ORIGIN OF LIFE ON EARTH

REFERENCE I Basic timeline

The basic timeline of a 4.6 billion year old Earth, with approximate dates:

    3.8 billion years of simple cells (prokaryotes),

    3.4 billion years of stromatolites demonstrating photosynthesis,

    2 billion years of complex cells (eukaryotes),

    1 billion years of multicellular life,

    600 million years of simple animals,

    570 million years of arthropods (ancestors of insects, arachnids and crustaceans),

    550 million years of complex animals,

    500 million years of fish and proto-amphibians,

    475 million years of land plants,

    400 million years of insects and seeds,

    360 million years of amphibians,

    300 million years of reptiles,

    200 million years of mammals,

    150 million years of birds,

    130 million years of flowers,

    65 million years since the dinosaurs died out,

    2.5 million years since the appearance of the genus Homo,

    200,000 years of anatomically modern humans,

    25,000 years since the disappearance of Neanderthal traits from the fossil record.

    13,000 years since the disappearance of Homo floresiensis from the fossil record

REFERENCE II

Ref.  http://origins.swau.edu/papers/life/javor1/default.html

(ORIGIN OF LIFE: A LOOK AT LATE 20TH-CENTURY THINKING.)

Theories to explain the presence of life on Earth.

The earliest historical records indicate that man has recognized the qualitative difference between living and non-living matter, and since then there never has been a shortage of theories to explain the presence of life on Earth. Yet the origin of life remains one of the greatest challenges to naturalistic interpretations.

According to Nobel laureate Max Delbruck, "... there has been an immense conceptual gap between all present-day life and no life," and the "how" of the transition of earth from no life to life is "perhaps the fundamental question of biology"

Nevertheless, the immense conceptual gap between life and non-life is neither recognized nor admitted by many evolutionary theorists. A 1978 review entitled "Chemical evolution and the origin of life" begins with these words: "Perhaps the most striking aspect of the evolution of life on earth is that it happened so fast'.

More recently, the first chapter of a college textbook on the molecular biology of the cell contains this summary statement: "Living cells probably arose on earth by the spontaneous aggregation ( massing together or clustering of independent but similar units, such as particles, parts, or bodies) of molecules about 3.5 billion years ago".

Regardless of their degree of optimism or enthusiasm, evolutionary theorists are forced to propose explanations for the spontaneous generation of life from non-living matter. In order for biological evolution to begin, some starting material is necessary. This need is met by the postulates of chemical evolution.

When the outlines of modern theories of chemical evolution (the natural processes on a "prebiotic earth" which gave rise to the first living matter) were formulated by A.I. Oparin and J.B.S. Haldane in the 1920s, very little was known about the biochemical intricacies of living matter. Consequently, there was plenty of freedom to postulate mechanistic processes by which organisms could come into existence.

Modern theories of chemical evolution found in current monographs and textbooks developed over a span of approximately 60 years. They suggest that early Earth was covered largely with a warm, slightly alkaline ocean. Though rich in carbon monoxide, carbon dioxide, ammonia, methane, hydrogen, and nitrogen, the atmosphere definitely did not contain atomic or molecular oxygen. Ultraviolet light from the sun, geothermal energy from volcanoes, shock waves from thunder, and cosmic radiation acted upon gases of the primitive atmosphere causing the formation of bio-monomers such as amino acids, sugars, purines, pyrimidines, and fatty acids. These substances polymerized to form the prototypes of more recent proteins, nucleic acids and cell membranes. In time they coalesced (to unite so as to form one mass, community, etc.) to form the first protocell, a collection of polymers enclosed in a membrane. Eventually these protocells became increasingly complex, until the first true living cell was born.

Why life cannot arise spontaneously

Some general considerations take the topic of the origin of life beyond listing various theories of chemical evolution and a discussion of their inadequacies. First, there is the tacit assumption by evolutionists that matter possesses some sort of internal drive which pushes it to self-organize into living structures. It is as if molecules constituting bio polymers would confer some sort of benefit to their constituent atoms.

There is no evidence that this is the case. Atoms and molecules respond to only one type of drive; that is, to exist in the lowest possible state of energy. Bio molecules are examples of exactly the opposite; they are complexes of atoms in a high energy state. If atoms had a choice, they would rather get out of being part of the high energy configurations called proteins and nucleic acids.

All mechanistic explanations of origins have two deficiencies.

One difficulty is in explaining the source of biological information, which ultimately dictates the structure and function of bio polymers. It is clear that chance cannot provide this information.

A second consideration which renders all mechanistic explanations invalid is that life processes are non-equilibrium events. If by chance all necessary bio polymers and small metabolites could have been produced in the primordial ( original; elementary) environment, brought together and enclosed in a membrane, a non-living cell would be the result. In the very process of assembly, reactants and their catalysts would be brought together, providing opportunity for individual chemical reactions to reach equilibrium.

There is such a concentration of living organisms on Earth's surface that it is difficult to locate any area that is sterile. Obviously, life had to start somehow.

The existence of a supernatural Intelligence who is capable of designing and creating the various living organisms found on Earth is inconceivable to the modern secular mind which is accustomed to explaining phenomenon by natural processes. But this is precisely the lesson to be learned from our chemical evolutionary efforts. Our inability; not only to create living matter but even to suggest how such could come into existence; forces us to admit that the existence of life demands the existence of a Creator.

REFERENCE III

Ref.  http://www.biology-questions-and-answers.com/origin-of-life.html

(The Origin of Life, Questions and Answers)

3. When did life appear on earth?

It is estimated that life on earth emerged about 3.5 billion years ago, thus 1 billion years after the formation of the planet.

4. Historically how has the origin of life on earth been explained?

The most recurrent explanation for the phenomenon of life on earth is the mythological. People from various parts of the world developed explanatory myths about the origin of animals and human beings. Some of those myths were incorporated into religions and almost all religions have metaphorical or transcendental explanations about the origin of life on the planet.

With the development of science new explanatory attempts have emerged. Notable among them are the spontaneous generation hypothesis, or abiogenesis, that asserted that living beings were created from nonliving material, the cosmic panspermia hypothesis, theory that life on earth is a result of seeding from the outer space, the autotrophic hypothesis, according to which the first living beings were autotrophs, and the heterotrophic hypothesis, the most accepted nowadays, that affirms that life emerged from heterotrophic cells.

At the end of the 1980s decade a new hypothesis known as the RNA world hypothesis was presented. This hypothesis asserts that primitive life had only RNA as genetic material and as structural molecules that later turned into DNA and proteins. The RNA world hypothesis is strengthened by the fact that RNA can play a catalytic role, like enzymes, and by the finding that some bacteria have ribosomes made only of RNA without associated proteins.

5. What is the spontaneous generation hypothesis?

The spontaneous generation hypothesis, or abiogenesis, asserts that life on earth has come from nonliving material. For example, the fact that with time rats appeared around waste was considered in the past a confirmation of this hypothesis. Some supporters of spontaneous generation associated it with the existence of an active principle that would be the source of life, a theory known as vitalism.

6. How did the experiments of Redi and Pasteur refute the hypothesis of spontaneous generation?

To refute the spontaneous generation hypothesis many experiments were performed. Francisco Redi, in 1668, verified that maggots appeared on meat only when there was exposition to the environment; within closed environments, they did not appear. In 1862, Louis Pasteur working with swan-neck flasks refuted the abiogenesis hypothesis definitively. In this experiment Pasteur demonstrated that boiled (to kill microorganisms) nutritive soups put in swan-neck flasks (with a curved down mouth so microorganisms could not enter easily) did not contaminate with microorganisms while the same soups within flasks with open upwards mouths were contaminated in a few days. The fact that both flasks were open refuted the argument of the vitalists that the vital elan could not enter the flasks. Pasteur broke the swan-necks of the flasks to demonstrate that proliferation of microorganism could happen if these beings were able to reach the broth.

7. What is panspermia?

Panspermia is a hypothesis that describes life on earth as not originated from the planet. The idea is that the first living beings that colonized the earth came from outer space, from other planets or even from other galaxies by traveling in meteorites, comets, etc. According to this hypothesis even the type of life now existent on earth could have also been seeded intentionally by extraterrestrial beings in other stellar and planetary systems.

8. What is the autotrophic hypothesis on the origin of life?

The autotrophic hypothesis on the origin of life asserts that the first living beings on earth were producers of their own food, just like plants and chemo synthetic microorganisms.

10. What is the most accepted hypothesis about the origin of life on earth? How does it compare to the other main hypotheses?

The heterotrophic hypothesis is the strongest and most accepted hypothesis about the origin of life.  

The spontaneous generation hypothesis has been excluded by the experiments of Pasteur. The panspermia hypothesis is not yet completely refuted but it is not well-accepted since it would be necessary to explain how living beings could survive long space journeys under conditions of extreme temperatures as well as to clarify the manner by which they would resist the high temperatures faced when entering the earth's atmosphere. The autotrophic hypothesis is weakened if one takes into account that the production of organic material from inorganic substances is a highly complex process requiring diversified enzymatic systems and that the existence of complex metabolic reactions on the primitive earth were not probable.

9. What is the heterotrophic hypothesis on the origin of life?

According to the heterotrophic hypothesis the first living beings were very simple heterotrophic organisms, i.e., not producers of their own food, which emerged from the gradual association of organic molecules into small organized structures (the Coacervates). The first organic molecules in their turn would have appeared from substances of the earth's primitive atmosphere submitted to strong electrical discharges, to solar radiation and to high temperatures.

16. What are coacervates?

Coarcervates are small structures made of the aggregation of organic molecules under water solution. By electrical attraction the molecules join into bigger and more organized particles distinct from the fluid environment forming a membrane-like structure that separates an internal region of the coacervate from the exterior. The coacervates might divide themselves and also absorb and excrete substances. It is believed that these structures may have been the precursors of cells.

Reference IV
Ref. Scientific American, September- 2009.

(This reference gives relatively latest position on the status of “Science” on the research of origin of life on the earth. It states that “Crating a life” is the necessary step in understanding the origin. So far no news in ‘success’ of creating a life, though some claim to have reached close to it).)

The actual nature of the first organisms and the exact circumstances of the origin of life may be forever lost to science. But research can at least help us understand what is possible. The ultimate challenge is to construct an artificial organism that can reproduce and evolve. Creating life anew will certainly help us understand how life can start, how likely it is that it exists on other worlds and, ultimately, what life is.

What is LIFE?

Scientists have long struggled to define “life” in a way that is broad enough to encompass forms not yet discovered. Here are some of the many proposed definitions.

1.  Physicist Erwin Schrodinger suggested that a defining property of living systems is that they self-assemble against nature’s tendency toward disorder, or entropy.

2.  Chemist Gerald Joyce’s “working definition,” adopted by NASA, is that life is “a self- sustaining chemical system capable of Darwinian evolution.”

3.  In the “cybernetic definition” by Bernard Korzeniewski, life is a network of feedback mechanism

Journey to the Modern Cell

After life got started, competition among life-forms fueled the drive toward ever more complex organisms. We may never know the exact details of early evolution, but here is a plausible sequence of some of the major events that led from the first proto-cell to DNA- based cells such as bacteria.

1 EVOLUTION STARTS

The first proto-cell is just a sac of water and RNA and requires an external stimulus (such as cycles of heat and cold) to reproduce. But it will soon acquire new traits.

2 RNA CATALYSTS

Ribozymes—folded RNA molecules analogous to protein-based enzymes—arise and take on such jobs as speeding up reproduction and strengthening the proto-cell’s membrane. Consequently, proto-cells begin to reproduce on their own.

3 METABOLISM BEGINS

Other ribozymes catalyze metabolism—chains of chemical reactions that enable proto-cells to tap into nutrients from the environment.

4 PROTEINS APPEAR

Complex systems of RNA catalysts begin to translate strings of RNA letters (genes) into chains of amino acids (proteins). Proteins later prove to be more efficient catalysts and able to carry out a variety of tasks.

5 PROTEINS TAKE OVER

Proteins take on a wide range of tasks within the cell. Protein-based catalysts, or enzymes, gradually replace most ribozymes.

6 THE BIRTH OF DNA

Other enzymes begin to make DNA. Thanks to its superior stability, DNA takes on the role of primary genetic molecule. RNA’s main role is now to act as a bridge between DNA and proteins.

7 BACTERIAL WORLDS 

Organisms resembling modern bacteria adapt to living virtually everywhere on earth and rule unopposed for billions of years, until some of them begin to evolve into more complex organisms.

My Comments:

It seems from the above references that the formation of life through the Coacervate structures, as suggested by Oparin is still the most accepted theory so far. It is also mostly held that the generation of life is from non-living matter. According to Nobel laureate Max Delbruck, "how" of the transition of earth from no life to life is "perhaps the fundamental question of biology" yet to be answered.

LIFE DEFINITION: Scientists have long struggled to define “life”. There are some of the many proposed definitions but yet no all accepted definition.

“The actual nature of the first organisms and the exact circumstances of the origin of life may be forever lost to science. But research can at least help us understand what is possible”. When fact based deductions are impossible, science should resort to logic based rational hypothesis. In a book like 'MIND POWER' and other publications written by Swami Vijnananand and published by Manashakti before 25 - 30 years, we will find such hypothesis not only for creation of life but also subsequent evolution till human being as of today. The role of MIND is the key in the process.

Vijay R. Joshi.