The first ocean lifeforms were microscopic, so small they would be invisible to the naked eye. Later, bizarre and alien-like creatures reigned supreme. Even creatures more familiar to us, like sharks, whales, and octopuses have long and storied pasts with ancestors very different than the creatures now roaming the seas. Some species existed for a geological moment before they went extinct, while others slowly adapted to changing seas. Evolution takes time, and when the ocean changed too rapidly for species to respond, mass extinctions occurred across the globe. This has happened five times and could happen again.
Another formidable predator, Hurdia victoria has been nicknamed the Tyrannosaurus rex of the Cambrian era due to its relatively large size. While it never reached the size of the largest anomalocarids, some specimens reached 50 cm (around 20 inches), which was large for a time when most animals were about as big as a fingernail. Its prey consisted of trilobites and other smaller animals crawling on the seafloor. But not all predators stalked their prey from above. The ancient worm Ottoia prolifica lived in a self-constructed u-shaped home below the ocean floor. From there, Ottoia prolifica ambushed prey, which it would swallow headfirst. Most of its prey were small shelled animals related to mollusks, as well as worms, though there is evidence that they sometimes resorted to cannibalism.
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Though they largely live in the deep ocean today, during the Cambrian through the Permian, crinoid forests covered parts of the seafloor. Known as sea lilies for their beautiful, feathered arms, these creatures are cousins of modern sea stars and sea urchins. When they grew in dense groups they created a protected, diverse ecosystem for other creatures to call home. But unlike the trees that make up the forests on land, crinoids are not plants. The invertebrates feed by catching drifting particles in their many arms. In a forest full of crinoids, competition for food was tough, so they evolved a variety of stalk heights which enabled them to capture food at different levels above the seafloor. The base of their stalks was modified to anchor the animal securely in the soft sediment. Crinoids were relative skyscrapers in the community, sometimes towering at heights of up to two meters (6.5 feet). In a crinoid community, lacy bryozoans occupied a lower level. Below them, huge numbers of brachiopods monopolized the muddy bottom. By the Permian, sharks cruised above these crinoid forests, while smaller bony fishes and shelled cephalopods weaved among the crinoid stalks.
One unique predator that swam in the ocean during the Permian, around 260-290 million-years-ago, was the shark called Helicoprion. This shark had a spiral set of teeth resembling a buzz saw, unlike any other shark. It is so unique that to this day scientists are still unsure as to how the teeth sat within the shark's jaw. Another predator, the placoderm, was a fish that had bony plates covering its body. Without teeth, it used the sharp edges of the plates covering its jaw to slice through its prey. Though initially highly successful and diverse, placoderms only existed for 50 million years, while sharks, a lineage that began at a similar time, have lasted to modern times.
The world during the Mesozoic Era was a place both foreign and yet familiar when compared to Earth today. At this time, Pangea broke apart, and the massive Panthalassa Ocean broke into multiple basins. The Tethys Ocean split Asia from the rest of the land and the Atlantic Ocean began to form. The world was warm, keeping large ice caps from forming, which led to high global sea levels by the Jurassic that continued into the Cretaceous.
Before large mammals, reptiles ruled the ocean. During the Mesozoic, the time period when dinosaurs roamed on land, many of these large creatures were the top predators in the ocean food chain and fed on fish, cephalopods, bivalves, and even one another. The most notable of these reptiles were the ichthyosaurs, plesiosaurs, mosasaurs, and sea turtles. Although they lived at a similar time as dinosaurs, marine reptiles were not dinosaurs since they evolved from a different ancestor. In fact, many of the reptiles in the ocean were only distantly related to one another. While the mosasaurs evolved from land-dwelling lizards, plesiosaurs, ichthyosaurs, and turtles each had their own separate evolutionary lineage.
Mosasaurs were relative latecomers during the span of the Mesozoic. While ichthyosaurs, plesiosaurs, and turtles reigned supreme since the early Triassic, the first mosasaur didn't emerge until the late Cretaceous, about 99 million years ago. But in a short period of time, they quickly diversified. Some developed bulbous teeth that they used to hammer away at oyster-like bivalves, while others developed razor-like teeth that could pierce and shred larger prey, including other mosasaurs. Most lived in shallow waters, but some, like the Tylosaurus, traveled far offshore and dove to deeper depths. Fossils of mosasaurs have been found on every continent, including Antarctica, indicating they lived throughout the entire globe. Like the dinosaurs and other reptiles in the sea, mosasaurs went extinct at the end of the Cretaceous.
The first fully marine turtles emerged during the Cretaceous Period, a span of time lasting between 145 and 66 million years ago. By 120 million years ago, they resembled the sea turtles we are familiar with today. The largest, Archelon, measured up to 15 feet from head to tail.
At the same time that baleen whales were growing to massive proportions feeding on tiny crustaceans, another marine mammal, Desmostylia, was grazing on kelp and seagrass in the shallows. These four-legged, gnarly-toothed creatures straddled the marine and terrestrial environments much like seals and sea lions of today, but with feet instead of flippers. By the middle of the Miocene they disappeared. They are the only order of marine mammals to go entirely extinct, and it is likely because sea cows and manatees were better suited for underwater life and outcompeted them for food.
Researcher Brian Huber studies microscopic fossils to learn about past climates. Specifically, he studies clues in the chemistry of foraminifera, a single-celled creature that both drifts in the ocean water column and sits at the bottom of the seafloor. The secret to how this microscopic creature informs us about our past climate lies in the shell. Foraminifera have an intricate shell covering that they build from molecules in the water. This shell is made of calcium carbonate and as the foraminifera builds its shell it takes oxygen molecules from the water to create the compound. The oxygen has different traits depending upon the temperature of the water. Some oxygen molecules are heavier than other oxygen molecules, a product of a bulkier core. The proportion of bulky oxygen to lighter oxygen enables scientists to determine what the temperature was when the foraminifera built its shell. By studying the shell chemistry of foraminifera over time scientists can see how temperature has changed. For example, shells from the Cretaceous show that the Antarctic ocean surface was a balmy 26 to 32 degrees C (79 to 90 degrees F).
In the middle of the Nevada desert there is a massive ichthyosaur gravesite. Berlin Ichthyosaur State Park is the resting place of many ancient reptiles called ichthyosaurs. About 37 Shonisaurus popularis have been uncovered so far. In the late 1800s miners searching for silver stumbled upon the fossils, and later in the 1950s they were unearthed and studied by Berkeley paleontologist Charles Camp. Today, Smithsonian scientists are using 3D scanning technology to continue the work of Camp and allow people from around the world to view the fossil skeletons.
The BBNJ Agreement has been a priority for the European Union and its Member States, that have led negotiations at global level through the BBNJ High Ambition Coalition (see below the list of countries in the coalition). This landmark agreement is a welcome addition to the United Nations Convention on the Law of the Sea (UNCLOS), which provides the legal framework within which all activities in the oceans and seas must be carried out.
While there is only one global ocean, the vast body of water that covers 71 percent of the Earth is geographically divided into distinct named regions. The boundaries between these regions have evolved over time for a variety of historical, cultural, geographical, and scientific reasons.
Historically, there are four named oceans: the Atlantic, Pacific, Indian, and Arctic. However, most countries - including the United States - now recognize the Southern (Antarctic) as the fifth ocean. The Pacific, Atlantic, and Indian are the most commonly known.
Over vast periods of time, our primitive ocean formed. Water remained a gas until the Earth cooled below 212 degrees Fahrenheit. At this time, about 3.8 billion years ago, the water condensed into rain which filled the basins that we now know as our world ocean.
In the 200-plus years since the industrial revolution began, the concentration of carbon dioxide (CO2) in the atmosphere has increased due to human actions. During this time, the pH of surface ocean waters has fallen by 0.1 pH units. This might not sound like much, but the pH scale is logarithmic, so this change represents approximately a 30 percent increase in acidity.
A pteropod shell is shown dissolving over time in seawater with a lower pH. When carbon dioxide is absorbed by the ocean from the atmosphere, the chemistry of the seawater is changed. (Image credit: NOAA)
The ocean absorbs about 30% of the carbon dioxide (CO2) that is released in the atmosphere. As levels of atmospheric CO2 increase from human activity such as burning fossil fuels (e.g., car emissions) and changing land use (e.g., deforestation), the amount of carbon dioxide absorbed by the ocean also increases. When CO2 is absorbed by seawater, a series of chemical reactions occur resulting in the increased concentration of hydrogen ions. This process has far reaching implications for the ocean and the creatures that live there. ff782bc1db