Atacama Desert

The Atacama Desert is a massive desert plateau located on the Pacific coast of South America. It sits in the northern part of Chile, stretching across a strip of land just west of the Andes Mountains.

The desert covers a vast area that grows even larger if you include the barren lower slopes of the Andes. It holds the title of the driest nonpolar desert on Earth. It is also the second driest desert overall, following specific spots in the McMurdo Dry Valleys. Additionally, it is recognized as the largest fog desert in the world.

The extreme dryness of the Atacama is caused by several complex geographic mechanisms. The desert is positioned between two massive mountain chains: the Andes to the east and the Chilean Coast Range to the west. These mountains are high enough to block moisture advection, which is the movement of water vapor through the air. This creates a two-sided rain shadow effect that prevents moisture from the Pacific or Atlantic Oceans from reaching the plateau.

Furthermore, a constant temperature inversion helps maintain this aridity. This inversion is caused by the cool, north-flowing Humboldt ocean current and a strong Pacific anticyclone. These factors work together to keep the air dry and the temperatures consistently mild.

Geographically, the Atacama ecoregion forms a continuous strip for nearly 1,000 kilometers. It runs along the northern third of Chile, from near Arica in the north to near La Serena in the south.

The boundaries of the desert are a subject of scientific discussion. The National Geographic Society includes the coastal area of southern Peru as part of the Atacama. However, other sources argue that the Peruvian portion is a different ecosystem called the Pampas de la Joya desert. To the east, the desert meets the less arid Central Andean dry Puna ecoregion. To the south, it borders the Chilean Matorral ecoregion.

The history of the Atacama's aridity spans millions of years. It may be the oldest desert on Earth. Hyper-aridity has likely existed since at least the Middle Miocene epoch. This began roughly 33 million years ago with the establishment of a proto-Humboldt current and the opening of the Tasmania-Antarctic passage. This passage allowed cold currents to move along the west coast of South America. This change prevented warm, humid air from the Amazon Basin from traveling to the Atacama.

While there were brief periods of higher humidity in the past, the desert has remained remarkably dry for much of its history.

Despite the harsh climate, life has found ways to adapt to this environment. The desert contains over 500 species of flora. Many plants rely on the camanchaca, a marine fog that provides essential moisture.

The llareta is a remarkable plant that grows at high altitudes. It forms dense, pillow-like shapes to retain heat. Because it grows at a rate of only 1 centimeter per year, some plants may be over 3,000 years old. You can also find various cacti, such as the candelabro, and animals like the Vallenar toad or the Andean flamingo.

In rare years with enough rain, the region experiences a "desert flowering" phenomenon.

The Atacama is also famous for its striking resemblance to the planet Mars. The dusty, rocky landscape and soil composition are very similar to the Martian environment.

Because of this, NASA and other scientists use the desert as a testing ground. They use it to simulate Mars expeditions and to test instruments for future space missions. In 2003, researchers even duplicated tests used by the Viking Mars landers in the soil near Yungay. They found that the soil was so dry it could even hide signs of life from certain tests. This makes the Atacama a vital site for understanding how life might exist on other planets.

Finally, the Atacama's unique conditions connect it to broader scientific studies of Earth's history. In December 2023, scientists reported finding a "dark microbiome" of unfamiliar microorganisms there.

Researchers also believe parts of the Puna de Atacama may resemble Earth during the Archean eon. This was a time when the first life forms appeared on our planet. By studying these extreme environments, scientists gain insight into the very beginnings of life and the limits of biology.