If decomposers are removed completely from the Earth, then dead bodies of plants and animals or other dead organic matter will remain undecomposed. The complex nutrients will not be made available back to atmosphere. After some time, the dead bodies of organisms will acquire the whole space on the Earth. Thus, existence of life will be impossible on the Earth.

The osmotic concentration of terrestrial forms is low. They can neither store nor eliminate high amounts of dissolved salt present in sea water. Therefore, they require fresh water to maintain the balance of salts within the body.

harmful effects of ozone depletion.
(i) Due to depletion of ozone layer more ultraviolet (UV) radiation will reach the earth. UV radiations cause skin cancer, damage to eyes and immune system.
(ii) UV radiation kills microorganisms, such as bacteria, even useful ones.
(iii) Ozone (causes greenhouse house effect) layer depletion may lead to variation in rainfall, ecological disturbances and dwindling of global food supply.

Fossil fuels such as coal wood, petroleum oil, naturals gas are burnt to provide energy. Their combustion not produces energy and carbon dioxide but other poisonous gases like carbon monoxide, sulphur dioxide, oxides of nitrogen and smoke particles also, thus lot of atmospheric pollution is caused by burning of fossil fuels.

Following are the four main steps involved in nitrogen cycle:
(i) Nitrogen fixation and assimilation of free atmospheric nitrogen by Rhizobium or blue-green algae.
(ii) Ammonification is conversion of organic nitrogen to ammonia by bacteria and fungi.
(iii) Nitrification is conversion of ammonium to nitrites by Nitrosomonas (nitrifying bacteria) and conversion of nitrites to nitrates by Nitrobactor. 
(iv) Denitrifications is breakdown of nitrates to free nitrogen by Pseudomonas (denitrifying bacteria).

The removal of the top fertile soil by water, wind or by other means is called soil erosion.
Measures for prevention of soil erosion:
(i) To retard the speed of flowing water in hilly or sloping areas, terracing practice should be adopted.
(ii) Trees should be planted on barren land.

Following are some of the causes of soil erosion:
(i) Deforestation
(ii) Leaving land uncultivated for long time
(iii) Excessive overgrazing 
(iv) Urbanisation
(v) Industrialization
(vi) Removal of top soil by wind or water. 

Top soil: The topmost layer of the soil which contains soil particles, humus and living organisms is called top soil.
Two factors are
(i) The average size of soil particles.
(ii) The amount of humus and the microscopic organisms found in it.

Type of soil depends upon:
(i) the average size of soil particles,
(ii) the amount of humus and
(iii) the microscopic organisms found in it.

The Lichen grow on rock stones and help in the soil formation.
Mode of Action: The Lichens while growing release certain substances that cause the rock surface to powder down and form a thin layer of soil.

Our atmosphere acts as a blanket because:
(i) It keeps the average temperature of the earth fairly constant during the day.
(ii) The atmosphere prevents the sudden increase in temperature during the daylight hours.
(iii) During the night, it slows down the escape of heat into outer space.

Atmosphere of our earth consists of many gases like nitrogen, oxygen, carbon dioxide and water vapour that helps life to exist on the earth. The percentage of in earth's atmosphere is very low. The major component of the atmosphere found on the Venus and Mars is carbon dioxide (95-97%), which does not support life. 

(i) Global warming 
(ii) Environmental pollution
(iii) Depletion of ozone layer.

Higher concentration of greenhouse gases, such as methane, nitrous oxide etc. in the atmosphere causes absorption of reflected heat (infrared radiations) or avoid their escape into the space. This phenomenon cause greenhouse effect. This leads to rise in the temperature of earth's atmosphere throughout the world causing global warming. This global warming caused by greenhouse gases like \({ CO }_{ 2 },{ CH }_{ 4 },\) etc. leads to melting of glacier and polar ice. This would cause rise in level of sea and other climatic changes.