Popular theories that will be presented are as follows, theory of special creation, cosmozic theory/panspermia, spontaneous generation/abiogenesis theory, biogenesis or the primodial soup theory and the RNA world theory.
What is life? And where life came from? These are the questions that our group project will try to present. Group 16 will present the theories of the Origin of life.
A popular theory that was held throughout the middle ages until the 19th century, is the hypothesis that some vital force contained in or given to organic matter can create living organisms from inanimate objects. Aristotle (384-322 B.C. )He proposed the theory of SpontaneousGeneration, when he observed that aphids arise from the dew which falls on plants, flies from putrid matter, mice from dirty hay, crocodiles from rotting logs at the bottom of bodies of water, and so on
mice appeared. In Egypt, when the Nile river flooded, along the river fertile mud is left behind and with it frogs appeared.In Europe, when farmers stored their grains in barns, molds spreads on the grains and From carcasses of meat in the old times, flies abound everywhere.
Francesco Redi , an Italian Physician in 1668 disproved spontaneous generation for large organisms by showing that maggots arose from meat only when flies laid eggs in the meat.
In his hypothesis, “rotten meat does not turn into a fly. Only flies can make more flies.”He found that if a flask was closed with a lid so adult flies could not get in, no maggots developed on the rotting meat within. In a flask without a lid, maggots soon were seen in the meat because adult flies had laid eggs and more adult flies soon appeared.
Needham theorized that if he took chicken broth and heated it, all living things in it would die. After heating some broth, he let a flask cool and sit at a constant temperature. The development of a thick turbid solution of microorganisms in the flask was strong proof to Needham of the existence of spontaneous generation
LazzaroSpallanzani (1765) later repeated the experiments of Needham, but removed air from the flask, suspecting that the air was providing a source of contamination. No growth occurred in Spallanzani's flasks and he took this as evidence that Needham was wrong. Proponents of spontaneous generation discounted the experiment by asserting that air was required for the vital force to work.
Louis Pasteur ended the debate with his famous swan-neck flask experiment, which allowed air to contact the broth. Microbes present in the dust were not able to navigate the tortuous bends in the neck of the flask
The swan neck flask experiment. Pasteur filled a flask with medium, heated it to kill all life, and then drew out the neck of the flask into a long S shape. This prevented microorganisms in the air from easily entering the flask, yet allowed some air interchange. If the swan neck was broken, microbes readily entered the flask and grew.
The origin of life
The Origin of Life Group 16 Nat Sci projectSubmitted to : Prof. Nerissa Torreta
Theories on the Origin of LifeI. Theory of • Emmaruth Fandialan Spontaneous Generation/Abiogen esis TheoryII. Biogenesis Theory • Byron CayabyabIII. Cosmozic • Paolo Amer Theory/PanspermiaIV. Theory of Special • Patricia Lijauco Creation • Emmaruth FandialanV. RNA World Theory
IntroductionBiology is known to be the study of life and living organisms. While thisdiscipline, which seeks to answer the question, “What is Life?”, is already quitea complicated subject to touch upon in scientific and philosophical terms, agreater debate arises from the question of “Where did life come from?”.Indeed, it seems that this topic has not only instigated a variety of discussionson what is the first life form on Earth, and when it appeared, but it has alsosparked a long-standing division between religion and science.It is perplexing how a simple question has given birth to a multitude ofhypotheses that aim to present a unique explanation for Creation and theOrigin of life, whether they be supported by tangible evidences and scientificfacts or not. Nevertheless, these theories prove to be quite interesting andrefreshing studies, which will ultimately allow us to comprehend the beginningof life.While there have been many theories that propose its own ideas on how lifecame into existence, here are some of the more popular theories, which arestill being recognized today: Patricia Lijauco
I. Spontaneous Generation/AbiogenesisAbiogenesis - or biopoiesis is the study of how biological life arises from inorganic matter through natural processes. (Abiogenesis. (2012, February 12). In Wikipedia, The Free Encyclopedia. Retrieved 22:03, February 13, 2012, fromhttp://en.wikipedia.org/w/index.php?ti tle=Abiogenesis&oldid=476469737 ) Aristotle (384-322 B.C. )Spontaneous Generation - A He proposed the theory of popular theory that was held Spontaneous throughout the middle ages until Generation, when he observed the 19th century, is the hypothesis that some vital force contained that aphids arise from the dew which in or given to organic matter can falls on plants, flies from putrid matter, create living organisms from mice from dirty hay, crocodiles from inanimate objects. rotting logs at the bottom of bodies of http://www.microbiologytext.com/index.php?module =Book&func=displayarticle&art_id=27 water, and so on. Abiogenesis. (2012, February 12). In Wikipedia, The Free Encyclopedia. Retrieved 22:03, February 13, 2012, fromhttp://en.wikipedia.org/w/index.php?title=Abiogenes is&oldid=476469737
Observations1. mice appeared. In Egypt, when the Nile river flooded, along the river fertile mud is left behind and with it frogs appeared.2. In Europe, when farmers stored their grains in barns, molds spreads on the grains and3. From carcasses of meat in the old times, flies abound everywhere.
Conclusions1. It was perfectly obvious to people back then that muddy soil gave rise to the frogs.2. It was obvious to them that the mice came from the moldy grain.3. The rotting meat that had been hanging in the sun all day was the source of the flies.
Abiogenesis Observations1. Put dirty shirt or some 2. A dead young rags in an open pot or barrel containing a few bull, was buried grains of wheat or in an upright some wheat bran, and in 21 days, mice will position so that appear. There will be its horns adult males and protrude from females present, and they will be capable of the ground. After mating and a month, a reproducing more mice. swarm of bees will fly out of the corpse.
Disproving Abiogenesis Theory• Francesco Redi , an Italian Physician in 1668 disproved spontaneous generation for large organisms by showing that maggots arose from meat only when flies laid eggs in the meat.
Redi’s Hypothesis & Findings• In his hypothesis, “rotten meat does not turn into a fly. Only flies can make more flies.”• He found that if a flask was closed with a lid so adult flies could not get in, no maggots developed on the rotting meat within.• In a flask without a lid, maggots soon were seen in the meat because adult flies had laid eggs and more adult flies soon appeared.
Disproving Redi• 1745, John Needham • Needham theorized that if he took chicken broth and heated it, all living things in it would die. After heating some broth, he let a flask cool and sit at a constant temperature. The development of a thick turbid solution of microorganisms in the flask was strong proof to Needham of the existence of spontaneous generation
Disproving Needham• Lazzaro Spallanzani (1765) later repeated the experiments of Needham, but removed air from the flask, suspecting that the air was providing a source of contamination. No growth occurred in Spallanzanis flasks and he took this as evidence that Needham was wrong. Proponents of spontaneous generation discounted the experiment by asserting that air was required for the vital force to work.
An End to the Conflict• Louis Pasteur ended the debate with his famous swan-neck flask experiment, which allowed air to contact the broth. Microbes present in the dust were not able to navigate the tortuous bends in the neck of the flask.
• The swan neck flask experiment. Pasteur filled a flask with medium, heated it to kill all life, and then drew out the neck of the flask into a long S shape. This prevented microorganisms in the air from easily entering the flask, yet allowed some air interchange. If the swan neck was broken, microbes readily entered the flask and grew.
References:• Abiogenesis. (2012, February 12). In Wikipedia, The Free Encyclopedia. Retrieved 22:03, February 13, 2012, from http://en.wikipedia.org/w/index.php?title=Abiogenesis& oldid=476469737• http://www.microbiologytext.com/index.php?module=B ook&func=displayarticle&art_id=27• http://www.newworldencyclopedia.org/entry/Origin_of _life
III. Cosmozic Theory • Also called Panspermia Theory • Panspermia is a Greek word that translates literally as "seeds everywhere" • It states that life exists throughout the Universe, distributed by meteoroids, asteroids and planetoids and that
Life on Earth• Panspermia theory suggests that life was brought to the earth via mechanisms that include the deflection of interstellar dust by solar radiation pressure and extremophile microorganisms traveling through space within an asteroid, meteorite or comet.• extremophile microorganisms are organisms that survive in and even may require physically or geochemically extreme conditions that are detrimental to the majority of life on Earth.• These spores/microorganisms then evolved to other organisms/living things inhabiting the planet
Proponents of CosmozoicTheory• Anaxagoras, a Greek Philosopher, was one of the first to propose the concept of Panspermia• Berzelius (1834), Richter (1865), Thomson (Lord Kelvin) (1871), and Helmholtz (1871) were among the first to argue the case for panspermia from a scientific standpoint• Swedish chemist Svante Arrhenius (1908) popularized the concept of life originating from space
Three Variations of Panspermia• Lithopanspermia or interstellar panspermia• Ballistic panspermia or interplanetary panspermia• Directed panspermia
Lithopanspermia• Also known as interstellar panspermia• impact-expelled rocks from a planets surface serve as transfer vehicles for spreading biological material from one solar system to another.• Assumes microorganisms survive: – the impact ejection process from the planet of origin – travelling through space, and – landing on a planet in another solar system.
Ballistic panspermia• Also known as interplanetary panspermia• impact-expelled rocks from a planets surface serve as transfer vehicles for spreading biological material from one planet to another within the same solar system• Assumes microorganisms survive: – the impact ejection process from the planet of origin – travelling through space, and – landing on a planet in another solar system.
Directed panspermia• Proposed by the late Nobel prize winner Professor Francis Crick, OM FRS, along with British chemist Leslie Orgel in 1973• the intentional spreading of the seeds of life to other planets by an advanced extraterrestrial civilization, or the intentional spreading of the seeds of life from Earth to other planets by humans
Limitations of the CosmozoicTheory• The theory assumes that life already exists elsewhere in the Universe and can only explain the appearance of life on earth. It does not explain origin of life itself nor does it explain how life could have originated else-where.• It also does not necessarily suggest that life originated only once and subsequently spread through the entire Universe, but instead that once started, life may be able to spread to other environments suitable for replication
Gallery ALH 84001 – meteorite found in Alan Hills, Antartica in 1984. There are claims that the meteorite may contain evidence of traces of life from Mars, as images from an electron microscope reveal chain structures in the meteorite fragment. (image courtesy of wikipedia.org)
Gallery The surface of Mars, while mostly is a frozen desert, have dried up channels and crater erosion. This leads us to believe that Mars was once warmer and drier, and may have housed rivers and oceans. Was Mars once a cradle of life? (image courtesy of wikipedia.org)
References• http://www.wikipedia.org• http://www.panspermia-theory.com• http://www.youtube.com/watch?v=AgeuRu kfZLE• http://www.hssrd.org/journal/summer2002/ origin.htm• Official Nat Sci 2 Book
What is the Special Creation Theory About?Unlike the other theories on the possible origin of life, the Special CreationTheory is not supported by scientific facts or evidences. However, it is heavilyinfluenced by faith, specifically by one’s belief of a Supreme Being, whocreated the heavens and the earth, including everything in it, from scratch.The term “Creationism” is not limited to the Christians, as a Creationist can beadhering to a Muslim, Buddhist, or an Islamic belief. Nevertheless, this studywill focus on the more popular notion that the Christian God is the Creator ofthe universe and everything that lives within it.In the first chapter of Genesis, which is the first book of the Bible written byMoses, the story of Creation is narrated, from the time that the heavens andthe earth were formed until the first man was given life. In terms of the Bible’stimeline, it is said that all of creation was created within six days. The passageson the next slides are taken from the New International Version Bible.
History of the Special Creation TheoryThe Special Creation Theory is basically a result of the people’s curiosity of howlife initially came to be. At that time, long before the 14th century, Creationismhas been widely accepted (though the term only became popular during the 19thcentury) , most likely because of the lack of evidences and disciplines, whichfocus on the disproving of this belief. This Pre-Scientific Era gave attention toboth a literal and allegorical meaning of the creation narrative in the book ofGenesis, which presented the different religions with a viable explanation onhow the world came into existence.It was in the 14th century when the Renaissance paved the way to modernscience, which sought to disprove this theory, contributing to the developmentof other theories that aim to explain when life first came into being. In spite ofthe introduction of naturalism, specialization, and skepticism, the religiousgroups, particularly the Protestant Reformation, strongly urged its advocates toimmerse themselves into the study of the Bible, as well as to adhere to theconviction that God is the Creator of all things.
History of the Special Creation TheoryDuring the Renaissance era’s development of the Protoscience, it is surprisinghow many scientists and philosophers have developed a study, which seek tostudy Creation, by using the book of Genesis as the main guide, such as CarolusLinnaeus’ research on the taxonomy, which he believed will reveal God’s originalplan in the creation of animal species. Disciplines like naturaltheology, naturalism, and even the evolution theory first started as a simplestudy to prove that the Biblical Creation story is real. It is perplexing how itseems that religion and science support and influence one another at thisparticular age.The late 17th century brought about the Scientific era, which contributed to morequestions and arguments against the Special Creation Theory. Many scientistsquestioned that if the universe and life have their beginnings and a living Creator(as the Bible says), then surely this Creator, God, also has a beginning. As thereare no means to prove this, these people relied on their own experimentationsand researches as evidences, creating other theories about life’s origin, whichare leaning toward a scientific sense.
History of the Special Creation TheoryIn spite of this Scientific Revolution, the Church held on firmly to its stand on theSpecial Creation Theory. In 1785, geologist James Hutton introduced his ideas onUniformitarianism in his paper entitled, “Theory of the Earth”, which promotedthe thought that the Earth is older than 6000 years old at that time, since greattime is required to develop lands from sediments, etc. With enough evidenceand support from fellow geologists, Hutton’s eventually was accepted by thescientific community.By the 18th and 19th century, a compromise was made between the religious andscientific community in the form of the Gap Theory, which accepted the six-daycreation, while still insisting that the Earth has already existed for several ages.Charles Lyrell, clergyman and geologist, wrote the Principles of Geology series,which supported Hutton’s Uniformitarianism, but still explained that Godcreated each species individually, but these creatures became extinct because oftheir habitat’s evolving nature.
History of the Special Creation TheoryIn 1859, Charles Darwin published his well-known theory of Evolution in theOrigin of Species. His work is the most famous paper, which focused on how lifeforms first existed on Earth, rather than the usual researches on how Earth cameto be. The main gist of his paper is that all species has a common descent, withman’s gradual evolution from primates as one of his main examples. Darwin’sdeath in 1882 didn’t stop his followers from pursuing further studies on hisEvolution theory, in spite of the controversy that Darwin supposedly became aChristian before he died.The early 20th century brought new life and hope to the Special CreationTheory, though it came not without drastic measures. Christian Fundamentalistsrejected Darwin’s Theory completely, and succeeded in banning his Evolutionideals from being taught in schools, in the place of Genesis’ Creation and Floodstories. This became the beginning of Darwinism’s eclipse, as many have startedto question his belief on natural selection, as well as the mechanics of evolution.As a result, Creationism became widely accepted again.
History of the Special Creation TheoryNowadays, there’s no doubt that the scientific and religious communities stillhave a raging battle to prove the true origin of life, based on viable evidencesand faith in the Bible. Nevertheless, both science and religion give people thechance to adhere to their own beliefs. Science even goes so far as to allowpeople to believe in any god.One probable reason why the Special Creation Theory has survived the test oftime is because of the equal survivability of the Bible. The traditions andpractices that the Churches have also established, in terms of studying the Bibleand looking at it in both the literal and allegorical sense, have also stayedthroughout the centuries, making the Special Creation Theory as one of the mostpopular, not to mention widely accepted, theories of how life came into being.
How is the Special Creation Theory Acceptable?The Special Creation Theory is widely accepted in the Christian community,with BIBLE as the sole basis. In spite of the lack of evidences, which serve asproof that life was created within six days, Christians have held on to theirfaith, as well as to the Scriptures. Simply put, the Christian community insiststhat everything you need to know about life is written in the Bible. Since theBible is said to be free from errors and non-contradictory, Christians have alsoquoted the New Testament as to oppose those people who say that theCreation Theory is only touched upon in the Old Testament portion.“Through him [Jesus Christ] all things were made; without him nothing wasmade that has been made.” – John 1:3 (NIV)“.. by his Son, through whom he made the universe.” – Hebrews 1:2b (NIV)These two verses are only two verses in the Scriptures that clearly states andrepeats that God is the Creator of everything, including man.
How is the Special Creation Theory Acceptable?The Christian community also believed that God is the head of everything increation, including science.“And God placed all things under his feet and appointed him [Jesus Christ] to behead over everything for the church.” – Ephesians 1:22 (NIV)In terms of the lack of evidence, which supports the Special Creation Theoryas true:“We live by faith, not by sight.” – 2 Corinthians 5:7 (NIV)“For since the creation of the world God’s invisible qualities—his eternal powerand divine nature—have been clearly seen, being understood from what hasbeen made, so that men are without excuse.” – Romans 1:20 (NIV)
How is the Special Creation Theory Acceptable?In the logical sense, the Special Creation Theory is considered by many as adivine miracle, which needs no further evidence or scientific support becausenobody has seen God, nor has the credibility and comprehension tounderstand how He created life in general. In terms of scientificdata, Creationists will only have to look at the complicated, Biological design ofeach species, which can only be created instantly by a Superior Being.As the scientific community still continues to probe into the possibility ofevolutionary theories as the best explanation for Creation, it is surprising howthe Christian community is being patient and tolerant of science’s furthersearch for the truth. Christians hold on to the fact that in spite of these severaldisciplines and studies, there’s still no infallible data or works that haven’t yetbeen disproved, which suggests that the Special Creation Theory did nothappen. Thus, until Creationism is thoroughly disproved, it remains to be acredible, and even scientific, explanation for the origin of life.
What Makes the Theory Unacceptable?Of course, the Special Creation Theory will not remain a theory withoutarguments or rejections from the scientific community. Without any scientificevidences that will guarantee that a Supreme Being created the universe andthe life forms, then it is just not possible for Creationism to be true. For theCreationists, the biggest foe that they’ve encountered so far are theEvolutionists.There are basically three main points, which the evolutionary theorists haverelied on to try and explain Creation, although these theories have beendebunked by Creationists, as well:Fossil EvidenceIn terms of the role of fossils in evolution, there has been a long-standingdebate on how an invertebrate (worm) became a vertebrate (fish) uponfossilization. Harvard University professor, Alfred Romer, said that while this ispossible, the time it will take to do so is 100 million years.
What Makes the Theory Unacceptable?Fossil Evidence (Cont.)However, there are no records that show the invertebrates in the process ofevolution. Indeed, Stephen Stanley from Johns Hopkins University hasconfirmed that not one fossil sample can support the theory of evolution, inwhich a species will continue to evolve, given the right time and conditions.Thus, it seemed that the remains were simply buried into the recesses of theearth and preserved by minerals. This basically has the same context ofDarwin’s primate to man theory, too.GeneticsGenetics has always been pointed as the key to evolution, since it involves themutation theory, which is supposed to contribute to the new creation ofspecies, and this is also concerned with the support of Darwin’s EvolutionTheory, by which he said that mutations happen to allow the creature to adaptto an ever-changing environment. While this can be quite possible, particularlybecause of the RNA’s ability to reproduce, scientists have failed to accept that
What Makes the Theory Unacceptable?Genetics (Cont.)evolution by mutation has its limitations, and it is not possible for the RNAchromosome to produce other samples, which it doesn’t have. Going back tothe creation narrative in Genesis 1, it clearly said that God allowed the plants,animals, and man to reproduce according to its kind. Therefore, the possibilityof an extraordinary genetic variation is very limited, regardless of the time orenvironmental conditions.Molecular BiologyThis has basically the same thrust in evolution as Genetics, in the sense thatthe scientists are pointing to the unique characteristics of a DNA structure tochange its frameworks overtime, resulting to a genetic variation, which couldultimately produce a new species. However, instead of focusing on the actualDNA and RNA materials, this is concerned more with the molecular activity inthe body. However, just to re-iterate, genetic variation through molecules andatoms is limited, if not impossible.
What Makes the Theory Unacceptable?The Special Creation Theory also doesn’t give the science community ascientific explanation of the origin of life. Since this theory is completely basedon faith, thorough experimentations and researches haven’t been done tosupport this belief. Plus, those who’d be willing to do such experiments willfind it impossible to do so because it’s not possible to measure God as asubject, as well as the precise environment at that time.As far as the scientific community is concerned, it is perfectly okay for some toaccept the Special Creation Theory out of faith. Nevertheless, this will not stopthem from trying to find out the truth about existence.
• The history of Earth and its life are two concepts that are inseparable. Researchers and scientists in different disciplines of science are still debating about the history of Earth and how and where life originated (Campbell et al., 1999). Many theories about the origin of life on Earth were formulated throughout the years. However, the validation of the said theories can be difficult because life is incessantly evolving.
Solar Nebula Theory or Nebular Hypothesis• This theory is the most accepted widely accepted theory that explains the formation and evolution of the solar system (Coffey, 2010). The said theory was first proposed in the 18th century by Immanuel Kant, Emanuel Swedenborg and Pierre – Simon Laplace. In 1755, Kant disputed that gaseous clouds— nebulae, which slowly rotate, gradually collapse and flatten due to gravity and eventually form stars and planets. Laplace’s proposed a similar model in which a protosolar cloud (a nebular cloud) contracted and cooled, flattening and shedding rings of material in the process which later collapsed to form the planets. Laplace proposed in his text, “The System of the World”, in 1796 a similar model in which a protosolar cloud (a nebular cloud) contracted and cooled, flattening and shedding rings of material in the process which later collapsed to form the planets. Over the course of the 20th century, this model came to be challenged by a number of theorists who proposed numerous models in an attempt to replace it. However, none of these attempts were successful and it was not until the 1970’s with Soviet astronomer Victor Safronov that the modern (and widely accepted) Solar Nebular Disk Model (SNDM) came into being (Williams, 2010).
• The key idea behind the solar nebula hypothesis is that once a rotating interstellar gas cloud has commenced gravitational collapse, then the conservation of angular momentum will force the cloud to develop a massive, central condensation that is surrounded by a less massive flattened ring, or disk of material. The nebula hypothesis asserts that the Sun forms from the central condensation, and that the planets accumulate from the material in the disk. The solar nebula model naturally explains why the Sun is the most massive object in the solar system, and why the planets rotate about the Sun in the same sense, along nearly circular orbits and in essentially the same plane (Net Industries, 2012).
The stages of solar nebula theory• Originally a large cloud of dust and gas (75% H and 24% He) became unstable. The densest part of the cloud started to collapse under the force of gravity Gravity pulled the dust and gas toward the center of the cloud, causing the cloud to take on a spherical shape.• As the size (radius) of the cloud decreased, the collapsing cloud increased its rate of rotation. The principle on which this conclusion is based is a law of physics called “the conservation of angular momentum”. The effect is similar to that of an ice skater who must pull in his or her arms in order to increase his or her rate of spin.
• The increased rotation of the cloud caused the cloud to change shape. It became flattened at the rotational poles. Thus the once spherical cloud became disk shaped. This rotating disk of dust and gas became the “solar nebula”. Most of the matter in the collapsing cloud ended up in a central bulge• As the cloud collapsed, gravitational energy was released, heating the central portion of the nebula where a protosun formed.• Meanwhile, condensation was occurring within the disk surrounding the protosun. Because temperatures within the disk varied with distance from the center of the nebula, different materials condensed at different locations within the disk. Closer to the center, where temperatures were high, high temperature condensates such as iron and silicates formed. Farther from the center, where temperatures were low, hydrogen, water and other low temperature condensates formed.• Collisions between the newly condensed particles caused larger bodies called planetesimals to accrete. This accretion process continued eventually forming the planets and moons. This violent and cataclysmic process of planetary formation is today evidenced by the cratered surfaces of Mercury and our Moon. The recent collision between comet Shoemaker-Levy and Jupiter also gave us a glimpse at what probably happened on a much grander scale when the solar system was very young.• The heat generated by these impacts and by radioactive decay of elements resulted in molten planets which subsequently became differentiated.• The evolving star at the center of the solar nebula passed through a T-Tauri star at which point it released bursts of energy. These bursts swept light elements such as hydrogen out of the outer solar system and into the outer solar system where it is swept up by the distant jovian planets.• The young protosun got hot enough to ignite the hydrogen its core. Thermonuclear reactions in the core are what distinguish a “sun” from a protosun.• The terrestrial planets evolved their secondary (Venus and Mars) and tertiary (Earth) atmospheres.
Miller – Urey Experiment This experiment is conducted in 1953 by Stanley Miller under the supervision of Harold Urey; the first experiment to test the Oparin-Haldane theory about the evolution of prebiotic chemicals and the origin of life on Earth. Figure 1. The Miller – Urey experiment
• A mixture of methane, ammonia, hydrogen, and water vapor, to simulate the version of Earths primitive, reducing atmosphere proposed by Oparin, was introduced into a 5-liter flask and energized by an electrical discharge apparatus to represent ultraviolet radiation from the Sun. The products were allowed to condense and collect in a lower flask which modeled a body of water on the Earths surface. Heat supplied to this flask recycled the water vapor just as water evaporates from lakes and seas, before moving into the atmosphere and condensing again as rain.• After a day of continuous operation, Miller and Urey found a thin layer of hydrocarbons on the surface of the water. After about a week of operation, a dark brown scum had collected in the lower flask and was found to contain several types of amino acids, including glycine and alanine, together with sugars, tars, and various other unidentified organic chemicals (The Encyclopedia of Science, N.D.).
From Coacervates to Heterotrophs to Autotrophs
Formation of Complex Organic Compounds• The smaller and simpler organic compounds that were formed initially in the earth, gradually started combining among themselves to form complex organic compounds. Simple sugars combined among themselves to form complex polysaccharides such as starch and cellulose. Fatty acids and glycerol molecules combined to form lipids. Amino acids combined among themselves to form polypeptides and proteins. Purines and pyrimidines combined with simple sugars and phosphates to form nucleotides, which in turn combined to form nucleic acids. Heat of the sun probably provided the energy required for the formation of complex organic compounds.• Haldane suggested that due to the accumulation of complex organic molecules, the sea ultimately became a sort of hot, dilute soup where in, the molecules collided, reacted and aggregated to form more complex molecules.
Formation of Molecular Aggregates• It is suggested that the large organic molecules formed abiotically in the primitive earth came together spontaneously and due to intermolecular attraction, formed large colloidal aggregates called Coacervates. An envelope of water molecules formed around each such aggregate due to the hydrophilic nature of some of these compounds. A membrane of fatty acids protected and enclosed these molecules, increasing the chances of chemical reactions. Gradually, breakdown and building up reactions started for which the energy required was provided by the breakdown reactions. The coacervates selectively absorbed proteins and other materials from the ocean resulting in their active growth. The coacervates not only started growing rapidly but also started multiplying.
Formation of First Cells (Protobionts)• The coacervates were in a state of dynamic equilibrium, constantly taking in new materials from the oceans and releasing degraded materials. Thus, they had all the basic properties of life such as metabolism, growth and reproduction. However, they lacked the complexity of molecular organization, catalytic proteins (enzymes) and precise control of nucleic acids. Later, the nucleic acids are said to have taken control of coacervate and the process of replication became precise in the due course of time. With the nucleic acids being established as the genetic material, the coacervates got transformed into the primitive living systems which have been called as protobionts or eobionts.• Some of the proteins in protobionts are said to have developed the ability to catalyse chemical reactions, thereby functioning as the first enzymes. The formation of enzymes greatly enhanced the rate of synthesis of various molecules in the protobionts.• In the course of time, the protobionts became enclosed by a protein lipid membrane, allowing the accumulation of some molecules and the exclusion of others. This property improved the ability of protobionts to survive and compete with others. With the processes of metabolism, growth and reproduction becoming regular, precise and regulated, the first cells or organisms were formed. The termprogenote has been suggested by Carl Woese to describe the first cell which served as the ancestor of all the forms of life existing today.• The first forms of life developed among the organic molecules, in the oxygen free atmosphere. Hence, they presumably obtained energy by the fermentation of organic compounds. They were heterotrophs, requiring ready-made organic compounds as food.
• Chemoheterotrophs-They were prokaryotic like bacteria. They were anaerobes. They must have been dependent on the organic molecules present in the broth for body building and obtaining energy.• Chemoautotrophs-They were unable to synthesize organic molecules from inorganic raw materials, with the help of chemical energy obtained by the degradation of chemical compounds present in the sea.• Photoautotrophic-The next step was to development of pigment molecules chlorophyll. It would absorb solar energy and convert it into chemical energy. This process is termed as photosynthesis. The earliest formed organisms were photoautotrophic bacteria. They were anaerobic and did not produce O2 as byproduct during photosynthesis, because they did not use water as a reagent.
Aerobic Photoautotrophs• They evolved 3300 to 3500 million years ago. They were like present day cyanobacteria and could release O2 into the atmosphere because they used water as the reagent. Thus, the whole reducing atmosphere changed to an oxidising atmosphere.• Autotrophs are said to have arisen much later in the primitive earth due to a mutation in the primitive heterotrophs. The appearance of autotrophs, particularly photo autotrophs changed the situation. The appearance of photosynthetic organisms resulted in the release of free molecular oxygen into the atmosphere gradually transforming it into an oxidizing type from the existing reducing type
Adaptation Modes for Survival• 1. Nutritional Adaptation• The first primitive cells called premonera were believed to be basically aquatic and heterotrophs, which derived food from their environment. Some of them most probably exhibited mutations in their nucleic acids. The nature of the mutations should have led to the development of new metabolic reactions which eventually led to the evolution of autotrophs (Rivero & Cao, 2005).• Autotrophs – organisms that have the capacity to produce their own food from an inorganic source of carbon through photosynthesis (light) or chemosynthesis (chemical) (Campbell et al., 1999).• Photosynthesis - is the process of converting light energy to chemical energy and storing it in the bonds of sugar (Carter, 1996).• Chemosynthesis - is the process by which certain microbes create energy by mediating chemical reactions.
2. Structural Adaptation• The first heterotrophs and autotrophs were in all probability prokaryotic, simple one – celled organisms. Bacteria and cyanobacteria are present day prokaryotes. Eukaryotes are believed to evolve from prokaryotes through endosymbiosis and invaginations (Rivero & Cao, 2005).• Endosymbiosis - a type of symbiosis in which one organism lives inside the other, the two typically behaving as a single organism. It is believed to be the means by which such organelles as mitochondria and chloroplasts arose within eukaryotic cells.• Invagination - an infolding of the outer layer of cells of an organism or part of an organism so as to form a pocket in the surface, as in the embryonic development of a gastrula from a blastula.
• The three-domain system, which classifies life on the planet into three different domains - Archaea, Bacteria and Eukaryote, was put forth by American microbiologist and physicist Carl Woese in 1990. Basically, it is a biological classification of the three domains of life based on the differences in their 16S rRNA genes. Other popular biological classification systems include the two-empire system - also referred to as the super-domain system, and the six-kingdom system.• Archaea Domain: Archaea are prokaryotic cells which are typically characterized by membranes that are branched hydrocarbon chains attached to glycerol by ether linkages. The presence of this ether containing linkages in Archaea adds to their ability of withstanding extreme temperature and highly acidic conditions. Extreme halophiles - i.e. organisms which thrive in highly salty environment, and hyperthermophiles - i.e. the organisms which thrive in extremely hot environment, are best examples of Archaea.• Bacteria Domain: Even though bacteria are prokaryotic cells just like Archaea, their membranes are made of unbranched fatty acid chains attached to glycerol by ester linkages. Cyanobacteria and mycoplasmas are the best examples of bacteria. As they dont have ether containing linkages like Archaea, they are grouped into a different category - and hence a different domain. There is a great deal of diversity in this domain, such that it is next to impossible to determine how many species of bacteria exist on the planet.
• Eukarya Domain: Eukaryote are eukaryotic cells which have membranes that are pretty similar to that of bacteria. Eukaryote are further grouped into Kingdom Protista (algae, protozoans, etc.), Kingdom Fungi (yeast, mold, etc.), Kingdom Plantae (flowering plants, ferns, etc.) and Kingdom Animalia (insects, vertebrates, etc.). Not all Eukaryotes have a cell wall, and even if they do they dont contain peptidoglycan as bacteria do. While cells are organized into tissues in case of kingdom Plantae as well as kingdom Animalia, the presence of cell walls is only restricted to the members of kingdom Plantae.• Each of these three domains of life recognized by biologists today contains rRNA which is unique to them, and this fact in itself forms the basis of three-domain system. While the presence of nuclear membrane differentiates the Eukarya domain from Archaea domain and Bacteria domain - both of which lack nuclear membrane, the distinct biochemistry and Figure 3, The three RNA markers differentiate Archaea and domains of life Bacteria domains from each other
The Five Kingdoms of Life within the Domain Eukarya
RNA World Theory• Darwins theory on natural selection implied that all current life-forms could have evolved from a single, simple progenitor which is referred to as the last common ancestor. One feature is the presence of genetic information and the means to replicate and carry out those heritable instructions for functioning and reproducing. In addition, the system for replicating genetic material had to allow for some random variation in the heritable characteristics of the offspring so that new traits could be selected and lead to the creation of diverse species
• Another commonality is that all living things consist of similar organic (carbon- rich) compounds. Also, the proteins found in present-day organisms are fashioned from one set of 20 standard amino acids. Furthermore, all contemporary organisms carry their genetic information in nucleic acids - RNA and DNA - and use essentially the same genetic code. From these findings, we can infer that the last common ancestor stored genetic information in nucleic acids that specified the composition of all needed proteins. It also relied on proteins to direct many of the reactions required for self perpetuation. The question now becomes where does the proteins and nucleic acids come from? Image Credit: DNA
Got to Start SomewhereIn 1983, Thomas R. Cech and Sidney Altmanindependently discovered the first known ribozymes, enzymes made of RNA, indicating that the ancient RNA may have been catalytic. However, no RNA molecules that direct the replication of other RNA molecules have been identified in nature. In the mean time, Cech and Jack W. Szostak have modified naturally occurring ribozymes so that they Thomas R. Cech Sidney Altman can carry out some of the most important subreactions of RNA replication, such as stringing together nucleotides or oligonucleotides.
The Chicken and Egg problem (nucleic acids and proteins)• Nowadays nucleic acids are synthesized only with the help of proteins, and proteins are synthesized only if their corresponding nucleotide sequence is present. It is extremely improbable that proteins and nucleic acids, both of which are structurally complex, arose spontaneously in the same place at the same time. Yet it also seems impossible to have one without the other. The paradox is resolved by the RNA world - a world in which RNA catalyzed all the reactions necessary for the precursor of lifes last common ancestor to survive and replicate. The RNA could subsequently have developed the ability to link the amino acids together into prteins. For the RNA world to exist, RNA needs the capacity to replicate without the help of proteins and an ability to catalyze every step of protein synthesis.
Why RNA is favored over DNA as the originator of the genetic system• The ribonucleotides in RNA • In an experiment, Szostak are more readily synthesized created a pool of random than are the oligonucleotides to deoxyribonucleotides in DNA. approximate the random It is easy to envision ways production presumed to have that DNA could evolve from occurred some 4 billion years RNA and then, being more ago. From that pool, he was stable, take over RNAs role as able to isolate a catalyst that the guardian of heredity. could join together Researchers suspect that RNA oligonucleotides. Also, the came before proteins because catalyst could draw energy for they face difficulty composing the reaction from a any scenario in which triphosphate group, the very proteins could replicate in the same group that now fuels absence of nucleic acids. most biochemical reactions in living systems.
• To explain how self-replicating RNA was created from its constituents, it is hypothesized that the nucleotides in RNA formed when direct chemical reactions led to joining of the sugar ribose with nucleic acid bases and phosphate. Then, these ribonucleotides spontaneously joined to form polymers, at least one of which happened to be capable of engineering its own reproduction.
From Molecules to OrganismIn the late 1990s Jim Ferris and his coworkersat the Rensselaer Polytechnic Instituteshowed that clay minerals enhance the process,producing chains of up to 50 or so nucleotides.(A typical gene today is thousands to millions ofnucleotides long.) The minerals’ intrinsic abilityto bind nucleotides brings reactive moleculesclose together, thereby facilitating the formationof bonds between them
RNA Breeding GroundsRNA Breeding GroundS After chemical reactions createdIn the water solutions in which the first genetic building they formed, nucleotides blocks and other organicwould have had little chance of molecules, geophysical combining into long processes brought them to newstrands able to store genetic environments and information. But under the concentrated them. The chemicalsright conditions—for example, if assembled into more molecular adhesion complex molecules and then intoforces brought them close primitive cells. And together between microscopic some 3.7 billion years agolayers of clay (above)— geophysics may have also nucleotides might link up into nudged these “protocells”tosingle strands similar to modern reproduce. RNA.
Journey to the modern cell• If a piece of RNA codes for a particularly good protein then there is nothing to stop that protein being used by other RNA molecules• If however the RNA is enclosed in a membrane then it can keep it’s protein to itself and gains a selective advantage• So membranes probably pushed evolution by natural selection forwards
• The phospholipids form lipid bilayers when they are surrounded by water• All the components of a simple prokaryotic cell were now assembled• They diversified in their metabolism• By 2 billion years ago free oxygen was appearing in the atmosphere due to the activity of photosynthetic bacteria