Theories on the Origin of Life
Dedicated to Dr Sandeep K.M. Nevina Kamath, M.Sc
Professor, Ecological Sciences
“The ultimate fate of a cell or any living thing is death and destruction. No dynamically functioning unit therefore can survive as a species without self-reproduction. The ability to reproduce, however, would have had to exist from the very beginning in any system, no matter how simple or complex, so that it could give rise eventually to a living thing. Yet the ability to reproduce requires such a complex mechanism that the machinery required for this process would have been the last thing that could possibly have evolved. This dilemma has no solution and thus poses the final insuperable barrier to the origin of life by a naturalistic process.”[i]
But what if reproduction did not require such a complex mechanism at all in the initial days? And if complex species could evolve over a period of a few billion years, then why not life itself? And, with due apologies to the creationists, if all life on earth as we see it today is by the hand of a “Creator” who made creatures out of nothing, then why did that Creator have to start with only the simplest of unicellular organisms? Why could that Supreme Being or super-intelligent alien not have created all the flora and fauna that we witness today, all the way back 3.6 billion years ago? Why has it taken eons for nature and the genetic material to interact to produce the mind-boggling variety of species we see today, from some only very rudimentary life forms that existed on a young Planet Earth?
We begin to comprehend that the effort to unravel the secrets behind the Origin of Life is a truly justifiable one...
Ever since the dawn of human consciousness, we have been plagued by questions regarding our origin: Where did we come from?
And as we grew in our understanding of the natural world around us, came the query: Where did these things come from?
The current assumption of solar system formation is the Nebular hypothesis, first proposed in 1755 by Immanuel Kant and independently formulated by Pierre-Simon Laplace. It states that our solar system was formed from a gaseous cloud called the Solar nebula.. As we understand it, the superheated mass of dust and gaseous matter on the outer edge of the disc cooled down to form the planets as well as rocks, earth, the atmosphere, and water on Earth.
There does not seem to be much debate on this issue, considering that the galaxy holds sufficient examples of such systems in formation.
But what of living things? Why is the debate still raging on the origin of life? What is it that makes living things so very different from the non-living, that we cannot accept a simple, straightforward theory of spontaneous generation? What makes life so unique and complex, that it cannot be explained in the manner of other natural phenomena? Why is it that we look at several different theories including that of creationism, to explain it? For answers to this conundrum, we shall have to look at a definition of life itself.
The Earth is estimated to be about 4.5 billion years old, and for much of that history it has been home to life in one strange form or another. Indeed, some scientists think that life appeared the moment our planet's environment was stable enough to support it. The earliest definite evidence for life on Earth comes from fossilized mats of cyanobacteria called stromatolites in Australia that are about 3.4 billion years old. Ancient as their origins are, these bacteria (which are still around today) are already biologically complex—they have cell walls protecting their protein-producing DNA, so scientists think life must have begun much earlier, perhaps as early as 3.8 billion years ago.
Despite knowing approximately when life first appeared on Earth, scientists are still far from answering how it appeared. "Many theories of the origin of life have been proposed, but since it's hard to prove or disprove them, no fully accepted theory exists," said Diana Northup, a cave biologist at the University of New Mexico. The answer to this question would not only fill one of the largest gaps in scientists' understanding of Nature, but would also have important implications for the likelihood of finding life elsewhere in the universe.[ii]
How do we define life?
As we all know, living things are differentiated from the non-living by certain characteristics: Respiration, Response to stimuli, Locomotion, Metabolism, Growth and Reproduction. But what is it that causes these special characteristics to occur in living things?
To get to the heart of the matter, we shall have to look at life from a very fundamental perspective, that of the cellular structure. Very simply described, each cell is constituted of a cell wall or membrane, the protoplasm or fluid substance within, and the organelles floating inside such as the Nucleus and the Mitochondria. These organelles contain biochemical information in the form of chains of molecular bases linked to sugar or phosphate groups, that code for every structure and function in the body, and drive every cellular process from metabolism to replication. These chains of bases with the attached backbone of sugar and phosphate molecules, constitute the ordered sequences of nucleic acids that hold the key to every life-process. It could be said therefore, that these building blocks of nucleic acids are the very basis of life. In other words, out of clusters of essentially ‘lifeless’ biochemical molecules, spring the basic processes and functions that define ‘life’.
How?
These nucleic acids are in fact, the master codes for the synthesis of proteins. As living organisms are complex systems, the multitude of daily functions are helped to be carried out by the hundreds of thousands of proteins existing inside each one of us. These proteins are produced locally, assembled piece-by-piece to exact specifications. An enormous amount of information is required to manage this complex system correctly. This coded information, detailing the specific structure of the proteins inside our bodies, is stored in the set of molecules called nucleic acids that comprise the DNA and RNA that we have discussed above.
Astrophysicist, Sir Fred Hoyle and his colleague Chandra Wickramasinghe argued that chance processes could not have formed the complex biochemical machinery of the cell, especially the enzymes. In their book, "Evolution from Space," they estimated that the probability of forming a single enzyme of protein at random, in the rich ocean of amino acids, was no more than 10 to the 20th power. They then calculated the likelihood of forming by chance all of the more than 2000 enzymes used in the life forms on earth. This probability was calculated at one in 10 to the 40,000th power.[iii]
“What I think the DNA material has done is to show that intelligence must have been involved….It now seems to me that the finding of more than fifty years of DNA research have provided materials for a new and enormously powerful argument for Design.” --- Antony Flew
Previously, in his fifty years of proclaiming atheism in university classrooms, books, and lectures, Professor of philosophy and leading atheist Flew had argued that science had all but disproved the existence of God![iv]
So, it was the origin of the highly ordered, extremely specific sequences in DNA and RNA which endowed these molecules with their marvelous biological activities. Truly astonishing !
So then, having outlined the functions of proteins, we need to take a look at their structure.
Proteins are made up of amino acids, and generally have from about a hundred up to several hundred amino acids arranged in a precise order or sequence. Twenty different kinds of amino acids are found in proteins, so it may be said that the protein "language" has twenty letters. Just as the letters of the alphabet must be arranged in a precise sequence to write this sentence, or any sentence, so the amino acids must be arranged in a precise sequence for a protein to possess biological activity.
To sum up, we can say that the macromolecules of life are structured in the following manner:
· Proteins are organic compounds that are essential biomolecules of all living organisms. Amino acids are the building blocks of proteins and they are arranged in a precise sequence to form various proteins. They are composed of the elements hydrogen, carbon, oxygen, nitrogen and sulphur. Human bodies only make use of 20 amino acids but in meteorites we can detect over 70 amino acids.
· The direction for the assembly and synthesis of amino acids to form proteins is carried out from the code detailed by the DNA and RNA in cells. These nucleic acids are organic molecular structures consisting of nitrogenous bases attached to a chain of sugar and phosphate molecules.
· In addition, there exists a group of fatty acids known as lipids which are a large group of organic compounds constituting cell membranes, and which have a multitude of other important roles.
We know very little about how organisation and assembly arises in nature. Unexpected properties emerge from biological systems, for example, the way cell membranes form. But nobody knows where such self organisation comes from. Objects ranging from a few nanometers to a tenth of a micrometer show special properties that do not occur on microscopic or macroscopic scales. At this size threshold, adding more particles make the material not just bigger, but entirely different. Groups of hundred to thousands of particles - dumb, inanimate matter, - suddenly begin to organize themselves in to patterns, that make them capable of responding to their surroundings. This self organisation eventually leads to the emergence of life itself as per the Nobel Prize winning Physicist Robert Laughlin of Stanford University, California. Some of the assembly principles that seem to apply to both living and inanimate matter have already been laid down, and these principles will be the thrust of science in the 21st century.[v]
So when could earliest life have begun?
· As we know, the Earth was thought to coalesce about 4.5 billion years ago.
· Microfossils found in ancient rocks from Australia and South Africa demonstrate that terrestrial life was flourishing by 3.5 billion years ago. Interestingly, even older rocks from Greenland, 3.9 billion years old, contain isotopic fingerprints of carbon that could have belonged to a living organism. In other words, only 100 million years or so after the earliest possible point when Earth could have supported life, organisms were already established well enough that evidence of them remains to this day.
Life : A biochemical phenomenon?
So how could the bio-molecules, which are the basis of life, have come to exist? The subject matter is generally divided into five stages:
1) The synthesis of organic compounds
2) The synthesis of biochemical substances (experiments have mainly reported on the production of amino acids under presumed pre-biological conditions).
3) The production of large molecules such as proteins.
4) The origin of organized cellular structures.
5) The evolution of macromolecules and metabolism.[vi]
We thus have a basic definition from which to explore the possible ways that life could have originated on planet Earth.
Theories on the origin of life:
The theories can be broadly classified as follows:
· Creationism or Intelligent Design (I.D.)
· Abiogenesis, or the beginning of life from non-living earthly matter
· Panspermia or Exogenesis, and
· Extraterrestrial Origin
In the recent past, the challenge to scientific theory has come from a new breed of sophisticated, scientifically trained creationists who are pushing the theory of "intelligent design" or I.D. The `ID-ers' do not interpret the Bible literally. They accept fossil records as evidence of the evolution of human beings from apes, and they accept that the earth is about 4.6 billion years old (and not 6,000 years old, as the earlier generation of Biblical creationists believed.) But they draw the line at natural selection, the hallmark of Darwinian evolution. They insist that the complexity in biological structures - the intricacy of the eye, for example - could not have come about by natural causes alone. From this they surmise that there must be an intelligent designer responsible for the wondrous complexity of life.
The more one learns of biochemistry, the more unbelievable it becomes ….unless there is some type of organizing principle….an Architect for believers. - - Cosmologist Alan Sandage
Proponents of I.D. bring in a Designer God to explain the existence of "irreducible complexity" of life, which they think cannot be explained by natural causes alone. Darwin is under attack in the United States yet again. Exactly 80 years since the Scopes "monkey trial", the teaching of Darwin's theory of evolution is facing legal challenges in many parts of the country. In the U.S. a court in Dover, Pennsylvania, recently ruled in favour of teaching Darwinian evolution in schools. The fate of another trial is awaited in Cobb County, Georgia. In all, 14 States in the U.S. are debating new regulations on teaching evolution. The state of Kansas had taken a lead by changing the very definition of science to make room for supernatural explanations of natural phenomena. President George W. Bush was in favour of "equal treatment" for creationism in biology classes. It is open season on Darwin.
Vedic Creationism : The Vedic creationists deny that different species of living beings, including humans, have evolved, or risen up, from simpler organisms, as Darwin claims. Instead, they claim that all species, including humans, have "devolved", or come down, from a highly evolved, super-intelligent being, which is pure consciousness itself. Different species of plants and animals are simply material forms adopted by pure consciousness, or Atman, as it transmigrates in endless cycles of births and rebirths over billions and billions of years. Spiritual growth is the driving force of evolution: higher species emerge when Atman trapped in all matter takes on a higher (more "subtle" and sattvic) life-form as a result of good karma, and lower species result when Atman "forgets" its purity and indulges in "gross desires".
Vedic creationists claim to derive this picture from the "Vedas", in which they include the Puranas as well, especially the Bhagvat Purana. Here it must be added that theories of spiritual or "integral" evolution have been proposed before, notably by Sri Aurobindo and Madame Blavatsky, the founder of Theosophy. But the Hare Krishnas are the first to support their theory with "scientific" data - if data from psychics and UFO sightings can be called scientific.
Like all fundamentalists, Vedic creationists take the Bhagvat Purana, along with the Bhagvad Gita, the Mahabharata and the Ramayana, to be literally true. They then proceed to use the "facts" described in these sacred texts to condemn Darwin and all of materialist science.
For example, Cremo and Thompson accept the notion of the "day of Brahma" lasting some 4.32 billion years as literally true. They also accept as fact the idea that the "current day of Brahma" began two billion (2,000, 000, 000) years ago. A literal reading of the Ramayana convinces them that humans and monkey-like hominoid creatures coexisted. Putting the two ideas together, they come up with the fantastic notion that the ancestors of modern human beings have existed for two billion years. They want us to believe that human beings walked the earth at a time when fossil records show that only bacteria existed on the earth.
This completely contradicts the best scientific evidence from fossil records and radiocarbon dating that show that the ancestors of modern human beings only appeared around 200,000 to 100,000 years ago: that is, after the appearance of fish, amphibians, and reptiles and other mammals and hominoid species, from which humans have evolved. Vedic creationists set aside all this evidence as a mere social construct of Western archaeologists and palaeontologists who, they say, have been brainwashed by an atheistic, materialistic worldview. Once you remove the "knowledge filter" of Western-Christian materialism, they tell us, "spiritual sciences" will become dominant again, just as they used to be before the "reductionist" science of the West banished the Gods from Nature.
ON the face of it, Vedic creationism with its longer time spans looks more "scientific" than the old-fashioned Bible literalists who insist that the earth is only 6,000 years old. But what the two creationists share is the belief - entirely unfounded on verifiable facts - that human beings have been around since the beginning of life, and that they have not descended from the apes. (In fact, A.C. Prabhupada, the founder of ISKCON, used to describe Darwinians as "rascals" and "fools" for believing in such "nonsense" as the evolution of humans from apes. Prabhupada's spirit lives on in Vedic creationism.)[vii]
Scientific Theories: Lots of ideas
“In the face of the enormous complexity that modern biochemistry has uncovered in the cell, the scientific community is paralyzed.”
---Professor Michael Behe
Today, there are several competing theories for how life arose on Earth. Some question whether life began on Earth at all, asserting instead that it came from a distant world or the heart of a fallen comet or asteroid. Some even say life might have arisen here more than once. "There may have been several origins," says David Deamer, a biochemist at the University of California, Santa Cruz. "We usually make 'origins' plural just to indicate that we don't necessarily claim there was just a single origin, but just an origin that didn't happen to get blasted by giant [asteroid] impacts."[viii]
Leading scientific theories based on abiogenesis or the spontaneous origin of life on Earth could be divided into two main groups:
a) the ‘RNA world’ hypothesis
b) origin under high temperature and pressure
The formation of amino acids and other organic compounds is presumed to have been a necessary step in the genesis of life; it is certain, at least, that somewhere along the line all life became dependent on DNA and RNA for reproduction. Scientists thus presume that the first self-replicating molecules were similar to the nucleic acids of modern organisms. (These early molecular systems need not have been as complex as the self-replicating systems that comprise modern cells. Researchers have recently shown, by deleting genes, that even the genetically simplest bacteria alive today can reproduce with much less than their full natural complement of DNA.) Once molecules that could self-replicate were formed, the process of evolution would account for the subsequent development of life. The particular molecules best adapted to the local environmental conditions would have duplicated themselves more efficiently than competing molecules. Eventually, primitive cells appeared; perhaps coacervates or other protobionts played a role at this stage in the genesis of life. Once cells became established, evolution by natural selection could have resulted in the development of all life-forms that have ever existed on Earth.[ix]
From organic molecules to proto-cells
The question "How do simple organic molecules form a proto-cell?" is largely unanswered. However, there are many different hypotheses regarding the path that might have been taken. Some of these postulate the early appearance of nucleic acids ("genes-first") whereas others postulate the initial evolution of biochemical reactions and pathways ("metabolism-first") as in the Iron-Sulphur World hypothesis. Recently, trends are emerging to create hybrid models that combine aspects of both.[x]
The ‘RNA world’
When there was no life on earth 4.3 billion years ago, and no oxygen, what jumpstarted life- processes? Scientists conceptualised the RNA world, (of self-replicating RNA), which has attributes of protein. This theory, a 20-year old proposal also known as the “RNA world hypothesis” holds that RNA was not only the first self-replicating molecule, but also that it initially carried out most of life’s functions, such as metabolism and cell formation.
Many researchers believe the first self-replicating molecule was RNA. This is because RNA can do various things in addition to carrying genetic information. Some of these activities seem similar to what would be required for self-replication, something that DNA can’t do, strictly speaking. “A few of the numerous important functions RNA carries out in each of our cells include acting as a transitional-molecule between DNA and protein synthesis, and functioning as an on-and-off switch for some genes.” [xi]
DNA needs the help of other molecules to copy itself. Also, since RNA still exists in living cells and performs various functions—some so very basic to life— many scientists think RNA must have been there from the beginning. "A lot of the most clever and most talented people in my field have accepted that the RNA World was not just possible, but probable," says Deamer.
Most biologists consider the RNA world hypothesis at least plausible, but it has some problems. It is not easy to explain how the first self-replicating RNA molecules might have arisen. One of the most promising explanations is as follows:
RNA molecules tend to fall apart under warm conditions outside of cells. This would prevent the buildup of the rather long, complex RNA molecules that would probably be needed to conduct life processes, according to Laura F. Landweber and her colleagues at Princeton University in New Jersey. Various conditions can prevent RNA molecules’ breakdown, the researchers argue. These include various types of water solutions, and freezing. But freezing may have been the one that most likely occurred on early Earth, they argued.
These scientists argue that ice might have been a favorable environment to generate the first self-replicating molecules, a precondition for life. New findings are backing up a theory that life originated in ice, researchers say. If it’s true, it could boost the chances that life might turn up in places considerably colder than our planet. The theory departs from mainstream thinking on the origins of life, which usually assumes a warm, or hot and wet environment was necessary.
Conditions associated with freezing, rather than ‘warm and wet’ conditions, could have been of key importance for the chemical reactions that led to life, wrote four researchers in the July 21 advance online issue of the Journal of Molecular Evolution, a research publication. These molecules would be of the type called ribonucleic acids, or RNA—a cousin of DNA which makes up genes.
Freezing usually slows down chemical reactions, which is why cold places are generally considered hostile to life. But freezing actually speeds up some of RNA’s key activities, Landweber and colleagues argue. This is because ice contains hard, tiny compartments that hold the molecules in one place, where they can react together. Some of these reactions result in the creation of bigger RNA molecules.
In liquid water by contrast, the molecules don’t come close enough together often enough to react as much. Thus they tend to fall apart faster than they can react to create bigger products. In essence, the small compartments in ice play the role that cells today play in bringing the molecules together to react, Landweber and her colleagues say. Dehydrated substances—a sort of primordial sludge, for instance—could also have provided a function similar to ice, they added, but ice works better.
Landweber’s group conducted an experiment to test the theory. Led by Alexander Vlassov of SomaGenics, a Santa Cruz, California -based biotechnology company, the researchers broke to pieces some RNA molecules found in normal cells. This process yielded more, smaller, RNA molecules. By doing this, the researchers produced RNA molecules of sizes that biologists think might have been available on early Earth. They then experimented to find out what sort of capabilities these smaller RNAs had.
Reporting their results in the May 25, 2004 issue of the journal Nucleic Acids Research, the researchers noted that the broken-up RNAs still could carry out some of the same functions as normal RNAs, but only in ice or sometimes in other extreme conditions, such as dehydration. These activities included grabbing other pieces of RNA and attaching them together, an activity called ‘ligation’ that is similar to self-replication.
To fully self-replicate, a molecule must attach other molecules together in such a way as to match the sequence of chemical pieces that characterize the first molecule. This process is called “template-directed” ligation. But ligation alone—even without the self-replication—can build up ever larger and more complex RNA molecules, which according to the RNA world hypothesis could eventually develop self-replicating abilities.
The theory that an icy environment might have helped jump-start life isn’t new. Researchers had proposed in 1994, for example, that repeated cycles of freezing and thawing could help accelerate some of the chemical reactions necessary for life. Such a scenario might have existed on early Earth, where according to some researchers, repeated meteor and comet impacts might have periodically melted an otherwise icy environment.
However, Landweber and her team seem to be the first to have provided an account of how the ‘RNA world’ might have fit into this scenario. Although Landweber and her colleagues also wrote that freeze-thaw cycles are helpful for the processes they describe, such cycles aren’t strictly necessary in their proposal. Moreover, they wrote in their Journal of Molecular Evolution paper, “It is worth noting that Jupiter’s moon Europa and even Mars are also thought to contain large amounts of liquid water and ice now, or at some time in the past.”
The possibility of RNA activities in ice, they added, “lends some credibility to claims that the rather extreme environments of these extraterrestrial locations could have provided suitable conditions for the emergence of life”.[xii]
But the RNA World hypothesis doesn't explain how RNA itself first arose. Like DNA, RNA is a complex molecule made of repeating units of thousands of smaller molecules called nucleotides that link together in very specific, patterned ways. While there are scientists who think RNA could have arisen spontaneously on early Earth, others say the odds of such a thing happening are astronomical. "The appearance of such a molecule, given the way chemistry functions, is incredibly improbable. It would be a once-in-a-universe long shot," says Robert Shapiro, a chemist at New York University. "To adopt this view, you would have to believe we were incredibly lucky."[xiii]
a) Origin under high temperature and pressure
Some scientists believe that the young Earth was too inhospitable a place for life to have developed on its surface at all. Lacking Oxygen, the atmosphere would also have lacked its present-day stratospheric layer of ozone (O3), which screens large quantities of harmful ultraviolet radiation from the surface. They believe that a more likely environment for abiogenesis (life from pre-life) was in the vicinity of deep-sea vents, which are gaps in the crust under the ocean from which hot, mineral-laden water flows.[xiv]
"Deep-hot biosphere" model of Gold:
A controversial theory put forward by Thomas Gold in the 1990s has life first developing not on the surface of the earth, but several kilometers below the surface. It is now known that microbial life is plentiful up to five kilometers below the earth's surface in the form of archaea, which are generally considered to have originated around the same time or earlier than bacteria, that mostly live on the surface including the oceans. It is claimed that the discovery of microbial life below the surface of another body in our solar system would lend significant credence to this theory. He also noted that a trickle of food from a deep, unreachable, source promotes survival because life arising in a puddle of organic material is likely to consume all of its food and become extinct.
In the 1980s, Gunter Wachtershauser in his Iron-Sulfur world theory, postulated the evolution of (bio) chemical pathways as fundamentals of the evolution of life. He presented a consistent system of tracing today's biochemistry back to ancestral reactions that provide alternative pathways to the synthesis of organic building blocks from simple gaseous compounds. In contrast to the classical Miller experiments, which depend on external sources of energy (like simulated lightning or UV radiation), "Wachtershauser systems" come with a built-in source of energy, sulfides of iron and other minerals. The energy released from redox reactions of these metal sulfides is not only available for the synthesis of organic molecules, but also for the formation of oligomers and polymers. It is therefore hypothesized that such systems may evolve into autocatalytic sets of self-replicating, metabolically active entities that would predate the life forms known today. The experiment produced a relatively small yield of dipeptides (0.4–12.4%) and a smaller yield of tripeptides (0.003%) and the authors noted that "under these same conditions the dipeptides hydrolysed rapidly." Another criticism of the result is that the experiment did not include any organomolecules that would most likely cross-react or chain-terminate.[xv]
Instability is a most fundamental objection to any type of system that can be proposed to bridge the gap between molecules and living cells. All of the proposed models, whether they be Oparin's coacervates, Fox's microspheres, or any other model, suffer this basic and fatal weakness. One of the reasons living cells are stable and can persist is that they have membranes that protect the system within the membrane and hold it together. The membrane of a living cell is very complex in structure and marvelous in its function. A coacervate or a protein microsphere may have a pseudomembrane, or a concentration or orientation of material at the point of contact with the surrounding medium, that gives it the appearance of having a membrane. There are no chemical bonds linking the macromolecules in this pseudomembrane, however, and it is easily broken up, and the contents of the coacervate or microsphere are then released into the medium.[xvi]
“Origin of life breakthrough”:
A team of Japanese researchers announced that they had managed to recreate the conditions from which life itself may have sprung. In a major breakthrough in the never-ending debate about how life started, Koichiro Matsuno and colleagues at the Nagaoka University of Technology, Japan, built an artificial system simulating the environment of undersea thermal vents, where water heated deep below erupts through the seabed into cooler ocean water. By this they were able to produce some of the elementary building blocks from which proteins essential to life are formed.
“For ten years, underwater hydrothermal vents have been thought to be the place where life began — and we were able to prove it”, Matsuno said.
Writing in the journal Science, Matsuno described how his team simulated a process called polymerisation, in which complex molecules — in this case oligopeptides, one of the elements that make up proteins — are formed from simpler amino acids. This process was likely to be repeated numerous times, possibly aided by “heating in dry and wet conditions, day-and-night cycles, tidal waves and dry-wet conditions in lagoons”, the author wrote.
The chemical products, synthesised in hot hydrothermal vents in the sea, could re-enter the vents after being quenched in the surrounding cold water and undergo further reactions. Matsuno and his team built a flow reactor that mimicked the heating and cooling parts of the cycle.
The two-chambered flow reactor circulated materials from hot to cold environments in roughly one-minute cycles. When they added the amino acid glycine, they found that this formed more complex oligopeptide molecules in a stepwise process. Key to the process was the addition of bivalent copper ions, one of many minerals present on the sea floor — an addition which Matsuno said, was serendipitous.[xvii]
Dr. George Cody's team of Geophysicists from Washington, have found that the reaction that occur in the vicinity of deep ocean hydro-thermal vents when iron sulphide is subjected to extreme temperature and pressure, formed organometallic compounds similar to those present in the active centers of certain metabolic enzymes of living organisms. These reactions also gave rise to pyruvic acid which is an energetic three carbon molecule that is critical to central metabolism in all life. There is nothing special about biology. Life may arise from the same set of organising principles that determine the arrangement of atoms or electrons in materials with unusual properties. This is called the world of 'Complex Adaptive Matter'.[xviii]
An Indian researcher A.K. Lal has mentioned in his paper the existence of ‘extremophiles’, which are usually unicellular microbes that can survive in the harshest of environments on earth. “Such microorganisms thrive in extreme cold, extreme heat, extreme acidic, and extreme alkaline conditions. Some thermophiles have been found to flourish at a depth of 2.8 km in gold mines in South Africa, while methane-oxidising microbes have been reported to be thriving at a record depth of 1.62 km beneath the Atlantic seabed at simmering temperature of 60-100 degree Celsius,” he writes in the paper.
Earth was formed about 4.5 billion years ago and recently probing a tiny grain of zircon, scientists have evidence that about 4.4 billion years ago, i.e. just after 100 million years after the earth was formed, the temperature had cooled to about 100 degree C range, creating conditions for the formation of life. The fact that all organisms share the same DNA-based mechanism for genetic transmission suggests that life emerged on earth only once during the planet’s entire history but the timing remains unknown. Lal concludes by saying that “the DNA mechanism is a common thread of all modern organisms, plants, animals, all living things. “Given the potential of extremophiles to survive in highly inhospitable environments on earth, the possibility of life on extraterrestrial bodies like Mars, Europa, Ganymede, Enceladus, Titan, in the solar system cannot be ruled out. Keeping in view the great survival instinct of extremophiles on earth, the possibility of traces of life being found on billions of unexplored planetary bodies outside our solar system cannot be negated either.” [xix]
A contradiction:
“New research links origin of life to ponds”
Debunking the popular theory that life emerged from oceans, latest research effort shows it could have emanated from fresh water ponds.
"New research shows that primitive cellular membranes assemble more easily in freshwater than in salt water. Although the oldest known fossil organisms were ocean dwellers, life may actually have developed in fresh water ponds," says the latest issue of popular international science journal ‘New Scientist’.
Most theories on the origin of cellular life presume that the first step was the formation of a spherical membrane called vesicle, that could enclose self-replicating chemical chains—the ancestors of modern DNA. The theory is that the ingredients for simple membranes were all present on the early earth and at some point spontaneously formed vesicles in water. It seemed most likely that this had taken place in the sea rather than in freshwater, largely because of the sheer size of the oceans. With their unique chemistry, deep-sea thermal vents and tidal pools are generally believed to be the most likely sites for such formation.
Now research by a team of graduate students led by Charles Apel of the University of California, Santa Cruz, has written off the ocean- theory claiming they were able to create stable vesicles using freshwater solutions of ingredients found on the early earth, and not with salty solutions. They have reported their findings in a popular issue of astrobiology.
"When sodium chloride or ions of magnesium or calcium were added, the membranes fell apart," Apel says. This happened in water that was even less salty than what the oceans are today. Geologist Paul Knauth of Arizona State University points out that the earth’s early oceans were 1.5 to 2 times saltier than what they are today, making it even more unlikely that viable cells could have arisen there. Giant salt deposits called evaporates that formed on the continents have actually made the seas less salty over time.
"No one in his right mind would use hot sea water for laboratory studies on early cellular evolution," says biochemist David Deamer of the University of California, Santa Cruz, who is reporting the work along with Apel. "Yet, for years we all have accepted without a question that life began in a marine environment. We were just the first to ask if we were really sure of that."
"This is a wake-up call", says mineralogist Robert Hazen of Carnegie Institution in Washington. "We’ve assumed that life formed in the ocean, but encapsulation in freshwater bodies on land is appearing more likely."
The finding would not have surprised Charles Darwin who over a century ago had speculated in his personal letters that the origin of life was "in some warm little pond with all sorts of ammonia and phosphoric salts, light, heat, electricity, etc present," the Journal exclaims.[xx]
3) Panspermia or Exogenesis
Did the first microorganisms arrive from space, riding piggyback on meteors that crashed into earth billions of years ago? Were the first seeds of life actually extraterrestrial ‘spores’, floating around in the infinite space on comets? This theory, known as Panspermia, is one that originated in the 19th century in opposition to the theory of spontaneous generation. It claims the ‘spores’ took root on primitive earth more than four billion years ago after the earth was bombarded by meteors for around 700 million years.[xxi] Panspermia propounded that reproductive bodies of living organisms exist throughout the universe and develop wherever the environment is favorable. The basic tenet of panspermia is that primitive life, which originated someplace else, was deposited on the Earth’s surface by means of a collision with some object that carried it. This theory has been re-popularized by the realization of the improbability that life formed through abiogenesis on earth, and is now more commonly called Exogenesis. The full theory of panspermia requires two events to explain the presence of life on earth:
1. The generation of life outside the earth, and then
2. The transfer of this life to earth
Many scientists have objected that the generation of life cannot occur, or have occurred, outside of a planetary environment, where heavier elements are plentiful. Almost the only elements present in interstellar space are hydrogen and helium--and the latter, being an inert or noble gas, is not a component of life in any form known to man.
The generation objection by itself would not destroy panspermia. But the transference event requires a transit through space, followed by a passage through the earth's atmosphere and then an impact on the ground or at sea. Either of these events is fraught with danger. The unprotected space outside of an atmosphere is subject to unfiltered radiation in various forms. These include the products of radioactive decay, cosmic rays (the highest-energy form of electromagnetic radiation known to man), and the stellar wind, a stream of particles that fly out from any star as it continuously burns. Even if any life forms could survive the spatial passage, it must then somehow penetrate the atmosphere and risk incineration from sheer friction, and then must survive the impact.[xxii]
A test done by attaching a piece of bacteria-smeared rock to a returning Russian spacecraft in September 2008 showed the difficulty of life surviving a fall through Earth's atmosphere, with temperatures on the rock reaching 1700 degrees Celsius, despite an entry speed which was a little more than half that a meteorite would experience. [xxiii]
4) Extraterrestrial origin
If we surmise that life was created from non-living chemicals, another possibility is that amino acids that were formed extra-terrestrially arrived on Earth via comets.
Why is the ‘Extraterrestrial origin of Life’ theory necessary?
- Scientists suspect that the early days on Planet Earth were hot, dry and sterile. It is now clear that space debris bombarded the young planet, creating cataclysms equivalent to the detonation of countless atomic bombs. Impacts of this kind, common until 4.0 billions years ago, surely aborted any fledgling life struggling to exist before that time. The short time span for life to emerge implies that the process might have required help from space molecules.
- Astronomers see signatures of a range of organic compounds throughout the universe, especially among the clouds. For example, a decade of research conducted by Allamandola and others has revealed that polycyclic aromatic hydrocarbons are the most abundant class of carbon-bearing compounds in the universe, trapping as much as 20 percent of the total galactic carbon in their molecular lattices.
· Experiments reveal that even at the extremely low temperatures and pressure of space, UV radiation can break chemical bonds. When the atoms are locked in ice, this bond-breaking process can make molecular fragments recombine into unusually complex structures that would not be possible if these fragments were free to drift apart. Bertein started with a simple ice of frozen water, methanol and ammonia - in the same proportions seen in space ice - the experiment yielded complex compounds such as the ketones, nitriles, ethers and alcohols found in carbon-rich meteorites. They also created hexamethylenetetramine, or HMT, a six-carbon molecule known to produce amino acids in warm, acidic water. David W. Deamer found that some of the molecules in the cloud-chamber ice grains form capsule-like droplets in water. These capsules are strikingly similar to extracts from the Murchison meteorite.
- Researchers found that interstellar amorphous ice too can flow, when exposed to radiation such as that found in deep space. Thus, it could be an explanation of how organic molecules may endure and react within the ice.
- Emerging consensus in planetary science agree that the early pre-biotic atmosphere was a neutral one rich in carbon dioxide and molecular nitrogen. Early CO2-rich atmospheres are implied by ‘hot accretion’ scenarios for Earth, in which core formation takes place quickly, leaving the upper mantle in an oxidized state. The short photo dissociation lifetimes of methane and ammonia in model paleo atmospheres reinforce this conclusion. There is a dense CO2 content in the early terrestrial atmosphere, consistent with the early ‘faint sun paradox’. Synthesis of key pre-biotic molecules such as hydrogen cyanide and formaldehye would have been much more difficult in CO2 atmospheres than in reducing ones.
- A long standing objection to extraterrestrial origin is that the organic compounds would be totally dissociated by the heat of cometary atmosphere passage and the ensuing impact. However, researchers speculated that aerobraking (slowing by atmospheric drag) and uneven distribution of shock energy throughout the impacting projectile will conspire to yield some region of the comet for which temperatures remain low enough to allow at least the hardier organics to survive. Because gas-phase results on shock pyrolysis are not available, it is estimated that the amino acid Alanine could withstand temperatures of upto 700K for 1 second, whereas other amino acids should withstand temperatures in the range of 600 to 800K. Through modelling, it is shown that dense CO2 atmospheres allow intact cometary organics to be delivered in large amounts to the surface of the planet.[xxiv]
A Critique:
According to Lynn Margulis, proponent of the groundbreaking Serial Endosymbiosis Theory of evolution and author of the book ‘Symbiotic Planet’, panspermia or extraterrestrial origin just shifts the puzzle of the origin of life from Earth to somewhere else in the Cosmos. If speculation hypothesizes that life must have originated somewhere else in the Universe, then we still need to find out how it could have happened there.
Ashwini Kumar Lal, Deputy Adviser to the Indian ministry of Statistics and Programme Implementation, has cast doubt on the leading theories of life’s origins. He has examined over 60 relevant research papers in the fields of Genetics, Astrobiology, and Space science before concluding that “Science has no clue about how life began.”
Lal, has also challenged the theory on the origin of life - known as abiogenesis - which says that life began from non-living chemicals. He says, “Ever since Alexander Oparin in Russia and J. B. S. Haldane in England initiated the modern theory of life’s origin from non-life in the 1930s, we have learnt much about how life operates, but almost nothing about how it originates. In his article ‘Origin of Life’ in the October 2008 issue of Astrophysics & Space Science, Lal says: “There is general consensus among biologists that bacterial cells cannot evolve from non-living chemicals in one step. It is speculated there must be some form of pre-cellular life from self-replicating RNA or ribonucleic acid.” It is a puzzle whose mystery will perhaps remain unknown to humanity ad infinitum.
Lal’s article notes that ‘Panspermia’ or theory of ‘Cosmic Ancestry’ propounded by Fred Hoyle and Chandra Wickramasinghe at Cardiff University 35 years ago as an alternative to abiogenesis is currently the most favoured theory of origin of life. But even this, he says, fails to address nagging uncertainties over “the exact timing and location for commencement of the process of evolution of life on the primitive Earth and elsewhere in the universe.” Nor does it provide any clue as to how prebiotic matter transformed into primitive bacteria in the early epoch of the earth. Lal concludes that origin-of-life investigators have proposed many theories, but evidence in favor of each of them is fragmentary at best.
As we know, the favoured theory on the origin of pre-cellular life is that during the early stages of evolution of life molecules of RNA replicated itself, forming the base for the evolution of DNA or Deoxyribonucleic acid, which contains the genetic instructions of all living organisms. But Lal says none of the experiments involving biologically produced RNA has provided concrete proof of RNA-World being the pathway between non-life and life. “Also, another flaw in the theory is that scientists have failed to answer how the RNA compounds came into being on the earth in the first place” Lal said, a conclusion shared by Gerald Joyce of the Scripps Research Institute in California.
Lal says that experiments conducted by scientists in laboratories worldwide “have not found the RNA in isolation to be self-replicating”. He said, “Experiments have failed to provide conclusive proof to support the RNA World theory, despite biotechnology tools. Scientists have not been successful in proving in the laboratory that inorganic compounds can become organic.”
Finally, Lal finds that prevailing theories like abiogenesis, RNA-World, iron-sulphur world (deep-sea-origin of life) and panspermia (life arrived from outer space) fail to provide clues on the exact origin of life.
The last word on this topic should definitely be Shapiro’s. He doesn't think it necessary to invoke scenarios of multiple universes or life-laden comets crashing into ancient Earth. Instead, he thinks life started with molecules that were smaller and less complex than RNA, which performed simple chemical reactions that eventually led to a self-sustaining system involving the formation of more complex molecules.
The current trend in origin of life research is to look for simpler, pre-RNA molecules to serve as genetic material. "If you fall back to a simpler theory, the odds aren't astronomical anymore," said Shapiro in the journal LiveScience.
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