CHAPTER 4
THE ORIGIN OF LIFE
There are two schools of thought concerning the origin of life on the Earth, one that includes divine intervention and one that doesn't. Since we are concerned with the latter, we'll explain scientists' best guesses on how life originated on this planet based on their studies of DNA, bacteria and viruses, the geological and fossil record, and the sciences of astronomy and cosmology (the origin of the universe and our solar system). We will discuss the timeline for the origin of life on this planet and show where the origin of cancer falls on that timeline.
One of the most important questions that scientists are concerned with is why life originated in the first place. There is one school of thought holding that life naturally occurs from non-life and that inanimate matter naturally organizes itself into the basic building blocks of life. Some proponents of this theory contend that life probably originated extra-terrestrially, on Mars, for example, but died out at an early stage (or possibly went underground) and that it may be originating on Europa, one of the moons of Jupiter, even now. Some scientists believe that life may have originated more than once on Earth, but that comets and asteroids colliding with the Earth, which occurred much more frequently when the Earth was young, repeatedly wiped out all traces of life. It was only when these collision events became much rarer that life could establish a foothold on the Earth. And when scientists examine the fossil record, it appears that life began almost without hesitation, as soon as it was safe to do so. Scientists estimate that the Earth originated about 4.6 billion years ago, but heat and radiation levels were too high for life to flourish until about 3.8 billion years ago. The first fossil traces of bacteria are thought to be about 3.5 billion years old and are similar to present-day cyanobacteria (see the section on stromatolites below).
Some scientists believe that inanimate chemicals can't help but organize themselves into cells, or what could be called "pre-cells," which are more like bubbles or simple structures with membranes. The development of a cell with a membrane was a crucial prerequisite for the origin of life, because a membrane keeps the contents of the cell from dissipating into the surrounding environment. When scientists examined how bubbles and membranes form, they discovered that chemicals seem to want to form these structures. Nobody yet knows why this is so.
It is also not known why nature seems to progress from simple molecules to more complex ones. It is obvious that both nature and humans seem to naturally evolve from simpler forms of organization to more complex ones. But scientists don't know the exact reasons why this should be so.
Another mystery is why certain species of animals and plants remain unchanged for millennia and others evolve into something else, except for the usual suspect of natural selection. Natural selection works relentlessly to weed out less successful species and reward the more adaptable and resilient. But it is not clearly understood why there are now both simple organisms and more complex ones; it seems like evolution should eventually result in just complex organisms, especially after four billion years. But life on this planet would not be possible, of course, without the simpler organisms, because they recycle nearly all of the basic requirements of life.
A requirement for a cell to be living is for it to absorb nutrients, use energy, and produce wastes. A cell can produce its energy in a number of different ways: through fermentation (without the use of oxygen), through glycolysis,* and through aerobic metabolism (using oxygen), which is how we derive our energy. Each method is increasingly more complex and parallels the evolution of the planet's atmosphere from a "reducing" one (high in hydrogen compounds) to an "oxidizing" one (which contains a large quantity of free oxygen).
*a metabolic process that breaks down carbohydrates and sugars through a series of reactions to either pyruvic acid or lactic acid and releases energy for the body in the form of ATP (adenosine triphosphate).
Here is the current thinking on the timeline for the origin and evolution of life on Earth, and when we believe cancer originated. The supporting evidence for our theory on the origin of cancer can be found in the next few chapters.
POTASSIUM-ARGON DATING, CARBON-14 DATING
How is it possible to know with any degree of certainty how old a rock or fossil is? How can scientists be so sure when they say that the oldest rocks on Earth are 3.8 billion years old? Scientists believe that all elements on Earth, such as carbon, gold, silver, uranium, oxygen, potassium, and so on, were formed in a nearby supernova billions of years ago. A supernova is created when much of the material in a star explodes, resulting in an extremely bright, short-lived celestial object, which emits enormous amounts of energy. Over time, all of these elements decay and gradually metamorphose into simpler elements on the Periodic Table. This is what happens to potassium, too. A beta particle hits a proton in the potassium atom and converts it into a neutron, transforming the potassium atom into an argon atom. (Argon is a Nobel gas, which is a much more stable element.) This process occurs at a known rate, which is in the millions of years. Scientists can measure the ratio of potassium and argon in a rock sample or fossil with very sensitive scientific instruments and calculate fairly accurately how old that sample is.
Carbon-14 dating works in a similar way, but its time scale is in the thousands of years instead of in the hundreds of millions of years. Carbon-14 dating is used for much more recent artifacts and fossils.
THE BIG BANG
We've all heard astronomers and others talk about the Big Bang, which is the prevailing theory on the origin of the universe. It is based on the observation made by astronomers that the universe appears to be expanding and that the farther out you look with the most powerful telescopes on Earth and in space, the faster the galaxies and stars seem to be receding or moving away from us. By working backwards from the present locations of these galaxies and stars, astronomers have deduced that the universe was created from a massive explosion that occurred at one definite point in the universe about 13.7 billion years ago—hence, the name Big Bang. All of the galaxies, stars, planets, the Earth, and all life on this planet, including humans, were created from this explosion.
About four and a half billion years ago, the Solar System formed from a spinning cloud of hot dust and other star stuff. The early Earth had little or no oxygen in its atmosphere at that time, because this was before the evolution and rise of photosynthetic organisms, which throw off oxygen as a waste by-product of their metabolism. As a result, there was no protective ozone layer in the upper atmosphere and the surface of the Earth was under constant bombardment by ultraviolet, gamma, and other forms of radiation from the sun. At the same time, the young Earth was under a constant barrage of asteroids and comets, some large enough to cause devastation on a global scale. (These collisions would result in the mass extinctions of many life forms later in Earth's history.) Volcanic eruptions, too, were occurring much more frequently on the surface of the early Earth.
View of the Moon's North Polar Region (JPL NASA photo)
The moon, too, has been hit by many celestial objects, such as comets, meteors, and asteroids. In the photo above, you can see many craters and whitish areas where the subsurface soil material has been ejected by impacting objects. The same process was and is occurring to the Earth, but because large areas of this planet are covered by oceans and because of wind, rain, and tectonic plate drift, we don't see as many craters on the surface of the Earth.
WHAT ARE COMETS, ASTEROIDS AND METEORITES?
Comets resemble dirty snowballs and are a mixture of ice, pebbles, and rocks. They are generally about a half mile to 100 miles wide. The most famous comet is Halley's Comet, which is visible in the sky every seventy-six years (see the amazing photo of Halley's Comet below). Asteroids are larger "mini-planets" that are mostly found in the asteroid belt between Mars and Jupiter. Asteroids sometimes come within a few hundred thousand miles of the Earth, and some have even hit the Earth in the past, as previously mentioned, causing planet-wide devastation and mass extinction of species. Meteorites (also known as "shooting stars") are small pieces of rock or ice that have broken off of asteroids or comets and fallen through the Earth's atmosphere.
Gaspara asteroid (taken from the Galileo spacecraft-JPL NASA Photo)
An actual photograph of Halley's Comet (the Giotto Mission-EPA Photo)
A supernova (NASA false-color photo) -
"We are all star stuff." - Carl Sagan
As the Earth cooled, comets brought organic molecules such as amino acids, which are the basic building blocks of proteins, and enormous quantities of water to the Earth—so much water, in fact, that the oceans now cover about seventy percent of the surface. Comets also carry with them such chemicals as methane and carbon monoxide. When life first appeared on the Earth four billion years ago, the number of comets in the vicinity of the sun was hundreds or thousands of times greater than it is now, so the quantity of these chemicals must have been quite substantial.
Some scientists believe that life originated at the bottom of the oceans near volcanic vents that spew out sulfides and other noxious chemicals, safe from the killer radiation of the sun and the raining down of comets and asteroids. From this, these scientists surmise that the earliest life forms on Earth probably had a sulfur-based, non-photosynthetic metabolism.
THE INVENTION OF PHOTOSYNTHESISThe next great evolutionary leap forward in the history of life was the invention of photosynthesis. As the Earth cooled and water could collect in liquid form and not burn off as steam, there was a great deal of selection pressure on life forms to conquer new frontiers and escape from predators in the volcanic vents, their old stomping grounds. Organisms soon developed the means to use water, carbon dioxide, and the energy of the sun to live on. The fortuitous consequence of this was the fact that these life forms produced a waste by-product called oxygen.
Photosynthesis was such a successful invention that there was soon an evolutionary explosion of new organisms that adopted this way of life, and the oxygen level in the atmosphere started to rise precipitously. As the oxygen level rose, the ozone layer formed high in the atmosphere, filtering out much of the damaging UV and other radiation from sunlight (the Earth's magnetic field also helps in this process), making the Earth's surface much more hospitable to life. Because of this new development, life could leave the depths of the oceans and colonize the surface of the Earth. The increasing levels of oxygen in the oceans and atmosphere provided an incentive or selection pressure to use this element for metabolism. The result of using oxygen for metabolism was that about eighteen times as much energy could be derived from a molecule of sugar through oxidation than through fermentation. But because oxygen reacts so readily with other elements—in fact, scientists call oxygen the "Universal Poison"—nature had to invent new chemicals, such as vitamins C and E and superoxide dismutase, to minimize the damaging effects of this gas.
It was around 3 billion years ago that the so-called "red beds" and "Banded Iron Formations," or BIFs, appear in the geological record, as the oxygen that photosynthetic organisms released combined with the iron in the Earth's crust and oceans to form rust on a global scale. Once nature invented ways to deal with the corrosive effects of oxygen, there was another explosion of new life forms that adopted the aerobic way of life (including us).
PROGENOTES
The first life forms on Earth are called progenotes. Progenote is derived from the word progenitor, which means a direct ancestor or precursor. There is still some question as to whether progenotes originated here on Earth, or were brought to Earth by comets or other celestial bodies from elsewhere in the universe (this is called the Panspermia theory, which argues that life arrived on Earth from other parts of the universe). Because amino acids and the other building blocks of life have been found in comets, and because bacteria can exist in extremely inhospitable environments such as those in outer space, it has been proposed that life may have been brought to the Earth by comets. Because the underlying basis of metabolism for simple organisms such as bacteria and viruses is inorganic (it is based on the oxidation of iron), some scientists feel that life originates rather readily where even the minimum requirements are met.
Progenotes are RNA-based Monera, or single-celled organisms without nuclei. RNA is a much simpler genetic molecule than DNA and is still found in the cells of present-day organisms and is used for various cell functions, such as transmitting information from the nucleus to other parts of the cell.
ARCHAEBACTERIAThe Archaebacteria evolved after the progenotes and are a group of ancient bacteria made up of such single-celled organisms as the methanogenic (methane-producing) bacteria, the extreme halophilic bacteria (bacteria that can exist in high-salt environments, such as in the Great Salt Lake in Utah), and the thermoacidophilic bacteria (bacteria that can exist in high temperatures and highly acidic environments, such as in the geysers of Yellowstone National Park). Archaebacteria differ from other bacteria in the sequence of RNA in their ribosomes (which are tiny protein-synthesizing bodies in the cell), in the absence of muramic acid* in their cell walls, and in the lack of glyceryl esters, a type of sugar alcohol, in cell lipids (fats). They appear to be the remnants of a primitive group of organisms that were capable of synthesizing organic compounds before the evolution of photosynthesis.
Evolution of the eukaryotic cell by serial endosymbiosis
* muramic acid = an amino sugar C9H17NO7 that is a lactic acid derivative of glucosamine and is found especially in bacterial cell walls and in blue-green algae.
ENDOSYMBIOSISEvolutionary biologists believe that the original precursor cell was a prokaryotic bacterium like the mycoplasma bacterium. (See the picture above.) Through endosymbiosis, this bacterium merged with an aerobic bacterium creating a mitochondria-containing amoeboid-type organism, known as a protista. The aerobic bacterium that became the mitochondria has a modern-day relative, which still exists, called Bdellovibrio, an oxygen-using bacterium that invades other bacteria. Scientists are fairly certain that mitochondria evolved from a bacterium that merged with the host bacterium, because mitochondria have their own DNA, which is separate from the DNA in the nucleus. All life forms that evolved after this, including us, have mitochondria, which is inherited only from the mother. Thus, the bacterium that evolved into mitochondria could be considered the "mother (bacterium) of us all."
When the protista merged with a worm-like spirochaete, a more mobile bacterium was created with a whip-like tail that could propel it through its environment. The spirochaetes were probably responsible for another important contribution to evolution: it is now believed that they merged even farther into the interior of the cell and became responsible for the phenomenon of mitosis, where the DNA splits and makes an exact copy of itself and forms two identical "daughter" cells.
A typical cell
When the protista with the whip-like tail joined with a chlorophyll-containing blue-green bacterium, it created the precursor to all plant life on this planet. We can conclude from the fact that plants also develop tumors that the Cancer Cell trait inherited by all subsequent life forms originated before plants and animals diverged on our evolutionary timeline.
CYANOBACTERIACyanobacteria are aquatic and photosynthetic, which means that they live in the water and can manufacture their own food. Because they are bacteria, they are quite small and usually consist of only one cell, though some grow in colonies large enough to see. Their fossil remains are the oldest known fossils at more than 3.5 billion years old. Cyanobacteria are still around; in fact, they are one of the largest and most important groups of bacteria on Earth.
Many oil deposits are the result of cyanobacteria. They are also important providers of nitrogen fertilizer in the growing of rice and beans. The cyanobacteria have been a tremendously important force in shaping the course of evolution and in ecological change throughout Earth's history; they are responsible for creating the oxygen atmosphere that we depend on. Before they arrived on the scene, the Earth's atmosphere had a very different chemistry, which was inhospitable to life as we know it today, but was ideal for the origin of life. If it were not for the cyanobacteria, there would not be any plants. The chloroplast inside the cells of plants that allows them to manufacture their own food had its origins as a cyanobacterium that merged into certain eukaryotic bacteria through endosymbiosis.
STROMATOLITES
Fossilized stromatolites that are found in certain locations on Earth provide evidence of the earliest cyanobacteria. Stromatolites form in layers, as seen in the photos above, which were taken at Shark Bay on the west coast of Australia. Cyanobacteria photosynthesize, grow and reproduce within these layers, which trap sediment and organic matter. As the sediment layer grows and blocks sunlight, the cyanobacteria migrate upward to start a new layer and the old layers eventually fossilize.
The oldest stromatolites are three and a half billion years old, but the stromatolite-forming cyanobacteria really became abundant in the oceans only about 2.3 billion years ago. Photosynthesis by these cyanobacteria generated oxygen, which slowly accumulated in the atmosphere, eventually reaching present-day levels (approximately 21%) by about 1.8 billion years ago.
These cyanobacteria are common even today in the oceans, but the domed stromatolite shapes only form in lagoons with highly saline water where larger marine animals don't exist. In parts of the ocean where there are many marine animals, these creatures will eat through the layers so the layers don't survive long enough to form stromatolites.
WHAT IS DNA?
We've all heard about DNA, especially to identify criminals, but what exactly is DNA? DNA is a molecule that consists of a binary (actually, quaternary) code that is similar to the zeroes and ones used to program computers. (In fact, scientists are now using experimental DNA computers to perform computations.) DNA resembles a blueprint which contains the codes for the proteins that make up our bodily structures, enzymes and other biochemicals. The quaternary code consists of the following molecules, which are called nucleotides: adenine (A), thymine (T), cytosine (C), and guanosine (G). One of the rules of DNA formation is that adenine can only bond with thymine, and cytosine can only bond with guanosine. But even with this restriction, there can be millions and millions of different combinations or sequences of nucleotides. In human DNA, there are approximately three billion pairs of A & T and G & C, which are called base pairs, organized into about 30,000 genes. Each combination of three of these base pairs codes for a certain amino acid, which are the basic building blocks of proteins. There are only about twenty amino acids, but, from these amino acids, millions of different proteins can be created.
DNA is found in every living organism from the tiniest viruses to the largest mammals on Earth. It is passed on from generation to generation. Tiny flaws in the sequences can cause mutations; some of these mutations are favorable, some have no effect, and some are damaging to the organism. All of the species that presently exist on the Earth—maybe about ten million in all—and all that have ever existed on the Earth have developed over the last four billion years through these mutations—this assertion may be hard to believe, but there is now a great deal of evidence from microbiology (the study of bacteria and viruses), paleontology (the study of fossils), and molecular genetics (the study of DNA) that supports the theory of evolution.
If you examine the genes of yeast, flies, and worms, you see the same genes in all three species; these genes may not have exactly the same functions in the three species, but they will have similar functions. We humans, too, share genes with the lowly yeast cell. What does this mean? Again, it means that all life is basically one, and all species share a common ancestor.
How do new genes arise? Humans obviously have more complexity than yeast cells and have many more genes. How then are these new genes created? New genes are created by a doubling of old genes with a gradual change in function for the new genes.*
* Doubling of chromosomes - see page 115 in Christopher Wills's The Wisdom of the Genes, 1989, Basic Books.
WHAT ARE BACTERIA?
Four billion years ago, when bacteria evolved into being, the Earth was a very different place than it is now. As previously mentioned, there was no free oxygen in the atmosphere, which meant that there was no ozone layer to shield out the deadly radiation from the sun. There were frequent bombardments from meteors, comets, and asteroids, which wiped out any incipient life (probably many times). There were volcanic eruptions that spewed out sulphurous gases and other noxious chemicals, and much more radiation from decaying uranium 235, which was about fifty times more abundant then, in the soil, oceans, and atmosphere, than now. In spite of these deadly conditions, bacteria thrived and multiplied. New species arose to meet the challenges of different environments. There were bacteria that adapted to living in extremely acidic or alkaline environments, or in environments of extreme pressure, such as those found at the bottom of the deepest oceans. Temperature wasn't a problem either; there are bacteria that have been found growing at 112° Celsius (233° Fahrenheit) in geysers deep underground. Some bacteria can feed on nitrogen, sulphur, and other simple inorganic molecules; they don't require any organic food at all. There are bacteria that can live without sunlight, in the depths of the oceans where undersea geothermal vents provide the sulphurous compounds and the energy that these bacteria need. Certain bacteria can live on oil found in oil deposits miles beneath the surface.
There are even some bacteria that can create methane from carbon dioxide and hydrogen and derive energy from this process, then metabolize that methane for more energy, releasing carbon dioxide and hydrogen, in a kind of perpetual motion machine.
Perhaps the most remarkable fact about all of this is that all of these different kinds of bacteria still exist today, which is a good thing because we couldn't have developed our theory on the origin of cancer without them.
A KEY SOURCE FOR THIS CHAPTER:
For more information on endosymbiosis and the evolution of bacteria and viruses, see these books written by Dorion Sagan and Lynn Margulis (one of Carl Sagan's sons and his first wife, who was a distinguished professor of biology/geosciences at the University of Massachusetts in Amherst):
1) Garden of Microbial Delights. (1993). Kendall/Hunt Publishing Co., and
2) Microcosmos. (1986). University of California Press (see especially the section on mitochondria and cancer in Chapter 8).
3) The Origin of Eukaryotic Cells. (1970). Yale University Press. by Margulis, Lynn.
SUMMARY
1) Scientists think that the universe was created about 13.7 billion years ago with the Big Bang.
2) There are two schools of thought concerning the origin of life on the Earth: the Panspermia theory that says that life originated elsewhere in the universe and was brought to the Earth by celestial bodies, and the other theory that says that life originated natively here on Earth.*
3) The early Earth was a hellish place with many volcanoes and collisions with comets and asteroids. There was no ozone layer to shield the surface from UV-, cosmic-, and gamma-radiation.
4) The early Earth had a reducing atmosphere high in hydrogen and hydrogen compounds, which is toxic to most present-day life, but was perfect for the creation of life.
5) The first life forms were bacteria and viruses. The evolution of these life forms mirrors the composition of the atmosphere. The rise of the cyanobacteria that lived by photosynthesis produced a toxic byproduct called oxygen. Eventually, so much oxygen was produced that the atmosphere is now about 20% O2.
6) The earliest bacteria were the Archaebacteria that could live without oxygen or sunlight, in extremes of temperature and pressure.
7) The next bacteria to evolve were the eukaryotes, which had distinct nuclei. Some bacteria used endosymbiosis to merge and help each other survive. In fact, we are all just a collection of these bacteria that merged.
8) Metabolism using oxygen produces so much more energy per molecule of food that soon many organisms using this form of metabolism evolved. We are one of them.
*Note: Our theory on the origin of cancer does not claim that cancer originated extraterrestrially.
Version 3.2
© Copyright 2019. Phil Matsumoto. All rights reserved.
Last updated on 11/4/2019.