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| The Nature of Life |
One of the most intriguing applications of clear thinking is to gain a better understanding of the nature of life. One cannot account for human life without first considering all other forms of life on Earth. And one cannot account for life on Earth without first considering what is happening in the rest of the universe.
Everywhere we look in the very large realm, we find billions of galaxies filled with billions of stars. Each star began as a cloud of hydrogen atoms, and each of those clouds shrank under the force of gravity until a nuclear furnace was ignited at its core. The resulting nuclear reactions systematically built heavier atoms out of hydrogen, and in so doing generated enough energy to temporarily halt the gravitational contraction. Excess energy was radiated away as light.
That is what starlight tells us is happening across the universe. For billions of years, the force of gravity has led to the formation of stars with hot cores; nuclear reactions in those cores have converted simple hydrogen atoms into heavier atoms (ultimately iron and nickel); and excess energy has been radiated away as starlight.
The existence of starlight dramatically illustrates the conversion of primal energy into starlight. Each photon of starlight then undergoes a systematic change – over time it is eventually converted into a set of less energetic photons, each with a longer wavelength . This conversion occurs in a variety of interactions with matter that is scattered through space. And those interactions provide a connection between starlight and life on Earth.
From the point of view of the Universe, the early Earth was just a tiny lump of iron and nickel orbiting an average star. After comets bombarded the Earth, it became a bit more interesting. The comets left a thin scum of lighter rocks that formed the continents, water that formed the oceans, and gases that formed the atmosphere.
Photons from the Sun poured down on a variety of atoms and molecules on the surface of the Earth. Carbon atoms were abundant, and easily formed endless combinations of molecules. A few of these molecules turned out to be especially adept at extracting and converting energy from the Earth’s environment, and life began. (The concept of evolution is treated in more detail in section 5.4)
Ribonucleic acid (RNA) was one of those molecules, and is thought to be the fundamental building block of all life on Earth. RNA is a polymer consisting of ribose and phosphate groups. Each of these groups in the RNA polymer chain is adorned with one of four side-groups: adenine [A], uracil [U], cytosine [C], or guanine [G]. The structure of a particular RNA molecule can be described as a string of letters using A, U, C, and G; corresponding to the side-groups along its length. The A-U-C-G coding along an RNA molecule allows it to function either as a catalyst to initiate other chemical reactions, or as a store of information. RNA molecules have been found to play an essential role in the machinery of every living cell, and RNA has the potential to reproduce itself – the essence of life.
Collectively, living organisms on Earth behave like low temperature energy converters. Plant cells absorb photons from the Sun and then use that energy to power their activities. As cells, individually and collectively, slowly rework the surface of the Earth, they radiate their excess energy as heat in the infrared region of the spectrum. Thus, living cells participate in the universal conversion of higher energy photons to more numerous lower energy photons. The life force we know and experience can be traced back to cosmic origins! There is a subtle, but very important distinction between the energy processes on stars, like the Sun, and planets like the Earth. A star is essentially a closed system – virtually all of its energy derives from its own primal gas cloud. In contrast, a planet orbiting about a star is an open system – the planet’s energy resources are continuously augmented by photons from the parent star.
Normally, water runs down hill, but the Sun continuously pumps energy into the Earth’s biosphere. Water can be evaporated, carried uphill by winds, and deposited as snow at the top of mountains, over and over again. Just as solar energy drives the water cycle on Earth, it has also driven the evolution of complex life forms. If the Earth were drifting alone in the cold of interstellar space, it is very doubtful that any kind of life would have emerged on it.
The Earth has an age of about 4.6 billion years, and at the moment human beings are at the apex of Earthly evolution. Our bodies still retain that cosmic drive to convert energy: to reproduce, to be active, to create, and to destroy. The genes in every cell in your body want to be replicated and to get to work converting energy from highenergy photons to more low-energy photons.
From the universe’s point of view, you are a tiny, low-temperature energy-converter. From the viewpoint of life on Earth, your significance is analogous to that of a leaf on a tree. The branch on which you have grown is more important than you. The trunk is more important than any individual branch, and the forest is more important than any individual tree. You are a tiny component in the activities of the universe.
And yet!
From you and your family’s point of view, you have a valuable and unique personality. You actively participate in the social life of humans, and you have the amazing ability to be aware of the grand scheme being played out around you. You can observe the universe and try to predict what it will do next. You can even try to influence the flow of the universe in your immediate vicinity. You have the ability to ease the burdens of your fellow humans, and to make your brief appearance in the universe a grand occasion.
