Phosphates form the backbones of DNA, RNA and ATP (the chief source of energy for cells), and are major components of bones, teeth and cell membranes.
But about 4 billion years ago, while there was likely plenty of water and carbon dioxide in the atmosphere to work with, which are also essential for life's fundamental molecules, most of the planet's natural phosphorus was bound up in insoluble rock, and impossible to combine into organic phosphates. How, then, did Earth acquire these critical compounds?
Lightning strikes on early Earth potentially formed 10–1000 kg of phosphide and 100–10,000 kg of phosphite and hypophosphite annually. Therefore, lightning could have been a significant source of prebiotic, reactive phosphorus which would have been concentrated on landmasses in tropical regions. Lightning strikes could likewise provide a continual source of prebiotic reactive phosphorus independent of meteorite flux on other Earth-like planets, potentially facilitating the emergence of terrestrial life indefinitely.
Source: Hess et al., 2021. Nature Communications. doi: 10.1038/s41467-021-21849-2.