Seeking the oldest evidence of life on Earth

2004 ◽  
Vol 25 (1) ◽  
pp. 8
Author(s):  
Abigail Allwood ◽  
Adrian Brown
Keyword(s):  
Naked Eye ◽  
Terrestrial Life ◽  
Planetary Processes ◽  
Life On Earth

The search for the oldest evidence of terrestrial life is a search for answers to some of mankind?s oldest questions. But do we really have a chance of finding unequivocal fossils of the simple, soft bodied microorganisms that were the first inhabitants of this planet if we consider their lack of hard parts, their concealment from the naked eye, their simple morphologies, the timeframes and planetary processes since their formation (perhaps more than 3 billion years ago), and the rarity of suitable ancient rocks?

The Global Biosphere and Its Metaphysical Underpinnings: Ecumenical Alternatives in Animism and Astrobiology

Sociologus ◽  
2021 ◽  
Vol 71 (1) ◽  
pp. 55-72
Author(s):  
Istvan Praet
Keyword(s):  
Indigenous People ◽  
Home Environment ◽  
Ancient Greek ◽  
Extraterrestrial Life ◽  
Terrestrial Life ◽  
Familiar World ◽  
Life On Earth ◽  
Historical Accident

The term biosphere designates the “zone of life” on Earth. Outside this sphere, everything becomes “alien.” In this view of things, which I take to be canonical in the modern West, terrestrial life and biosphere overlap more or less neatly. Yet this idea of an almost perfect convergence is not the only view possible. This study presents two anthropological cases which demonstrate, a contrario, that the modern tendency to envisage the biosphere as “our home environment” or as “our familiar world” is in many ways a historical accident. Other ecumenical possibilities (by which I refer to the ancient Greek notion of the “inhabited world,” the oikumene) are by no means unthinkable. Examining the ecumenical originality of two communities that at first sight seem unrelated – Chachi indigenous people in Ecuador and scientists involved in the search for extraterrestrial life – will allow us to cast new light on the metaphysical underpinnings of the modern biosphere concept.

Searching for a shadow biosphere on Earth as a test of the ‘cosmic imperative’

2011 ◽  
Vol 369 (1936) ◽  
pp. 624-632 ◽  
Author(s):  
P. C. W. Davies
Keyword(s):  
Origin Of Life ◽  
Observable Universe ◽  
The Galaxy ◽  
Terrestrial Life ◽  
The Origin Of Life ◽  
Absence Of Evidence ◽  
Life On Earth ◽  
Second Genesis

Estimates for the number of communicating civilizations in the galaxy, based on the so-called Drake equation, are meaningless without a plausible estimate for the probability that life will emerge on an Earth-like planet. In the absence of a theory of the origin of life, that number can be anywhere from 0 to 1. Distinguished scientists have been known to argue that life on Earth is a freak accident, unique in the observable universe and, conversely, that life is almost bound to arise in the course of time, given Earth-like conditions. De Duve, adopting the latter position, coined the phrase that ‘life is a cosmic imperative’. De Duve’s position would be immediately verified if we were to discover a second sample of life that we could be sure arose from scratch independently of known life. Given the current absence of evidence for life beyond Earth, the best way to test the hypothesis of the cosmic imperative is to see whether terrestrial life began more than once. If it did, it is possible that descendants of a second genesis might be extant, forming a sort of ‘shadow biosphere’ existing alongside, or perhaps interpenetrating, the known biosphere. I outline a strategy to detect the existence of such a shadow biosphere.

Life as a cosmic imperative?

2011 ◽  
Vol 369 (1936) ◽  
pp. 620-623 ◽  
Author(s):  
Christian de Duve
Keyword(s):  
Origin Of Life ◽  
Extrasolar Planet ◽  
Second Stage ◽  
Physical Chemical ◽  
Terrestrial Life ◽  
Probable Site ◽  
The Origin Of Life ◽  
Chemical Conditions ◽  
Life On Earth ◽  
Two Stages

The origin of life on Earth may be divided into two stages separated by the first appearance of replicable molecules, most probably of RNA. The first stage depended exclusively on chemistry. The second stage likewise involved chemistry, but with the additional participation of selection, a necessary concomitant of inevitable replication accidents. Consideration of these two processes suggests that the origin of life may have been close to obligatory under the physical–chemical conditions that prevailed at the site of its birth. Thus, an extrasolar planet in which those conditions were replicated appears as a probable site for the appearance of extra-terrestrial life.

scholarly journals From climate models to planetary habitability: temperature constraints for complex life

2016 ◽  
Vol 16 (3) ◽  
pp. 244-265 ◽  
Author(s):  
Laura Silva ◽  
Giovanni Vladilo ◽  
Patricia M. Schulte ◽  
Giuseppe Murante ◽  
Antonello Provenzale
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Habitable Zone ◽  
Ambient Conditions ◽  
Thermal Thresholds ◽  
Planetary Evolution ◽  
Thermal Limits ◽  
Terrestrial Life ◽  
Earth Like Planets ◽  
Life On Earth

AbstractIn an effort to derive temperature-based criteria of habitability for multicellular life, we investigated the thermal limits of terrestrial poikilotherms, i.e. organisms whose body temperature and the functioning of all vital processes is directly affected by the ambient temperature. Multicellular poikilotherms are the most common and evolutionarily ancient form of complex life on earth. The thermal limits for the active metabolism and reproduction of multicellular poikilotherms on earth are approximately bracketed by the temperature interval 0°C ≤ T ≤ 50°C. The same interval applies to the photosynthetic production of oxygen, an essential ingredient of complex life, and for the generation of atmospheric biosignatures observable in exoplanets. Analysis of the main mechanisms responsible for the thermal thresholds of terrestrial life suggests that the same mechanisms would apply to other forms of chemical life. We therefore propose a habitability index for complex life, h050, representing the mean orbital fraction of planetary surface that satisfies the temperature limits 0°C ≤ T ≤ 50°C. With the aid of a climate model tailored for the calculation of the surface temperature of Earth-like planets, we calculated h050 as a function of planet insolation, S, and atmospheric columnar mass, Natm, for a few earth-like atmospheric compositions with trace levels of CO2. By displaying h050 as a function of S and Natm, we built up an atmospheric mass habitable zone (AMHZ) for complex life. At variance with the classic habitable zone, the inner edge of the complex life habitable zone is not affected by the uncertainties inherent to the calculation of the runaway greenhouse limit. The complex life habitable zone is significantly narrower than the habitable zone of dry planets. Our calculations illustrate how changes in ambient conditions dependent on S and Natm, such as temperature excursions and surface dose of secondary particles of cosmic rays, may influence the type of life potentially present at different epochs of planetary evolution inside the AMHZ.

scholarly journals The Precambrian Evolution of Terrestrial Life

1985 ◽  
Vol 112 ◽  
pp. 201-211
Author(s):  
A. H. Knoll
Keyword(s):  
Chemical Evolution ◽  
Environmental Conditions ◽  
Fossil Record ◽  
Geological Time ◽  
Early Appearance ◽  
Time Table ◽  
Terrestrial Life ◽  
History Of ◽  
Life On Earth ◽  
Biological History

Paleontological evidence indicates that terrestrial life existed at least 3500 Ma ago, and it is quite possible that the earliest cells arose well before that time. The early appearance of life on Earth suggests that under appropriate environmental conditions the probability of chemical evolution proceeding to the point of biogenesis may be reasonably high. Most of biological history has been the history of microorganisms, with tissue-grade plants and animals characterizing only the most recent 15% or so of the fossil record. Intelligent life has occupied only the latest instant in geological time. The time table of terrestrial evolution is governed more by the particulars of our planet's physical and biological history than by some universal tempo of evolutionary change. One aspect of terrestrial life that is likely to be universal is the organization of populations into efficient biogeochemical systems.

The maximum growth rate of life on Earth

2017 ◽  
Vol 17 (1) ◽  
pp. 17-33 ◽  
Author(s):  
Ross Corkrey ◽  
Tom A. McMeekin ◽  
John P. Bowman ◽  
June Olley ◽  
David Ratkowsky ◽  
...  
Keyword(s):  
Growth Rate ◽  
Growth Rates ◽  
Maximum Rate ◽  
Reaction System ◽  
Maximum Growth ◽  
Maximum Growth Rate ◽  
Rate Curve ◽  
Temperature Dependent ◽  
Terrestrial Life ◽  
Life On Earth

AbstractLife on Earth spans a range of temperatures and exhibits biological growth rates that are temperature dependent. While the observation that growth rates are temperature dependent is well known, we have recently shown that the statistical distribution of specific growth rates for life on Earth is a function of temperature (Corkreyet al., 2016). The maximum rates of growth of all life have a distinct limit, even when grown under optimal conditions, and which vary predictably with temperature. We term this distribution of growth rates the biokinetic spectrum for temperature (BKST). The BKST possibly arises from a trade-off between catalytic activity and stability of enzymes involved in a rate-limiting Master Reaction System (MRS) within the cell. We develop a method to extrapolate quantile curves for the BKST to obtain the posterior probability of the maximum rate of growth of any form of life on Earth. The maximum rate curve conforms to the observed data except below 0°C and above 100°C where the predicted value may be positively biased. The deviation below 0°C may arise from the bulk properties of water, while the degradation of biomolecules may be important above 100°C. The BKST has potential application in astrobiology by providing an estimate of the maximum possible growth rate attainable by terrestrial life and perhaps life elsewhere. We suggest that the area under the maximum growth rate curve and the peak rate may be useful characteristics in considerations of habitability. The BKST can serve as a diagnostic for unusual life, such as second biogenesis or non-terrestrial life. Since the MRS must have been heavily conserved the BKST may contain evolutionary relics. The BKST can serve as a signature summarizing the nature of life in environments beyond Earth, or to characterize species arising from a second biogenesis on Earth.

Homochirality as the Signature of Extra-Terrestrial Life

1997 ◽  
Vol 161 ◽  
pp. 505-510
Author(s):  
Alexandra J. MacDermott ◽  
Laurence D. Barron ◽  
Andrè Brack ◽  
Thomas Buhse ◽  
John R. Cronin ◽  
...  
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Optical Rotation ◽  
Physical Origin ◽  
Natural Choice ◽  
Rosetta Mission ◽  
Terrestrial Life ◽  
Subsurface Layers ◽  
Solar System Bodies ◽  
Origin Of Homochirality

AbstractThe most characteristic hallmark of life is its homochirality: all biomolecules are usually of one hand, e.g. on Earth life uses only L-amino acids for protein synthesis and not their D mirror images. We therefore suggest that a search for extra-terrestrial life can be approached as a Search for Extra- Terrestrial Homochirality (SETH). The natural choice for a SETH instrument is optical rotation, and we describe a novel miniaturized space polarimeter, called the SETH Cigar, which could be used to detect optical rotation as the homochiral signature of life on other planets. Moving parts are avoided by replacing the normal rotating polarizer by multiple fixed polarizers at different angles as in the eye of the bee. We believe that homochirality may be found in the subsurface layers on Mars as a relic of extinct life, and on other solar system bodies as a sign of advanced pre-biotic chemistry. We discuss the chiral GC-MS planned for the Roland lander of the Rosetta mission to a comet and conclude with theories of the physical origin of homochirality.

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