Antarctica as we know it was formed roughly 34 million years ago, when the continent was enveloped by the massive ice sheet it is known for today. But Antarctica wasn’t always the great southern continent covered in ice. Many millions of years ago it drifted over the equator, and fossils show it was once home to rainforests and dinosaurs.
Let’s look back in time and see how Antarctica was formed.
A dynamic planet
The surface of the Earth is always in motion. Earthquakes, tsunamis and volcanic eruptions are evidence of our planet’s constantly moving crust, where enormous rocky plates slide, collide and pull apart on a bed of molten rock.
This constant movement transports continents across the globe: hundreds of millions of years ago, the world map would have looked very different from today.
Antarctica in Gondwana
Around 500 million years ago, a great supercontinent called Gondwana was formed. It was made up of several landmasses, including what would become present-day India, Africa, South America, Madagascar, Australia and Antarctica. At this time, the land that would become Antarctica was sitting over the equator.
Gondwana began to split apart around 180 million years ago. One by one vast blocks tore away, South America and Africa first, followed by India and Madagascar around 40 million years later. This left the remains of Gondwana (what would become Australia and Antarctica) to drift towards the south.
How do we know? Continental Drift and Plate Tectonics
If you look at the coastlines of Africa and South America on a map, you will be able to see that they seem to fit together like a jigsaw puzzle. This was noticed by mapmakers as early as the 1500s, and was the first clue that the continents may once have been connected.
Over time, biologists and geologists identified similar plant and animal fossils, and rock formations across these continents, adding to the evidence that they were once connected.
In 1912, German geophysicist and meteorologist Alfred Wegener proposed the revolutionary idea that the continents had moved across the Earth’s surface, coming together and drawing apart over time. While this explained the observations made by other scientists, there was a lot of resistance to the idea as no one could explain how or why they moved.
It wasn’t until the 1960’s that this theory became widely accepted, with the development of tectonic plate theory, which explains how enormous plates of the Earth’s crust move across the globe.
A hot Antarctica
One hundred million years ago, Gondwana continued its journey south across a planet that looked very different from the one we live on today. It was the Cretaceous era, and the Earth was going through one of the hottest periods in its history. Temperatures were soaring, the polar regions were completely free of ice and sea levels were about 200 metres (650 feet) higher than today.
In this steamy climate, the land that would one day become Antarctica would have been unrecognisable to us. Thickly forested with temperate rainforest and home to dinosaurs, marine reptiles and an abundance of invertebrates, Gondwana was a southern oasis in a hot, tropical world.
About 50 million years ago, Gondwana split again. Australia drifted north and an ice-free Antarctica continued its journey to the south.
The Antarctic ice sheet is formed
Around 35 million years ago, Antarctica may have looked a little like the European Alps today, with mountain peaks covered in alpine glaciers.
Over the next few hundred thousand years, glaciers began to creep down from Antarctic mountains, thickening and filling entire valleys, cloaking the continent in a blanket of ice.
Exactly what caused the sudden growth of Antarctica’s glaciers is not clear. However, paleoclimatologists have found evidence of several factors that played a part. Small changes in the Earth’s orbit, which occur in regular cycles, changed the amount of solar energy reaching the planet. The Antarctic Circumpolar Current strengthened around Antarctica, changing global ocean circulation, and atmospheric carbon dioxide fell sharply, causing the planet to cool. It is likely that these three factors helped create the conditions for the Antarctic ice sheet to form.
Today, the Antarctic ice sheet holds 90% of the ice on our planet, and 70% of its freshwater. It covers an area roughly twice the size of Australia, and is 4776 metres (15, 669 feet) deep at its deepest point.
Words by Nina Gallo, Aurora Expeditions’ historian and certified PTGA polar guide.
Nina has been drawn to the polar regions since her first otherworldly experience of the midnight sun in 2002. Since then she has spent time in far northern Canada, the Himalayas, the Alps and deserts in America and Australia, always seeking out quiet, wild corners to explore. She feels immensely privileged to travel to these places and shares her passions for the natural world, human stories and adventure with all the wonderful people she meets. Nina is the author of Antarctica, published by Australian Geographic in September 2020.