plate sinks beneath the eastern edge of the Philippine plate.
Typically, the plates slide past each other at the rate of a few inches a year. But sometimes the plates get stuck—hung up on a mountain, say. Over time the strain on the bending plate builds and builds until the plates slip, lurching past each other suddenly. The resulting earthquake can be massive and can lift the ocean surface, creating a tsunami.
In the case of the tsunami that hit Japan in March 2011, strain had been building along the subduction zone of the Japan Trench. When it slipped, it released 8,000 times more energy than the atomic bomb dropped on Hiroshima during World War II.
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).
By descending down ocean trenches, scientists can get a close look at rocks exposed along the plate boundaries in these subduction zones. They can examine the condition of these rocks, which may reveal evidence of how much stress might be building between the sliding plates.
Learning more about the physical properties of the plate boundaries could help scientists develop models about the potential for earthquakes (and resulting tsunamis) in high-risk regions of the world.
PHYSICAL CONDITIONS FAVORING THE ORIGIN OF LIFE
Some scientists theorize that ocean trenches—specifically the serpentine mud volcanoes that can develop near them—may have provided the right conditions for life to emerge on Earth. Today, the only active serpentine mud volcanoes known are in the Mariana Trench, making them an important window into the past.
When one tectonic plate slides under another, as at the Mariana Trench, the inner slope of the trench is fractured. As it descends into the Earth’s interior, the down-going plate is warmed and squeezed by increasing pressure. It releases fluids that rise up through the faults from as deep as 8 miles (13 kilometers). The cool fluid mixes with ground rock in the fault zones, and a resulting bluish green serpentine mud can erupt at the seafloor alongside the trench. The eruptions can form immense mud volcanoes over millions of years, and the springs on top sometimes form “chimneys.” The chimneys can resemble saguaro cactuses and develop when minerals solidify after coming into contact with seawater.
So what does this have to do with the origin of life? When the fluids from the down-going plate rise and react with the overlying mantle rock, hydrogen and methane gas are released. These are important nutrients for single-celled organisms. Billions of years ago, fluid seeps on serpentine mud volcanoes would have provided the ideal location for the development of amino acids—molecules that are the building blocks of life.
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