No known form of life can exist without water.
Our bodies need to be flooded with water all the time because without it, we wouldn’t be able to move anything to where it’s supposed to go. Water is a chemical that is specially equipped to move other chemicals through the pipelines of our blood system, among other things.
To find out why, it’s going to help if we zoom right out and look at our planet as a whole.
Our planet is fortunate enough to be saturated with water. It covers 71% of the Earth’s surface as streams, lakes, oceans, glaciers, icebergs, clouds, dew, rain, snow, and fog.
Science fiction author Arthur C. Clarke said:
How inappropriate to call this planet Earth, when clearly it is Ocean.
When biologists say the Earth is in the ‘Goldilocks zone‘ that’s the perfect temperature range for life, they often mean that it’s perfect for water.
If it was too hot, the oceans would boil away and permanently become clouds. Too cold, and the icecaps would expand to cover the planet.
Earth’s temperature is so perfectly balanced that a molecule of water can evaporate, condense, and freeze all in a single day.
It will travel vast distances as a cloud, and in the cold of the upper atmosphere it will freeze and fall as snow.
It will collect in lakes and oceans where the sun evaporates it, returning it to the clouds in the sky.
The Earth is enraptured with the movement of water.
But what makes water the chemical of life is the fact that it’s a ‘solvent’, which means there is something about its molecules that makes it good at dissolving other chemicals.
You probably know that water is also known as H²O, so it contains one oxygen atom and two hydrogen atoms. They are joined in a covalent bond, which means the oxygen has a slight negative charge and the hydrogen has a slight positive charge.
But you might not know that the water molecule has a peculiar shape. The oxygen and the hydrogens don’t form a straight line, they form up in a ‘v’ shape.
The ‘v’ shape makes the oxygen stick out, which gives that end of the molecule a subtle negative charge, and the hydrogen ends a subtle positive charge. This tiny, subtle difference in the molecule has a cascade of effects when one thousand trillion water molecules join together to form a drop of water. It’s these effects that makes life as we know it possible.
First among them is that it makes water molecules attracted to other water molecules. This results in what’s called ‘surface tension’, and it’s why leaves and bugs can lie on water like it is a solid surface. The attraction forms an invisible lattice that supports the leaf or bug falls and keeps it afloat, even though they are heavier than water.
You can see the effect of this lattice in a pool, where the water seems to hold on to the swimmers for just a few extra moments before breaking.
The second effect of water’s attraction is that it dissolves certain things really well, like salt.
Salt is an ionic molecule, which means that its molecules are entirely held together by mutual attraction caused by their charged atoms.
Water breaks them apart by being more attractive to them than each other, and suspends them among its own molecules. So when you drop a pinch of salt into a glass of water, it disappears, pulled into solution with the water itself.
Not all molecules dissolve in water, but water’s charge interferes with a great many of them in a similar way.
Most water on Earth contains molecules that are mixed up or dissolved within it, and it carries them around the planet like a giant ladle that mixes up the soup of materials on the Earth.
In doing so, the movement of water brings our planet alive.
Life learned very early in its history to use these same properties of water for its own needs. It floods its own cells and bodies with water through its bloodstream and uses it to transport proteins, DNA, polysaccharides, as well as dissolved chemicals like salt around its body, like a microcosm of the Earth itself.
There are no other substances that we know of that have the unique combination of water’s abundance and special abilities.
The lasting effects of the simple chemical rules that water follows are visible everywhere. It has carved valleys, fjords, and canyons in the crust of the Earth, and forms our oceans, ice caps, and weather.
Without water, our planet would neither have spectacular scenes like the one below, nor any life to wonder about them.