How Well Do You Know Earth's Atmosphere?

Gas layer surrounding Earth

The atmosphere of Earth is the layer of gases that surrounds the planet and creates pressure, absorbs most meteoroids and ultraviolet solar radiation, warms the surface through heat retention, allowing life and liquid water to exist on the Earth's surface, and reduces temperature extremes between day and night.
Dry air contains 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere.
Earth's early atmosphere consisted of gases in the solar nebula, primarily hydrogen. The atmosphere changed significantly over time, affected by many factors such as volcanism, life, and weathering. Human activity has also contributed to atmospheric changes, such as global warming, ozone depletion and acid deposition.
The atmosphere has a mass of about 5.15×10 kg, three-quarters of which is within about 11 km of the surface. The atmosphere becomes thinner with increasing altitude, with no definite boundary between the atmosphere and outer space.
The atmosphere can be divided into five main layers: troposphere, stratosphere, mesosphere, thermosphere, and exosphere. The troposphere is the lowest layer, and the exosphere is the outermost layer.
The exosphere is mainly composed of extremely low densities of hydrogen, helium, and several heavier molecules including nitrogen, oxygen, and carbon dioxide closer to the exobase. The exosphere no longer behaves like a gas, and the particles constantly escape into space.
The thermosphere is the second-highest layer of Earth's atmosphere, and the temperature gradually increases with height and can rise as high as 1500 °C, though the gas molecules are so far apart that its temperature in the usual sense is not very meaningful.
The mesosphere is the third highest layer of Earth's atmosphere, and the temperature drops with increasing altitude to the mesopause that marks the top of this middle layer of the atmosphere. It is the coldest place on Earth.
The stratosphere is the second-lowest layer of Earth's atmosphere, and it contains the ozone layer, which is the part of Earth's atmosphere that contains relatively high concentrations of that gas. The stratosphere defines a layer in which temperatures rise with increasing altitude.
The troposphere is the lowest layer of Earth's atmosphere, and it contains roughly 80% of the mass of Earth's atmosphere. The temperature usually declines with increasing altitude in the troposphere because the troposphere is mostly heated through energy transfer from the surface.
Within the five principal layers above, several secondary layers may be distinguished by other properties.
The average atmospheric pressure at sea level is defined as 101325 pascals. Total atmospheric mass is 5.1480×1018 kg.
The study of Earth's atmosphere and its processes is called atmospheric science and includes multiple subfields, such as climatology and atmospheric physics.Properties and Evolution of Earth's Atmosphere
The Earth's atmosphere is composed of gases held in place by the planet's gravity, and it is divided into several layers based on temperature.
Atmospheric pressure is the weight of the air above a unit area and varies by location and weather.
The entire mass of the atmosphere would terminate abruptly at an altitude of 8.50 km if it had a uniform density from sea level upwards.
Air pressure decreases exponentially with altitude, dropping by half every 5.6 km or by a factor of 1/e every 7.64 km for altitudes out to around 70 km.
The average mass of the atmosphere is about 5 quadrillion tonnes or 1/1,200,000 the mass of Earth.
The temperature of the atmosphere decreases with altitude up to 11 km, stabilizes over a large vertical distance through the rest of the troposphere, and then increases with height in the stratosphere and thermosphere.
The speed of sound in the atmosphere takes on the form of a complicated temperature profile and does not mirror altitudinal changes in density or pressure.
The density of air at sea level is about 1.2 kg/m3 and decreases as the altitude increases.
The refractive index of air is close to, but just greater than 1, leading to the bending of light rays over long optical paths.
The atmosphere is subject to large-scale movement of air through the troposphere, which serves as a means by which heat is distributed around Earth.
The Earth's atmosphere has evolved over time, with the first atmosphere consisting of gases in the solar nebula, followed by a second atmosphere consisting largely of nitrogen plus carbon dioxide and inert gases and a third atmosphere that emerged through the process of plate tectonics.
Air pollution is the introduction of chemicals, particulate matter, or biological materials into the atmosphere, causing harm or discomfort to organisms.