We will not fully understand life until we find life that has evolved on another planet. Biologists have determined how Earth life evolved and the conditions under which such life is possible. Most biologists share a speculation that life can, and probably has evolved elsewhere in the Universe. But that is speculation until we have an independent example. The recent searches for planets orbiting other stars focus on conditions meeting the narrow limits of Earth in light, temperature, and chemistry. These conditions are determined by the properties of water.
Hydrogen is the most abundant element in the Universe: 74-percent of ordinary matter. Oxygen is about 1-percent. The other elements are found in diminishing amounts. Carbon, Nitrogen, Iron, and Copper are necessary; but Hydrogen and Oxygen make up the greatest components of living organisms and, in the form of water, are absolutely critical for life on Earth.
Chemists have pictorial ways to represent atoms and molecules. None of these are real, in the sense of being an exact picture. The shared electron model, where the bond is shown as paired electrons, is useful to show how atoms react to form compounds. The ball and stick model is commonly used to represent the structure of drugs. You can see all the different representations by searching “water molecule” and looking at the pictures.
Imagine mixing a container of Hydrogen and a container of Oxygen. The Hydrogen atoms from one container have shared an electron, bonding to form molecules (H2). The Oxygen atoms from the other container can share an electron and have bonded to form molecules (O2). If you introduce a little energy, in the form of a spark, the mixture explodes with some violence to form… Water. The explosion releases energy in the form of heat and the water is much more stable.
This reaction is properly written as 2H2 + O2 = 2H2O to balance the equation. Anton Lavoisier revolutionized chemistry by establishing this concept of combustion and identifying the component “Oxygen” – giving rise to modern chemistry and, ultimately, the chemical industry in the 19th-century.
Consider water, H2O. It is composed of one oxygen atom bonded to two hydrogen atoms. An Oxygen atom has 6-electrons capable of being shared. A Hydrogen atom has only 1-electron capable of being shared. The unshared electrons of the Oxygen atom tend to arrange themselves together, away from electron shared with Hydrogen. This reduces the repulsion force between the electrons in the system. The result of this rearrangement makes the water molecule act as if it were “V” shaped, with Oxygen at the apex. The shared electrons form bonds at an angle of 104-degrees and each bond about 3.8-billionth of an inch long.
What is important is that this V-shape creates the forces between water molecules. These forces determine many of the properties of water, such as boiling point, melting point, solvent properties, and why ice floats. All of which are very important to life.
The lopsided arrangement of more negative electrons on one side of the molecule means that, although the total electrical charge is zero, the four electrons gathered at one end of the molecule make that end slightly more electrically negative. This tends to attract the Hydrogen end of another water molecule, forming a weak bond called a “Hydrogen bond”. That weak bond is what gives water its “surface tension”. You have seen insects run on the surface of still water because of the weak bond (surface tension) between all the molecules at the water surface. It also accounts for capillary action, where water flows of its own accord up a narrow tube. Tiny primitive organisms depend entirely on capillary action and surface tension for their survival. Larger, more complex organisms evolved later with pumping mechanisms to move water or blood.
Specific Heat is a measure of how much energy must be absorbed by water to increase its temperature and how much heat is given off by water to a colder environment. Adding heat to water, as in your water heater, causes the water molecules to jostle about and move. But the weak Hydrogen bond between water molecules must be overcome for this movement. The result is that water has a very high Specific Heat. This makes it a good cooling liquid, a good heat-transmitting liquid, and a good heat-storage liquid. It protects organisms from cold. The body of a 10-pound human infant contains about 7.5-pounds of water at a temperature of 98.6-degF. It takes 7.5-Btu of cooling energy to lower the temperature of that infant 1-degF. That is why a light insulating blanket keeps a well-nourished infant warm.
Even more important for life than Specific Heat is the fact that ice floats on water. Most liquids become more dense as they freeze because the distances between molecules becomes less as their thermal motion decreases, but the weak Hydrogen bonds between water molecules lock in the distance between them as the water crystallizes, so ice is about 9% less dense than liquid water, and floats. This was critical for the evolution of aquatic creatures. With good insulation they can live in the deeps below the ice. Life initially evolved in water.
Finally, water is an incredible solvent; an astonishing number of chemicals will dissolve in water. The weak Hydrogen bonds make one end of each water molecule negative with respect to the other end. Most chemicals react to such polar molecules, either being attracted to one end or the other. This attraction facilitates water’s ability to dissolve so many substances.
So, water is clearly the “magic stuff” for life on earth. It set the temperature range and chemical range for evolution and preservation of life. Possibly life would always evolve on similar water worlds. We can imagine that.
What we cannot imagine, at least yet, is the evolution of life on a different world with a temperature range outside that of liquid water, or a mineral composition not compatible with a water world. Or, indeed, what might happen if the conditions of Earth exceed the limits of life.
This article first appeared in the December 21, 2016 issue of the Rossmoor News, author Wayne Lanier, Ph.D.