The atmosphere is the layer of gases that surrounds the Earth. It is very important because it keeps us all alive! All living animals and plants on the planet need the atmosphere to survive. The atmosphere is held to the Earth by gravity.

A mixture of gases makes up the atmosphere, including:

  • 78% nitrogen
  • 21% oxygen
  • 0.9% argon
  • ~ 0.1% carbon dioxide, nitrous oxides, methane, and ozone

Water vapor is also present in the atmosphere, varying in amount depending on where you are and what time it is. For example, humid tropical regions have more water vapor in the atmosphere (up to 4%), and cold Arctic regions have less water vapor (usually less than 1%).

There is also some dust in the Earth’s atmosphere. This dust consists of a mixture of solid and liquid particles, including particles from pollution, volcanic eruptions, and soil that the wind has lifted.

The bottom of the atmosphere is heavier than the top. 98% of the atmosphere’s mass is contained in the bottom 30 km. It gradually thins at higher altitudes until it reaches space, where there is no atmosphere. There is no definitive boundary between the atmosphere and outer space; it just gets thinner the higher you go until it blends with outer space.

We do not notice the atmosphere because it is so spread out and formed of invisible gases, but it is quite heavy! Its weight equals a 10-meter-deep layer of water covering the whole planet.

Scientists believe that most of the gases in the Earth’s atmosphere come from early volcanoes, and the oxygen came later from primitive organisms, such as bacteria, during photosynthesis: the process that plants use to make food from sunlight and other ingredients. As more complex plant life developed, more oxygen would have been added to the atmosphere until we arrived at the 21% oxygen that makes up the atmosphere today. This amount of oxygen took millions of years to accumulate.

Why is the atmosphere important?

The atmosphere allows life to exist on Earth because:

  • The air we breathe is in the atmosphere.
  • The atmosphere blocks harmful UV radiation from the Sun from reaching the Earth’s surface.
  • The heat from the Sun is trapped by the atmosphere, so it doesn’t escape back into space, and Earth doesn’t get too cold.
  • Earth’s climate is regulated by the atmosphere.
  • It is a major element of the water cycle.

The atmosphere acts as a giant filter, keeping out the harmful radiation from the Sun, which causes sunburns and can damage living things. But it lets in solar heat (warm rays from the Sun), which is necessary for life to survive on Earth.

What are the different layers of the atmosphere?

The Earth’s atmosphere comprises layers extending from the ground to the sky. The boundaries between these layers are quite fluid, as they change depending on latitude and season. The layers of the atmosphere from the ground up are the troposphere, stratosphere, mesosphere, ionosphere, thermosphere, and exosphere.

What is the troposphere?

All weather develops in the troposphere, the lowest layer of the atmosphere. This is because almost all the atmospheric water vapor is in the troposphere. Winds in this layer of the atmosphere move air masses and different high-pressure and low-pressure areas, which causes weather changes and patterns. The troposphere can change suddenly and violently.

This layer begins at the ground and extends to about 6 km at the poles and about 16 km at the Equator. As we go further up in the troposphere, the air thins, and the temperature decreases. This is why the top of a mountain is colder than the valleys below.

The heat from the Sun can penetrate the troposphere easily. Winds high up in the troposphere are very useful for planes! This is because jet streams are at the top of the troposphere, which are fast-moving winds that planes can fly in to save time and money. Flying in a jet stream is quicker and more efficient than in the thicker air below.

What is the stratosphere?

This calm layer of the atmosphere reaches from the troposphere to about 50 km above the Earth’s surface. It is a very dry layer without many clouds. Any clouds in the stratosphere are thin and wispy. As you get higher up in the stratosphere, the temperature increases: the opposite of the troposphere! The planes that can fly in this layer are lucky because there are strong horizontal winds to aid the flight but little turbulence.

We are also lucky that the stratosphere exists because it helps protect us from harmful UV radiation from the Sun due to containing small amounts of ozone (a form of oxygen). The part of the stratosphere with this thin ozone layer is called the ozone layer. Unfortunately, the amount of ozone in the Earth’s atmosphere is decreasing, which scientists believe is due to chemicals called CFCs being released from aerosol sprays. CFCs are banned in most countries worldwide, and the ozone layer is slowly recovering.

What is the mesosphere?

The mesosphere is the coldest layer of the atmosphere, with a minimum temperature of -120 degrees Celsius. It stretches to about 85 km above the Earth’s surface, and the highest clouds in the atmosphere form here, which look like silvery wisps you can see after the Sun sets. These clouds are made of ice because the mesosphere is so cold! So when we see shooting stars, we see them in the mesosphere.

This is the layer that scientists know least about because it is too high up for planes or weather balloons but too low for spacecraft. Two phenomena happen in the mesosphere that we don’t yet understand the causes of, which are called sprites and elves!

What is the ionosphere?

Zap! This layer of the atmosphere conducts electricity. This is where the Northern and Southern lights form: the colorful patterns of light in the sky that you can see from the poles. These beautiful light displays are created by charged particles in the ionosphere reflecting the solar wind, a stream of charged particles from the Sun.

Radio waves bounce off particles in the ionosphere. This was proved by Marconi, who sent a radio signal from England to Canada in 1901. Marconi demonstrated that radio signals bounce off the ionosphere rather than traveling in straight lines.

What is the thermosphere?

The thermosphere is the thickest layer in the atmosphere, extending to 690 km above the Earth’s surface. Consequently, the lightest gases can be found, including oxygen, helium, and hydrogen.

This layer is home to the International Space Station (ISS) and the Hubble Space Telescope! These satellites are in what is called ‘low-Earth orbit.’ Gas molecules are very spread out in the thermosphere. Temperatures here can be very high, reaching 1500 degrees Celsius, but it is not very hot in the thermosphere because there is not much pressure. Heat is caused when molecules pass energy onto each other in an area of high pressure.

What is the exosphere?

This is the layer of the atmosphere you can see in satellite images of the Earth as the fuzzy blue layer surrounding our planet. The exosphere is home to many weather satellites in ‘low-Earth orbit’ or ‘medium-Earth orbit.’

Hydrogen is the main element in the exosphere, with only trace amounts of helium, carbon dioxide, oxygen, and other gases. The exosphere stretches and shrinks depending on what is happening with the Sun. The exosphere is squeezed to about 1000 km above the Earth when solar storms happen. When the Sun is calm, the exosphere stretches to about 10,000 km.

Climate change

The greenhouse effect is a process that happens in the atmosphere and causes the Earth to warm up, which leads to climate change. The greenhouse effect is when greenhouse gases in the atmosphere, such as carbon dioxide and methane, trap energy from the Sun. Humans have increased the number of greenhouse gases in the atmosphere by burning fossil fuels like coal and oil. We need a certain amount of these gases in our atmosphere to retain heat from the Sun enough to warm up the Earth. But too much is not good news! This is because too much heat can cause the Earth to warm up too much, damaging the planet and life on Earth.

The atmosphere on different planets

As well as studying the Earth’s atmosphere, scientists study the atmospheres of all the planets in our solar system. We know that none of these planets has an atmosphere that contains the right ingredients for life as we know it. This is because life is impossible without a stable atmosphere of hydrogen, oxygen, nitrogen, and carbon in the right balance. Water must also be present on a planet for life to form. To read more about the different worlds, check out our Wiki on the solar system.

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