Volcanoes of the Deep Sea

Paleodictyon, ancient mystery of the deep: The video Volcanoes of the Deep Sea takes the audience to the coast of Spain where a unique hexagonal fossil pattern is being recovered from the rugged cliffs by eminent German geologist and paleontologist Dr. Dolf Seilacher. The sedimentary rock layers have obviously been tilted up by tectonic forces. These rock layers (beds) are called turbidites and are formed by deep sea muddy avalanches (called turbidity currents) off the continental shelf and into very deep water. Remember what they look like. These are very common sedimentary rocks and are now found in many places on the continents due to mountain building especially in areas of subduction. The fossils trapped in layers of ancient seafloor were, over millions of years, thrust upright along this section of the Spanish seacoast. The fossils Dr. Seilacher found preserve, in intricate detail, a hexagonal pattern of holes (tunnels?). The story of the Paleodictyon (pronounced ʻpal-ee-oh-DIK- tee-onʼ) began with the discovery of small hexagonal imprints in rock formations in Europe. The imprints, about the size of a poker chip, are made up of dozens of smaller hexagons. Dr. Dolf Seilacher, a paleontologist and geologist, first discovered these mysterious structures in the 1950s. Identifying the patterns as trace fossils, Dr. Seilacher collected and analyzed samples, dated them to 60 million years and named them Paleodictyon nodosum. The mystery of these fossils was reignited 1977, far away from the mountains in Europe. From a video camera towed behind a submersible, marine geologist Dr. Peter Rona observed hexagonal imprints made up of tiny holes in the sediment near hydrothermal vents, deep in the Atlantic Ocean. Dr. Rona nicknamed these formations ʻChinese Checkerboardsʼ because they resemble the board of that popular game. These strange shapes also were the size of poker chips, but the patterns here were in sediment (mud), not in rock. Dr. Rona concluded that they had been made recently by a creature very much alive. Unable to identify the organism that had made these patterns, Dr. Rona published pictures of the mysterious checkerboards in a scientific journal, describing what he had found and where he had found them. Dr. Seilacher read the article and contacted Dr. Rona immediately, explaining he had found the same hexagonal pattern 25 years earlier, but as trace fossils rocks. Together, Dr. Rona and Dr. Seilacher hypothesized that the same species that left the trace fossils in the rocks of many European mountain outcrops had made the identical imprint on the sea floor. Maybe so, but what is the animal making this pattern? and why does it create this pattern? In the video Volcanoes of the Deep Sea, Drs. Rona and Seilacher team up in the spirit of scientific inquiry to try to solve the mystery of who made the checkerboards in the deep. They dive to the bottom of the ocean in search of the elusive creature that has been decorating the Mid-Atlantic Ridge with hexagonal patterns. Finding the maker of the imprint is of key importance, yet extremely difficult as deep-sea sediments are fragile, and difficult to core and retrieve from the deep sea for study in a laboratory. And even after doing all the work, there are no guarantees you will find what you are looking for! After all, the critter may have died or left the site to build another. As you watch this video, fill in the blanks. Also keep in mind the underlying story, finding and learning what kind of a life form Paleodictyon nodosum is. We pick up the story, flying toward a distant ship in a vast sea.

1. Ahead is the research vessel Atlantis with a destination of the mid-______-ridge system, 500 miles ahead and ______feet down. Besides the crew and the two old fossils (a geologist and paleontologist) is the deep ocean submersible named ______. 2. The underwater story actually begins on a dive 30 years earlier off South America along the Galapagos Rift in the Pacific Ocean some 8,600 feet down. The scientists were interested in a temperature differential related to volcanisms that was building elaborate underwater structures. (Today these structures when active are usually referred to as “black smokers”. I think you can see why.) The geologic processes at that time were not well understood but took a back seat to the organisms they found. The water around the black smokers was hot enough to melt ______and heavily laden with hydrogen sulfide. There should have been nothing alive here at all. In water hot enough to boil a lobster bright red were millions of the Pompeii worms, Alvinella pomejana. 3. Diving to the Mid-Atlantic-Ridge the scientists passed many soft bodied organism, perhaps many new to science, which could have been around millions or even hundreds of million years. They are so thin and delicate they may not have ever fossilized. Traveling to the seafloor and back will use of ______hours of Alvinʼs oxygen and battery power. At the bottom, if you were only expecting mud, you would be very surprised. You are looking at hardened pillow lavas which are the form lava takes when erupted on the sea bottom. It is volcanic rock ______which forms the ocean crust. Remember it is at the mid-ocean-ridges where the oceanʼs crust forms. This is where the North American and European are forming and moving away from each other; the crack being filled with new crustal basalt. The mid-ocean-ridge here is ______feet high, 500 miles wide and ______miles long. It is the largest geological feature on the face of the earth. 4. After eruptions along the ridge have ended and the rock has cooled, new organisms colonize the rock formations. One of the most interesting is the octopus they called ______that has what look like big moving ears. Rocks that are hot enough are covered with 6 foot long, red and white ______worms. These worms have no mouth and no stomach, so how to they live? They contain specialize bacteria in their ______that use chemical energy to manufacture food for themselves and for the worms. The red filaments on the top of worm draw hydrogen sulfide from the water for the bacteria to use for this for chemical metabolism (chemosynthesis). The red color of the worms is from blood containing hemoglobin similar to that in human blood. 5. Five billion years ago a supernova (giant exploding star) threw out enough matter to form new smaller stars like our sun. Along with our sun, the planets and other objects of the solar system formed about four and a half billion years ago. We now know that the sun is not the only source of energy for lifeʼs organisms. The Earth has internal heat from radioactive decay that provides, at the black smokers, hydrothermal heat and chemicals that can be used for chemosynthesis. 6. Many of the oldest fossils we find are simply tracks or traces of something crawling or burrowing through the mud. Some trace fossils, like Paleodictyon nodosum, are distinctive patterns. P. nodosum is very unusual with a honeycomb like appearance of hexagonal holes or tunnels. The organism that left these unusual traces has been around since at least the Cambrian Period (540 million years) surviving many extinction events.The big question is what is it? As scientists studied the life of hydrothermal vents (black smokers) they began to understand how that ecosystem works. Growing on the rocks are hundreds of species of specialized ______that are able to use chemical energy for their metabolism. Shrimp graze on these organisms for their food and bigger animals feed on the shrimp. This is a food chain not based on ______like the most food chains near the surface. 7. When a hydrothermal vent shuts down, they no longer vent hot mineral laden water, the ecosystem and its food chain shuts down as well. This area becomes a deep sea desert. These areas became the focus of Dr. Ronaʼs and Dr. Seilacherʼs search. They will look in the mud for traces made by Paleodictyon nodosum. Surprisingly, they found them quickly; they were present in the thousands. They were able to take many cores containing the hexagonal tunnels of P. nodosum. What did they find? What was the creature? It turned that the scientists found ______. However, the scientists did come up with ideas. Perhaps the organism is a worm that is ______bacteria in its tunnels. Scientists are not sure of this but are convinced that the organism that made the traces fossilized in the rocks along the Spanish coast is the ______as the one that made the patterns in the mud miles below the oceanʼs surface.