Desert

A desert is a landscape defined by extremely low levels of precipitation. This means the region receives very little rain, snow, mist, or fog. Approximately one-third of the Earth's total land surface is classified as arid or semi-arid.

Deserts are vital to our planet because they help moderate global temperatures. They have a high albedo, meaning they reflect more incoming sunlight than forests or the ocean. This reflection helps manage how much heat the Earth absorbs. Scientists define these regions by their lack of moisture and insufficient vegetation cover.

Desert landscapes are shaped by intense weathering processes. Large temperature variations between day and night put physical strain on rocks. This thermal stress causes the rocks to break into smaller fragments. When rare rain falls on hot rocks, the sudden temperature change can cause them to shatter.

Once the rocks break, the wind takes over as a primary sculptor. Wind picks up sand and dust particles, which can remain airborne for long periods. This process can create massive sandstorms or dust storms. Wind-blown sand grains can also abrade solid objects, smoothing down rocks over time.

Wind movement also sorts sand into specific geological formations. The wind can deposit sand into level sheets or pile it into billowing dunes.

In some areas, the wind blows all fine material away. This leaves behind flat, stony plains known as desert pavements. These surfaces consist of a mosaic of smooth stones where little further erosion occurs. Other features include rock outcrops, exposed bedrock, and clays left by ancient flowing water. In basins, temporary lakes may form and then evaporate. This evaporation often leaves behind salt pans or flat areas called playas.

Deserts are classified by several different factors. Scientists look at total precipitation, the number of precipitation days, temperature, and humidity. Deserts can be categorized by their geographical location or the causes of desertification. Some are hot deserts, such as the Sahara, which is the largest hot desert in the world.

Others are polar deserts, also known as cold deserts. These occur in the Arctic and Antarctic regions. Antarctica is the world's largest cold desert, consisting of about 98% thick ice and 2% barren rock.

The Atacama Desert in South America provides a unique example of extreme aridity. It is one of the driest non-polar places on Earth. It is largely blocked from receiving moisture by the Andes mountains and the Chilean Coast Range.

Some weather stations in the Atacama have never recorded rainfall. It is so dry that mountains reaching 6,000 meters are completely free of glaciers. However, some specialist plants survive there by obtaining moisture from dew and Pacific fogs. In other deserts, rare rain can cause violent flash floods. These floods rush through dry stream channels called wadis or arroyos.

Life in these environments requires specialized biological adaptations. Plants are often tough and wiry with small or no leaves. Many possess a water-resistant cuticle or sharp spines to deter animals from eating them.

Some plants are annuals that germinate and die within weeks of rainfall. Others are long-lived and use deep root systems to reach underground moisture. Animals must also find ways to stay cool and conserve water. Many are nocturnal, staying underground during the day to avoid heat.

Some animals enter a state of dormancy until the next rare rainfall occurs.

Humans have interacted with desert landscapes for many millennia. Nomads have traditionally moved herds to find grazing land.

Oases provide spots for more settled life where underground water reaches the surface. These areas may be fed by springs or large aquifers. The Nubian Sandstone Aquifer System under the Sahara is the largest known accumulation of fossil water. Historically, trade routes like those in the Sahara were used by camel caravans.

These caravans carried valuable goods like salt, gold, and ivory. Today, deserts are also used for mineral extraction and solar energy capture.