Climate

Mesosphere

(in the classification of the earth's atmosphere by chemical properties) the region between the ionosphere and the exosphere, extending from about 250-650 miles (400-1050 km) above the surface of the earth.

How do we know that there was no oxygen in the atmosphere before 2.3 billion years ago?

Changes in the Atmosphere Earth's early atmosphere contained only small amounts of free oxygen, probably produced entirely by the reaction of sunlight with water vapor from volcanoes. The oxygen-rich atmosphere that evolved later, and upon which oxygen-breathing life now depends, was a result of the origin of photosynthesis. During the Precambrian, vast numbers of single-celled algae and cyanobacteria living in the seas eventually released enough oxygen to transform the environment. The oldest evidence of cyanobacteria dates to 2.7 billion years ago, although oxygen did not begin to build up in the environment until about 2.3 billion years ago. During the transition from oxygen-poor to oxygen-rich atmosphere, the first banded iron formations may have formed.

How do we know about the past composition of the atmosphere in general?

Earth's atmosphere is composed of about 78% nitrogen, 21% oxygen, and 0.93% argon. The remainder, less than 0.1%, contains many small but important trace gases, including water vapor, carbon dioxide, and ozone. All of these trace gases have important effects on the earth's climate. The atmosphere can be divided into vertical layers determined by the way temperature changes with height. 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.

If hydrogen is by far the most common element in the universe, why doesn't earth's atmosphere have a lot of hydrogen?

Hydrogen was probably "discovered" many times. Many early chemists reported finding a "flammable gas" in some of their experiments. In 1671, for example, English chemist Robert Boyle (1627-91) described experiments in which he added iron to hydrochloric acid (HCl) and sulfuric acid (H 2 SO 4 ). In both cases, a gas that burned easily with a pale blue flame was produced.

What produced the most of the oxygen in the earth's atmosphere?

It's hard to keep oxygen molecules around, despite the fact that it's the third-most abundant element in the universe, forged in the superhot, superdense core of stars. That's because oxygen wants to react; it can form compounds with nearly every other element on the periodic table. So how did Earth end up with an atmosphere made up of roughly 21 percent of the stuff?

Thermosphere Exosphere

The exosphere is the uppermost region of Earth's atmosphere as it gradually fades into the vacuum of space. Air in the exosphere is extremely thin - in many ways it is almost the same as the airless void of outer space.

Methane

a colorless, odorless, flammable gas, CH 4 , the main constituent of marsh gas and the firedamp of coal mines, obtained commercially from natural gas: the first member of the methane, or alkane, series of hydrocarbons.

Carbon dioxide

a colorless, odorless, incombustible gas, CO 2 , present in the atmosphere and formed during respiration, usually obtained from coal, coke, or natural gas by combustion, from carbohydrates by fermentation, by reaction of acid with limestone or other carbonates, or naturally from springs: used extensively in industry as dry ice, or carbon dioxide snow, in carbonated beverages, fire extinguishers, etc.

Greenhouse effect

an atmospheric heating phenomenon, caused by short-wave solar radiation being readily transmitted inward through the earth's atmosphere but longer-wavelength heat radiation less readily transmitted outward, owing to its absorption by atmospheric carbon dioxide, water vapor, methane, and other gases; thus, the rising level of carbon dioxide is viewed with concern.

Tropopause

the boundary, or transitional layer, between the troposphere and the stratosphere.

Exosphere

the highest region of the atmosphere, where the air density is so low that a fast-moving air molecule is more than 50 percent likely to escape from the atmosphere instead of hitting other molecules.

Troposphere

the lowest layer of the atmosphere, 6 miles (10 km) high in some areas and as much as 12 miles (20 km) high in others, within which there is a steady drop in temperature with increasing altitude and within which nearly all cloud formations occur and weather conditions manifest themselves.

Magnetosphere

the outer region of the earth's ionosphere, where the earth's magnetic field controls the motion of charged particles, as in the Van Allen belts

Stratosphere

the region of the upper atmosphere extending upward from the tropopause to about 30 miles (50 km) above the earth, characterized by little vertical change in temperature