The earth is the only astronomical object known in the Universe to contain any forms of life as on today. It is formed nearly 4.5 TO 4.6 Billion years back from the Sun. The Moon is formed 4.4 billion years ago from the Earth perhaps by a hit of an object with the earth resulting in a part being detached. Life in rudimentary form has started on the earth nearly 3.5 billion years back slowly becoming more complex life forms culminating in present human life. This has happened because of factors supporting life form on earth like presence of water, oxygen, ozone layer, Green House gases, a favorable atmosphere around the earth, a suitable temperature range etc. Main greenhouse gases (GHGs) in the atmosphere include CO2 , CH4, N2O, CFCs. The greenhouse effect actually makes the earth habitable. Without the greenhouse effect, the earth would be much colder (- 180 C). We live on this planet earth and so our survival and future depends on this planet.

The Earth Atmosphere-

The Atmosphere is not physically uniform although air is well mixed throughout the atmosphere. There is significant variations in temperature and pressure with altitude, which define a number of atmospheric layers. These include the Troposphere (0 to 16 km), Stratosphere (16 to 50 km), Mesosphere (50 to 80km) and Thermosphere (80 to 640km). The boundaries between these four layers are defined by abrupt changes in temperature, and include respectively the Tropopause, Stratopause and Mesopause. In the Troposphere and Mesosphere, temperature generally falls with increasing altitude, whilst in the Stratosphere and Thermosphere, temperature rises with increasing altitude.

In addition to temperature, other criteria can be used to define different layers in the atmosphere. The ionosphere, for example, which occupies the same region of the atmosphere as the Thermosphere, is defined by the presence of ions, a physico-chemical criterion. The region beyond the ionosphere is known as the exosphere. The Ionosphere and the Exosphere together make up the upper atmosphere (or Thermosphere). The Magnetosphere is the region above the Earth's surface in which charged particles are affected by the Earth's magnetic field.

Another well-known layer of the Atmosphere is the Ozone layer, occupying much of the Stratosphere. This layer is defined by its chemical composition - where ozone is especially abundant.

Figure-Layers of the Atmosphere

Fig- Atmospheric layers with brief descriptions

Figure- Temperature, Pressure gradients at various Altitudes

1) Troposphere

The lowest layer of the atmosphere is called the Troposphere. It ranges in thickness from 8km at the poles to 16km over the equator. The Troposphere is bounded above by the Tropopause, a boundary marked by stable temperatures. Above the Troposphere is the Stratosphere. Although variations do occur, temperature usually declines with increasing altitude in the Troposphere. It will be several degrees cooler on the top of a mountain than in the valley below.

The Troposphere is denser than the layers of the atmosphere above it (because of the weight compressing it), and it contains up to 75% of the mass of the atmosphere. It is primarily composed of nitrogen (78%) and oxygen (21%) with only small concentrations of other trace gases. Nearly all Atmospheric water vapor or moisture is found in the Troposphere.

The Troposphere is the layer where most of the world's weather variation takes place. Since temperature decreases with altitude in the troposphere, warm air near the surface of the Earth can readily rise, being less dense than the colder air above it. In fact air molecules can travel to the top of the Troposphere and back down again in a just a few days. Such vertical movement or convection of air generates clouds and ultimately rain from the moisture within the air, and gives rise to much of the weather which we experience. The Troposphere is capped by the tropopause, a region of stable temperature. Air temperature then begins to rise in the Stratosphere. Such a temperature increase prevents much air convection beyond the tropopause, and consequently most weather phenomena, including towering cumulonimbus thunderclouds, are confined to the Troposphere


Sometimes the temperature does not decrease with height in the troposphere, but increases. Such a situation is known as a temperature inversion. Temperature inversions limit or prevent the vertical mixing of air. Such atmospheric stability can lead to air pollution episodes with air pollutants emitted at ground level becoming trapped underneath the temperature inversion.


The Stratosphere is the second major layer of the atmosphere. It lies above the Troposphere and is separated from it by the tropopause. It occupies the region of atmosphere from about 12 to 50 km, although its lower boundary tends to be higher nearer the equator and lower nearer the poles.

The Stratosphere defines a layer in which temperatures rises with increasing altitude. At the top of the Stratosphere the thin air may attain temperatures close to 0°C. This rise in temperature is caused by the absorption of ultraviolet (UV) radiation from the Sun by the Ozone layer. Such a temperature profile creates very stable atmospheric conditions, and the Stratosphere lacks the air turbulence that is so prevalent in the troposphere. Consequently, the Stratosphere is almost completely free of clouds or other forms of weather.

The Stratosphere provides some advantages for long-distant flight because it is above stormy weather and has strong, steady, horizontal winds. The Stratosphere is separated from the mesosphere above by the Stratopause.


The Mesosphere (literally middle sphere) is the third highest layer in our atmosphere, occupying the region 50 km to 80 km above the surface of the Earth, above the Troposphere and Stratosphere, and below the Thermosphere. It is separated from the Stratosphere by the Stratopause and from the Thermosphere by the Mesopause. Temperatures in the Mesosphere drop with increasing altitude to about -100°C. The Mesosphere is the coldest of the atmospheric layers. In fact it is colder then Antarctica's lowest recorded temperature. It is cold enough to freeze water vapor into ice clouds. You can see these clouds if sunlight hits them after sunset. They are called Noctilucent Clouds (NLC). NLCs are most readily visible when the Sun is from 4 to 16 degrees below the horizon.

The Mesosphere is also the layer in which a lot of meteors burn up while entering the Earth's atmosphere. From the Earth they are seen as shooting stars. In fact the upper atmosphere extends much further out, into the Thermosphere.

The Thermosphere (literally "heat sphere") is the outer layer of the atmosphere, separated from the Mesosphere by the Mesopause. Within the Thermosphere temperatures rise continually to well beyond 1000°C. The few molecules that are present in the Thermosphere receive extraordinary amounts of energy from the Sun, causing the layer to warm to such high temperatures. Air temperature, however, is a measure of the kinetic energy of air molecules, not of the total energy stored by the air. Therefore, since the air is so thin within the Thermosphere, such temperature values are not comparable to those of the Troposphere or Stratosphere. Although the measured temperature is very hot, the Thermosphere would actually feel very cold to us because the total energy of only a few air molecules residing there would not be enough to transfer any appreciable heat to our skin.


The lower part of the Thermosphere, from 80 to 550 km above the Earth's surface, contains the Ionosphere. Beyond the Ionosphere extending out to perhaps 10,000 km is the exosphere or outer Thermosphere, which gradually merges into space. The Ionosphere is a layer of ionized air in the atmosphere extending from almost 80 km above the Earth's surface altitudes to 600 km and more. Technically, the Ionosphere is not another atmospheric layer. It occupies the same region of the upper Atmosphere as the Thermosphere. In this region of the atmosphere the Sun's energy is so strong that it breaks apart molecules and atoms of air, leaving ions (atoms with missing electrons) and free-floating electrons. The Ionosphere is the region of the atmosphere where the Aurorae occur. Ionization of air molecules in the ionosphere is produced by ultraviolet radiation from the Sun, and to a lesser extent by high-energy particles from the Sun and from cosmic rays. The large number of free electrons in the Ionosphere allows the propagation of electromagnetic waves. Radio signals - a form of electromagnetic radiation - can be "bounced" off the ionosphere allowing radio communication over long distances.


The Exosphere is the highest layer of the atmosphere. Together with the Ionosphere, it makes up the Thermosphere. The Exosphere extends to 10,000 km above the Earth's surface. This is the upper limit of our atmosphere. The atmosphere here merges into space in the extremely thin air. Air atoms and molecules are constantly escaping to space from the exosphere. In this region of the atmosphere, hydrogen and helium are the prime components and are only present at extremely low densities. This is the area where many satellites orbit the Earth.

Size and Shape of the Earth-

Earth, the third planet from the sun, is the fifth largest planet in the solar system; only Jupiter, Saturn, Uranus and Neptune are bigger. Earth is the largest of the terrestrial planets of the inner solar system, bigger than Mercury, Venus and Mars.

The mean radius of Earth is 3,959 miles (6,371 kilometers). However, Earth is not quite a sphere. The planet's rotation causes it to bulge at the equator due to Centrifugal forces. Earth's equatorial diameter is 7,926 miles (12,756 kilometers), but from pole to pole, the diameter is 7,900 miles (12,720 km) — a difference of only 40 miles (64 km) The circumference of Earth at the equator is about 24,902 miles (40,075 km), but from pole-to-pole — the meridional circumference — Earth is only 24,860 miles (40,008 km) around. This shape, caused by the flattening at the poles, is called an oblate spheroid.

Earth's density is 5.52 grams per cubic centimeter. Earth is the densest planet in the solar system because of its metallic core and rocky mantle. Jupiter, which is 318 more massive than Earth, is less dense because it is made of gases, such as hydrogen. Earth's mass is 6.6 sextillion ton (5.9722 x 1024 kilograms). It volume is 1.08321 x 1012 km. The total surface area of Earth is about 197 million square miles (509 million square km). About 71 percent is covered by water and 29 percent by land.
Mount Everest is the highest place on Earth above sea level, at 29,028 feet (8,848 meters), but it is not the highest point on Earth — that is, the place most distant from the center of the Earth. That distinction belongs to Mount Chimborazo in the Andes Mountains in Ecuador. Although Chimborazo is about 10,000 feet shorter (relative to sea level) than Everest, this mountain is about 1.5 miles (2.4 km) farther into space because of the equatorial bulge. The lowest point on Earth is the Mariana Trench in the western Pacific Ocean 36,200 feet (11,034 meters) below sea level.

Earth's Interior-

Earth is the densest of the terrestrial planets as it is made up of a crust, mantle and core. The Earth's crust is the thinnest of these layers while the mantle comprises 84% of Earth's volume and extends 1,800 miles (2,900 km) below the surface. What makes Earth the densest of these planets however is its core. It is the only terrestrial planet with a liquid outer core that surrounds a solid, dense inner core. Earth's average density is 5515 × 10 kg/m3. Mars, the smallest of the terrestrial planets by density, is only around 70% as dense as Earth.


The Earth's Crust is like the skin of an apple. It is very thin in comparison to the other three layers. The crust is only about 3-5 miles (8 kilometers) thick under the oceans(oceanic crust) and about 25 miles (32 kilometers) thick under the continents (continental crust). The temperatures of the crust vary from air temperature on top to about 1600 degrees Fahrenheit (870 degrees Celsius) in the deepest parts of the crust. The crust of the Earth is broken into many pieces called plates. The plates "float" on the soft, plastic mantle which is located below the crust. These plates usually move along smoothly but sometimes they stick and build up pressure. The pressure builds and the rock bends until it snaps. When this occurs an Earthquake is the result. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along these plate boundaries.

World Population Dynamics Historical-

The main causes of the earth's impurity is admittedly Anthropogenic. The population has dramatically increased in last 500 years from a meager sub billion figure to over 7 billion now likely to touch 10 billion at the end of this century. This is where we have to work on Globally and nationally if we want the carbon and climate of atmosphere to stabilize.

The huge population growth caused Greenhouse gases (abbrev. GHG) whose increase in post Industrial revolution era beyond 1850 AD is responsible for the Global warming and Climate Change. They are gases in the atmosphere that absorb and emits radiation within the thermal infrared range. This process is the fundamental cause of the green house effect. The primary greenhouse gases in Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and Halocarbons (a group of gases containing fluorine, chlorine and bromine) and Others (Fluorinated gas or F- gas, Black carbon, Ozone etc) . It is a fact that GHGs are required for us as without greenhouse gases, the average temperature of Earth's surface would be about −18 °C (0 °F). The carbon dioxide alone contributes 74 percent to Global warming followed by 14 percent by methane and 8 percent by Nitrous oxide.

Historically the carbon Dioxide concentration has remained 180 to 290 PPM in the World from last 400 thousand years till 1880. However it started increasing with Industrial Revolution in Nineteenth Century.The 2013 carbon dioxide emissions (fossil fuel and cement production only) breakdown is coal (43%), oil (33%), gas (18%), cement (5.5%) and gas flaring (0.6%). land use change 8% etc as per global Carbon Project.org 2014. CO2 concentration in air till 1880 was about 300 ppm and today it is 409 ppm in 2018. There is increase of nearly 3 ppm per year now which is going up year after year. An increase of 100 ppm has given a Temperature rise of nearly 0.85 degree centigrade and if there is a limit of 2 degree rise fixed by UNFFCC , IPCC and COP meetings, we have to keep the concentration below 500 ppm only. This is the challenge as we have to convince one and all thereby putting pressure on the Governments world over.

Earth a difficult terrain to map and Measure-

The earth by its rough undulating surface over a ellipsoid is difficult to map in 2 dimensions without sacrificing accuracy. The lateral relative movement of the plates typically varies from zero to 100 mm annually. This movement has a potency of altering the GPS readings over a length of time. The Australian plate is moving the fastest requiring corrections of the GPS Coordinates. The moving magnetic meridian of earth over time that too varying between -90 degrees to + 90 degrees globally in many places make the chain compass survey outdated. These issues will be discussed in a separate article by the Author in detail.

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