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Earth is a dynamic system. The thermodynamics conditions of Earth vary drastically depending on the depth, ranging from ambient temperature and pressure at the surface to 360 GPa and 6600 K at the core. Consequently, the physical and chemical properties of Earth’s constituents (e.g., silicate and carbonate minerals) are strongly affected by their immediate environment. In the past 30 years, there has been a tremendous amount of progress in both experimental techniques and theoretical modeling methods for material characterization under extreme conditions. These advancements have elevated our understanding of the properties of minerals, which is essential in order to achieve full comprehension of the formation of this planet and the origin of life on it. This article reviews recent computational techniques for predicting the behavior of materials under extreme conditions. This survey is limited to the application of the first-principles molecular dynamics (FPMD) method to the investigation of chemical and thermodynamic transport processes relevant to Earth Science. Keywords: High pressure, High temperature, Earth mantle, Molecular dynamics, Density functional method, Transport properties, Chemical reactivity

The astronomical community is devoting an enormous effort to detect environments where life may have emerged in space and seeks for evidence of that. The ultraviolet (UV) spectrum carries crucial information for this research. Moreover, the actual knowledge of the UV radiation field is instrumental for the interpretation of data (obtained at any wavelength) related with magnetic activity, photon driven heating, and astrochemistry. These are the issues addressed in this chapter. First, the main effects of UV radiation on matter within the context of astrobiological research are addressed. Then, the UV observations of forming planetary systems and exoplanets are described as well as, the on-going research to detect biosignatures and amino acids in space. Finally, we outline the UV observations relevant for the investigation of the processes involved in the formation and spread of the key atomic elements in biomolecules. The work concludes with a short list of requirements for future UV missions.

Meteorites contain prebiotic, bio-relevant organic compounds including amino acids. Their syntheses could result from diverse sources and mechanisms and provide a window on the conditions and materials present in the early solar system. Here we constrain alanine’s synthetic history in the Murchison meteorite using site-specific 13C/12C measurements, reported relative to the VPDB standard. The δ13CVPDB values of −29 ± 10‰, 142 ± 20‰, and −36 ± 20‰ for the carboxyl, amine-bound, and methyl carbons, respectively, are consistent with Strecker synthesis of interstellar-medium-derived aldehydes, ammonia, and low-δ13C nebular or interstellar-medium-derived CN. We report experimentally measured isotope effects associated with Strecker synthesis, and use them to constrain the δ13C values of the alanine precursors, which we then use to construct a model that predicts the molecular-average δ13C values of 19 other organic compounds of prebiotic significance found in Murchison if they were made by our proposed synthetic network. Most of these predictions agree with previous measurements, suggesting that interstellar-medium-derived aldehydes and nebular and/or pre-solar CN could have served as substrates for synthesis of a wide range of prebiotic compounds in the early solar system.

Ever since the origin of life upon earth, organic matter has been interacting with inorganic matter, countenancing life to thrive and sustain upon mineral deposits generated through such interactive processes. As a result of microbial biosynthetic processes, inorganic nanoparticles can be produced by intracellular/extracellular routes. Genetic engineering uses biological techniques to directly manipulate genetic and metabolic patterns within microbial cells resultantly conferring improved abilities and/or novelty to a target organism. Its culmination with nanotechnology at a molecular level to synthesize nanosized objects using microorganisms through integrative techniques has been proven successful. This has in fact resulted in the augmented tailor-made production of proteins, peptides, biofuels, and other secondary metabolites; hence, genetically modified microbial cell factories are functional platforms contributing to nanobiosynthesis and allied nanobiotechnological applications. A profound comprehension of such biosynthetic pathways and genetic engineering techniques opens doors to wider horizons for industrial exploitation of microbial nanofactories. This chapter envisages the concepts of knowledge, challenges, and bioprospects for the development of nanoscale materials using microbial nanotechnology and breakthrough applications.

A range of astronomical observations are shown to be in accord with the theory of cometary panspermia. This theory posits that comets harbor a viable biological component in the form of bacteria and viruses that led to origin and evolution of life on Earth. The data includes (1) infrared, visual and ultraviolet spectra of interstellar dust, (2) infrared spectra of the dust released from comet Halley in 1986, (3) infrared spectra of comet Hale-Bopp in 1997, (4) near and mid-infrared spectra of comet Tempel I in 2005, (5) the discovery of an amino acid and degradation products attributable to biology in the material recovered from the Stardust Mission in 2009, (6) jets from comet Lovejoy showing both a sugar and Ethyl alcohol and finally, (7) a diverse set of data that has emerged from the Rosetta mission. The conjunction of all the available data points to cometary biology and interstellar panspermia as being inevitable.

Viruses are extremely abundant and diverse parasites of cells. They might have arisen during an early phase of the evolution of life on Earth dominated by RNA or RNA-like macromolecules, or when a cellular world was already well established. The theories of the origin of life on Earth shed light on the possible origin of primitive viruses or virus-like genetic elements in our biosphere. Some features of present day viruses, notably error-prone replication, might be a consequence of the selective forces that mediated their ancestral origin. Two views on the role of viruses in our biosphere predominate: viruses considered as opportunistic, selfish elements, and viruses considered as active participants in the construction of the cellular world via lateral transfers of genes. These two models bear on considering viruses predominantly as disease agents or predominantly as cooperators in the shaping of differentiated cellular organisms.

This current volume is, in many ways, a 2020 update to the important 1999-2000 compendium by Sir Fred Hoyle and Professor N. Chandra Wickramasinghe's "Astronomical Origins of life: Steps towards Panspermia." The emerging new paradigm of biology that connects life on Earth with the wider cosmos is covered in considerable depth showing that terrestrial biological evolution is best understood as a cosmically derived habitat and an interconnected genetic system. The various chapters here discuss all aspects of this interconnectedness, particularly relevant now in this time of the coronavirus pandemic (COVID-19) as the human race reacts to the many microbes and viral pathogens that arrive regularly from space.

The theory of cometary panspermia argues that life cannot have originated on Earth in the time available. It must have an ultimate, but still undiscovered cosmological source. The origin of life remains an open question. Life on Earth was introduced by impacting comets, and its further evolution was driven by the subsequent acquisition of cosmically derived genes. Explicit predictions of this theory stating how the acquisition of new genes drives evolution, are compared with recent developments in relation to horizontal gene transfer, and the role of retroviruses in evolution. Precisely stated predictions of the theory of cometary panspermia are shown to have been verified.

The origin of all extant life on earth is intimately linked to the establishment of the principal components of the Genetic Code. Aminoacyl-tRNA synthetases (aaRS), by virtue of their universality and essential functions in protein synthesis, count among the biomolecules that evolved to a level of complexity comparable to their extant state before the advent of the Last Universal Common Ancestor (LUCA). Despite the enormous technical difficulties in analyzing such an ancient process, proposals have been put forward to describe the emergence and evolution of the two aaRS families. In this chapter, I critically review some of these proposals and place them along a hypothetical timeline based on other essential aspects of the origin of life. This chapter focuses on the evolution of the aaRS prior to LUCA. Readers will be referred to excellent literature that covers the phylogeny of aaRS in the three extant domains of life.

Non-equilibrium thermodynamics is a relevant framework from within which to address formidable difficulties encountered in explaining the origin of life; from molecular synthesis and complexation, enzyme-less proliferation, to evolution (including the acquisition of homochirality and information). From within this framework we have proposed that the origin of life was the origin of the dissipative structuring of organic pigments which became the fundamental molecules of life (e.g. RNA and DNA) proliferated through autocatalytic photochemical reactions under the thermodynamic imperative of dissipating the imposed UVC solar photon flux available at the Archean surface. Here we present experimental evidence demonstrating that the absorption and dissipation of UVC light by synthetic DNA of 25 base pairs (and also natural salmon sperm DNA) over a range of temperatures, including below their melting temperature, leads to denaturing. Since denaturing is a non-trivial step on route to enzyme-less replication, our data suggest the possibility of a dissipative route to DNA replication at the origin of life. Such a dissipation-replication relation provides a simple mechanism for the early accumulation of both homochirality and information. Possible mechanisms of UVC photon-induced denaturing of DNA are discussed.

15 páginas.--10 figuras.-- 2 tablas.-- 87 referencias.-- Supplementary data related to this article can be found at https://doi.org/10.1016/j.apgeochem.2018.07.011., Continental active serpentinization of ultramafic rocks is today recognized as a key process triggering a sequence of phenomena involving the passage from inorganic, to organic and metabolic reactions. These may have a role in the origin of life, and may explain the occurrence of abiotic hydrocarbons on Earth and other planets. Production of hyperalkaline waters and abiotic methane (CH4) are two critical steps in this sequence. They were described independently by specific hydrogeological and geochemical models. Here, we update and combine these models into a unified scheme using and integrating geological, hydrogeological, hydrogeochemical, gas-geochemical and microbial analyses acquired from 2002 to 2014 in the Cabeço de Vide (CdV) study site, Portugal. The hyperalkaline (pH > 10.5), Na-Cl/Ca-OH mineral water of CdV evolve from groundwater-peridotite interaction (serpentinization) generating hydrogen (H2), which, according to multiple theoretical, laboratory and field evidence, likely reacted with CO2 within metal- (catalyst) rich rocks, abiotically producing CH4 (up to 1.2 mg/L; -24.4°/oo < δ13C-CH4 < -14.0°/oo and -285°/oo < δ2H-CH4 < -218°/oo). The hyperalkaline water hosts hydrogen oxidizing bacteria “Serpentinomonas” which may explain the paucity of H2 observed in the dissolved gas. The CdV gas-rich mineral waters ascend along a fault at the boundary of the peridotite intrusion. Temporal changes of pH and CH4 concentration result from episodic mixing with shallower Mg-HCO3-type waters. Soil-gas analyses show that methane migrates to the surface along the fault, also independently from the water emergences, consistently with non-aqueous abiotic CH4 production. Our integrated model is generally compatible with observations from other gas-bearing continental serpentinization sites., This study was supported by FCT/MEC (PIDDAC) funds under the scope of the Project PTDC/AAG-MAA/2891/2012, CERENA/IST acknowledges the FCT (the Portuguese Science and Technology Foundation) support through the UID/ECI/04028/2013 Project and C2TN/IST author gratefully acknowledge the FCT support through the UID/Multi/04349/2013. The study on gas origin and emission, performed by INGV, was supported by the Deep Carbon Observatory – Deep Energy community. Work performed at the Jet Propulsion Laboratory, California Institute of Technology, was done under contract with NASA and funded by the NASA Astrobiology Institute (grants 08- NAI5-0021 and 13-13NAI7_2-0024). The authors would like to thank Benjamin Tutolo and an anonymous reviewer for their comments and suggestions in order to improve a previous draft of the manuscript. The authors also would like to thank José Teixeira and Helder Chaminé for redrawing Figs. 1 and 12. The authors also would like to thank L. Rocha, Technical Director of Cabeço de Vide thermal spa, for his support during field work campaigns. Special thanks to the Junta de Freguesia of Cabeço de Vide for all the logistical support during this study. No competing financial interests exist

Moore's law is an empirical observation that the complexity of computer chips measured by the number of transistors doubles every 18–24 months. Because there is similarity between the evolution of human technology and living organisms, it is intriguing if an exponential increase in complexity can be found in the biological evolution. Functional complexity of organisms can be roughly approximated by the size of the nonredundant functional genome. It appears that genome complexity increased nearly exponentially and doubled in size every 340 million years. Several positive feedback mechanisms including gene cooperation and duplication with subsequent specialization may have caused the exponential growth. An extrapolation of this trend to earlier times suggests that life originated 9.7 ± 2.7 billion years ago, assuming that life started from systems with simple heritable molecules that are functionally equivalent to a nucleotide or coenzyme. The common assumption that life began on Earth may be one of our last anthropocentrisms. This cosmic time scale for the evolution of life has important consequences: (1) Earth was likely seeded by panspermia (but not by directed panspermia as Crick suggested); (2) life took ca. 5 billion years to reach the complexity of bacteria; (3) experimental replication of the origin of life from scratch may have to emulate many cumulative rare events; (4) the environments in which life originated and evolved initially may have been quite different from those envisaged on Earth; and (5) the Drake equation for predicting the number of civilizations in the universe is likely wrong, as intelligent life has just begun appearing in our universe. Evolution of advanced organisms has accelerated via development of additional information-processing systems: epigenetic memory, continuing differentiation, primitive mind, multicellular brain, language, books, computers, and Internet. These higher-level systems are characterized by much faster rates of complexity increase as compared to genome complexity. Finally, we discuss the issue of the predicted “technological singularity” and give a biosemiotics perspective on the increase of life's complexity.

The nature of organic matter in meteorites reveals information about early solar system chemistry and the histories of parent bodies as recorded in the effects of physical and chemical processes that occurred over the past 4.5 billion years. Asteroids and their fragments impact the Earth with approximately 40 million kg of material each year and contributed to the inventory of organics available for the origin of life. Analyses of primitive carbonaceous chondrites over the last five decades have revealed a major insoluble organic component, as well as a complex and highly diverse suite of soluble organic molecules that includes aliphatic and aromatic hydrocarbons, carboxylic acids, hydroxy acids, N-heterocycles, polyols, amino acids, amines, and many other molecules that have not yet been identified. Thermal and aqueous alteration in primitive asteroids played an important role in the formation and destruction organics, including amplification of L-amino acid and D-sugar acid enantiomeric excesses that may have contributed to the origin of homochirality in life on Earth.

Our Sun is approximately 5 billion years old and the Universe is 14 billion years old, which leaves more than 9 billion years between the Big Bang and the emergence of life on Earth. Here we ask, “are we the first, or has life emerged numerous times in many places elsewhere in the Universe prior to the formation of our Solar System and the subsequent emergence of life on Earth?” Since we have experience of only one life, we need to work with the “tools” which we currently have access to—e.g., deeper knowledge of chemistry. In this chapter, we postulate that life could possibly also be a widespread phenomenon in the Universe, by investigating and unraveling the physical and chemical mechanisms that led to the origins of life on Earth and correlating these with ongoing discoveries in space (e.g., the formation of organic molecules). We consider the formation of the complex organic molecules required for life in the interstellar medium, which is one of the factors affecting the eventual emergence of life. We analyzed various hypotheses that may help to explain the origins of life on Earth and the possibility of life elsewhere in our Solar System (e.g., Enceladus). In addition, the role of genetics, viruses, and extremophiles is examined before coming to a probabilistic conclusion.

We discuss cultural implications of life before its origin on Earth. We still lack reviews of the possibility that terrestrial life emerged only at the end of a long process of biological evolution elsewhere. Some astrobiological implications of the origin of life in the universe are covered in this chapter for cultural aspects, other than science. Additional considerations are needed if life on Earth happened to be a latecomer in cosmic evolution.

The appearance of eukaryotes is analyzed in detail in connection with the geophysical, geochemical, atmospheric, and astrophysical events impacting the Earth in the Hadean, Archaean, and early Proterozoic eons. We conclude that neither these events nor proposed biological constraints explain the roughly 2 Gy delay from LUCA at 4 Ga to eukaryogenesis, resulting in LECA, at roughly 2 Ga. Rather, we consider a proposal by Eugene V. Koonin that the archaeal component of the initial symbiosis producing LECA, later shown to be in the Lokiarchaeota, was “complex.” A biosemiotics approach to the evolution of this complexity suggests a process that accelerated after a while, exponentially accumulating many innovations which came together through rare events of horizontal gene transfer, a refinement of the “slow-drip” hypothesis. We predict that examination of the higher order structure of many Archaeal and bacterial genomes might lead to an understanding of what innovations were necessary for eukaryogenesis, when they came about, and whether they were delayed or accelerated by specific events during the Precambrian. We may thus arrive at an explanation of why this step of megaevolution took so long to get to the threshold for a successful symbiosis. In summary, a single cell called LUCA gave rise to two lines of prokaryotes, Archaea and Bacteria, which proliferated into large numbers of species. As innovations occurred in both lines, they were passed between species of both types via horizontal gene transfers. While many symbioses may have occurred, two individual cells, the α-proteobacterium precursor of mitochondria (B-euk) and the Lokiarchaeota-like precursor of the Archaea cell (A-euk), fused to become LECA. What was unique about A-euk and B-euk is that their combined innovations resulted in one cell that successfully started the whole line of eukaryotes. This was a rare event, resulting from many previous rare events, with a cosmic amount of time required before it could occur. This then provides a model for why life stayed so long in the prokaryotic state and suggests that an analogous interval may have been needed for the origin of life and its transition to LUCA, implying an origin of Earth life before Earth.

Tensegrity refers to the stability of a complex three-dimensional structure supported by the balance of tension and compression between its components. Here we suggest that new shapes of primordial living systems may have emerged via tensegrity mechanisms. As a simple physical model, we explore the emergence of shape using simple cooled oil droplets suspended in water in the presence of surfactants, which could have occurred on early Earth or on any exoplanet with water. According to some models of the origin of life, primordial living systems were composed mostly of oil and/or assemblies of lipids (i.e., lipid world). Models for the origin of life from oil droplets, which we now can consider also as shaped droplets, are consistent with phylogenetic evidence that life started from an oily state. Membrane-enclosed cells may have formed later via double droplets known as water-oil-water emulsions. A potential advantage of a polygonal protocell is that it provides structure and edges along which linear polymers, perhaps predecessors of the cytoskeleton and/or nucleic acids, could align. This is consistent with the ancient origin of cytoskeleton and recent evidence of its central role in prokaryote cell function. In addition, the shape of an organism or protocell may provide advantages in survival, nutrient uptake, and motility. The significance of polygonal shape among extant unicellular organisms warrants investigation. Presently, flat polygonal shapes with sharp corners occur in many halophilic Archaea and diatom valves. Flat polygonal shapes with rounded corners occur in some bacteria, desmids, and diatoms. All of these polygonal shapes may be consequences of hoop compression mechanisms resulting in tensegrity structures. We demonstrate a physical toy model using magnets that takes on flat, polygonal configurations to show the basic mechanics. It may be analyzed as a one-dimensional Ising lattice with sharp phase transitions.

Mapping of Mars by orbiters revealed significant geologic evidence of past water activity, including enormous outflow channels carved by floods, ancient river valley networks, and lake beds. Further clues of water activity have come from the identification of aqueously altered rocks at the surface and from Martian meteorites. Three possible sources for organics are considered: a primitive atmosphere, hydrothermal systems, and space delivery of meteorites and micrometeorites. So far, the inventory of organic molecules found on Mars is rather poor, mostly in Martian meteorites. The early histories of Mars and Earth clearly show similarities, having in common liquid water and organic material. Chemistry being reproducible, processing identical ingredients should have produced the same effects. There are, however, some limitations: the complexity of the origin of terrestrial life and the three specific features of the Earth (generalized plate tectonics, global magnetic field, and a large moon generating oceanic tides). The discovery of a second independent genesis of life would demonstrate that life is not a magic one-shot process, but probably a rather common phenomenon.

Some fundamental molecules of life are suggested to have been formed, proliferated, and evolved through photochemical microscopic dissipative structuring and autocatalytic proliferation under the UV-C/UV-B solar environment prevalent at Earth’s surface throughout the Archean. Evidence is given in the numerous salient characteristics of these, including their strong absorption in this spectral region and their rapid non-radiative excited state decay through inherent conical intersections. The examples of the dissipative structuring and dissipative proliferation of the purines and of single strand DNA are given. UV-C and UV-B-induced stationary state isomerizations and tautomerizations are shown to be crucial to the formation of the purines from hydrogen cyanide in an aqueous environment under UV-C light, while UV-C induced phosphorylation of nucleosides and denaturing of double helix RNA and DNA are similarly important to the production and proliferation of single strand DNA. This thermodynamic dissipation perspective provides a physical-chemical foundation for understanding the origin and evolution of life.

The origin of life is still a mystery with many unsolved puzzles. How were molecules created? How did they assemble into large structures? Among the many mysteries, the “chirality” phenomenon upon which amino acids and sugars form is particularly exciting. Single chiral molecules in any chemical system play a very particular role, and these are the only systems where one can be sure that they display 100% enantiomer excess. If this kind of system is a sub-sytem of reaction mixtures where highly sensitive autocatalytic reactions may develop, as for example in the case of the Soai reaction, the presence of this initial chiral molecule can decisively influence the subsequent stereochemical developments. In the work presented here we try to understand how the phenomenon of chirality is related to single molecules, and how this starting situation could influence the outcome of reactions where the product(s) is(are) of high molecular weight, such as synthetic or biological polymers.

Conscious behavior serves to optimize feelings, eg, Epicurean delight, “dopaminergic reward,” Freud's “pleasure principle,” spiritual bliss, and altruism (it feels better to give than to receive). However, Darwinian evolution is viewed as genetic survival, perhaps because science cannot yet account for feelings or consciousness (“qualia,” the “hard problem”). Sir Roger Penrose proposed mental properties including qualia accompany self-collapse of the quantum wave function by objective reduction (OR), a threshold in the structure of spacetime geometry. Such OR qualia would be occurring ubiquitously in random environments throughout the universe, but be noncognitive and merely protoconscious. The Penrose-Hameroff Orch OR theory suggests OR events in cytoskeletal microtubules within brain neurons are organized, or orchestrated by inputs, memory, and vibrational resonances, and terminate by orchestrated OR to give meaningful conscious moments. Supporting evidence for Orch OR includes (1) anesthetic gases act to erase consciousness in pi resonance quantum channels within microtubules, and (2) microtubules have quantum resonances coupled to mechanical vibrations, eg, in megahertz. On a grand scale, Orch OR implies life originated, and the brain evolved to orchestrate and optimize pleasurable protoconscious OR qualia present in the universe. It is suggested here that billions of years ago in the primordial soup, pi resonance clouds of dopamine-like amphipathic molecules coalesced within micelle-like precursors of biomolecules, organelles, and cells. In these quantum channels (collectively the quantum underground), quantum events were shielded from random, polar interactions, enabling more intense and pleasurable OR qualia. Pi stack geometry in micelles and biomolecules optimized OR qualia and precipitated life. Microtubules, and eventually the brain, evolved to orchestrate OR-mediated resonance, optimizing pleasure and its behavioral pursuits.

This chapter begins with a brief general introduction, which includes the origin of single-cell organisms in oceans, extinction events that affected life on Earth, a clue to life on Earth at least 4.1 billion years ago, and an understanding of the complexities of seafloors and oceans. This is followed by discussion on topics such as subseafloor microbial life, organisms living above 100°C under anaerobic conditions (eg, deep subseafloor sediments, submarine hydrothermal areas, submarine volcanoes), significance of deep-sea hydrothermal vents, and microbial activity in hydrothermal fluids. There are also discussions on issues related to DNA and RNA. Adequate attention is given to Darwin's theory of natural selection. The chapter ends with a discussion of the discoveries in 2015 of Lokiarchaeota and a new Homo genus named Homo naledi.

Discussion about an interdisciplinary topic such as “Astronomical and Biological Organizational Relationships” demands a background description of astronomy and cosmology. In view of this requirement, this chapter begins with a description of fundamental discoveries in astronomical and cosmological sciences including the big bang theory of the origin of the Universe. This is followed by discussion of chemical evolution leading to origin of life, and the role of primitive oceans and submarine hydrothermal vents in triggering biological evolution. An interesting, but rather unnoticed, topic of linkage between biological and astronomical organizations is discussed next. The role of islands in biological evolution is given adequate attention. To strengthen the biological versus astronomical correlation, another related subject—self-organization in the origin of the Universe and biological evolution—is also addressed. The chapter winds up with a comprehensive discussion on the puzzle attached to the origin of life mystery, and how religious and scientific views have sometimes been at loggerheads and at times even clashed.

Theories addressing the origin of life strive to explain the transition from rocks, water, inorganic carbon, and chondritic carbon (carbon from space) on the early Earth to living things (cells). The origin of life is generally regarded as the greatest of all evolutionary transitions and as one of the most difficult questions in all of the natural sciences. Energy, molecular organization, and the nature of the earliest life forms help to constrain the problem and link it to geochemical processes on the early Earth.

This chapter begins with an introduction to the overall subject matter covered in this chapter. This is followed by a brief description of the formation of hydrothermal vents and tectonic and magmatic controls on hydrothermal activity. The concept of serpentinization is described as an important set of geochemical reactions. Composition and temperature of vent fluids are addressed next. Both shallow water and deep-sea hydrothermal activities are discussed under different headings. Biological significances of submarine hydrothermal vents are addressed in detail. Due attention is given to unique thermostable enzymes in hydrothermal vent worm. The exotic world of marine organisms around cold seeps and their source of food are described in some detail. Several technologies that are used for studies of hydrothermal vents and seeps are briefly touched upon. This chapter winds up with a conclusion section, which provides a bird’s-eye view of several aspects of hydrothermal vents and seeps, and their probable role in the origin of life on this planet.

How life started is a very big question. All answers, including those proposed here are strictly hypothetical. This is because nobody was present 4 billion years ago to witness how life started and because there are no first life-forms alive on Earth today. Yes, the earth had to cool down and form a solid hot mass before life had a chance of starting. That limits us to around 4.2 billion years ago (BYA). Furthermore, the atmosphere needed to change from hydrogen and helium to a volcanic atmosphere of carbon dioxide, carbon monoxide, nitrogen, steam, methane, and ammonia before life had a chance to start. That change occurred around 4.4 BYA. The Earth's volcanic onslaught possibly needed to stop as did the bombardment of Earth from space by comets and meteorites before life could take a grasp. They both stopped by around 3.8 BYA.

This chapter includes a discussion of the origin of life, early evidences for life, the origin of photosynthesis, possibilities of extraterrestrial life, major events in the biosphere in the last 2 Gyr, and the origin eukaryotes and multicellular organisms. It briefly summarizes the Cambrian explosion of life and the evolution of Phanerozoic life forms. A final topic is mass extinctions including a review of causes and extinction mechanisms.

The history of the ‘origin of life’ question is rooted in ancient philosophy and continues in research today. It was a central aspect of a wide range of philosophies, belief systems, and scientific investigations, including in the modern period, as well as the experimental physical and life sciences. This article explores only several of the periods and approaches to this question. At its core, the search for the elusive answers to ‘the origin of life’ defines our understanding of our place on the Earth and in the cosmos.

The RNA World hypothesis is that (1) there was an early stage in the evolution of life on Earth in which RNA sequences played the role of both genes and catalysts, and (2) the origin of life occurred by the formation of systems of RNA sequences that were able to replicate themselves. This article discusses the support for the RNA World that comes from laboratory experiments with catalytic RNAs and from theoretical models for replicating systems.

The examination of contemporary systems and the rock record has demonstrated that the biosphere and geosphere are intimately linked, presumably since life's origin. The geosphere provides trace and essential nutrients for life, sources of reduced compounds and electron acceptors, that is, the energy for life to occur, and habitats ranging from ‘simple’ surfaces to grow on to unique endolithic environments formed at least in part by the microorganisms themselves. The hydrosphere is perhaps more important than the lithosphere, because it provides the solvent necessary for biogeochemical reactions and life to occur. The major question about how life originated cannot be readily answered; however, the question of habitability is relatively easy. Using Earth as our role model, there are several candidate extrasolar bodies within our solar system, for example, Mars and Europa, that could support life.

Coevolution is a process in which unrelated but mutually interdependent kinds of organisms evolve in a coordinated fashion. Coevolution of grasses and grazers is a well-known example, in which grasses evolved sod growth and abrasive leaves to cope with increasingly hard hooves and high-crowned teeth of grazers. Other plants could not withstand the grazing and other animals could not digest the grasses. The result was creation within the past 30 million years of a new ecosystem type, grasslands, with carbon sequestration, water balance, and albedo unlike other terrestrial ecosystems. These forces for global change arose because both grazers and grasses coevolved in response to biological rather than only physicochemical selection. Such coevolutionary processes can be understood not only in the linkages of interdependence between coevolving partners but also in historical patterns of change, such as promotion of global cooling by grassland coevolution. Such processes have taken Earth far from its primordial state, creating biosignatures that set it apart from known barren worlds such as the Moon, Venus, Mars, and asteroids. Plausible biosignatures of coevolutionary processes on Earth include its inflammable atmosphere, permanent liquid water, carbon-based life, spheroidal weathering, granitic rocks, convex slopes, calcic horizons, argillic horizons, mollic epipedons, and civilizations. A coevolutionary view of the origin of life requires natural selection of interacting interdependent groups of minerals or molecules. As a hypothetical example, erosion resistance (selected property) of soils could be promoted by clay (consumers) formed from hydrolytic weathering of high-temperature minerals (producers). Other soils, lacking clay cements or with clays cracking too much on desiccation, would be eroded and dispersed by wind, water, and impacts. Naturally selected clayey soils with their millions of warm little pools of intergranular water could have been a stable laboratory for the origin of life and remain the source of nutrients fundamental for life.

Life continually arises spontaneously . A widespread belief from the time of the ancient Romans through and beyond the Middle Ages was that organic life routinely generates from non-life, such as when rats emerge from a heap of trash, amphibians appear each spring from swampy mud, or maggots swarm from rotting meat. This standard folklore is known as abiogenesis, or the origin of life via spontaneous generation.

Life originated long after the Earth had formed. Darwin and other evolutionary biologists were well aware of fossils, but had few ways to date them beyond the relative gauge of stratigraphy itself – the realization that more recent forms of life typically appear above more ancient forms of life in stratified layers of sedimentary rock. Many paleontologists surmised that the origin of life was so improbable an event that it must have taken many eons for life to emerge after the Earth’s formation. Especially challenging to understand was the relatively sudden appearance in the fossil record of a wide variety of animal types at the Pre-Cambrian/Cambrian boundary, “merely” some 600 million years ago. This Cambrian explosion implied that plant lineages and microbes must have made their appearances much earlier, but exactly when remained a mystery.

Primitive meteorites contain significant amounts of carbon, the majority of which is present as organic matter. Low molecular weight compound classes include aliphatic and aromatic hydrocarbons, amino acids, nucleic acid bases, carboxylic acids, phosphonic acids, sulfonic acids, sugar-related compounds, and organohalogens. Yet, the low molecular weight compounds are minor components relative to a high molecular weight, predominantly aromatic network. Some of the organic matter exists in morphologically distinct microvesicles or nanoglobules and appears to associate with clay minerals in the matrix. As bona fide prebiotic organic compounds, the meteoritic organic matter provides valuable insights into the chemical evolution in the early solar system and the reactions that preceded the origin of life on Earth.

The origin of life falls outside the emerging evolutionary genetic framework. Before the macromolecules of heredity and biochemistry were well characterized, it seemed inconceivable to most scientists that life’s mode of origin could be understood in great detail, much less replicated in the laboratory.

Several evolutionary models proposed that molecular hydrogen (H2) was the primary energy source on the early Earth, exerting a major influence on the origin of life. Hydrogenase, the enzyme catalyzing the interconversion of H2 into protons and electrons, is thus considered an ancestral invention, for which the molecular structure and architecture have been thoroughly adapted for specialized tasks, undertaken in peculiar environments, during the course of the evolution. Three different types of hydrogenase can be distinguished on the basis of the metal content of their active site, namely, [NiFe]-hydrogenase, [FeFe]-hydrogenase, and [Fe]-hydrogenase. Although they share common features, taxonomic distribution, maturation apparatus, and physiological role differ substantially among the three different classes of hydrogenases. These metalloenzymes are thus considered a classical example of convergent evolution. The notion that “there is much to learn from nature” holds great promise for biohydrogen applications, and this has been demonstrated by the emergence of bioengineering strategies used to design synthetic metabolic pathways and improve the O2 tolerance of hydrogenases. This chapter provides an overview of the diversity and physiological role of hydrogenases, with a particular emphasis on their biotechnological potential.

Modern advances in biology, geology, chemistry, and astronomy have allowed us to elaborate models and hypotheses on the origin of life on Earth within the framework of the evolutionary theory. About four billion years ago, a rich inventory of organic compounds accumulated on the planet, as a product of volcanic, atmospheric, and cosmic chemistry. As chemical systems became increasingly more complex, a critical point was reached with the appearance of self-replicative polymers. This marks the possibility of optimizing abiotic systems by natural selection and historical contingency, which were added to the determinism of abiotic chemistry. A landmark of the origin of life was the articulation of suprachemical systems, such as self-reproductive vesicles, self-maintained chemical networks, and self-replicative polymers, under the conditions of the primitive Earth. Albeit most details remain unknown, the stepwise processes involved in the origin of life are scientifically comprehensible and experimentally reproducible.

Bernal first suggested the role of clay minerals in the origin of life because of the ordered arrangement of the clay mineral particles, the large adsorption capacity, shielding against ultraviolet radiation, ability to concentrate organic chemicals and ability to serve as polymerization templates. Clay minerals were proposed as possible genetic material. This appealing hypothesis was not yet supported by experimental data. Many experiments were run to correlate biological one-handedness to clay mineral chemistry but convincing data were not obtained. However, clay minerals act as very efficient catalysts in the polymerization of amino acids and nucleotides, thus supporting the possible existence of an RNA world preceding a cellular world. RNA adsorbed to clay minerals can be encapsulated within vesicles. Once formed, such vesicles could grow by incorporating fatty acids and divide, thus mediating vesicle replication through cycles of growth and division. The data obtained so far suggest that clay minerals played an active role in the abiotic origin of life.

The oceans have been regarded as the origin of life on the Earth and represent the vast range of habitats which facilitate the various forms of life. Competition amongst the microorganisms for the space and nutrients in the marine environment has been a significant selective force leading towards evolution, which prompted the marine microorganisms to develop enzyme systems adapted to complicated environments. The oceans account for more than 70% of the total surface of the planet Earth and marine habitats contain countless microorganisms having biochemical and molecular secrets for their adaptation. Therefore, the marine microbes can offer novel biocatalysts and other value added molecules. While the enzymes have been isolated and purified from microorganisms, animals and plants, the microorganisms represent the most common source due to their broad biochemical diversity, feasibility of their mass cultivation and the ease of their genetic manipulation. The actinomycetes have been traditionally explored from soil for their valuable secondary metabolites. However, the actinomycetes from the aquatic ecosystems have been explored only in the limited sense with respect to their diversity and value added molecules. During recent years, novel actinomycetes from the various marine habitats have been isolated and these marine actinomycetes produce different types of new enzymes. The limited work on the occurrence, diversity and enzymatic potential of the marine actinomycetes highlights their huge potential. With the rapidly increasing interest in the extremophilic actinomycetes, the studies on their diversity, enzymatic profiling, physiology and adaptive features assume significance.

Ribozymes are RNA molecules that can carry out enzymatic function by speeding up the rate of a chemical reaction. There are nine known classes of ribozymes extant in nature, and many more that have been designed in the laboratory. The known biological ribozymes are phylogenetically widespread, although more have been discovered from viruses and bacteria than from other groups. Ribozymes play a central role in the evolutionary history of life on the Earth. They may in fact have been part of the first self-replicating biological entities that arose some 4 billion years ago, and today they are found in central positions in cellular biochemistry as a result of their antiquity.

Piezonuclear reactions, which occur in inert and nonradioactive elements, are induced by high pressure and, in particular, by brittle fracture phenomena in solids under compression. These low energy reactions generally take place in nuclei with an atomic weight that is lower or equal to that of iron (Fe). The experimental evidence, obtained from repeatable measurements of neutron emissions, can be also recognized considering the anomalous chemical balances of the major events that have affected the Earth’s crust, oceans and atmosphere, over the last four billion years. These anomalies include: (i) the abrupt variations in the most abundant elements in correspondence to the formation of tectonic plates; (ii) the Great Oxidation Event (2.7 to 2.4 billion years ago), with a sharp increase in atmospheric oxygen and the subsequent origin of life; (iii) the increase of carbon and nytrogen concentrations in the primordial atmosphere.

‘Homochirality’ or one-handedness is a characteristic hallmark of terrestrial life, which is based on nucleic acids made of all- D sugars coding for proteins made of all- L amino acids. But why is life made of L -amino acids and not their ‘unnatural’ D mirror images? In this article we consider at what stage in the origin of life homochirality first arose, and whether life's handedness was selected by chance or by a chiral influence. We discuss in detail the two most popular chiral influences – circularly polarized radiation, and parity-violation by the weak force – together with mechanisms to amplify small enantiomeric excesses to homochirality. We focus in particular on the ‘parity-violating energy difference’ or ‘PVED’ between enantiomers, and review calculations of the PVED, which show that in most cases the natural enantiomers are indeed of slightly lower energy than their ‘unnatural’ mirror images. We also review proposed methods to measure the PVED. We conclude with a review of the new field of ‘exochirality’ (chirality outside Earth), and discuss proposed instruments to search for homochirality as a signature of life both in situ on solar system bodies and remotely on extra-solar planets.

The first organisms to appear on earth, about 3.8 billion years ago, were the Archae, the root organism for the Tree of Life. From Class Archae came Class Bacteria and Class Eukaryota. The argument for this particular is that many archaean species observed today are extremophiles that thrive under environmental conditions that are similar to the conditions on earth about 3.8 billion years ago. The members of Class Eubacteria are better-suited for a temperate, oxygen-rich atmosphere, such as we have today. Presumably, the eubacteria evolved after the archaeans appeared, from archaean ancestors. The eukaryotes, like all other living organisms on earth, replicate and transcribe DNA and translate RNA into proteins. Key structures of the genetic machinery of eukaryotes (chromosomal proteins and ribosomal RNA) are more similar to archaeans than to the eubacteria. Hence, it is presumed that the eukaryotes evolved from an archaean ancestor. In this book, we will not go into any of the arguments for or against any of the “origin of life” hypotheses. Readers can accept the observation that every serious evolutionary biologist is obsessed with the minutiae of these arguments; and rightly so. Biologists believe that the cell is a living book, recording the history and predicting the future of life on earth. It is the responsibility of biologists to correctly interpret the contents of the book of life.

Over billions of years, the ocean is regarded as the origin of life on Earth, and the ocean includes the largest habitats hosting the most life forms. Competition among microorganisms for space and nutrients in the marine environment is a powerful selective force, which has led to the evolution. The evolution prompts the marine microorganisms to generate multifarious enzyme systems to adapt to the complicated marine environments. Therefore, marine microbial enzymes can offer novel biocatalysts with extraordinary properties. This review deals with the research and development work done on the occurrence and bioprocessing of marine microbial enzymes.

All life, as we know it, springs from already existing life. But how did it all begin? We argue that evolution preceded life, and we must understand the origin of evolvable chemical systems as their gradual increase of complexity lead to the appearance of the first living entity. In this chapter, we discuss various theoretical models that have been proposed to explain the origin of evolvable systems (including template replicators, autocatalytic cycles, polymer autocatalytic sets, and the GARD model) and translate the critical properties of evolution to features of chemical networks.

This chapter discusses the various theories related to the origin of life on earth. The belief in spontaneous generation of large plants and animals began to wane throughout the 17th and 18th centuries. According to some scientists, as no one has yet created life in the laboratory, this means that life cannot be created but must come from existing life. Thus if life can only originate from life, then life on Earth must have originated in outer space and come to Earth on meteorites in the form of cosmozoa, microbes, spores, or seeds. This theory is called panspermia. This leads to another assumption that life arose from lifeless matter in the earth. According to Harold Urey, who had been studying the atmosphere of Jupiter, the atmosphere of the early Earth, like that of Jupiter's, may have been reducing, and thus may have consisted largely of hydrogen, methane, ammonia, and water. Experiments conducted by Stanley Miller, in which a gaseous mixture of methane, ammonia, hydrogen, and water was connected to a flask of boiling water, resulted in the production of glycine and alanine. This result indicated that amino acids may have been present on the early Earth before the advent of life. Under prebiotic conditions, amino acids can polymerize into polypeptides without the aid of enzymes or a template. Even more complex structures like proteinoid microspheres can form under prebiotic conditions. Such proteinoid microspheres may have joined together with phospholipids, which can also be synthesized under prebiotic conditions to form the first plasma membranes in a process of self-assembly.