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- The atmosphere is a mixture of gases that surrounds the Earth. It helps make life possible by providing us with air to breathe, shielding us from harmful ultraviolet (UV) radiation coming from the Sun, trapping heat to warm the planet, and preventing extreme temperature differences between day and night.
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Nitrogen and oxygen are by far the most common gases in our atmosphere. Dry air is composed of about 78% nitrogen (N 2 ) and about 21% oxygen (O 2 ). The remaining less than 1% of the atmosphere is a mixture of gases, including argon (Ar) and carbon dioxide (CO 2 ) .
The three major constituents of Earth's atmosphere are nitrogen, oxygen, and argon. Water vapor accounts for roughly 0.25% of the atmosphere by mass.
Oct 19, 2023 · Earth’s atmosphere is composed of about 78 percent nitrogen, 21 percent oxygen, 0.9 percent argon, and 0.1 percent other gases. Trace amounts of carbon dioxide, methane, water vapor, and neon are some of the other gases that make up the remaining 0.1 percent.
- Overview
- Energy budget
atmosphere, the gas and aerosol envelope that extends from the ocean, land, and ice-covered surface of a planet outward into space. The density of the atmosphere decreases outward, because the gravitational attraction of the planet, which pulls the gases and aerosols (microscopic suspended particles of dust, soot, smoke, or chemicals) inward, is greatest close to the surface. Atmospheres of some planetary bodies, such as Mercury, are almost nonexistent, as the primordial atmosphere has escaped the relatively low gravitational attraction of the planet and has been released into space. Other planets, such as Venus, Earth, Mars, and the giant outer planets of the solar system, have retained an atmosphere. In addition, Earth’s atmosphere has been able to contain water in each of its three phases (solid, liquid, and gas), which has been essential for the development of life on the planet.
The evolution of Earth’s current atmosphere is not completely understood. It is thought that the current atmosphere resulted from a gradual release of gases both from the planet’s interior and from the metabolic activities of life-forms—as opposed to the primordial atmosphere, which developed by outgassing (venting) during the original formation of the planet. Current volcanic gaseous emissions include water vapour (H2O), carbon dioxide (CO2), sulfur dioxide (SO2), hydrogen sulfide (H2S), carbon monoxide (CO), chlorine (Cl), fluorine (F), and diatomic nitrogen (N2; consisting of two atoms in a single molecule), as well as traces of other substances. Approximately 85 percent of volcanic emissions are in the form of water vapour. In contrast, carbon dioxide is about 10 percent of the effluent.
During the early evolution of the atmosphere on Earth, water must have been able to exist as a liquid, since the oceans have been present for at least three billion years. Given that solar output four billion years ago was only about 60 percent of what it is today, enhanced levels of carbon dioxide and perhaps ammonia (NH3) must have been present in order to retard the loss of infrared radiation into space. The initial life-forms that evolved in this environment must have been anaerobic (i.e., surviving in the absence of oxygen). In addition, they must have been able to resist the biologically destructive ultraviolet radiation in sunlight, which was not absorbed by a layer of ozone as it is now.
Once organisms developed the capability for photosynthesis, oxygen was produced in large quantities. The buildup of oxygen in the atmosphere also permitted the development of the ozone layer as O2 molecules were dissociated into monatomic oxygen (O; consisting of single oxygen atoms) and recombined with other O2 molecules to form triatomic ozone molecules (O3). The capability for photosynthesis arose in primitive forms of plants between two and three billion years ago. Previous to the evolution of photosynthetic organisms, oxygen was produced in limited quantities as a by-product of the decomposition of water vapour by ultraviolet radiation.
Britannica Quiz
27 True-or-False Questions from Britannica’s Most Difficult Science Quizzes
Earth’s atmosphere is bounded at the bottom by water and land—that is, by the surface of Earth. Heating of this surface is accomplished by three physical processes—radiation, conduction, and convection—and the temperature at the interface of the atmosphere and surface is a result of this heating.
The relative contributions of each process depend on the wind, temperature, and moisture structure in the atmosphere immediately above the surface, the intensity of solar insolation, and the physical characteristics of the surface. The temperature occurring at this interface is of critical importance in determining how suitable a location is for different forms of life.
- Roger A. Pielke
- The Atmosphere's Importance. We are lucky to have an atmosphere on Earth. The atmosphere supports life and is also needed for the water cycle and weather.
- The Atmosphere and Living Things. Most of the atmosphere is nitrogen, but it doesn't do much. Carbon dioxide and oxygen are the gases in the atmosphere that are needed for life.
- The Atmosphere and the Sun’s Rays. The atmosphere protects living things from the Sun’s most harmful rays. Gases reflect or absorb the strongest rays of sunlight (Figure below).
- The Atmosphere and Earth’s Temperature. Gases in the atmosphere surround Earth like a blanket. They keep the temperature in a range that can support life.
Jun 25, 2024 · We live at the bottom of an invisible ocean called the atmosphere, a layer of gases surrounding our planet. Nitrogen and oxygen account for 99 percent of the gases in dry air, with argon, carbon dioxide, helium, neon, and other gases making up minute portions.
Key points. Earth is surrounded by a mixture of gases called the atmosphere. The composition of the atmosphere is 78 % nitrogen and 21 % oxygen, with the remaining 1 % consisting of water vapor, argon, carbon dioxide, and small amounts of other gases.
