Every winter, water freezes all over the globe with millions of cubic meters transforming into ice along the shifting shores of Antarctica and Greenland. But our planet has experienced much colder periods, making freezing far more common in the past. These cold periods are known as glaciations. They have occurred multiple times over the last 2.6 million years. Glaciations are not to be confused with ice ages.

These refer to long cold periods marked by recurring glaciations, while glaciations are the specific events within those periods when glaciers expanded all over the Earth. Around 130,000 years ago, during the coldest of these periods, glaciers covered vast areas of the Earth. They extended from the Polar Sea down to the Netherlands, across Canada and into Kansas in the United States, much of western Siberia and down the slopes of major mountain ranges like the Himalayas and the Andes.

Ice has fascinating properties that you may not be aware of. Even though it's solid, it can behave like a thick liquid similar to honey. This occurs when more than 50 meters of ice builds on top of itself. At this point, the ice becomes so heavy, it starts to move under its own weight. This is why glaciers creep fairly slowly downhill towards the sea. When they eventually reach the ocean, they break off to form huge icebergs in a process known as calving.

But what happens beneath all this ice is even more remarkable. The immense weight and slow movement of ice erodes all rocks and sediments beneath it. This process, known as glacial erosion, has created valleys more than one kilometer deep in mountain ranges.

Another great example to illustrate the power of ice is to look at Sahul, a paleocontinent made up of the present-day landmasses of Australia, Tasmania and New Guinea. Around 20,000 years ago, in the last glaciation's coldest period, ocean levels were approximately 125 meters lower than they are today. This huge drop in sea level happened because much of Earth's water was trapped in glaciers in the northern hemisphere. Because of this, Australia, Tasmania and New Guinea were connected as a single landmass separated from Southeast Asia by a narrow strait of water. As the glacier ice melted, rising sea levels slowly submerged much land around all the continents, including Sahul.

If we fast-forward to today, we are in an interglacial period that began 11,700 years ago. Although it's much warmer today, remnants of these ancient ice sheets still exist in Greenland and Antarctica, reminding us of the lasting impact of glaciations on our planet's geography and climate. In the next module, we will explore the role of melted ice or liquid water in shaping our planet's surface.