Antarctica was once located on the equator during the Cambrian Period, but moved south to its current location. It had a tropical or subtropical climate until 40 million years ago when glaciers began to form. Today, 98% of the continent is covered in ice. The sparse flora supports mostly small invertebrates, while coastal birds and marine animals thrive in the waters around Antarctica. The continent is also home to a small human population of researchers.
500 million years ago, during the Cambrian Period, Antarctica was located on the equator, a warm climate surrounded by life in the shallow seas of its continental shelf. Over the next 140 million years, the continent moved south, centering on the South Pole, where it has remained ever since. Despite its location, most of the time, Antarctica was a relatively hot continent, even becoming a hot desert for tens of millions of years. Until 50 million years ago, Antarctica had a tropical or subtropical climate, complete with marsupial fauna, descendants of which are found today in Australia and parts of South America.
About 40 million years ago, the supercontinent of which Antarctica was a part, Gondwana, began to break up. This allowed cold water to form and circulate in the southern continent, displacing the warm north-south currents that previously made the area warm. Over tens of millions of years, glaciers began to form on the continent, mostly covering it from 15 million years ago. Only 6 million years ago the ice caps reached their current extent. Today 98% of the continent is covered in ice.
Contemporary Antarctic fauna is mostly supported by the continent’s sparse flora, which grows only during the summer, and usually for a few weeks at most. Most plants are the same plants that first evolved to live on land: non-vascular plants such as mosses and liverworts. Numerous microorganisms make up the majority of all photosynthetic organisms on the continent. In all, Antarctica contains about 200 lichen species, 50 non-vascular plants, and just a few flowering plants, Antarctic hairgrass and Antarctic pearl. In recent years, due to global warming, germination rates among seeds have increased, resulting in a twenty-fivefold increase in the number of plants in some areas.
In the present, most Antarctic animals are small invertebrates, such as microscopic mites, lice, ticks, nematodes, tardigrades, rotifers, and springtails. The largest exclusively land-based member of the Antarctic animals is a flightless midge (very small fly), Belgica antarctica, measuring just 12 millimeters (0.5 inches). The bodily fluids of many of these insects contain glycerol, an antifreeze that allows them to survive temperatures as low as -34°C (-30°F). These animals are most common on the Antarctic Peninsula, which despite the extreme cold, aridity and wind, is actually more habitable than the continent’s vast interior.
Antarctic animals and their larvae have a number of other adaptations for surviving in Antarctica, including a tendency to clump together and the ability to survive without oxygen for weeks at a time. Some Antarctic animal larvae are a dark blue-black color, thought to help absorb heat and possibly block ultraviolet radiation caused by the ozone hole over Antarctica. They can tolerate wide swings in salinity and pH, caused by seasonal immersion in penguin guano, salty ocean water, and freshwater from melt ice. Adult Antarctic animals are all wingless, to prevent them from being blown away.
Antarctica is one of the most habitable places on Earth and may superficially resemble the terrain (in terms of hostility) created after the worst environmental stresses on the planet, such as supervolcano eruptions or large asteroid impacts. This gives us a glimpse of what life might be like today if the asteroid that wiped out the dinosaurs was many times larger than it was, mostly invertebrate. The huge temperature swings and drought are reminiscent of the harshest desert conditions in the history of the planet, such as the interior of the supercontinent Pangea.
Antarctica has a small selection of freshwater fauna that live in small lakes and streams created by meltwater during the summer. These include small crustaceans called copepods, fairy shrimp (thought to be the ancestors of terrestrial arthropods), and common nematodes. Antarctica’s longest river, the Onyx River, is only 30 km (18.6 mi) long, so freshwater organisms are clearly not abundant here, but can be found where they can survive.
Most familiar Antarctic animals are coastal birds, especially penguins such as the emperor penguin, Adélie penguin, rockhopper penguin, king penguin, chinstrap penguin, and gentoo penguin. The beautiful White Snow Petrel is one of only three birds that breed exclusively in Antarctica and the only bird sighted at the South Pole. All of these birds survive due to their ability to fly over the northernmost ice floes during the harsh Antarctic winter. During the summer, the Antarctic coast is tolerable, reaching temperatures between 5°C and 15°C (41°F and 59°F). Large colonies of penguins can be seen covering small coastal islands, basking in the sun.
The waters around Antarctica are surrounded by numerous animals, including squid, crabs, icefish, krill, prey fish, elephant and leopard seals, giant petrels and Antarctic terns, humpback and killer whales, and many more. Although penguins nest on land, they spend most of their lives and get all of their food from water. Some of the animals around the Antarctic coast exhibit polar gigantism, a property whereby animals tend to get larger as they move away from the equator. Search teams have found starfish and crabs more than two feet in diameter. This is a great example of Bergmann’s rule, a generality that states that animals get bigger the closer you get to the poles.
The last of the Antarctic animals is the familiar man, Homo sapiens, whose population reaches 4,000 during the summer months when researchers come to do fieldwork and occasionally bring their families too. About 70 research bases are maintained on the continent, producing substantial scientific returns for the large investments required to ship supplies. Some of the biggest draws for researchers are unique fossils found on the slopes of the Antarctic mountains, McMurdo Dry Valleys, ghostly gravel valleys in the interior of Antarctica, the Antarctic Plateau free of electromagnetic interference and light pollution, used as a site for telescopes and neutrino observatories, and Lake Vostok, a subglacial lake that was sealed under the ice sheet for 500,000 to more than a million years.
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