In arid environments such as deserts, nitrogen is often themost limiting nutrient for biological activity. The majorityof the ecosystem nitrogen flux is typically thought to be drivenby production and loss of reactive nitrogen species by microorganismsin the soil.

Meter for meter, peatlands store more carbon
than any other terrestrial ecosystem. Covering only about 3% of Earth's
land area, they hold the equivalent of half of the carbon that is in
the atmosphere as CO₂.

Meter for meter, peatlands store more carbon
than any other terrestrial ecosystem. Covering only about 3% of Earth's
land area, they hold the equivalent of half of the carbon that is in
the atmosphere as CO₂.

Unsatisfied with merely halting environmental destruction, some conservationists are trying to reconstruct ecosystems of the past. Emma Marris travels back in time with the rewilders.