There is overwhelming objective evidence that the universe began about 13.8 billion years ago with a gigantic explosion that we call the “Big Bang.” The Big Bang, after cooling, produced the conditions needed to start the process of evolution, both on our planet Earth and theoretically on many other planets possessing the similar mild conditions amenable to life.
Formation of the Chemical Elements Necessary for Life as We Know It
In our universe, after the temperature of the Big Bang cooled below about ten billion degrees Kelvin, protons and neutrons formed lightweight chemical elements—initially mainly hydrogen and helium, with trace amounts of lithium and beryllium, according to some theoreticians’ calculations. All stars convert hydrogen to helium, with the by-products being heat, light, and subatomic radiation. Supernovas produced oxygen, carbon, sulfur, and nitrogen, as well as the higher atomic weight elements such as chlorine, sulfur, phosphorus, sodium, calcium, potassium, and magnesium. These elements were expelled into space. The last few seconds of existence of some supernovas may have produced heavier atoms such as iron (the core of the oxygen carrier in hemoglobin), cobalt (the catalytic center of vitamin B12), and copper (an essential carrier of electrons in the metabolism of glucose, fats, and many other biological molecules). We assume that there was some overlap between the nucleosynthesis of lighter elements by the Big Bang with the nucleosynthesis by supernovae. Even today, as our planet sweeps through space it picks up chemical elements that were ejected into space, along with meteorites of various sizes. It has been estimated that as much as one-quarter of household dust is of extraterrestrial origin. This means that we are made of the ashes and cinders of stars spewed into space, since all of the constituents of present living organisms originated from the initial Big Bang and subsequent supernovas.
There are an estimated one hundred to two hundred billion stars in an average galaxy. This means that based on the approximately five thousand extrasolar planets found by terrestrial astronomers to date, there are as many as 100 billion planets in each of the estimated two hundred to 1,200 billion galaxies in the known universe. At least an estimated 1 percent of these planets are assumed to be hospitable to life as we know it, places where evolution can occur.
The Inevitable Formation of Small Molecules Is the Prologue to Evolution
How the building blocks of proteins, called “amino acids,” were formed was the object of study of many researchers. In 1952, the pioneering experimenters Stanley Miller and Harold Urey synthesized amino acids by mixing water, ammonia, hydrogen, hydrogen sulfide, and methane (the compounds then thought to exist on a primitive, lifeless Earth) in a sealed flask. The flask was heated to boiling and electric sparks fired between electrodes to simulate lightning as the source of energy to initiate chemical reactions. (Recently, the number of lightning strikes on the planet Earth has been estimated at one hundred per second. Lengths vary, but each bolt contains up to a billion volts.) Other possible sources of energy are hot springs and the deep-ocean vents that exist at the boundaries of the tectonic plates that comprise Earth’s crust. These vents are of special interest because many release hydrogen sulfide gas. The sulfur in this gas could be incorporated into the essential amino acid methionine, as well as into other known biochemicals. Large meteorites composed partly of metals, which could act as catalysts when they struck the Earth, will have generated considerable heat on impact that could have lasted long enough to produce amino acids and the precursors of nucleic acids that comprise the genetic code. (About one hundred different amino acids were found in one uncontaminated meteorite.)
The Large Molecule Porphyrin Was t the Start of Evolution
With evolutionary modifications, this key molecule lies at the very heart of the plant and animal kingdoms. Porphyrin is found in chlorophyll, where it uses the energy from the sun to rip oxygen from carbon dioxide molecules, the waste-product of animals. Photosynthesis simultaneously traps energy from the sun in the form of high-energy bonds in the water-soluble circulating molecule adenosine triphosphate (ATP). Its energy can synthesize complex molecules in plants for growth and reproduction. Evolution took a giant short-cut by ingesting the photosynthetic mechanism found in micro-organisms into cells that later became plants. These organelles are now called “chloroplasts.” Humanity should now increase the efficiency of photosynthesis by making further genetic modifications to feed the ever-increasing population.
Animals use the food synthesized from plants to provide nutrition and energy, relying on oxygen carried by hemoglobin to perform metabolic oxidations. Hemoglobin also carries away waste carbon dioxide, which is recycled to plants. Hemoglobin, which contains iron, and chlorophyll, which contains magnesium, are two large, complex molecules that are related to each other because they are based on modifications of a small, five-atom ring consisting of four carbon and one nitrogen atom called “pyrrole.” Four of these rings are joined by one carbon bridge to form larger, chemically stable rings called “porphyrin.” The nitrogen atoms face each other and bind metals that can catalyze chemical reactions.
Digestion in animals breaks down plant and animal tissues to ready their molecules to be metabolized to carbon dioxide and water in a stepwise process involving an interconnected series of metal-porphyrins. The energy from this slow combustion is incorporated into the formation of high-energy phosphate bonds of ATP, the source of energy for life, as mentioned before. ATP allowed the muscles of the body to evolve to become stronger, for example, enabling humans to exceed running speeds of a mile in four minutes.
Animal cells are the beneficiaries of a similar evolutionary shortcut: the ingestion of once-independent micro-organisms that had already evolved a mechanism to metabolize food-stuffs. These organelles, named “mitochondria,” are found in almost all animal cells. They even have their own DNA for reproduction independent from that of the host or parent cells.
These similarities between photosynthesis and animal biological oxidations are no coincidence, because in each case porphyrins were the building blocks available for evolution to utilize. The porphyrin structure is akin to an adjustable wrench in a toolbox. Studies of optical spectra—how molecules absorb or emit different frequencies of light—prove almost conclusively that magnesium porphyrin complexes exist in deep space. The existence of this macromolecule in lifeless space shows how avidly chemical reactions produce larger, more complex, stable molecules. Evolution should occur on planets with mild temperatures such as we have on our planet Earth, with no need for intervention by a divinity.
A person might conclude that fairly complex molecules such as porphyrins have an infinitesimally low probability of being formed by fortuitous collisions, but because of the many planets that apparently exist and the eons of time that have been available for such compounds to form, statistics suggests that the elements will have combined many different ways. For example, spectra have been found in space corresponding to a complex sixty-carbon compound soccer-ball shaped organic chemical named “Buckminsterfullerene.” This cage-like molecule was named after the brilliant architect Buckminster Fuller, who designed homes composed of hexagonal plates. Any objective observer would estimate the odds of sixty carbon atoms simultaneously colliding to form a Buckminsterfullerene (“Buckyball”) sphere to be infinitesimally low, except here we’re dealing with billions of years and billions of cubic light years to allow for these coincidences to occur. Evolution appears to be inevitable.
The Formation of the Genetic Code
The general cellular route to growth and reproduction is a path in which deoxyribonucleic acid (DNA) produces ribonucleic acid (RNA) that, in turn, synthesizes protein. The structure of nucleotides consists of a sugar attached to a phosphate and a nitrogenous base. The interlocking questions we must answer include how RNA or DNA, which encode for protein structures that can also reproduce themselves, first appeared billions of years ago. We know from the previously discussed pioneering experiments of Urey and Miller that amino acids could be formed in an atmosphere mimicking the low-oxygen conditions hypothesized for early Earth. Subsequent investigators showed that variations of those experiments produced related constituents of RNA and DNA, namely, sugars, purines, and pyrimidines. A key experiment involved replicating the conditions of interstellar space close to a star system (to provide radiation energy). Ammonia (as a source of nitrogen), methane (to provide carbon), and water (for hydrogen and oxygen) were mixed in a vacuum. The final “soup” contained ribose, a key constituent of RNA; the sugar sorbitol; and glycerol, a constituent of many fats. Experimenters finding two of the four nucleotides that make up RNA suggest that RNA could have formed spontaneously. Elsewhere, two of the nucleotide bases in DNA were found in meteorites. Organic precursors of RNA and DNA were found in interstellar dust and asteroids. The lesser stability of DNA indicates that DNA may have appeared after RNA. What is important is that once life began, evolution was driven by survival of the fittest. Gaps in our knowledge will eventually be filled, just as the composition of the “dark” or unknown matter and the nature of the “dark” or unknown energy that is expanding our universe will one day be elucidated.
The myriad successful experiments involving many of the constituents of the genetic code strongly suggest that there may have been multiple routes to the genetic code we know today. This supposition is based by analogy on the presently known eight hominid ancestors between human beings and early primates according to the fossil records, all competing for survival and reproduction. However, all seemed to have shared many genetic sequences. It’s well known that humans and some primates a have about 98.5 percent of their DNA in common. The banana eaten by chimpanzees and humans alike is about 25 percent similar to our DNA. The digestive enzymes worms use to assimilate discarded banana skins contain long stretches of amino acids similar to human enzymes. This is truly efficient.
The genetic code raises, again, the question of life on other planets. It is important when scheduling future space flights to examine the liquid water on Saturn’s moon Titan to look for evidence of life, since aqueous ammonia has the potential to produce constituents needed for life. Extrapolating to the trillions and trillions of stars in the universe adds further impetus to find extrasolar life. Just as the compositions of some atmospheres on extrasolar planets can be inferred from spectral studies, perhaps distant, extremely trace elements indicative of contaminants created by civilizations can be untangled from background chemicals.
Evolution of the complex human brain, whose signal transmission is also powered by ATP, has created traits such as curiosity. A great example is how humans proved the existence of gravitational waves—caused by the collision of two black holes, each many times larger than our sun—by observing infinitesimal changes in the geometry of detectors. Proud traits found in some other species, and thus not unique to humanity, are altruism, courage, and voluntary care for the helpless. Humor and comedy routines are almost universally enjoyed, even by members of tribes and nations possessing different cultures. The best example may be slapstick, which evokes almost universal laughter without knowledge of the language. Many humans have in common with rats the trait of showing apparent pleasure when tickled.
Human communication has gone past chirps, grunts, and gestures to lengthy stories, novels, and plays. Special examples of creativity include novels, plays, art, and music. They show us, for example in the gripping, insightful play Othello and the emotion-filled opera Otello, that human prejudices against others with different skin pigmentation are despicable. A more shameful trait many humans possess, as we consider the hundreds of millions injured or killed over the centuries, undergirds the beliefs that one particular religious worship of god is the “true” one and that nonbelievers must endure torture, massacres, famine, war, and even death.