Science Facts

Why Does Earth Have Deserts? – Formation & History


The deserts of today were not deserts in the past Earth. About 8,000 years ago, deserts were moister and a more livable place. The fossilized bones of hippopotamus and elephants have been discovered in the Sahara Desert! There are two kinds of deserts: Hot deserts and Cold deserts. The cold deserts like the Atacama are desert plateau located in South America. The largest desert in the world is located in Africa.

Planet Earth is a constantly shifting landscape of 8 biomes, ranging from rainforest to grassland, desert to the taiga. Twenty-two thousand years ago, the Sahara was pretty much uninhabited, except for the area around the Nile Valley. Then, about 10,500 years ago, monsoon rains rolled in to get it up. Climates change. It happens, and sometimes they change dramatically, like when whole deserts completely shift their borders.

Why does earth have deserts?

Deserts are often defined as areas of land that receive less than 10 inches of rainfall each year. These regions are low in humidity and can even be moisture-deficient, evaporating faster than it is received. While most deserts are found in the mid-latitudes, these diverse ecosystems occur on all seven continents. And these makeup nearly one-third of Earth’s total landmass.

Deserts are sometimes classified into four major types: subtropical, semiarid, coastal, and polar.

Subtropical: Subtropical deserts are found along the equator, the Tropic of Cancer and the Tropic of Capricorn. They are the hottest deserts on Earth, with daytime temperatures that can reach 120 degrees Fahrenheit.

Semiarid: Semiarid deserts are located in Asia, Europe, and North America. These cold-winter deserts often form when tall mountain ranges block moisture through a process called the rain-shadow effect.

Coastal: Coastal deserts form alongside the tropical western edges of certain continents. Despite their proximity to water, coastal deserts remain dry.

Polar: Polar deserts are found in the Arctic and Antarctic. The other end of the extreme, winter temperatures in the Antarctic Desert average around 50 degrees Fahrenheit.

Only a few thousand years ago, the Sahara was green and lush. Research has found the Sahara’s shifting sands are expanding, causing die-offs of vegetation, failure of agriculture, and increased erosion without plants to hold the soil in place. But this wasn’t always the case. Scientists hypothesized that an ancient river ran through Western Sahara, feeding the land and securing it with vegetation. Clues were left off the coast of Mauritania, where researchers found sediment resembling that of a huge river. But there was no river around, only arid sands. They called this ancient waterway the Tamanrasset.

According to a recent study by the Japanese Advanced Land Observing Satellite, it’s real! It was confirmed recently using microwave radar. If it were still there, the Tamanrassat river would be the 12th largest on Earth, winding 300 miles inland (500km) to the Mauritanian coast.

As the researchers point out, climate change happens fast. For example, a study in Earth and Planetary Science Letters looked at 30,000 years of dust blown from Africa into the Atlantic. Over the millennia, the amount of blown dust rose and fell in lockstep with moisture on the continent.

  • Less moisture, more dust, more moisture, less dust.

As dryness, the majority of the sediment in the Atlantic is from Saharan dust! Therefore, it can reach North America! By looking at this dust, they know about 6,000 years ago, the African Humid Period ended suddenly, coinciding with an axial change in the Earth’s orbit.

  • According to NASA and climate scientists’ research, the deserts exist because the Earth’s spin changed, decreasing Northern Hemisphere monsoons.
  • Vegetation died very quickly, and the third-largest desert in the world took over North Africa, all in less than 300 years!

In a separate study in the journal Science, one jet stream moves hot, dry air across the planet’s Equator. As a result, it has shifted northward, causing the tropics to expand 140 miles northward in the last 26 years. With it, the deserts of Earth occur.

Deserts formation

Deserts are usually formed between 15 and 30 degrees north and south of the equator.

  • In the interior of continents.
  • In rain shadows of large mountain belts.

The Hadley cell is a large-scale atmospheric convection cell that features air rising near the equator flowing poleward at the height of 10 to 15 kilometers above the Earth’s surface. It descends in the subtropics and then returns to the equator near the surface. This whole process starts because the equator region receives a higher amount of solar radiation.

So there have warmer air and lots of evaporation. The whole region is usually very humid because warm air can hold more moisture than cool air. And warmer air tends to rise, and it will do so until it reaches about 10 to 15 kilometers high. As the air rises, the temperature decreases. So there will be many precipitation events as the air masses rise and start their trip towards the north and south. Air masses will continue flowing southward and northward. But they will get drier and drier because of the rain events and colder and colder since they are leaving the equator and going towards the poles.

At around 30 degrees south and 30 degrees, north air masses tend to descend towards the planet’s surface. So these regions will be dominated by dry air without much precipitation, which creates the perfect environment for deserts to form. Some deserts are also located in the interior of continents. In a very simplistic way, they may be farther from the main sources of moist air. The main source of moist air that promotes rain is the ocean, far from the interior of continents.

So there is usually more rain near the coasts, and once the air masses reach the interior of continents, they are already dry. But this effect includes many other factors, and one of them is the rain shadow effect. So rainshadow regions are perfect settings for deserts to form. One example of rain shadow is the Tibetan Plateau north of the Himalayas. This is because the winds mainly come from the south. So when they encountered the Himalayas, the air masses tend to rise, and a lot of precipitation tends over there. However, when the air masses cross the Himalayas towards the Tibetan Plateau, they are already very dry. So this region is much arider.

Desert existance

According to NASA’s Jet Propulsion Laboratory, the melting of Greenland ice is changing the way the Earth spins. It is changing the tilt of Earth’s axis by 2.6 centimeters per year, increasing that tilt on the horizon!

As the distribution of ice and water on the planet changes, the Earth’s axis changes in a process called precession. Thus, the sun will hit different earth’s latitudes at different intensities than before, drastically changing the weather systems.

The jetstream is already shifting, causing the tropical deserts to expand into a previously lush territory. But scientists don’t believe this is a natural phenomenon. It is happening way too fast, and the rates are increasing.

As desertification hits the American plains, South Asia, and the Mediterranean, humans feel the effects through drought, climate changes, and, eventually, economics. In a 2005 report about desertification from United Nations University, the state 10 to 20 percent of these “drylands” has been negatively impacted by losing farmland and biodiversity.

That was a decade ago, and at the time, 2.1 billion people lived in the drylands of our planet. It’s clear the deserts have and will expand. As they continue to do so, farmland will dry, vegetation will disappear, and people will have to move or completely alter their lifestyles.

Desert ecosystems

While deserts experience extreme temperatures and receive very little precipitation, they are still essential habitats for plants and animals. They have evolved to withstand harsh desert conditions by burrowing into the cool ground and emerging at night when desert temperatures drop. In addition, many desert plants, including the saguaro cactus, have established long and shallow root systems to absorb minimal moisture in the ground better.

Highly specialized to survive in such a harsh environment, desert wildlife is particularly vulnerable to ecological changes. Existing deserts have become less habitable because of rising temperatures. That dry up scarce water resources and increase the risk of wildfires. Additionally, new desert areas are beginning to form through desertification. This phenomenon occurs when deforestation, climate change, and resource mismanagement degrade biological productivity, creating a desert.

For instance, poor irrigation practices and excessive water usage in Central Asia dried up the Aral Sea and formed the youngest desert on the planet. Thus, it may be possible to curb desertification while protecting our surprisingly rich desert ecosystems.

  • By practicing responsible agriculture, better management of limited water resources, and limiting further development.

Frequently asked questions

Why is desert dry?

The first reason is deserts are located in the ‘rain Shadow area.’ These are areas that have a mountain range between them and the sea. The air that rises from the sea has moisture in it and reaches the deserts. Therefore, they must travel over the mountain ranges. In doing so, the moisture in the airdrops over the mountains is rain and snow. When it reaches the deserts, the air has no water, and therefore, no rain!

The deserts are situated on the western coasts of the continents. Here the ocean currents are cold. Hence they don’t carry much moisture and are relatively dry. An example of a rain shadow area desert is the Atacama Desert In Chile caused by the Andes Mountains.

Another reason deserts are dry is that they are located in areas where the air pressure is high. The air travels in the upper atmosphere and sinks at approximately 30° north and 30° south of the Equator. When the air sinks, it creates an area of high pressure. These high-pressure areas experience very dry and warm conditions. As a result, these areas have calmer and dryer weather, resulting in a hot desert climate like the Sahara Desert.

Why are deserts so cold at night?

In the day, there’s little moisture in the air. So when the sun’s beating down, it gets really hot. As soon as the sun starts to set, there’s very little moisture, so it only holds very little heat. It starts to cool dramatically, and most deserts have clear cloudless skies. So there’s nothing to keep the heat in. The result is that most efforts have very low temperatures at night. Even the summer’s hottest days can have the coldest nights.

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