The Mysterious World of Prehistoric Antarctica

Now little more than a vast icy desert, the Earth’s southernmost continent wasn’t always this way. In fact, prehistoric Antarctica was teaming with life.

Today’s Antarctica hides a fascinating story beneath its millions of square miles of ice sheet, which covers 98% of the continent. Its bitterly cold temperatures, which can drop to levels more frigid than those commonly found on the surface of Mars, make it a barren wasteland. No wonder it’s completely uninhabited, save for a summer-time maximum of around 5,000 people working shifts at the various scientific research stations dotted sporadically around the icy desert.

Despite the modern desolation of the vast Southern Land, Antarctica hasn’t always been this way. In fact, just like every other region of the globe, it has undergone profound change over the hundreds of millions of years of its evolution. Long ago, the coldest, driest, windiest continent on Earth was home to every bit as much biodiversity as some of the most colourful places on the planet. This week, I’m going to be exploring the mysterious geological history of this great unknown land.

Gondwanan Origins

Ghedoghedo

Lystrosaurus, one of the few survivors of the Permian-Triassic mass extinction, lived in Antarctica, India and South Africa.

600 million years ago, the ancient supercontinent of Gondwana formed, incorporating the present-day continents of the Middle East, India, Africa, Australia, South America and Antarctica. Earth was amid the Ediacaran Period at the time, with life being predominantly microscopic. However, marine animals, particularly sponges, had also started to appear during the preceding Cryogenian Period. The lands that make up modern Antarctica were very different in these far-off times.

Although the land was completely barren and void of macroscopic life until the Silurian Period, ancient Antarctica shared the same evolutionary path with the rest of Gondwana. Oxygen and carbon dioxide levels were skyrocketing, leading to a world much warmer than it is now.

When the evolutionary arms race of prehistoric marine life heralded the Cambrian Explosion 541 million years ago, Antarctica enjoyed, for the most part, a mild climate. A small region of the modern continent even extended into the Northern Hemisphere and the east ran along the equator, but the much higher sea levels of the time meant that it was significantly smaller than its current form. In fact, there was probably no ice at all at the poles during the Cambrian.

Antarctica shared the rapidly evolving terrestrial biodiversity of the Devonian, Carboniferous and Permian Periods before the rise of the dinosaurs in the Late Triassic. Fossils of ancient Palaeozoic life have been found hidden beneath the frozen wastes of the modern continent, indicating that the land was abundant with life. The plant-eating lystrosaurus, which lived around 250 million years ago, was one of the many animals that lived among the ancient swamps and fern forests of Antarctica.

The lystrosaurus was one of the few survivors of the Earth’s worst mass extinction event; that which heralded the end of the Permian Period and the Palaeozoic Era, long before the first dinosaurs appeared. In fact, studies of Antarctic fossils suggest that the now barren continent served as a refuge during the Great Dying.

Frozen Dinosaurs

Nobu Tamura

Cryolophosaurus was the apex predator of its region when it hunted in the lands of Jurassic Period Antarctica.

The Great Dying brought with it soaring global temperatures, which turned much of Gondwana into a hot and arid wasteland. Antarctica, however, appears to have remained relatively temperate during this time, hence the ubiquity of early mammal-like reptiles such as the lystrosaurus and other synapsids and therapsids. By the Jurassic Period, early dinosaurs had also started to colonise the continent, along with vast swathes of coniferous forests.

One of the most important fossil sites is located at Mount Kirkpatrick in the south of the continent. This place is known as the Hansen Formation and, despite its modern desolation, it tells a fascinating story about Antarctica’s ancient past. Extensive research of the site has revealed without a doubt that Antarctica was once home to forests of cycads and conifers, which supported a rich ecosystem consisting of dinosaurs, synapsids, pterosaurs and more.

Antarctica appears to have had its own representatives of all the major dinosaur and other animal groups of the time. The cryolophosaurus, for example, was a saurischian predator akin to the tyrannosaurus rex, albeit significantly smaller. It was a contemporary, and perhaps preyed upon, the glacialisaurus, a sauropod discovered in 2007 and estimated to have weighed up to six tonnes.

Dinosaur evolution continued in Antarctica right up to their extinction 66 million years ago. Other iconic animals of the time, such as plesiosaurs and mosasaurs, have also been discovered there as well as small pterosaurs, namely a dimorphodon fossil. There’s no doubt a vast trove of dinosaur and other fossils still waiting to be discovered in this most inaccessible and inhospitable region of the world.

During the Cretaceous Period, Gondwana broke up, and the map started to vaguely resemble that which we know today. South America drifted northward, although it would again be joined to Antarctica via a land bridge during the Cenozoic Era. Only Australia remained attached for now, while Antarctica drifted into its current location. Nonetheless, the continent remained mild, although there is increasing evidence that inland regions cooled significantly and may have even been subjected to glaciation.

Great Migrations

Nilsson, M. A.; Churakov, G.; Sommer, M.; Tran, N. V.; Zemann, A.; Brosius, J. R.; Schmitz, J. R.

This phylogenetic tree shows the South American origins of marsupial mammals

Like many other areas of the world, certain regions of Antarctica show evidence of the Chicxulub impact fallout, which occurred all the way north off the coast of what is now Mexico’s Yucatan Peninsula. Specifically, Seymour Island, just off the coast of the Antarctic Peninsula, shows the victims of ecosystems left devastated by the event. There’s also an unusually high presence of iridium, an element with almost exclusively extraterrestrial origins, amongst rocks dating from this time. Though Antarctica appears to have served as a refuge during the Permian-Triassic mass extinction, nothing could escape the impact winter following the dinosaur-killing asteroid.

The first major glaciations may have started in Antarctica during the early Palaeogene, but an intense warming phase began around 52 million years ago which saw coastal regions of the continent return to their former glory. The veritable Eden, Antarctica’s now frozen expanses were once again home to tropical plants such as palms and baobabs.

Sea levels, which had been dropping since the Mid Cretaceous, saw the formation of a land bridge between South America and Antarctica, which was also still joined to Australia. This remained the case until as recently as 34 million years ago, a fact that had profound effects on the evolution of Australia’s ecosystem. Antarctica was a bridge between the two continents on the other side of the world from one another, allowing animals to move between the two.

It’s now known that marsupials originated in South America, first coming to Australia after migrating through subtropical northern Antarctica. In fact, in 1982, a team of scientists discovered direct evidence of this when they found the first ever fossil of a marsupial mammal in the southern lands. The fossils, found on Seymour Island, belong to an extinct marsupial suborder called polydolomorphia, a rat-size creature so far characterised only by a remaining fragment of its jawbone and a few teeth.

Icy Wilderness

Pixabay

Today, 98% of Antarctica is covered by ice, and no trees or other large plants grow anywhere on the continent.

As the ice spread outwards from the frozen heart of the vast and now isolated continent, it devoured everything in its path. By about 15 million years ago, most of the continent was already covered by ice sheet, forming a thick blanket over the ancient forests beneath.

Still, some pockets of colour managed to cling on to the foothills of the Transantarctic Mountains until around three million years ago. Intermittent warm periods allowed small, stunted versions of the southern beech tree, among other plants, to survive, but their time was limited too. When the Pleistocene (and ongoing) ice age began 2.59 million years ago, the Antarctic ice sheet enveloped all that remained, and the Southern Land became the cold, dead world we know today.

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Antarctica hides a fascinating history, and one that’s made all the more mysterious by the fact it’s so difficult to explore. It’s the last true great wilderness on Earth, and there’s no doubt countless amazing discoveries still to be made. What do you think we’ll find in the Southern Land in the coming years? Let me know in the comments below!

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