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By Suzanne O'Connell, Wesleyan University
It is amazing but true that we know more about the surface of the moon than the sea floor of the Earth. Much of what we know comes from scientific ocean drilling – the systematic collection of core samples taken from the deep seabed. This groundbreaking process began 50 years ago when the drill ship Glomar Challenger entered the Gulf of Mexico on August 11, 1968, during the first expedition of the federally funded offshore drilling project.
I participated in my first scientific ocean drilling expedition in 1980, and since then I have participated in six other expeditions, including in the extreme North Atlantic and in the Antarctic Weddell Sea. In my lab, my students and I work with basic samples from these expeditions. Each of these cores, cylinders 4.4 m long and 7.6 cm wide, looks like a book whose information is waiting to be translated into words. Holding a newly opened core, filled with rocks and sediments from the bottom of the ocean, amounts to opening a rare treasure chest that records the passage of time in the history of the Earth.
For more than half a century, scientific ocean drilling has proven the theory of plate tectonics, created the domain of paleoceanography and redefined our vision of life on Earth by revealing a huge variety and volume of life in the world. deep marine biosphere. And there is still a lot to learn.
The JOIDES Resolution science drill ship arrives in Honolulu after successful sea trials and testing of scientific equipment and drilling. Image via IODP.
Technological innovations
Two key innovations allowed research vessels to collect core samples at specific locations in the depths of the ocean. The first, known as Dynamic Positioning, allows a vessel to remain stationary during the drilling and recovery of cores, one above the other, often at over 12,000 feet ( 2 1/2 miles). meters) of water.
Anchoring is not possible at these depths. Instead, the technicians place a torpedo-shaped instrument called a transponder on the side. A device called transducer, mounted on the hull of the ship, sends an acoustic signal to the transponder, which responds. The computers on board calculate the distance and the angle of this communication. The propellers on the hull of the ship maneuver so that the ship stays exactly in the same place, countering the forces of currents, wind and waves.
Another challenge arises when the drills need to be replaced during operation. The oceanic crust is composed of igneous rock that lasts long before the desired depth is reached.
The re-entry cone is welded together around the drill pipe and lowered into the tube to guide re-insertion before changing the drills. Image via IODP.
When this happens, the drill team brings the entire drill pipe to the surface, mounts a new drill and returns to the same hole. This requires guiding the pipe in a funnel-shaped taper, less than 4.6 m (15 feet) in width, placed in the ocean floor, at the mouth of the borehole. This process, first performed in 1970, turns a long spaghetti strand into a quarter-inch wide funnel at the bottom of an Olympic pool.
Confirmation of plate tectonics
When offshore scientific drilling began in 1968, the theory of plate tectonics was a topic of active debate. A key idea was the creation of a new oceanic crust at the seabed ridges, where the oceanic plates separated from each other and where the magma from the inside of the Earth rose between they. According to this theory, the crust should be a new material at the crest of the ocean ridges, and its age should increase with the remoteness of the ridge.
The only way to prove it was to analyze sediments and rock cores. In the winter of 1968-1969, the Glomar Challenger drilled seven sites in the South Atlantic Ocean, east and west of the Mid – Atlantic Ridge. The igneous rocks of the ocean floor and the overlying sediments have aged in perfect agreement with the predictions, confirming that the oceanic crust formed at the ridges and that the plate tectonics were correct.
See the complete picture. | Part of a basic section of Chicxulub impact crater. It's suevite, a type of rock formed during impact that contains rock fragments and molten rocks.
Reconstruction of Earth's history
Oceanic recording of Earth's history is more continuous than terrestrial geological formations, where erosion and redeposition by wind, water and ice can disrupt the recording. In most ocean regions, sediments are deposited as particulate matter, microfossils as microfossils, and remain in place, eventually succumbing to pressure and turning into rocks.
The microfossils (plankton) preserved in the sediments are beautiful and instructive, although some are smaller than the width of a human hair. Like the fossils of larger plants and animals, scientists can use these delicate structures of calcium and silicon to reconstruct past environments.
Through scientific ocean drilling, we know that after the strike of an asteroid that killed all non-avian dinosaurs 66 million years ago, a new life colonized the crater rim in the space of 30 years and, after 30,000 years, a complete ecosystem was in full swing. Some deep ocean organisms have survived the impact of the meteorite.
Ocean drilling has also shown that ten million years later, a massive discharge of carbon – probably due to significant volcanic activity and methane released from the fusion of methane hydrates – has caused intense and abrupt warming. hyperthermal, the thermal maximum of Paleocene-Eocene. During this episode, even the Arctic reached more than 22.8 ° C (73 ° F).
The ocean acidification resulting from the release of carbon into the atmosphere and the oceans has resulted in massive dissolution and changes in the ecosystem of the great oceans.
This episode is an impressive example of the impact of rapid global warming. It is estimated that the total amount of carbon released during PET is about equal to that released by humans if we burn all fossil fuel reserves on Earth. However, an important difference is that the carbon released by volcanoes and hydrates was at a much slower rate than the one we are currently releasing from fossil fuel. We can therefore expect even more dramatic climate and ecosystem changes unless we stop emitting carbon.
Improved scanning electron microscope images of phytoplankton (left, diatom, right, coccolithophore). Different phytoplankton species have distinct climatic preferences, making them ideal indicators of surface ocean conditions. Image via Dee Breger.
Find life in ocean sediments
Scientific drilling in the ocean also showed that there were about as many cells in marine sediments as in the ocean or soil. Shipments found life in sediments at depths greater than 8000 feet (2400 m); in seabed deposits 86 million years old; and at temperatures above 60 ° C (140 ° F).
Today, scientists from 23 countries are proposing and conducting research as part of the International Ocean Discovery Program, which uses scientific ocean drilling to recover data from sediments and rocks in the seabed and monitor environments in the ocean. under the ocean floor. Core drilling provides new information on plate tectonics, such as the complexity of ocean crust formation and the diversity of life in the depths of the oceans.
This research is expensive and intense technologically and intellectually. But it is only by exploring the deep sea that we can recover the treasures it contains and better understand its beauty and complexity.
Suzanne O'Connell, Professor of Earth and Environmental Sciences at Wesleyan University
This article is republished from The conversation under Creative Commons license. Read the original article.
Bottom line: What science has learned from 50 years of core samples taken from the ocean floor.
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