Origins of life: A comparison of theories and application to Mars

Davis, W. R.; McKay, Christopher P.

doi:10.1007/bf01808160

Cited by 77 publications

(37 citation statements)

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“…However, our understanding of the origin of life is speculative and so we can only assume that planets that have a diversity of habitable environments are also generative of life (1). As shown in Fig.…”

Section: Origin Of Lifementioning

confidence: 99%

“…4, it is useful to divide theories for the origin of life on Earth into two main categories, depending on whether life originated independently on a world or was carried to that world from somewhere else (1). The latter category is usually called panspermia, and versions that involve both natural and directed panspermia have been considered (1).…”

Section: Origin Of Lifementioning

confidence: 99%

“…The most important area in which we lack knowledge about life on Earth is its origin. We have no consensus theory for the origin of life nor do we know the timing or location (1). What we do know about life on Earth is what it is made of, and we know its ecological requirements and limits.…”

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confidence: 99%

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Requirements and limits for life in the context of exoplanets

McKay

2014

Proc. Natl. Acad. Sci. U.S.A.

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135

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The requirements for life on Earth, its elemental composition, and its environmental limits provide a way to assess the habitability of exoplanets. Temperature is key both because of its influence on liquid water and because it can be directly estimated from orbital and climate models of exoplanetary systems. Life can grow and reproduce at temperatures as low as −15°C, and as high as 122°C. Studies of life in extreme deserts show that on a dry world, even a small amount of rain, fog, snow, and even atmospheric humidity can be adequate for photosynthetic production producing a small but detectable microbial community. Life is able to use light at levels less than 10 −5 of the solar flux at Earth. UV or ionizing radiation can be tolerated by many microorganisms at very high levels and is unlikely to be life limiting on an exoplanet. Biologically available nitrogen may limit habitability. Levels of O 2 over a few percent on an exoplanet would be consistent with the presence of multicellular organisms and high levels of O 2 on Earth-like worlds indicate oxygenic photosynthesis. Other factors such as pH and salinity are likely to vary and not limit life over an entire planet or moon.extremophiles | Mars | astrobiology T he list of exoplanets is increasing rapidly with a diversity of masses, orbital distances, and star types. The long list motivates us to consider which of these worlds could support life and what type of life could live there. The only approach to answering these questions is based on observations of life on Earth. Compared with astronomical targets, life on Earth is easily studied and our knowledge of it is extensive--but it is not complete. The most important area in which we lack knowledge about life on Earth is its origin. We have no consensus theory for the origin of life nor do we know the timing or location (1). What we do know about life on Earth is what it is made of, and we know its ecological requirements and limits. Thus, it is not surprising that most of the discussions related to life on exoplanets focus on the requirements for life rather than its origin. In this paper we follow this same approach but later return briefly to the question of the origin of life. Limits to LifeThere are two somewhat different approaches to the question of the limits of life. The first approach is to determine the requirements for life. The second approach is to determine the extreme environments in which adapted organisms-often referred to as extremophiles-can survive. Both perspectives are relevant to the question of life on exoplanets.It is useful to categorize the requirements for life on Earth as four items: energy, carbon, liquid water, and various other elements. These are listed in Table 1 along with the occurrence of these factors in the Solar System (2). In our Solar System it is the occurrence of liquid water that appears to limit the occurrence of habitable environments and this appears to be the case for exoplanetary systems as well.From basic thermodynamic considerations it is clear that life ...

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Section: Origin Of Lifementioning

confidence: 99%

Section: Origin Of Lifementioning

confidence: 99%

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Requirements and limits for life in the context of exoplanets

McKay

2014

Proc. Natl. Acad. Sci. U.S.A.

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135

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“…Davies and McKay [1] divided them into the categories of Extraterrestrial and Terrestrial origins. Bada [2] classified the Terrestrial theories into two categories "The prebiotic soup theory" and "The metabolist theory" and tried to build a consensus by incorporating them into a general scheme of "the transition from abiotic organic compounds to autonomous self-replicating molecules capable of evolving by natural selection into ones of increasing efficiency and complexity …" The unified theory culminated in the RNA World.…”

Section: Introductionmentioning

confidence: 99%

On the Origin of Biological Functions

Umantsev¹

2011

JMP

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We consider the problem of structure and functions of the first forms of living matter and present a hypothesis that they were formed through a physico-chemical process known as dendritic crystallization. According to this hypothesis the branching, dendritic structures helped build living systems by lending them functions so that organic chemical evolution is just one natural consequence of the evolution of matter in the universe. We conclude that a self-replicating biological system with adaptation emerged from simple molecules using completely abiotic mechanism of formation, which acted simultaneously or intermittently at different places on the early Earth and created similar structures everywhere. The dendritic hypothesis of origin of the functions explains similarities in the living systems and supports the assumption of a 'second genesis of life'. The dendritic scenario does not need carbon/phosphorus-based solutes in water-based solutions, which may have important implications for exobiology and extraterrestrial origin-of-life scenarios. An experiment to test the hypothesis is suggested.

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“…The question of "How life on Earth evolved" is intimately related to another, perhaps more tractable, question "When did the Earth become suitable for habitation?" The later question is relevant regardless of whether life evolved on Earth or, if as some suggest, life "arrived" on Earth from an extraterrestrial source [Davis and McKay, 1996]. The establishment of conditions suitable for life on Earth is the end product of our planet's earliest geologic evolution, and the differentiation of the terrestrial hydrosphere and atmosphere.…”

Section: Introduction/backgroundmentioning

confidence: 99%

Mission to Very Early Earth

Hutcheon¹,

Weber²,

Fallon³

et al. 2007

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SummaryThe Hadean Earth is often viewed as an inhospitable and, perhaps, unlikely setting for the rise of primordial life. However, carbonaceous materials supplied by accreting meteorites and sources of chemical energy similar to those fueling life around modern deep-sea volcanic vents would have been present in abundance. More questionable are two other essential ingredients for life -liquid water and clement temperatures. Did the Hadean Earth possess a hydrosphere and temperate climate compatible with the initiation of biologic activity? If so, the popular model of an excessively hot planetary surface characterized by a basaltic crust, devoid of continental material is invalid. Similarly, establishment of an Hadean hydrosphere prior to the cessation of heavy asteroid bombardment may mean that primitive life could have evolved and then been extinguished, only to rise again. The most effective means of determining the environmental conditions on this young planet is through geochemical analysis of samples retrieved from the Early Earth. While rocks older than 4 billion years (4 Ga) have not been found, individual zircon grains, the detritus of rocks long since eroded away, have been identified with ages as old as 4.4 Ga -only ~160 million years younger than the Earth itself. If we can use the geochemical information contained in these unique samples to infer the nature of their source rocks and the processes that formed them, we can place constraints on the conditions prevailing at the Earth's surface shortly after formation. This project utilizes a combined analytical and experimental approach to gather the necessary geochemical data to determine the parameters required to relate the zircons to their parent materials. Mission to Early Earth involves dating, isotopic and chemical analyses of mineral and melt inclusions within zircons and of the zircons themselves. The major experimental activity at LLNL focused on the partitioning of trace elements between zircon and melt to elucidate the relationships between host zircons and mineral inclusions and between zircons and crustal fluids. Mission to Early Earth utilizes a broad array of new analytical facilities at LLNL supporting a variety of national security programs and has already become instrumental in developing these instrumental capabilities and a new cadre of qualified users for this and more applied programs.

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Origins of life: A comparison of theories and application to Mars

Cited by 77 publications

References 98 publications

Requirements and limits for life in the context of exoplanets

Requirements and limits for life in the context of exoplanets

On the Origin of Biological Functions

Mission to Very Early Earth

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