Layers of the Atmosphere

The Atmosphere

The atmosphere is the layer of gases that surrounds Earth, held in place by gravity. Even though we can’t see it, the atmosphere is essential for life. It’s made mostly of nitrogen (78%), oxygen (21%), and small amounts of other gases like carbon dioxide, argon, and water vapor.

The atmosphere acts like a protective blanket around our planet. It blocks harmful radiation from the Sun, helps regulate temperature, and provides the oxygen we need to breathe. Without it, Earth would be either freezing cold or scorching hot, and life as we know it couldn’t survive.

Scientists divide the atmosphere into different layers based on temperature changes:

Troposphere

The troposphere is the lowest layer, where we live and breathe. It contains most of the atmosphere’s air (80% of the Earth's air) and almost all weather—clouds, storms, rain, and snow. Temperatures get colder as you go higher in this layer. It extends from Earth’s surface up to about 8 miles. Air pressure at Earth's surface is approximately 1000 millibars (mb), but the pressure decreases rapidly with increasing altitude.

At the summit of Mount Everest, the world's tallest mountain, the atmospheric pressure drops so much that the human body only receives around 30-33% of the oxygen available at sea level. This is why supplemental oxygen is needed when climbing the mountain.

2. Stratosphere

Above the troposphere is the stratosphere, which stretches up to about 30 miles and contains roughly 19.9% of the Earth's air. This layer contains the ozone layer, which absorbs harmful ultraviolet (UV) radiation from the Sun. Unlike the troposphere, temperatures here increase with altitude because the ozone absorbs energy from sunlight.

3. Mesosphere

The mesosphere lies above the stratosphere. It goes up to about 50 miles above Earth's surface and contains about 0.1% of the Earth's air. This is the coldest layer of the atmosphere, and temperatures drop sharply as altitude increases. It’s also where meteors burn up when they enter Earth’s atmosphere, creating “shooting stars.”

4. Thermosphere

The thermosphere extends from about 50 to 500 miles above Earth and contains roughly 0.002-0.01% of the Earth's air. Temperatures rise dramatically here—up to thousands of degrees Celsius—because the thin air absorbs high-energy radiation from the Sun. The auroras (Northern and Southern Lights) also occur in this layer.

5. Exosphere

The exosphere is the outermost layer, gradually thinning until it merges with outer space. It extends up to about 6,000+ miles. The air is extremely thin (<0.0001% of Earth's air), and particles can travel hundreds of miles without hitting each other. Satellites orbit within or above this layer.

Pauses

As you move upward through the atmosphere, the air is divided into layers like the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. But between each of these layers is a special boundary called a “pause.” These pauses mark where the temperature trend changes—because each layer warms or cools differently.

Think of the atmosphere like a staircase. The layers are the steps, and the pauses are the flat platforms between them.

Tropopause

The tropopause is the boundary between the troposphere (where temperature decreases with altitude) and the stratosphere (where temperature increases with altitude).

It’s where the cooling stops and the warming begins.
The tropopause also traps most weather below it, acting like a lid over storms and clouds.
The air pressure here is approximately 100 millibars (mb)

2. Stratopause

The stratopause separates the stratosphere from the mesosphere.

In the stratosphere, temperatures rise because the ozone layer absorbs sunlight.
At the stratopause, that warming stops; above it, in the mesosphere, temperatures start decreasing again.
This pause is one of the warmest places above Earth’s surface.
The air pressure here is approximately 1 millibars (mb)

3. Mesopause

The mesopause marks the boundary between the mesosphere and the thermosphere.

The mesosphere gets colder with height and is the coldest layer.
After the mesopause, temperatures rise sharply in the thermosphere due to absorption of high-energy sunlight.
The mesopause is actually the coldest point in Earth’s atmosphere.
The air pressure here is approximately 0.01 millibars (mb)

4. Thermopause (Exobase)

The thermopause or exobase marks the top of the thermosphere and the transition into the exosphere, the outermost layer of the atmosphere.

Above the thermopause, the air becomes extremely thin, almost like space.
Temperatures stop increasing significantly, even though the few particles present can still be extremely energetic.
It’s essentially the “ceiling” of Earth’s atmosphere, where it gradually merges with outer space.

The Ozone Layer

Why is Ultraviolet (UV) Radiation Harmful for Humans?

Ultraviolet (UV) light from the Sun is a type of high-energy radiation that can be dangerous to living things. What makes UV light harmful is that it has enough energy to damage cells at the molecular level. One of the biggest problems is that UV radiation can break chemical bonds in DNA, which can cause mutations. If too many mutations build up, cells may begin to grow uncontrollably, leading to skin cancer. Even before that happens, UV exposure can injure or kill skin cells, resulting in sunburns, peeling skin, and long-term aging effects like wrinkles and loss of elasticity.

UV light can also harm the eyes, which are very sensitive to bright, high-energy radiation. Over time, too much UV exposure can damage the cornea and contribute to cataracts, reducing vision. The immune system can also be affected. When skin cells are damaged by UV light, the body’s defense responses can be weakened, making it harder to fight off infections.

How Does the Ozone Layer Work?

A UV photon from the Sun hits an ozone molecule (O₃).
The energy from the UV light is absorbed by the molecule.
That energy causes the ozone molecule to split apart into an oxygen molecule (O₂) and a single oxygen atom (O).
Later, those oxygen pieces can recombine to form ozone again.

This cycle allows the ozone layer to continuously absorb UV light, especially UV-B and UV-C, preventing most of it from reaching the surface.

Why This Matters

UV-C (the most dangerous type) is almost completely blocked by ozone.
Most UV-B is also absorbed—only a small amount reaches Earth, which is why it can still cause sunburns.
UV-A mostly passes through, but it’s less damaging.

Without the ozone layer, Earth’s surface would receive far higher doses of radiation, making life much more difficult—especially for humans, animals, plants, and even ocean plankton.

The Hole in the Ozone Layer

In the 1980s, scientists discovered a large “hole” in the ozone layer over Antarctica. This hole wasn’t an actual empty space—it was an area where the ozone concentration had dropped dramatically. The main cause was man-made chemicals called chlorofluorocarbons (CFCs), which were used in things like aerosol sprays, refrigerators, and air conditioners. When CFCs reach the stratosphere, they break down ozone molecules, creating thin spots in the protective layer.

The good news is that the ozone hole is healing. In 1987, countries around the world signed the Montreal Protocol, an international agreement to phase out ozone-destroying chemicals. Since then, levels of CFCs in the atmosphere have dropped, allowing the ozone layer to slowly recover. Each year, scientists measure the size of the hole, and in recent years it has been smaller than in past decades.

Even though some CFCs stay in the atmosphere for decades, the ozone layer is steadily repairing itself. Experts estimate that the Antarctic ozone hole could largely close by around 2065 if current protections continue. This recovery shows how global cooperation and science can protect the planet and keep life safe from harmful UV radiation.

Fun Fact:

Normally, recreational skydivers jump from somewhere between 10,000-14,000 feet (1.89-2.65 miles) above sea level. They will fall for about 30-60 seconds before they pull their chute, during which time they reach terminal velocity - 120 mph.

The current world record for the highest skydive (highest altitude parachute jump) is held by Google's Alan Eustace (USA), set on October 24, 2014.

Altitude — 135,889 feet (approximately 25.74 miles) above average sea level in the stratosphere.
Eustace ascended via a helium balloon while wearing a specialized pressure suit. During his jump he fell for about 4 minutes and 30 seconds, and reached reached speeds over 800 mph (Mach 1.23).

This record surpassed the previous one set by Felix Baumgartner in the 2012 Red Bull Stratos project (127,852 feet). As of today, Eustace's mark remains unbroken.