  Since the Archean, N2 has been a major atmospheric constituent in Earth's
atmosphere. Nitrogen is an essential element in the building blocks of life,
therefore the geobiological nitrogen cycle is a fundamental factor in the long
term evolution of both Earth and Earth-like exoplanets. We discuss the
development of the Earth's N2 atmosphere since the planet's formation and its
relation with the geobiological cycle. Then we suggest atmospheric evolution
scenarios and their possible interaction with life forms: firstly, for a
stagnant-lid anoxic world, secondly for a tectonically active anoxic world, and
thirdly for an oxidized tectonically active world. Furthermore, we discuss a
possible demise of present Earth's biosphere and its effects on the atmosphere.
Since life forms are the most efficient means for recycling deposited nitrogen
back into the atmosphere nowadays, they sustain its surface partial pressure at
high levels. Also, the simultaneous presence of significant N2 and O2 is
chemically incompatible in an atmosphere over geological timescales. Thus, we
argue that an N2-dominated atmosphere in combination with O2 on Earth-like
planets within circumstellar habitable zones can be considered as a
geo-biosignature. Terrestrial planets with such atmospheres will have an
operating tectonic regime connected with an aerobe biosphere, whereas other
scenarios in most cases end up with a CO2-dominated atmosphere. We conclude
with implications for the search for life on Earth-like exoplanets inside the
habitable zones of M to K-stars.
