Sandy. Dry. Hot. These are the words typically used to describe the desert. But the endless, windswept dunes that come to mind only make up a small percentage of the deserts on the planet. A desert is actually just a place that has very little precipitation.

Subtropical deserts like the Sahara are what people generally imagine when they think about the desert. The Sahara has rocky plateaus as well as sand dunes. During the summer, the temperature in the Sahara can reach over 50°C (122°F), making it one of the hottest deserts on Earth. Despite these temperatures, the Sahara is home to olive trees, antelope, jerboa, scorpions, jackals, and hyenas. It is even home to some people, with several major cities located there, including Egypt’s Cairo, Libya’s Tripoli, and Mali’s Timbuktu. At 9.4 million square kilometers (3.6 million square miles), the Sahara is also the largest hot desert on Earth.

The largest desert on Earth is Antarctica, which covers 14.2 million square kilometers (5.5 million square miles). It is also the coldest desert on Earth, even colder than the planet’s other polar desert, the Arctic. Composed of mostly ice flats, Antarctica has reached temperatures as low as -89°C (-128.2°F). The ice that covers the area is on average 2.45 kilometers (1.5 miles) thick. There is almost no vegetation in Antarctica, so the animals that live there are mostly carnivores, such as penguins, albatrosses, whales, and seals. Antarctica’s waters are abundant with sea life, including fish, krill, and sea sponges.

How can both the Sahara and Antarctica be deserts? The reason is that they both see little precipitation during the course of a year, typically around 25 centimeters (10 inches), or less. This makes them both difficult places for plants and animals to live. Both deserts have fossil evidence suggesting that this was not always true. Based on fossil evidence, the Sahara and Antarctica appear to have been the homes of many plants and animals in the past.