is a tiny impurity. A touch of salt

a grain of clay did absolutely crucial to the raindrops existence

In fact, without these microscopic pieces of dirt there would be no rain because

water vapor can't condense into droplets on its own,

which is kind of weird because water molecules like each other

If they didn't, they wouldn't cling to each other like this. And in the air

vaporized water molecules collide and stick together all the time

But they also break apart all the time thanks to bond breaking heat energy

Only when air cools down past a certain point called the dew point

does this breaking apart slow down enough for little clusters of water

molecules to grow into droplets

But actually that's only true if the cluster is big

to start with. If it's too small, it's surface is curve

the molecules on the outside have few neighbors to bond to, which makes them

easy to break off

So the cluster as a whole has higher chances are losing molecules than gaining them

even below dewpoint, which means that up until a certain critical size

a cluster chances of shrinking are better than it's odds of growing

Unfortunately that critical size is 150 million molecules

And while there are millions of 5 molecule clusters in a golf ball sized volume of air to dewpoint

odds are that only one of those clusters will grow to a size of 10

and you'd need a golf ball of air ten million miles across to find a

single fifty molecule cluster

which basically means that clusters of water molecules never get to that 150 million mark on their own.

Fortunately they don't have to, they can start

of it that critical size by condensing onto one of the good Jillians of little pieces of little dirt

floating in our atmosphere, and then grow and grow until their are droplet in a rain cloud

and ultimately if these little pieces of dirt surrounded by water

that make life possible on our big piece of dirt surrounded by water

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