what is atmosphere ? give its composition
Answers
Answer:
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Explanation:
Earth’s atmosphere is composed of about 78% nitrogen, 21% oxygen, and 0.93% argon. The remainder, less than 0.1%, contains such trace gases as water vapor, carbon dioxide, and ozone. All of these trace gases have important effects on Earth’s climate. The atmosphere can be divided into vertical layers determined by the way temperature changes with altitude. The layer closest to the surface is the troposphere, which contains over 80% of the atmospheric mass and nearly all the water vapor. The next layer, the stratosphere, contains most of the atmosphere’s ozone, which absorbs high-energy radiation from the sun and makes life on the surface possible. Above the stratosphere are the mesosphere and thermosphere. These two layers include regions of charged atoms and molecules, or ions. The upper mesosphere and lower thermosphere are called the ionosphere, this region is important to radio communications, because radio waves can bounce off the layer and travel great distances. It is thought that the present atmosphere developed from gases ejected by volcanoes. Oxygen, upon which all animal life depends, probably accumulated as excess emissions from plants that produce it as a waste product during photosynthesis. Human activities may be affecting the levels of some important atmospheric components, particularly carbon dioxide and ozone.
Composition of the atmosphere
Major gases
The most common atmospheric gas, nitrogen (chemical symbol N2) is largely inert, meaning that it does not readily react with other substances to form new chemical compounds. The next most common gas, oxygen (O2), is required for the respiration (breathing) of all animal life on Earth, from humans to bacteria. In contrast to nitrogen, oxygen is extremely reactive. It participates in oxidation, examples of which include apples turning from white to brown after being sliced, the rusting of iron, and the very rapid oxidation reaction known as fire. Just under 1% of the atmosphere is made up of argon (Ar), which is an inert noble gas, meaning that it does not take part in any chemical reactions under normal circumstances. Together, these three gases account for 99.96% of the atmosphere. The remaining 0.04% contains a wide variety of trace gases, several of which are crucial to life on Earth.
Important trace gases
Carbon dioxide (CO2) affects Earth’s climate and plays a large support role in the biosphere, the collection of living things that populate Earth’s surface. Only about 0.0325% of the atmosphere is CO2. Carbon dioxide is required by plant life for photosynthesis, the process of using sunlight to store energy as simple sugars, upon which all life on Earth depends. Carbon dioxide is also one of a class of compounds called greenhouse gases. These gases are made up of molecules that absorb and emit infrared radiation, which is felt as heat. The solar energy radiated from the sun is mostly in the visible range, within a narrow band of wavelengths. This radiation is absorbed by Earth’s surface, then re-radiated back out to space not as visible light, but as longer wavelength infrared radiation. Greenhouse gas molecules absorb some of this radiation before it escapes to space, and re-emit some of it back toward the surface. In this way, these gases trap some of the escaping heat and increase the overall temperature of the atmosphere. If the atmosphere had no greenhouse gases, it is estimated that Earth’s surface would be 90°F (32°C) cooler.
Explanation:
The atmosphere is composed of gases, water vapour and dust particles. This composition of the atmosphere is not static. It changes according to the time and place. The proportion of gases varies in the higher layers of the atmosphere so that oxygen will be almost in negligible quantity at the height of 120 km. Similarly, carbon dioxide and water vapour are found only up to 90 km from the earth’s surface.