>1.4×10^9 lightning bolts/year
||Olivia P. Judson, The energy expansions of evolution, Nature ecology & evolution, 28 April 2017 | Volume: 1 | Article number: 0138 p.5 left column 3rd paragraph
|| Christian, H. J. et al. Global frequency and distribution of lightning as observed from space by the Optical Transient Detector. J. Geophys. Res. 108, 4005 (2003) DOI: 10.1029/2002JD002347 link
||P.5 left column 3rd paragraph: "Of all the planets and moons in the Solar System, Earth is the only one to have fire. This is because, to have fire, all of three conditions must be met. (1) Fire needs a source of ignition—such as lightning strikes. Throughout Earth history, these have been abundant, today, there are more than 1.4 billion lightning strikes per year (primary source), of which an appreciable number ignite wildfires (ref 116). Lightning occurs on other planets (ref 117), but none of these meets the other two conditions [oxygen & fuel]."