What is the origin of the dominant atmospheric nitrogen content in Earth's atmosphere? Comparing the atmospheric compositions of Earth with our nearest neighbours:



As the table shows, the Earth's atmospheric nitrogen concentration is 78%, compared to 3.8% for Venus and 2.7% for Mars Image source.

I have read the excellent question and answer Why do Earth and Venus have different atmospheres?, but the answer focuses on the $\ce{CO2}$ content of the planets, this question is about the $\ce{N2}$ content. Also, have read Why do some planets have lots of $\ce{N2}$ and others none?, but in this question, I am looking at how nitrogen concentrations dominated over the other chemicals in Earth's atmosphere, not looking at similarities between planetary processes.

In modern Earth, the nitrogen cycle maintains nitrogen levels, however the early pre-biotic atmosphere, was believed by


  most of the scientific community now believes that the early Earth's atmosphere was not reducing. Instead, scientists beleive the atmosphere was full of oxidants, such as $\ce{CO2}$ and $\ce{N2}$.


Source: Duke University Pre-Biotic Earth webpage

What is the origin of the dominant atmospheric nitrogen content in Earth's atmosphere?
According to the recent paper in Nature Geoscience: Nitrogen speciation in upper mantle fluids and the origin of Earth's nitrogen-rich atmosphere, $N_2$ originates from regions of the Earth where plates are converging.  Venus and Mars lack plate tectonics and therefore lack $N_2$ in their atmospheres.  In other regions of Earth upper mantle, and in Venus and Mars, nitrogen is expected to exist as aqueous ammonium and not enter the atmosphere.