How does gravity affect oxygen?

A shell made of gas

Seen from space, it appears like a fine bluish veil that surrounds the earth: the atmosphere. It is the envelope of air that surrounds our planet. Compared to the diameter of the earth, this shell is quite thin: if the earth were the size of an apple, the atmosphere would be about the thickness of its shell.

Without the atmosphere there would be no life on this planet, because plants, animals and humans need air to breathe. It protects us from the cold and from harmful radiation from space. It also lets meteorites burn up before they can hit the surface of the earth. This atmosphere is vital to us - but what is it actually made of?

The atmosphere is a mix of different gases. A large part of this gas mixture is nitrogen: At 78 percent, that's almost four fifths of the entire atmosphere. Only 21 percent consists of oxygen, which we need to breathe. The remaining one percent is made up of various trace gases - gases that only occur in traces in the atmosphere. These trace gases include methane, nitrogen oxides and, above all, carbon dioxide, or CO for short2 called. Although the CO2-Proportion is quite low, this trace gas has a tremendous impact on our earth's climate. This can be seen in the greenhouse effect, which is heating up our planet.

The fact that the earth has an atmosphere at all is due to gravity. It holds the gas molecules on earth and prevents them from simply flying out into space. In fact, the air becomes thinner and thinner with increasing altitude and thus decreasing gravity. Even at 2000 meters above sea level, this can become uncomfortable for people: He suffers from altitude sickness with shortness of breath, headaches and nausea. Extreme mountaineers who want to climb high peaks like the 8000m high in the Himalayas therefore usually take artificial oxygen with them on their tour.


No sensible person would have thought that possible: Reinhold Messner and Peter Habeler climbed the highest mountain on earth without an oxygen device. The two extreme mountaineers arrived at the base camp yesterday, completely exhausted but happy.

Your climb to the summit on Everest begins on May 8, in the morning at half past five, after an icy night in a tent. They have been on their way up from base camp since May 6th. They are not frightened by the warnings of many doctors: They want to climb the roof of the world without artificial oxygen. A failed attempt is already behind them. Another attempt now follows from a height of almost 8,000 meters. The ascent in the thin mountain air is an ordeal, every step is torture. But both of them are in top form and they have experience.

At noon they reach an altitude of 8,800 meters. The legs are heavy as lead, the tiredness can hardly be described. But they overcome their pain and trudge on, as if in a trance. Finally they achieve the seemingly impossible: You are standing on the summit of Everest. World record! From exhaustion, they let themselves fall into the snow. After a long break, Messner takes his camera out of his backpack and films. Back in the tent, they radio the base camp: They made it!

During the night Messner is tormented by terrible pain in his eyes: he is snow-blind. Habeler's ankle is injured. Nevertheless, the two manage to descend to base camp on May 10th. Only now do they understand their success, a feeling of triumph fills them. The sensation is perfect: Peter Habeler and Reinhold Messner have proven that Mount Everest can also be climbed without an oxygen device.

In the death zone

Doctors had warned Reinhold Messner and Peter Habeler: Moving around 8,000 meters above sea level without artificial oxygen is extremely dangerous to health. Brain cells could die and suspend controlled thinking, including the threat of unconsciousness. "You will come back as idiots," it was said briefly and drastically.

In fact, altitude sickness is not to be trifled with. From around 2,000 meters, the thinning air can make itself felt through shortness of breath, dizziness, headache or vomiting. The lungs take in less and less oxygen with increasing altitude, and the body is undersupplied. Above 7,000 meters - in the death zone - most people will pass out if they do not get extra oxygen. In the worst case, the extreme altitude leads to death. This fact has already cost many climbers their lives. The fact that Habeler and Messner climbed the summit without breathing apparatus actually borders on a miracle. It can only be explained with meticulous planning, incredible physical fitness and an iron will.


The Austrian Felix Baumgartner fell from a balloon capsule from a height of 39 kilometers. In his death-defying jump, he broke the sound barrier and reached a top speed of 1,342 kilometers per hour. After four minutes and 19 seconds of free fall, he was back on solid ground.

“It was much more difficult than we assumed,” Baumgartner said later. Yesterday, over the US state of New Mexico, he let himself be carried into the stratosphere by a balloon capsule. His jump goes according to plan, but shortly afterwards the 43-year-old Austrian gets into a tailspin. Again and again he overturns. The images are broadcast around the globe, and the whole world holds its breath at the sight. "It was brutal," remembers Baumgartner of the near-disaster: "For a few seconds I thought I was going to lose consciousness." Finally, he succeeds in stopping the deadly tumult with his arms.

When he finally lands safely on earth with his parachute, he kneels on the desert sand. He stretches his hands up to the sky: He actually survived the maddening leap. But something else worries him: “I hope we flew supersonic,” he calls out. The measurements confirm: During his jump he broke the sound barrier and reached a top speed of 1,342 kilometers per hour.

This makes him the first person to move faster than sound without an airplane or spaceship. In addition, he now holds the record for the highest manned balloon flight. And never before had a person jumped with a parachute from such a ludicrous height. "Congratulations from us to Felix Baumgartner, a very, very courageous skydiver!" Then congratulated the European Space Agency ESA on Twitter.

Perfect preparation

Felix Baumgartner had been preparing for his life-threatening leap for five long years. Physically he is in top shape. But that's not enough for such a risk: A fire-resistant pressure suit was his life insurance. The heated suit ensured the body temperature during the jump. A hole in it would have been fatal, because temperatures of up to minus 70 degrees Celsius and extremely low air pressure prevail at high altitudes. Oxygen is scarce, so the Austrian was supplied with breathing air through the helmet. During the fall, he was able to maintain contact with his team on the ground through the helmet. He could also have opened an umbrella that stabilized the flight using the emergency buttons on the suit. He didn't use it: that would have endangered his record.

The layers of the atmosphere

Similar to the floors of a multi-storey house, the atmosphere is divided into several layers. These layers have different properties - let's start on the "ground floor":

Dark storm clouds or blue skies, gentle breezes or strong winds: almost all weather events take place up to a height of 15 kilometers. This lower layer of the atmosphere is therefore also called the weather layer. Scientists say Troposphere to. About 90 percent of all air and almost all of the water vapor in the earth's atmosphere are contained in this layer. The higher the position in the troposphere, the colder it gets: At its upper limit, icy temperatures of up to minus 80 degrees Celsius prevail.

In the layer above, the stratosphere, the temperature suddenly rises again. At an altitude of around 50 kilometers, the thermometer even reaches a value of around 0 degrees Celsius. The reason for this warming is the ozone layer, which lies within the stratosphere. This works like a heater: it absorbs the sun's UV radiation and converts it into heat.

Above the stratosphere lies at an altitude of 50 to 80 kilometers Mesosphere. Because this layer does not contain ozone, it becomes bitterly cold again, down to minus 100 degrees Celsius. This makes the mesosphere the coldest layer in the atmosphere. Here dust particles and smaller rocks from space are stopped, which would otherwise fall to earth as meteorites. We can sometimes see these celestial bodies as shooting stars in the sky at night.

The air is getting thinner and thinner above the mesosphere. The gravity weakens with increasing altitude and can therefore hold the gas particles less and less. So that forms Thermosphere a smooth transition into space over hundreds of kilometers. The thermosphere takes its name from the high temperatures that prevail here: They rise up to 1700 degrees. In our opinion, however, it is not hot, because too few gases are buzzing around for the feeling of heat.

The oxygen cycle

The air we breathe contains about a fifth of oxygen. This gas is invisible, has no smell and no taste - but it is vital to us. Because we need oxygen in order to gain energy from our metabolism. Without this gas, neither humans nor most animals can survive.

Almost all of the oxygen in the air is made by plants through photosynthesis. During this process, the plant forms important nutrients from carbon dioxide and water with the help of sunlight. Oxygen is also produced as a by-product of photosynthesis.

The oxygen that the plant does not need is released into its environment. For example, a large beech tree produces about as much oxygen in one hour as 50 people need to breathe in the same time. Humans and animals breathe in this oxygen, use it up and breathe out carbon dioxide. Plants absorb this carbon dioxide during photosynthesis while at the same time generating new oxygen. A cycle is created between plants, humans and animals.

In the course of the earth's history, much more oxygen has been released than living things have used to breathe. So more and more oxygen got into the atmosphere. The ozone layer, which protects us from dangerous UV radiation, could form from the growing proportion of oxygen high up in the stratosphere.

Since people have been burning more and more oil, natural gas and coal, this natural oxygen cycle has been severely disrupted: burning consumes oxygen and at the same time carbon dioxide is also emitted. For this reason, the amount of carbon dioxide in the air has risen sharply over the past 250 years. The increase in this trace gas is the main cause of the man-made greenhouse effect and thus also of the warming of the atmosphere.

The greenhouse effect

In a greenhouse, vegetables or flowers can thrive even when it's cold outside. That's because greenhouses are built out of glass. The glass - or a transparent film - allows the short-wave rays of the sun to enter the interior unhindered: the air warms up. On the other hand, the glass is impermeable to long-wave heat radiation, so the heat can no longer get out. That’s why it’s cozy and warm in a greenhouse.

Something similar is happening on a large scale on Earth. The greenhouse gases carbon dioxide (CO2) and water vapor are naturally present in the atmosphere. Water vapor enters the air through evaporation, carbon dioxide through the exhalation. Volcanic eruptions also contribute to the natural carbon dioxide content of the air. Both gases have the same effect as the glass in a greenhouse: They allow the short-wave rays of the sun to penetrate to the earth. At the same time, like an invisible barrier, they hinder the long-wave thermal radiation on its way back into space. The heat builds up and the atmosphere heats up.

Without this natural greenhouse effect, life on earth would hardly be possible, because it would be far too cold for most living things. Instead of the current average temperature of plus 15 degrees, it would be an icy minus 18 degrees Celsius. The surface of the earth would be frozen!

The problem starts when we increase the amount of greenhouse gases in the atmosphere. This is mainly done by burning oil, natural gas and coal. Heating the apartment, driving a car, burning rubbish: all of these processes emit carbon dioxide. This CO2 has the largest share in the man-made greenhouse effect. But the cultivation of rice or cattle farming also intensify the effect: large amounts of methane (CH4) - also a greenhouse gas. In addition, nitrous oxide, ozone and fluorocarbons are among the greenhouse gases. Because all these gases slow down the earth's heat radiation, the temperatures on our globe continue to rise.

How was our air we breathe created?

What do people and animals need to live? Food and water, of course, but above all oxygen! We get it from the air we breathe. But that was not always the case: the primordial atmosphere consisted of water vapor and poisonous gases such as carbon dioxide and foul-smelling hydrogen sulfide. We would immediately suffocate in this “air”. But what has changed since then? Why is there oxygen in the atmosphere today? And since when?

If you look back in the history of the earth, you can find traces of living things that must have needed oxygen more than two billion years ago. So there must have been oxygen in the air back then.

Petrified traces of microscopic bacteria, called blue-green algae, are much older. And they have it all: These organisms were the first to use the energy of sunlight for their metabolism. They absorbed water and carbon dioxide from their environment and, with the help of solar energy, converted them into sugar, which they used to store energy. In addition, this chemical reaction produced oxygen - as a waste product, so to speak. However, the bacteria could not do anything with the oxygen and simply released it into the environment.

At that time there was plenty of sunlight and carbon dioxide, and the world's oceans were comparatively warm. These were the best conditions for the blue-green algae to multiply and spread. In doing so, they produced more and more oxygen, which accumulated over millions of years, first in the oceans and later in the atmosphere.

The waste product of these bacteria created the conditions for higher forms of life in water and on land. From the bacteria later emerged the chloroplasts, which to this day capture the solar energy in every plant. The principle of so-called photosynthesis has also remained the same: With the help of sunlight, water and carbon dioxide are converted into sugar and oxygen. The sugar serves as a nutrient for the plant, the oxygen is released into the air and inhaled by humans and animals.