Chemical evolution on earth

SLFC PROJECT
Chemical origin of Life and Life on other Planets
Drishta Gopala, Sarthak Malhotra, Srividya, Suprigya Dipangi

Theories for Chemical Evolution Of Life On Earth
Introduction

According to a mechanistic, naturalistic view of the universe, and thus of origins, the whole of reality is evolution — a single process of self-transformation. Everything in the universe, according to this view, has evolved from a primordial chaotic or random state of matter. This evolutionary continuum thus requires that life arose on this planet (or on some planet, at least) from inanimate matter via chemical and physical processes still operating today. It is generally believed that these processes acted for many tens of millions of years, most likely hundreds of millions of years, before true cellular life was brought into being.
The Dilemma
The first thing that may be said about theories on the origin of life is that none satisfy the criteria of a scientific theory. There were no human observers of the origin of life, and it is impossible to re-enact the process. If such a process did occur, it could have left no fossil record or history. There is no way to observe or test any postulated evolutionary origin of life. All such theories are mere postulates, all related laboratory experiments are mere exercises in organic chemistry. This has been acknowledged even by a number of prominent evolutionists.
Different Theories for Origin of Life on Earth
Theory of Spontaneous Generation or Abiogenesis
This theory assumed that living organisms could arise suddenly and spontaneously from any kind of non-living matter
He believed that dead leaves falling from a tree into a pond would transform into fishes and those falling on soil would transform into worms and insects. He also held that some insects develop from morning dew and rotting manure. Egyptians believed that mud of the Nile river could spontaneously give rise to many forms of life. The idea of spontaneous generation was popular almost till seventeenth century.
Biogenesis
The belief that living things come only from other living things (e.g. a spider lays eggs, which develop into spiders). It may also refer to biochemical processes of production in living organisms. The Law of Biogenesis, attributed to Louis Pasteur, states that life arises from pre-existing life, not from nonliving material. Pasteur's (and others') empirical results were summarized in the phrase Omne vivum ex vivo, Latin for "all life [is] from life", also known as the "law of biogenesis". Pasteur stated: "La génération spontanée est une chimère" ("Spontaneous generation is a dream").
Inorganic Incubation
Proposed by Professor William Martin, of Düsseldorf University, and Professor Michael Russell, of the Scottish Environmental Research Centre in Glasgow, this theory states that Instead of the building blocks of life forming first, and then forming a cell-like structure, the researchers say the cell came first and was later filled with living molecules. They say that the first cells were not living cells but inorganic ones made of iron sulfide and were formed not at the Earth's surface but in total darkness at the bottom of the oceans. The theory postulates that life is a chemical consequence of convection currents through the Earth's crust and, in principle, could happen on any wet, rocky planet.
Endosymbiotic Theory
This theory, espoused by Lynn Margulis, suggests that multiple forms of bacteria entered into symbiotic relationship to form the eukaryotic cell. The horizontal transfer of genetic material between bacteria promotes such symbiotic relationships, and thus many separate organisms may have contributed to building what has been recognized as the Last Universal Common Ancestor (LUCA) of modern organisms. James Lovelock's Gaia theory, proposes that such bacterial symbiosis establishes the environment as a system produced by and supportive of life. His arguments strongly weaken the case for life having evolved elsewhere in the solar system.
Cosmozoic Theory (Theory of Panspermia)

According to this theory, life has reached this planet Earth from other heavenly bodies such as meteorites, in the form of highly resistance spores of some organisms. This idea was proposed by Richter in 1865 and supported by Arrhenius (1908) and other contemporary scientists. The theory did not gain any support. This theory lacks evidence, hence it was discarded.
Marine Theory
The Marine Theory suggests that life may have begun at the submarine hydrothermal vents; their rocky nooks could then have concentrated these molecules together and provided mineral catalysts for critical reactions. Even now, these vents are rich in chemical and thermal energy that sustains vibrant ecosystems.

Theory of Chemical Evolution

This theory is also known as Materialistic Theory or Physico-chemical Theory. According this theory, Origin of life on earth is the result of a slow and gradual process of chemical evolution that probably occurred about 3.8 billion years ago. This theory was proposed independently by two scientists - A.I.Oparin, a Russian scientist in 1923 and J.B.S Haldane, an English scientist, in 1928.
According to this theory,
Spontaneous generation of life, under the present environmental conditions is not possible.
Earth's surface and atmosphere during the first billion years of existence, were radically different from that of today's conditions.
The primitive earth's atmosphere was a reducing type of atmosphere and not oxidising type.
The first life arose from a collection of chemical substances through a progressive series of chemical reactions.
Solar radiation, heat radiated by earth and lighting must have been the chief energy source for these chemical reactions.

Primitive Earth Scenario

Origin of life theories require a primitive earth model that includes conditions that would tolerate postulated chemical reactions which are believed to have been involved in processes leading to the origin of life. It is the general consensus of geologists that the oceans would have formed rapidly, and thus early in the earth's history, and it has been generally assumed that the pH and temperature of the ocean would always have been approximately the same as at the present time. Evolution of life theorists are forced to postulate, however, that the primitive earth atmosphere was very different from the present atmosphere.
The present atmosphere consists of about 78% nitrogen, 21% oxygen, and 1% of other gases, including argon, carbon dioxide, and water vapor.
If the primitive earth atmosphere contained a significant quantity of oxygen, however, an evolutionary origin of life would have been thermodynamically impossible, since all substances would have been oxidized to carbon dioxide, water, nitrogen, and other oxidized products, leaving no organic chemical compounds to serve as precursors for biochemical evolution. Evolutionists are thus forced to assume, a priori, that the primitive earth atmosphere contained no oxygen, but rather contained hydrogen, and that carbon existed mainly in the form of methane and/or carbon monoxide.
Hypotheses for Chemical Origin of Life
There is no "standard model" of the origin of life. Most currently accepted models draw at least some elements from the framework laid out by the Oparin-Haldane hypothesis. Under that umbrella, however, is a wide array of disparate discoveries and conjectures such as the following.

‘Primordial Soup’ Hypothesis
In 1924, Alexander Oparin reasoned that atmospheric oxygen prevents the synthesis of certain organic compounds that are necessary building blocks for the evolution of life.
In his The Origin of Life, Oparin proposed that the "spontaneous generation of life" that had been attacked by Louis Pasteur did in fact occur once, but was now impossible because the conditions found on the early Earth had changed, and pre-existing organisms would immediately consume any spontaneously generated organism.
Oparin argued that a "primeval soup" of organic molecules could be created in an oxygenless atmosphere through the action of sunlight. These would combine in evermore complex ways until they formed coacervate droplets. These droplets would "grow" by fusion with other droplets, and "reproduce" through fission into daughter droplets, and so have a primitive metabolism in which those factors which promote "cell integrity" survive, and those that do not become extinct. Many modern theories of the origin of life still take Oparin's ideas as a starting point.
J. B. S. Haldane suggested that the Earth's prebiotic oceans—different from their modern counterparts—would have formed a "hot dilute soup" in which organic compounds could have formed.
In 1952, in the Miller–Urey experiment, a mixture of water, hydrogen, methane, and ammonia was cycled through an apparatus that delivered electrical sparks to the mixture. After one week, it was found that about 10% to 15% of the carbon in the system was now in the form of a racemic mixture of organic compounds, including amino acids, which are the building blocks of proteins.
Autocatalysis
In 1993 Stuart Kauffman proposed that life initially arose as autocatalytic chemical networks.
Autocatalysts are substances that catalyze the production of themselves, and therefore have the property of being a simple molecular replicator. In experiments performed by Julius Rebek and his colleagues they combined amino adenosine and pentafluorophenyl esters with the autocatalyst amino adenosine triacid ester (AATE). One system from the experiment contained variants of AATE which catalysed the synthesis of themselves. This experiment demonstrated the possibility that autocatalysts could exhibit competition within a population of entities with heredity, which could be interpreted as a rudimentary form of natural selection.
Clay hypothesis A model for the origin of life based on clay was forwarded by A. Graham Cairns-Smith of the University of Glasgow in 1985 and explored as a plausible illustration by several scientists. The Clay hypothesis postulates that complex organic molecules arose gradually on a pre-existing, non-organic replication platform of silicate crystals in solution.
In 2007, Kahr and colleagues reported their experiments that tested the idea that crystals can act as a source of transferable information, using crystals of potassium hydrogen phthalate. "Mother" crystals with imperfections were cleaved and used as seeds to grow "daughter" crystals from solution. They then examined the distribution of imperfections in the new crystals and found that the imperfections in the mother crystals were reproduced in the daughters, but the daughter crystals also had many additional imperfections. For gene-like behavior to be observed, the quantity of inheritance of these imperfections should have exceeded that of the mutations in the successive generations, but it did not. Thus Kahr concluded that the crystals, "were not faithful enough to store and transfer information from one generation to the next"
Gold's "deep-hot biosphere" model
In the 1970s, Thomas Gold proposed the theory that life first developed not on the surface of the Earth, but several kilometers below the surface
It is now reasonably well established that microbial life is plentiful at shallow depths in the Earth, up to 5 kilometres (3.1 mi) below the surface, in the form of extremophile archaea, rather than the better-known eubacteria (which live in more accessible conditions). It is claimed that discovery of microbial life below the surface of another body in our solar system would lend significant credence to this theory. Thomas Gold also asserted that a trickle of food from a deep, unreachable, source is needed for survival because life arising in a puddle of organic material is likely to consume all of its food and become extinct. Gold's theory is that the flow of such food is due to out-gassing of primordial methane from the Earth's mantle; more conventional explanations of the food supply of deep microbes (away from sedimentary carbon compounds) is that the organisms subsist on hydrogen released by an interaction between water and (reduced) iron compounds in rocks.
"Primitive" extraterrestrial life
An alternative to Earthly abiogenesis is the hypothesis that primitive life may have originally formed extraterrestrially (Extraterrestrial life),[108][109] either in space, on Mars or elsewhere. (Note that exogenesis is related to, but not the same as, the notion of panspermia).
Organic compounds are relatively common in space, especially in the outer solar system where volatiles are not evaporated by solar heating. Comets are encrusted by outer layers of dark material, thought to be a tar-like substance composed of complex organic material formed from simple carbon compounds after reactions initiated mostly by irradiation by ultraviolet light. It is supposed that a rain of material from comets could have brought significant quantities of such complex organic molecules to Earth.

Extraterrestrial organic molecules
Another idea is that amino acids which were formed extraterrestrially arrived on Earth via comets. In 2009 it was announced by NASA that scientists had identified one of the fundamental chemical building blocks of life in a comet for the first time: glycine, an amino acid, was detected in the material ejected from Comet Wild-2 in 2004 and grabbed by NASA's Stardust probe.
Based on computer model studies, the complex organic molecules necessary for life may have formed in the protoplanetary disk of dust grains surrounding the Sun before the formation of the Earth. According to the computer studies, this same process may also occur around other stars that acquire planets

Lipid world

The lipid world theory postulates that the first self-replicating object was lipid-like. It is known that phospholipids form lipid bilayers in water while under agitation – the same structure as in cell membranes. These molecules were not present on early Earth, but other amphiphilic long chain molecules also form membranes. Furthermore, these bodies may expand (by insertion of additional lipids), and under excessive expansion may undergo spontaneous splitting which preserves the same size and composition of lipids in the two progenies. The main idea in this theory is that the molecular composition of the lipid bodies is the preliminary way for information storage, and evolution led to the appearance of polymer entities such as RNA or DNA that may store information favourably.
Polyphosphates
The problem with most scenarios of abiogenesis is that the thermodynamic equilibrium of amino acid versus peptides is in the direction of separate amino acids. What has been missing is some force that drives polymerization. The resolution of this problem may well be in the properties of polyphosphates. Polyphosphates are formed by polymerization of ordinary monophosphate ions PO4−3. Several mechanisms for such polymerization have been suggested. Polyphosphates cause polymerization of amino acids into peptides. They are also logical precursors in the synthesis of such key biochemical compounds as ATP. A key issue seems to be that calcium reacts with soluble phosphate to form insoluble calcium phosphate (apatite), so some plausible mechanism must be found to keep calcium ions from causing precipitation of phosphate. There has been much work on this topic over the years, but an interesting new idea is that meteorites may have introduced reactive phosphorus species on the early Earth
Multiple genesis
Different forms of life may have appeared quasi-simultaneously in the early history of Earth.[187] The other forms may be extinct, leaving distinctive fossils through their different biochemistry (e.g., using arsenic instead of phosphorus), survive as extremophiles, or simply be unnoticed through their being analogous to organisms of the current life tree. Hartman[188] for example combines a number of theories together, by proposing that:
The first organisms were self-replicating iron-rich clays which fixed carbon dioxide into oxalic and other dicarboxylic acids. This system of replicating clays and their metabolic phenotype then evolved into the sulfide rich region of the hotspring acquiring the ability to fix nitrogen. Finally phosphate was incorporated into the evolving system which allowed the synthesis of nucleotides and phospholipids. If biosynthesis recapitulates biopoiesis, then the synthesis of amino acids preceded the synthesis of the purine and pyrimidine bases. Furthermore the polymerization of the amino acid thioesters into polypeptides preceded the directed polymerization of amino acid esters by polynucleotides.
Lynn Margulis's endosymbiotic theory suggests that multiple forms of archea entered into symbiotic relationship to form the eukaryotic cell. The horizontal transfer of genetic material between archea promotes such symbiotic relationships, and thus many separate organisms may have contributed to building what has been recognised as the Last Universal Common Ancestor (LUCA) of modern organisms.

Future Space Missions
Introduction
If one looks only for the shiniest pennies in the fountain, chances are one misses most of the coins because they shimmer less brightly. This, in a nutshell, is the conundrum astronomers’ face when searching for Earth-like planets outside our solar system.

Astronomers at the University of Arizona are part of an international team of exoplanets hunters developing new technology that would dramatically improve the odds of discovering planets with conditions suitable for life -- such as having liquid water on the surface.
The team presented its results at a scientific conference sponsored by the International Astronomical Union in Victoria, British Columbia.
Terrestrial planets orbiting nearby stars often are concealed by vast clouds of dust enveloping the star and its system of planets. Our solar system, too, has a dust cloud, which consists mostly of debris left behind by clashing asteroids and exhaust spewing out of comets when they pass by the sun.
Current technology allows us to detect only the brightest clouds, those that are a few thousand times brighter than the one in our solar system. While the brighter clouds are easier to see, their intense glare makes detecting putative Earth-like planets difficult, if not impossible.
If you see a dust cloud around a star, that's an indication of rocky debris, and it increases the likelihood of there being something Earth-like around that star. From previous observations, we know that these planets are fairly common one can expect that if a space telescope dedicated to that mission were to look around a certain area of sky, we'd expect to find quite a few.
Hinz and Defrère are working on an instrument that will allow astronomers to detect fainter clouds that are only about 10 times -- instead of several thousand times -- brighter than the one in our solar system.
That level of sensitivity is the minimum we need for future space telescope missions that are to characterize Earth-like planets that can sustain liquid water on the surface the goal is to eliminate the dust clouds that are too bright from the catalogue of candidates because they are not promising targets to detect planets suitable for life.
With a bright dust cloud, which is 1,000 times brighter than the one in our solar system, its light becomes comparable to that of its star, which makes it easier to detect.
Fainter clouds, on the other hand, can be about 10,000 times less bright than their star, so it becomes difficult or impossible for observers to make out their faint glow in the star's overpowering glare.
Funded by NASA, the team is in the middle of carrying out tests to demonstrate the feasibility of these observations using both apertures of the Large Binocular Telescope, or LBT, in Arizona. The project aims at determining how difficult it would be to achieve the desired results before committing to a billion-dollar space telescope mission.
According to Hinz, NASA's goal is to be able take a direct picture of Earth-like, rocky planets and record their spectrum of light to analyze their composition and characteristics such as temperature, presence of water and other parameters.
To do that, one would need a space telescope specifically designed for this type of imaging the goal is to do a feasibility study of whether it would be possible to distinguish the light emission of the planet from the background emission of the dust cloud through direct observation."
The researchers take advantage of a technique known as nulling interferometry and the unique configuration of the LBT, which resembles a giant pair of binoculars. Light from two apertures is combined, cancelling out the light from the central star, and with that it becomes easier to see the light from the dust cloud," Hinz explained. "To achieve this, we have to cause the two light paths to interfere with each other, which requires lining them up with very high precision. We'll always have some starlight left because of imperfections in the system, but our goal is to cancel it out to a level of 10,000 to get down to where we can at least detect the faint glow of the dust cloud."
The work presented at the conference used the same technique with the two large telescopes of the Keck Observatory in Hawaii in order to detect the dust cloud around the star Fomalhaut located 25 light years from our sun.
Based on the observations at the European Very Large Telescope Interferometer, we knew that Fomalhaut was surrounded by a bright dust cloud located very close to the star. Using the Keck Interferometer, it was found out that Fomalhaut has a less bright, more diffuse cloud orbiting close to the habitable zone that resembles the Main Asteroid Belt in our solar system. This belt is likely in dynamical interaction with yet undetected planets."

NASA announced two new projects headed for a 2017 launch, one of which, the Transiting Exoplanet Survey Satellite (TESS), will cover an estimated 400 times as much sky than any previous mission as it locates planets orbiting nearby stars.
Led by George Ricker of the Massachusetts Institute of Technology (MIT), scientists plan to focus the spacecraft's efforts on examining planets located in the habitable zones of their host stars and specifically those similar in size to Earth.
Euclid
There are two dark energy missions that will obtain data on the abundance of exoplanets. The first of these, Euclid, is an ESA mission that has been approved and funded, with a launch targeted for 2020. It will feature a one-meter aperture telescope that will image distant galaxies in the infrared in order to detect the influence of dark energy. As a secondary goal, Euclid will conduct several observing runs looking for the signature of exoplanet microlensing events, making it the first space mission to utilize this approach. Microlensing refers to the fact that as a planet passes in front of a distant star, its gravity will bend that star’s light, as a consequence of Einstein’s general theory of relativity. This bending effect causes a temporary brightening of the distant star, acting as a virtual lens. Given the small mass of planets, the brightening is minimal but detectable. A space telescope that can stare at one patch of the Milky Way for weeks or months is the best way to observe these fleeting and unpredictable events. The importance of microlensing is that it can detect all types of exoplanets at all distances from their parent star. A mission such as Euclid should be able, as a result, to acquire valuable statistics on the architectures of solar systems.
In addition, as Euclid is looking for microlensing events, it will also be able to detect transits like those observed by Kepler. Euclid will observe in the near-infrared, and so is optimized to look for planets around cooler M-class dwarf stars. However, Euclid’s target star field is crowded and the target stars are faint, making transit detection much more difficult than with Kepler. Still, this capability will add to the database of exoplanet abundance.

NASA to expand its Search for Earth-like Planets

Artist’s rendition of Zarmina
Astronomers confirm there are two potentially habitable planets orbiting Gliese 581-- the potentially habitable "second Earth" 20 light years away, also known as Zarmina
The mind reels to imagine the discoveries that lie ahead for TESS (concept art pictured above); after all, Kepler may be designed to survey just one small corner of the Milky Way, but in four short years it's managed to revolutionize the field of exoplanet research.

Kepler is very good at its job – and at the rate it's finding planets, most astronomers agree the current planet-hunting mission is close to discovering its first Earth twin (assuming it hasn't found it already). But by expanding the range of sky surveyed, TESS stands to take the search for extrasolar planets and take it right up to 11.
TESS is slated to launch in 2017, one year after funding for Kepler runs dry. Coincidentally (yeah right), 2017 is also one year before the projected launch of the James Webb Space Telescope – an observatory so powerful, it will be able to study the atmospheres of planet candidates outside our solar system. The telescope will therefore work in tandem with planet-hunting missions. Kepler and TESS find the planets, JWST checks them out up close. Quite the cosmic tag-team.

The James Webb Space Telescope

The James Webb Space Telescope (JWST), previously known as Next Generation Space Telescope (NGST), is a planned space telescope optimized for observations in the infrared, and a scientific successor to the Hubble Space Telescope and the Spitzer Space Telescope. The main technical features are a large and very cold 6.5-meter (21 ft) diameter mirror, an observing position far from Earth, orbiting the Earth–Sun L