So this is when they point out that rain drops in fact Can Not fossilize but if conditions are right, the impact that the drop makes when it hits the ground WILL in fact cause a fossilization event. Those conditions require an ongoing volcanic event that is regularly depositioning fine layers of ash. It has to rain soon after an event and then the volcano needs to lay a fine layer over the rain drops. All of this effort to figure out what kind of atmosphere our planet used to have.
Check out the pic above for what the ancient rain drops look like fossilized and here is the link to the Dvice article