What makes water essential for life?
Water is everywhere around and within us. Nearly 70% of our planet’s surface is covered with it. Nearly 60% of the human body is made of it. It is the most abundant compound found in the universe mainly because it is made up of hydrogen and oxygen (H20) which themselves are among the top 3 abundantly found elements of the known world.
Even though the water is ubiquitous, most of what we see, whether in our solar system or beyond, is in the form of vapor or ice. Liquid water is hard to come by. Water remains liquid over a very short range (relatively speaking) of temperature, but in fact, it is this short range and the liquidity of water, which is of tremendous interest to the enthusiasts who are not only looking for extraterrestrial life but also for potential habitable planets where human species could migrate in distance future for survival or expansion.
The mantra of all the space agencies of the world, when it comes to the search for suitable places where life could exist is, “follow the water”. Dedicated telescopes are deployed at various corners of our globe and orbits around the Earth, and there are people making careful observations on them, day and night, tirelessly, just to search for and catalog the planets which falls in the so called “habitable zone”. This zone is referred to the right kind of distance the planet has from its host star such that water could remain in the liquid form on its surface.
But why only water? Why do people think life is where water is? Why people are not searching for something else so intensely? Well, this is because we have seen life that could exist without oxygen, sunlight, and other building blocks but, till date, we have not seen even a single organism that could live without water.
There are a category of organisms who don’t need oxygen to generate energy for their metabolic processes. Plants don’t need oxygen to survive, they stay up and running consuming carbon dioxide for their food. There are organisms living on the deep ocean floors who have never seen sunlight but still goes about their business just fine. But every living thing need water to survive. Life ceases to exist without water.
These are the crucial properties water possess that makes it conducive to life as we know it.
Ice floats on Water
Ice is a peculiar solid form. It floats in the liquid water. Unlike most of the materials, the solid state of water is less denser than its liquid state. This is extremely rare. Only few substances exhibit such behavior.
If Ice didn’t float on water, life on our planet wouldn’t have existed. Since the first life arose in water, if Ice was denser, in winters it would have filled the oceans from bottom up. Forcing the life forms to move upwards towards the top surface of the ocean where they would have frozen to death due to colder atmosphere.
But because Ice floats on water, the marine life survives the harsh winters. In winters when the temperature reaches 0 degree Celsius, the top surface of the lake freezes, and converts to ice. But this process happens from top-down. The ice formed at the top surface doesn’t sink to the bottom of the lake, rather it stays afloat protecting the water below it from extreme temperatures of the atmosphere. It acts as an insulating layer due to which the rest of the water below the top surface stays warm, and in its liquid form, and the marine life sustains in it.
Universal solvent
Our body needs nutrients and vitamins to function. We need a medium to intake those items easily. Our body also generates waste and toxic components which it wants to throw out to prevent damages. We also need a medium to deposit these unwanted items. Turns out, water is the perfect medium for both the tasks.
Water does this because it is an amazing solvent, in fact, it is called the Universal solvent. Ever wondered why salt, sugar, and pretty much anything when mixed in water, gets dissolved in it seamlessly. Water is able to do this because of a peculiar chemical concept called polarity. In simple terms, all it means is the chemical structure of the water is such that it can easily mix with molecules of other substances.
Also, liquid state of matter is a much better transport system to take something in and out of the body, than its solid state. Water stays liquid for a wide range of temperatures on our planet, hence it is the ideal medium to transport nutrients in our body and dispose the toxic waste by dissolving both of them in it.
Stickiness
Water molecules sticks to one another. Hydrogen atom of one water molecule bonds with oxygen atom of the neighboring water molecule. Water has this property again thanks to its polarity.
This is very helpful because it enables water to get consumed or circulated as a constant stream. Plants suck water from the ground using their roots. If the water didn’t posses the stickiness, plants could have only consumed a handle of water molecules, which would have been detrimental to their survival.
Thanks to its stickiness, water could be consumed by the plants upwards from the ground against the force of gravity. Similarly, water also gets circulated in our blood vessels upwards against gravity.
Distribution
We are lucky to have the right kind of temperature to naturally turn water to its gases state. This helps water to be distributed across the planet. The sunlight cause the water to convert to water vapor. The vapor molecules, being less denser, floats in the atmosphere.
They have affinity towards one another (thanks to their stickiness property) and forms a cloud. The wind then takes them far and wide, across the length and breath of the planet, where they open their gut to shower rain.
Temperature Regulator
Water has a high heat capacity. All it means is, water can absorb the excess heat of the surroundings, and keeps it moderate. They become the giant heat sinks which prevents high temperatures fluctuations.
Due to this property the coastal cities have less temperature variance than the drier in-land regions. The temperature of Mumbai varies between 20 degrees to 40 degrees throughout the year due the presence of the Arabian Ocean whereas Delhi sees the variance of 0 degree to 50 degrees.
Water in our bodies helps regulate our body temperature. In fact, this is the principle behind sweating. When the temperature of your body increases, water molecules take the excessive heat within them and comes out of the body in the form of sweat leaving the body cooler.
Due to these 5 properties, water is extremely conducive for life. That doesn’t mean all kinds of life out there would be based on water, but just the life, as we know it. We certainly want to hinge our hopes on water, and hence, water is the most sought after molecule in our quest for life in outer space.
Side Note: There are two other candidate molecules, Ammonia (NH3) and Methane (CH4), on which life could be based elsewhere. They exhibit similar properties like water. Both are made up of hydrogen which is abundance in the universe. Both are polar molecules like water which makes them a good solvent to transport vitamins. In fact, on Saturn’s moon Titan, methane exists in the liquid form, and hence scientists are curious to search for life forms there.
