Earth's atmosphere is a layer of gases surrounding the planet Earth and retained by the Earth's gravity. It contains roughly 78% nitrogen and 21% oxygen 0.97% argon and carbon dioxide 0.04% trace amounts of other gases, and water vapor. This mixture of gases is commonly known as air.
Earth is the only planet where the environmental conditions are favorable to support life. Different layers of the earth are atmosphere, geosphere, biosphere and hydrosphere.
Atmosphere surround the earth like the blanket and protect the organisms from the harmful sun rays. Atmosphere is the envelope of all the gases that surrounds the earth. Atmosphere is important for the maintenance of life on the planet earth.
Fossils; present-day species have been shown to be closely related to some extinct species from the past as shown by fossils.
Molecular biology; biochemical analysis of biomolecules such as DNA and proteins show that species are related to one another and share a common ancestor.
Anatomy; Certain anatomical structures between species have shown convergent or divergent homology indicating sharing a common ancestry.