Where does the ni­tro­gen in the air come from?

BBC Earth (Asia) - - Q&a -

Ni­tro­gen makes up 78 per cent of the air we breathe, and it’s thought that most of it was ini­tially trapped in the chunks of pri­mor­dial rub­ble that formed the Earth. When they smashed to­gether, they co­a­lesced and their ni­tro­gen con­tent has been seep­ing out along the molten cracks in the planet’s crust ever since. Ni­tro­gen can only be used by liv­ing or­gan­isms af­ter it has been ‘fixed’ into more re­ac­tive com­pounds such as am­mo­nia or ox­ides of ni­tro­gen. Ni­tro­gen fix­a­tion is car­ried out by bac­te­ria, al­gae and hu­man ac­tiv­ity, and once or­gan­isms have ben­e­fited from it, some of the ni­tro­gen com­pounds break down and go back into the at­mos­phere as ni­tro­gen gas. Along with top-ups from vol­canic erup­tions, the ‘ni­tro­gen cy­cle’ has kept the level pretty con­stant for at least 100 mil­lion years. RM

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