What is special about nitrogen and what is its main function in the atmosphere?

Nitrogen is special in that it makes part of the nucleic acids namely DNA and RNA without which there can be no continuity of life  on earth.

Nitrogen is essential to all living systems. About  78 percent of earth's atmosphere is made up of nitrogen gas.

The function of nitrogen in the atmosphere is that forms part of the nitrogen cycle which is essential to life on earth.

During electrical storms, large amounts of nitrogen in the air are oxidized and united with water to form an acid that falls to earth in rainfall and deposits nitrates in the soil.

Plants take up nitrates, essential to plant growth and development,  and convert them to plant protein. Animals consume the plants as food and so life is sustained.

answer; 60-100; beats per minute

he forelimbs below belong to four species that descended in a direct line from the ancestral mammal shown above. of the four descendants shown, which species most likely appeared earliest in evolutionary history?