Sacred Water

Humans have always understood the significance of water for life and this is well documented in ancient cultures and religious practices. In greek mythology, crossing the river Styx symbolised the journey to the afterlife, where water serves as a metaphor for transition between between life and death. Ancient Egyptian cosmology has a creation myth that involves water as the origin of life, where water represents the primordial chaos which the world emerged. Although impossible to know for certain, there are good reasons to believe life did first evolve in water and I have previously investigated its cosmic origins here.

Although ancient myths are symbolic, the truth that water is indeed essential for life on Earth is certain and there are a great number of scientific reasons for this. This article explores the unique properties of water and Earth’s systems that make life possible.

Water Chemistry

The chemical properties of water are quite unusual and the molecule configuration leads to its many useful properties as we shall see. So to start at the beginning is to start with the chemistry. Water is of course 2 x Hydrogen atoms and 1 x Oxygen atom that form 2 covalent bonds. Each Hydrogen atom is seeking another electron and the Oxygen atom is seeking 2 more, so they unite and team up. Covalent bonds are formed and a non-symmetrical molecule is formed, which then creates a slight differential charge across the molecule as known as a dipole. Covalent bonds are strong and take a significant amount of energy to break. Each water molecule forms a weaker Hydrogen bond with other water molecules. The partial positive charge on hydrogen atoms is attracted to the partial negative charge on oxygen atoms of neighbouring water molecules. These bonds can be seen below.

The dipole within each water molecule leads to Hydrogen bonding between water molecules, which in turn results in the many processes that are essential for life on earth. These bonds are weaker than covalent bonds and give water many of its unique properties such as high boiling & melting points, high surface tension and the ability to dissolve polar substances. Next we shall explore why each of these characteristics is essential for life on Earth.

High Heat Capacity

Water has an unusually high specific heat capacity, meaning it can absorb a lot of heat without changing temperature quickly. Hydrogen bonds act as an energy "buffer," delaying kinetic movement.

Mechanism: Hydrogen bonds between water molecules require significant energy to break. When heat is added to water, much of this energy is absorbed to disrupt the hydrogen bonds before the molecules can increase in kinetic energy (before the temperature rises). Conversely, as water cools, hydrogen bonds reform, releasing energy and slowing the rate of temperature decrease. Sweating and transpiration rely on water's high heat of vaporisation, a property stemming from hydrogen bonds. These processes cool organisms by removing heat.

Outcomes: This buffering effect stabilises temperatures in aquatic environments and organisms. For example, large bodies of water act as thermal reservoirs, protecting ecosystems from extreme temperature swings. In humans, water in the blood and tissues helps maintain a stable body temperature. This property is why oceans regulate Earth's climate, absorbing and redistributing heat over vast areas. This stabilises the Earth's climate and helps regulate temperature in ecosystems, making it a crucial factor in maintaining a habitable environment. Its all great for making a cup of tea or an espresso!

Cohesion & Adhesion

Water molecules are sticky and either stick together through hydrogen bonding or stick to unlike molecules.

Mechanism: Through cohesion water molecules stick together due to hydrogen bonding, allowing surface tension to form. This is why water droplets hold together and why insects can walk on water. Adhesion occurs when water molecules form hydrogen bonds or other interactions with polar or charged surfaces like the cellulose walls of plant xylem or soil particles.

Outcomes: This interplay of cohesion and adhesion drives capillary action, where water rises in narrow tubes against gravity. In plants, this mechanism allows water and dissolved nutrients to move from the roots to the leaves, sustaining photosynthesis and overall plant health. Some organisms, like water striders, exploit the surface tension created by hydrogen bonds to move across water surfaces. Through capillary action, hydrogen bonding enables water to travel from roots to leaves in plants via xylem. Cohesion keeps the water column intact, while adhesion helps water stick to the walls of the xylem.

Universal Solvent

Water is often called the “universal solvent” because it can dissolve more substances than any other liquid. This property allows it to carry nutrients, minerals, and chemicals within organisms, through ecosystems, and across the planet's surface, facilitating essential biological and geochemical processes. Water’s polarity, enhanced by hydrogen bonding, allows it to dissolve a wide range of polar substances, including salts, sugars, and gases. This makes water an ideal medium for transporting nutrients and waste in organisms.

Mechanism: Water’s hydrogen bonds create a polar environment, where the partial positive charges on hydrogen and partial negative charges on oxygen interact with solutes. Polar and ionic compounds (like salts) are dissolved as water molecules surround and stabilise individual ions (hydration shells), breaking ionic or molecular bonds.

Outcome: This property enables the transport of essential nutrients and ions in biological systems. For instance, in the human bloodstream, water dissolves electrolytes (like sodium and potassium) and biomolecules (like glucose) for distribution to cells.

Density and Ice Formation

Hydrogen bonds cause ice to be less dense than liquid water, making it float. This property insulates aquatic ecosystems, protecting life during freezing temperatures.

Mechanism: At lower temperatures, hydrogen bonds between water molecules become more structured, forming a hexagonal lattice. This lattice maximises the space between molecules, making ice less dense than liquid water. In liquid water, hydrogen bonds are constantly breaking and reforming, allowing molecules to pack more closely and increase density.

Outcome: Ice floats on liquid water, insulating aquatic ecosystems and preventing entire bodies of water from freezing solid. This property ensures that life can survive beneath ice layers in cold climates. If ice was denser than liquid water, it would sink and remove the insulation it was providing and expose more water to colder temperatures and create more ice. In cold climates the entire water body could freeze.

Facilitating Chemical Reactions

Water’s properties make it an exceptional medium for facilitating chemical reactions, both in cellular processes (within life forms) and in the broader natural environment.

Solvent for Biochemical Reactions: Water’s polarity allows it to dissolve polar and ionic substances by surrounding solutes with hydration shells, reducing intermolecular forces and enabling dissociation. Reactants freely interact in aqueous solutions, facilitating metabolic reactions (e.g., glucose metabolism) and transport of nutrients and waste in biological systems.

Stabilises Molecular Structures: Water forms hydrogen bonds with biomolecules, maintaining their specific shapes and interactions (e.g., DNA helix, protein folding). Ensures structural integrity of DNA, proteins, and cell membranes, enabling proper function in cellular activities like replication, signalling, and catalysis.

Water Enables Energy Release Through ATP Hydrolysis: Water directly participates in the hydrolysis of ATP, releasing energy needed for cellular functions. ATP hydrolysis is the universal energy currency in cells, powering muscle contraction, active transport, biosynthesis, and signalling. Every heartbeat, nerve impulse, and molecular assembly relies on water-driven ATP hydrolysis.

Liquid water is essential for facilitating these chemical reactions and various species have found ways of using it for their life functions. Jellyfish contain the most water by percentage at around 98% and the Tardigrade can survive with as little as 2% for extended periods of time!

The Goldilocks Zone

Despite the miraculous abilities that water possess, they are not enough alone to support life on Earth. Fortunately for us all, Earth is located within the Goldilocks Zone, or habitable zone, which is a region around a star where conditions are "just right" for liquid water to exist on the surface of a planet. Liquid water is considered essential for life as we know it, making the Goldilocks zone a key concept in understanding Earth's ability to support life and in the search for life on other planets. Here we find water is liquid, gas and solid phases.

The Goldilocks Zone for our Solar System is estimated to range from about 0.95 to 1.4 Astronomical Units (AU).

Inner Edge (~0.95 AU): Closer to the Sun, water would evaporate due to the greenhouse effect (Venus).

Outer Edge (~1.4 AU): Farther from the Sun, water would freeze due to insufficient heat (Mars).

Earth Provides

The Goldilocks zone seems to be essential, but it only lays the first foundations and the Earth needs to do the rest.

Abundance in Liquid Form: Earth has an abundant supply of liquid water, unlike any other known planet. The right balance of distance from the Sun and atmospheric conditions keeps water primarily in liquid form, which is essential for supporting life as we know it.

Atmosphere: Earth's atmosphere contains greenhouse gases (like carbon dioxide and water vapor) that trap heat, maintaining a climate suitable for life. Without this balance, Earth could have ended up like Mars (too cold) or Venus (too hot). This creates a pressure of 1 atm and this means water boils at 100 degrees C. 2 atm of pressure would create a higher boiling point of 120 and 0.5 atm would reduce the boiling point to around 80 degrees C. The earths atmosphere and ojur place in the goldilocks zone means that we can experience liquid, solid and gaseous water.

Magnetic Field: Earth’s magnetic field protects the atmosphere from solar wind, preventing the loss of water and other essential molecules to space.

Geological Activity: Plate tectonics and volcanic activity help recycle carbon and other essential elements, regulating the climate over geological timescales.

Earth’s Water Cycle: The water cycle on Earth—encompassing evaporation, condensation, precipitation, and infiltration—ensures the continuous movement and renewal of water, distributing it across different regions and enabling diverse ecosystems to thrive.

Climate and Weather Influence: Water in oceans, rivers, and the atmosphere plays a major role in climate regulation and weather patterns, helping to distribute solar energy around the planet through currents and atmospheric processes.

What are the alternatives?

There are some alternatives to H2O for life as we know it, but the list is quite terrifying and as you can see below, they just don’t compare to water. Other liquids, like methane (CH4), are not dipoles because their molecular shapes are symmetrical, so the polar bonds cancel each other out, resulting in no net dipole moment. The combination of asymmetry and electronegativity differences makes water uniquely polar compared to many other liquids.

So is Water Essential for Life?

Yes absolutely, at least for our Earthly life forms so lets take a moment to acknowledge that and take great care of our water! When looking away from earth, my personal opinion is that its not essential for life, but can certainly lead to life elsewhere. We are very likely limiting ourselves with our natural anthropological perspective and from a sample size of one. This lacks imagination. But, if we could determine that life originated and evolved more than once on Earth, then that would be more compelling. However, just because our lifeforms work with the conditions of our blue planet doesn’t mean that these are universal truths. I am more open minded to what other life could be like and admire the Polish authors Stanisław Lem’s ideas that alien life could be so….. well alien, that we may not even recognise it as life at all if we lived with it in our homes or be able to understand it if if were to reach out to us.

The Miracle Molecule: How Water’s Properties Sustain Life on Earth