Lets Go on a Discovery Trail to the Deep Dark Ocean!
TOPSY TURVY WORLD:
Wiwaxia lived on the seafloor 530 million years ago, yet this fossil was found high above sea level in Canada's Rocky Mountains. This shows just how much the Earth's surface has changed, with land, originally formed under the sea, forced up to form mountain chains.
STILL HERE TODAY:
The 180-million-year old fossil brittle star looks like its living relative (above). Brittle stars have a round central disk and five, very fragile, jointed arms, that can easily break. Today, as in the past, large numbers are often found on sandy or muddy seabeds.
Compared to their sift-bodied relatives the anemones and jellyfish, corals were preserved well as fossils in rocks because of their hard skeletons, such as this 400-million-year-old fossil coral. Each coral animal formed a skeleton joining that of its neighbor to create chains with large spaces between them.
One giant ocean, Panthalassa, surrounded the supercontinent Pangaea (1), 290-240 mya (million years ago). At the end of this period, many kinds of marine life became extinct. Pangaea broke up, with part drifting north and part south, with the Tethys Sea between.
The northern part split to form the North Atlantic 208-146 mya (2). The South Atlantic and Indian Oceans began to form 146-65 mya (3). The continents continued to drift 1.64 mya (4). Today the oceans are still changing shape- the Atlantic Ocean gets wider by an inch or so each year.
DEAD AND GONE:
Trilobites, one of the most abundant creatures living in the ancient seas, first flourished over 510 million years ago. They had joined limbs and an external skeleton like insects and crustaceans (such as crabs and lobsters) but they died out some 250 million years ago.
Scientists scanning the deep interior of Earth have found evidence of a vast water reservoir beneath eastern Asia that is at least the volume of the Arctic Ocean.
Looking Down Deep
The pair analyzed more than 600,000 seismograms — records of waves generated by earthquakes traveling through the Earth—collected from instruments scattered around the planet. [Image Gallery: This Millennium's Destructive Earthquakes] They noticed a region beneath Asia where seismic waves appeared to dampen, or "attenuate," and also slow down slightly. "Water slows the speed of waves a little," Wysession explained. "Lots of damping and a little slowing match the predictions for water very well."
Previous predictions calculated that if a cold slab of the ocean floor were to sink thousands of miles into the Earth's mantle, the hot temperatures would cause water stored inside the rock to evaporate out.
"That is exactly what we show here," Wysession said. "Water inside the rock goes down with the sinking slab and it's quite cold, but it heats up the deeper it goes, and the rock eventually becomes unstable and loses its water." The water then rises up into the overlying region, which becomes saturated with water [image]. "It would still look like solid rock to you,” Wysession told LiveScience. "You would have to put it in the lab to findthe water in it."
Although they appear solid, the composition of some ocean floor rocks is up to 15 percent water. "The water molecules are actually stuck in the mineral structure of the rock," Wysession explained. "As you heat this up, it eventually dehydrates. It's like taking clay and firing it to get all the water out." The researchers estimate that up to 0.1 percent of the rock sinking down into the Earth's mantle in that part of the world is water, which works out to about an Arctic Ocean's worth of water.
"That's a real back of the envelope type calculation," Wysession said. "That's the best that we can do at this point."
The discovery marks the first time such a large body of water has found in the planet's deep mantle. [The World's Biggest Oceans and Seas] The finding, made by Michael Wysession, a seismologist at Washington University in St. Louis, and his former graduate studentJesse Lawrence, now at the University of California, San Diego, will be detailed in a forthcoming monograph to be published by the American Geophysical Union.