Life
Life | |
---|---|
Diversity of Spirochete
| |
Diversity of Giant sequoia, Entodinium, Amanita caesarea, Pterois antennata, Algae blooms, Chrysotoxum verralli, Xanthoparmelia lichen, Dictyostelium, and Pillar coral
| |
Scientific classification ![]() | |
Domains and Supergroups | |
Life on Earth:
|
![]() |
This article is one of a series on: |
Life in the Universe |
---|
Astrobiology |
Habitability in the Solar System |
Life outside the Solar System |
|
Life is a quality that distinguishes
that studies life.The
Death is the permanent termination of all biological processes which sustain an organism, and as such, is the end of its life. Extinction is the term describing the dying-out of a group or taxon, usually a species. Once extinct, the extinct species or taxon cannot come back to life. Fossils are the preserved remains or traces of organisms.
Definitions
The definition of life has long been a challenge for scientists and philosophers.[9][10][11] This is partially because life is a process, not a substance.[12][13][14] This is complicated by a lack of knowledge of the characteristics of living entities, if any, that may have developed outside of Earth.[15][16] Philosophical definitions of life have also been put forward, with similar difficulties on how to distinguish living things from the non-living.[17] Legal definitions of life have also been described and debated, though these generally focus on the decision to declare a human dead, and the legal ramifications of this decision.[18] As many as 123 definitions of life have been compiled.[19]
Biology
Since there is no consensus for a definition of life, most current definitions in biology are descriptive. Life is considered a characteristic of something that preserves, furthers or reinforces its existence in the given environment. This characteristic exhibits all or most of the following traits:[11][20][21][2][22][23][24]
- Homeostasis: regulation of the internal environment to maintain a constant state; for example, sweating to reduce temperature
- Organisation: being structurally composed of one or more cells– the basic units of life
- Metabolism: transformation of energy by converting chemicals and energy into cellular components (anabolism) and decomposing organic matter (catabolism). Living things require energy to maintain internal organisation (homeostasis) and to produce the other phenomena associated with life.
- Growth: maintenance of a higher rate of anabolism than catabolism. A growing organism increases in size in all of its parts, rather than simply accumulating matter.
- Adaptation: the evolutionary process whereby an organism becomes better able to live in its habitat or habitats.[25][26][27]
- Response to multicellular organisms. A response is often expressed by motion; for example, the leaves of a plant turning toward the sun (phototropism), and chemotaxis.
- Reproduction: the ability to produce new individual organisms, either asexually from a single parent organism or sexually from two parent organisms.
These complex processes, called physiological functions, have underlying physical and chemical bases, as well as signaling and control mechanisms that are essential to maintaining life.
Alternative definitions
From a
Others take a
Viruses
Whether or not viruses should be considered as alive is controversial. They are most often considered as just
Biophysics
To reflect the minimum phenomena required, other biological definitions of life have been proposed,
Living systems theories
Living systems are open

Some scientists have proposed in the last few decades that a general living systems theory is required to explain the nature of life.[52] Such a general theory would arise out of the ecological and biological sciences and attempt to map general principles for how all living systems work. Instead of examining phenomena by attempting to break things down into components, a general living systems theory explores phenomena in terms of dynamic patterns of the relationships of organisms with their environment.[53]
Gaia hypothesis
The idea that Earth is alive is found in philosophy and religion, but the first scientific discussion of it was by the Scottish scientist James Hutton. In 1785, he stated that Earth was a superorganism and that its proper study should be physiology. Hutton is considered the father of geology, but his idea of a living Earth was forgotten in the intense reductionism of the 19th century.[54]: 10 The Gaia hypothesis, proposed in the 1960s by scientist James Lovelock,[55][56] suggests that life on Earth functions as a single organism that defines and maintains environmental conditions necessary for its survival.[54] This hypothesis served as one of the foundations of the modern Earth system science.
Self-maintainable information
All living entities posess
This approach provides a lather-like hierarchy of entities depending on their ability to maintain themselves, their evolvability, and their distinctness. It also distinguishes between life as a phenomenon, a living individual, and an alive individual.[35]
Nonfractionability
Property of ecosystems
A systems view of life treats environmental
Complex systems biology
Complex systems biology (CSB) is a field of science that studies the emergence of complexity in functional organisms from the viewpoint of
Darwinian dynamic
It has also been argued that the evolution of order in living systems and certain physical systems obeys a common fundamental principle termed the Darwinian dynamic.[67][68] The Darwinian dynamic was formulated by first considering how macroscopic order is generated in a simple non-biological system far from thermodynamic equilibrium, and then extending consideration to short, replicating RNA molecules. The underlying order-generating process was concluded to be basically similar for both types of systems.[67]
Operator theory
Another systemic definition called the operator theory proposes that life is a general term for the presence of the typical closures found in organisms; the typical closures are a membrane and an autocatalytic set in the cell[69] and that an organism is any system with an organisation that complies with an operator type that is at least as complex as the cell.[70][71][72][73] Life can also be modelled as a network of inferior negative feedbacks of regulatory mechanisms subordinated to a superior positive feedback formed by the potential of expansion and reproduction.[74]
History of study
Materialism

Some of the earliest theories of life were materialist, holding that all that exists is matter, and that life is merely a complex form or arrangement of matter. Empedocles (430 BC) argued that everything in the universe is made up of a combination of four eternal "elements" or "roots of all": earth, water, air, and fire. All change is explained by the arrangement and rearrangement of these four elements. The various forms of life are caused by an appropriate mixture of elements.[75]
Democritus (460 BC) thought that the essential characteristic of life is having a soul (psyche). Like other ancient writers, he was attempting to explain what makes something a living thing. His explanation was that fiery atoms make a soul in exactly the same way atoms and void account for any other thing. He elaborates on fire because of the apparent connection between life and heat, and because fire moves.[76]
Plato's world of eternal and unchanging
Stoics adopted a divine teleology ... The choice seems simple: either show how a structured, regular world could arise out of undirected processes, or inject intelligence into the system.[77]— R.J. Hankinson, Cause and Explanation in Ancient Greek Thought
The mechanistic materialism that originated in ancient Greece was revived and revised by the French philosopher René Descartes (1596–1650), who held that animals and humans were assemblages of parts that together functioned as a machine. This idea was developed further by Julien Offray de La Mettrie (1709–1750) in his book L'Homme Machine.[78]
In the 19th century the advances in cell theory in biological science encouraged this view. The evolutionary theory of Charles Darwin (1859) is a mechanistic explanation for the origin of species by means of natural selection.[79]
At the beginning of the 20th century Stéphane Leduc (1853–1939) promoted the idea that biological processes could be understood in terms of physics and chemistry, and that their growth resembled that of inorganic crystals immersed in solutions of sodium silicate. His ideas, set out in his book La biologie synthétique[80] was widely dismissed during his lifetime, but has incurred a resurgence of interest in the work of Russell, Barge and colleagues.[81]
Hylomorphism

Hylomorphism is a theory first expressed by the Greek philosopher
This account is consistent with
Spontaneous generation
Spontaneous generation was the belief that living organisms can form without descent from similar organisms. Typically, the idea was that certain forms such as fleas could arise from inanimate matter such as dust or the supposed seasonal generation of mice and insects from mud or garbage.[85]
The theory of spontaneous generation was proposed by Aristotle,[86] who compiled and expanded the work of prior natural philosophers and the various ancient explanations of the appearance of organisms; it was considered the best explanation for two millennia. It was decisively dispelled by the experiments of Louis Pasteur in 1859, who expanded upon the investigations of predecessors such as Francesco Redi.[87][88] Disproof of the traditional ideas of spontaneous generation is no longer controversial among biologists.[89][90][91]
Vitalism
Vitalism is the belief that the life-principle is non-material. This originated with
During the 1850s
Origin
The age of Earth is about 4.54 billion years.[98][99][100] Evidence suggests that life on Earth has existed for at least 3.5 billion years,[101][102][103][104][105][106][107][108][109] with the oldest physical traces of life dating back 3.7 billion years;[110][111][112] however, some hypotheses, such as Late Heavy Bombardment, suggest that life on Earth may have started even earlier, as early as 4.1–4.4 billion years ago,[101][102][103][104][105] and the chemistry leading to life may have begun shortly after the Big Bang, 13.8 billion years ago, during an epoch when the universe was only 10–17 million years old.[113][114][115] Time estimates from molecular clocks, as summarized in TimeTree, generally place the origin of life around 4.0 billion years ago or earlier.[116]
More than 99% of all species of life forms, amounting to over five billion species,[117] that ever lived on Earth are estimated to be extinct.[118][119]

Although the number of Earth's catalogued species of lifeforms is between 1.2 million and 2 million,
All known life forms share fundamental molecular mechanisms, reflecting their
There is no current scientific consensus as to how life originated. However, most accepted scientific models build on the Miller–Urey experiment and the work of Sidney Fox, which show that conditions on the primitive Earth favoured chemical reactions that synthesize amino acids and other organic compounds from inorganic precursors,[129] and phospholipids spontaneously form lipid bilayers, the basic structure of a cell membrane.
Living organisms synthesize
However, because genes and proteins are both required to produce the other, the problem of considering which came first is like that of the chicken or the egg. Most scientists have adopted the hypothesis that because of this, it is unlikely that genes and proteins arose independently.[132]
Therefore, a possibility, first suggested by
One issue with the RNA world hypothesis is that synthesis of RNA from simple inorganic precursors is more difficult than for other organic molecules. One reason for this is that RNA precursors are very stable and react with each other very slowly under ambient conditions, and it has also been proposed that living organisms consisted of other molecules before RNA.[136] However, the successful synthesis of certain RNA molecules under the conditions that existed prior to life on Earth has been achieved by adding alternative precursors in a specified order with the precursor phosphate present throughout the reaction.[137] This study makes the RNA world hypothesis more plausible.[138]
Geological findings in 2013 showed that reactive
In 2009, experiments demonstrated
Prebiotic compounds may have originated extraterrestrially.
In March 2015, NASA scientists reported that, for the first time, complex
According to the
Environmental conditions
The diversity of life on Earth is a result of the dynamic interplay between
Biosphere
The biosphere is the global sum of all ecosystems. It can also be termed as the zone of life on
Life forms live in every part of the Earth's
The biosphere is postulated to have
In a general sense, biospheres are any closed, self-regulating systems containing ecosystems. This includes artificial biospheres such as Biosphere 2 and BIOS-3, and potentially ones on other planets or moons.[173]
Range of tolerance

The inert components of an ecosystem are the physical and chemical factors necessary for life—energy (sunlight or
Extremophiles
To survive, selected microorganisms can assume forms that enable them to withstand
Investigation of the tenacity and versatility of life on Earth,
Chemical elements
All life forms require certain core
DNA
Deoxyribonucleic acid is a
DNA stores biological information. The DNA backbone is resistant to cleavage, and both strands of the double-stranded structure store the same biological information. Biological information is replicated as the two strands are separated. A significant portion of DNA (more than 98% for humans) is non-coding, meaning that these sections do not serve as patterns for protein sequences.
The two strands of DNA run in opposite directions to each other and are, therefore,
Within cells, DNA is organised into long structures called
DNA was first isolated by
Classification
Antiquity
The first known attempt to classify organisms was conducted by the Greek philosopher Aristotle (384–322 BC), who classified all living organisms known at that time as either a plant or an animal, based mainly on their ability to move. He also distinguished animals with blood from animals without blood (or at least without red blood), which can be compared with the concepts of
Linnaean
The exploration of the Americas revealed large numbers of new plants and animals that needed descriptions and classification. In the latter part of the 16th century and the beginning of the 17th, careful study of animals commenced and was gradually extended until it formed a sufficient body of knowledge to serve as an anatomical basis for classification.
In the late 1740s, Carl Linnaeus introduced his system of binomial nomenclature for the classification of species. Linnaeus attempted to improve the composition and reduce the length of the previously used many-worded names by abolishing unnecessary rhetoric, introducing new descriptive terms and precisely defining their meaning.[189] The Linnaean classification has eight levels: domains, kingdoms, phyla, class, order, family, genus, and species.
The fungi were originally treated as plants. For a short period Linnaeus had classified them in the taxon
As new discoveries enabled detailed study of
As microbiology, molecular biology and virology developed, non-cellular reproducing agents were discovered, such as viruses and viroids. Whether these are considered alive has been a matter of debate; viruses lack characteristics of life such as cell membranes, metabolism and the ability to grow or respond to their environments. Viruses can still be classed into "species" based on their biology and genetics, but many aspects of such a classification remain controversial.[194]
In May 2016, scientists reported that 1 trillion species are estimated to be on Earth currently with only one-thousandth of one per cent described.[123]
The original Linnaean system has been modified over time as follows:
Linnaeus 1735[195] |
Haeckel 1866[196] |
Chatton 1925[197] |
Copeland 1938[198] |
Whittaker 1969[199] |
Woese et al. 1990[192] |
Cavalier-Smith 1998[200] |
Cavalier-Smith 2015[201] |
---|---|---|---|---|---|---|---|
2 kingdoms | 3 kingdoms | 2 empires | 4 kingdoms | 5 kingdoms | 3 domains | 2 empires, 6 kingdoms | 2 empires, 7 kingdoms |
(not treated) | Protista | Prokaryota
|
Monera | Monera | Bacteria | Bacteria | Bacteria |
Archaea | Archaea | ||||||
Eukaryota
|
Protoctista
|
Protista | Eucarya | Protozoa | Protozoa | ||
Chromista | Chromista | ||||||
Vegetabilia
|
Plantae | Plantae | Plantae | Plantae | Plantae | ||
Fungi | Fungi | Fungi | |||||
Animalia | Animalia | Animalia | Animalia | Animalia | Animalia |
Cells
Cells are the basic unit of structure in every living thing, and all cells arise from pre-existing cells by division. Cell theory was formulated by Henri Dutrochet, Theodor Schwann, Rudolf Virchow and others during the early nineteenth century, and subsequently became widely accepted.[202] The activity of an organism depends on the total activity of its cells, with energy flow occurring within and between them. Cells contain hereditary information that is carried forward as a genetic code during cell division.[203]
There are two primary types of cells.
The molecular mechanisms of cell biology are based on proteins. Most of these are synthesised by the ribosomes through an enzyme-catalyzed process called protein biosynthesis. A sequence of amino acids is assembled and joined based upon gene expression of the cell's nucleic acid.[206] In eukaryotic cells, these proteins may then be transported and processed through the Golgi apparatus in preparation for dispatch to their destination.[207]
Cells reproduce through a process of
Multicellular organisms may have first evolved through the formation of colonies of identical cells. These cells can form group organisms through cell adhesion. The individual members of a colony are capable of surviving on their own, whereas the members of a true multi-cellular organism have developed specialisations, making them dependent on the remainder of the organism for survival. Such organisms are formed clonally or from a single germ cell that is capable of forming the various specialised cells that form the adult organism. This specialisation allows multicellular organisms to exploit resources more efficiently than single cells.[209] In January 2016, scientists reported that, about 800 million years ago, a minor genetic change in a single molecule, called GK-PID, may have allowed organisms to go from a single cell organism to one of many cells.[210]
Cells have evolved methods to perceive and respond to their microenvironment, thereby enhancing their adaptability.
Extraterrestrial
Though life is confirmed only on Earth, many think that
Beyond the Solar System, the region around anotherA "Confidence of Life Detection" scale (CoLD) for reporting evidence of life beyond Earth has been proposed.[220][221]
Artificial
Artificial life is the simulation of any aspect of life, as through computers, robotics, or biochemistry.[222] The study of artificial life imitates traditional biology by recreating some aspects of biological phenomena. Scientists study the logic of living systems by creating artificial environments—seeking to understand the complex information processing that defines such systems. While life is, by definition, alive, artificial life is generally referred to as data confined to a digital environment and existence.
Synthetic biology is a new area of biotechnology that combines science and biological engineering. The common goal is the design and construction of new biological functions and systems not found in nature. Synthetic biology includes the broad redefinition and expansion of biotechnology, with the ultimate goals of being able to design and build engineered biological systems that process information, manipulate chemicals, fabricate materials and structures, produce energy, provide food, and maintain and enhance human health and the environment.[223]
Death
Death is the termination of all vital functions or life processes in an organism or cell.
One of the challenges in defining death is in distinguishing it from life. Death would seem to refer to either the moment life ends, or when the state that follows life begins.[225] However, determining when death has occurred is difficult, as cessation of life functions is often not simultaneous across organ systems.[226] Such determination, therefore, requires drawing conceptual lines between life and death. This is problematic, however, because there is little consensus over how to define life. The nature of death has for millennia been a central concern of the world's religious traditions and of philosophical inquiry. Many religions maintain faith in either a kind of afterlife or reincarnation for the soul, or resurrection of the body at a later date.[227]
Extinction
Extinction is the process by which a group of
Fossils
Fossils are the preserved remains or
See also
Notes
- ^ The "evolution" and classification of viruses and other similar forms is still uncertain. Therefore, this listing may be paraphyletic if cellular life evolved from non-cellular life, or polyphyletic if the most recent common ancestor were not included.
- ^ Infectious protein molecules prions are not considered living organisms, but can be described as "organism-comparable organic structures".
- subviral agents, including virus-dependent entities: satellites and defective interfering particles, both of which require another virusfor their replication.
- ^ Viruses are strongly believed not to descend from a common ancestor, with each realm corresponding to separate instances of virus coming into existence.[1]
- ^ To a first approximation this means that the enzymes needed for the system to function must be products of the system itself.
References
- PMID 32341570.
- ^ a b "Life". Merriam-Webster Dictionary. Archived from the original on 13 December 2021. Retrieved 25 July 2022.
- ^ a b "life | Definition, Origin, Evolution, Diversity, & Facts". Encyclopedia Britannica. Archived from the original on 12 July 2022. Retrieved 25 July 2022.
- ^ "2.2: The Basic Structural and Functional Unit of Life: The Cell". LibreTexts. 2 June 2019. Archived from the original on 29 March 2020. Retrieved 29 March 2020.
- ^ Bose, Debopriya (14 May 2019). "Six Main Cell Functions". Leaf Group Ltd./Leaf Group Media. Archived from the original on 29 March 2020. Retrieved 29 March 2020.
- ^ "Virus". Genome.gov. Archived from the original on 11 May 2022. Retrieved 25 July 2022.
- ^ "Are Viruses Alive?". Yellowstone Thermal Viruses. Archived from the original on 14 June 2022. Retrieved 25 July 2022.
- ^ "How Many Species Exist?". National Wildlife Federation. Archived from the original on 25 July 2022. Retrieved 25 July 2022.
- ^ PMID 19519215.
- ^ Emmeche, Claus (1997). "Defining Life, Explaining Emergence". Niels Bohr Institute. Archived from the original on 14 March 2012. Retrieved 25 May 2012.
- ^ PMID 15367939.
- Bibcode:1997JBIS...50...93M. Archived(PDF) from the original on 2 November 2012.
- ISBN 978-0-476-00330-9. Archived(PDF) from the original on 2 November 2012.
- ^ McKay, Chris (18 September 2014). "What is life? It's a Tricky, Often Confusing Question". Astrobiology Magazine.
- from the original on 3 January 2016.
- (PDF) from the original on 2 November 2012.
- S2CID 44573374.
- S2CID 36535062.
- PMID 21875147.
- PMID 11910092.
- ISBN 978-0-618-70173-5.
- ^ "Habitability and Biology: What are the Properties of Life?". Phoenix Mars Mission. The University of Arizona. Archived from the original on 16 April 2014. Retrieved 6 June 2013.
- S2CID 8616562. Archived from the original(PDF) on 27 January 2012. Retrieved 12 January 2012.
- ^ Zimmer, Carl (11 January 2012). "Can scientists define 'life' ... using just three words?". NBC News. Archived from the original on 14 April 2016. Retrieved 12 November 2016.
- ISBN 978-1-4684-8096-2. Archivedfrom the original on 30 July 2022. Retrieved 23 July 2022.
- from the original on 30 July 2022. Retrieved 23 July 2022.
- from the original on 30 July 2022. Retrieved 23 July 2022.
- ^ Luttermoser, Donald G. "ASTR-1020: Astronomy II Course Lecture Notes Section XII" (PDF). East Tennessee State University. Archived from the original (PDF) on 22 March 2012. Retrieved 28 August 2011.
- ^ Luttermoser, Donald G. (Spring 2008). "Physics 2028: Great Ideas in Science: The Exobiology Module" (PDF). East Tennessee State University. Archived from the original (PDF) on 22 March 2012. Retrieved 28 August 2011.
- S2CID 123220355. Archived from the original(PDF) on 2 June 2016. Retrieved 3 May 2016.
Life as we know it has been described as a (thermodynamically) open system (Prigogine et al. 1972), which makes use of gradients in its surroundings to create imperfect copies of itself.
- PMID 21162682.
- ISBN 978-0-511-56497-0. Archivedfrom the original on 27 May 2013. Retrieved 27 May 2012.
- ^ Overbye, Dennis (28 October 2015). "Cassini Seeks Insights to Life in Plumes of Enceladus, Saturn's Icy Moon". The New York Times. Archived from the original on 28 October 2015. Retrieved 28 October 2015.
- PMID 21162682.
- ^ S2CID 80625250.
- ISBN 978-0-521-83113-0. Archivedfrom the original on 3 September 2016.
- from the original on 11 May 2017.
- PMID 26965225.
- ^ Rybicki, EP (1990). "The classification of organisms at the edge of life, or problems with virus systematics". S Afr J Sci. 86: 182–86.
- PMID 17914905.
- PMID 20198436.
- PMID 16984643.
- ^ Rybicki, Ed (November 1997). "Origins of Viruses". Archived from the original on 9 May 2009. Retrieved 12 April 2009.
- ^ "Giant Viruses Shake Up Tree of Life". Astrobiology Magazine. 15 September 2012. Archived from the original on 17 September 2012. Retrieved 13 November 2016.
{{cite news}}
: CS1 maint: unfit URL (link) - ISBN 978-3-540-20490-9.
- ISBN 978-0-521-42708-1.
- ISBN 978-0-520-22021-8.
- ISBN 978-0-19-286218-1.
- ISBN 978-981-238-399-0.
- ^ Nosonovsky, Michael (July 2018). "Cultural implications of biomimetics: changing the perception of living and non-living". Applied Bionics and Biomechanics. 2 (4): 230–6.
- PMID 32323410.
- ^ Clealand, Carol E.; Chyba, Christopher F. (8 October 2007). "Does 'Life' Have a Definition?". In Woodruff, T. Sullivan; Baross, John (eds.). Planets and Life: The Emerging Science of Astrobiology. Cambridge University Press.
In the absence of such a theory, we are in a position analogous to that of a 16th-century investigator trying to define 'water' in the absence of molecular theory. [...] Without access to living things having a different historical origin, it is difficult and perhaps ultimately impossible to formulate an adequately general theory of the nature of living systems
- ^ Brown, Molly Young (2002). "Patterns, Flows, and Interrelationship". Archived from the original on 8 January 2009. Retrieved 27 June 2009.
- ^ ISBN 978-0-19-286030-9.
- S2CID 33821197.
- ^ Lovelock, James. "Geophysiology". Papers by James Lovelock. Archived from the original on 6 May 2007. Retrieved 1 October 2009.
- .
- ISBN 978-0-231-07565-7.
- ISBN 978-0070420151.
- ^ Fiscus, Daniel A. (April 2002). "The Ecosystemic Life Hypothesis". Bulletin of the Ecological Society of America. Archived from the original on 6 August 2009. Retrieved 28 August 2009.
- ISBN 978-0-300-05483-5. Archivedfrom the original on 5 September 2016.
- ISBN 978-1-59947-154-9. Archivedfrom the original on 3 September 2016.
- S2CID 4673166.
- .
- .
- from the original on 17 November 2017.
- ^ S2CID 83956410.
- ISBN 978-0-691-05011-9.
- ISBN 978-90-5011-443-1.
- ^
Jagers Op Akkerhuis, Gerard A. J. M. (2010). "Towards a Hierarchical Definition of Life, the Organism, and Death". Foundations of Science. 15 (3): 245–262. S2CID 195282529.
- ^
Jagers Op Akkerhuis, Gerard (2011). "Explaining the Origin of Life is not Enough for a Definition of Life". Foundations of Science. 16 (4): 327–329. S2CID 195284978.
- from the original on 16 April 2021. Retrieved 16 April 2021.
- ISBN 978-3-642-28110-5.
- PMID 11312589.
- ^ Parry, Richard (4 March 2005). "Empedocles". Stanford Encyclopedia of Philosophy. Archived from the original on 13 May 2012. Retrieved 25 May 2012.
- ^ Parry, Richard (25 August 2010). "Democritus". Stanford Encyclopedia of Philosophy. Archived from the original on 30 August 2006. Retrieved 25 May 2012.
- ISBN 978-0-19-924656-4. Archivedfrom the original on 4 September 2016.
- ^ de la Mettrie, J.J.O. (1748). L'Homme Machine [Man a machine]. Leyden: Elie Luzac.
- ISBN 978-0-262-01728-2. Archivedfrom the original on 3 September 2016.
- ^ Leduc, S (1912). La Biologie Synthétique [Synthetic Biology]. Paris: Poinat.
- PMID 24697642.
- ^ Aristotle. On the Soul. Book II.
- ISBN 978-0-7656-0216-9. Archivedfrom the original on 31 March 2021. Retrieved 25 August 2020.
- ISBN 978-0-521-76278-6. Archivedfrom the original on 3 September 2016.
- ^ Stillingfleet, Edward (1697). Origines Sacrae. Cambridge University Press.
- ISBN 978-0-521-56475-5. Retrieved 7 January 2009.
- ^ Levine, Russell; Evers, Chris. "The Slow Death of Spontaneous Generation (1668–1859)". North Carolina State University. National Health Museum. Archived from the original on 9 October 2015. Retrieved 6 February 2016.
- ^ Tyndall, John (1905). Fragments of Science. Vol. 2. New York: P.F. Collier. Chapters IV, XII, and XIII.
- LCCN 67098482.
- ISBN 978-0-12-781910-5.
- ISBN 978-0-19-850294-4.
- ISBN 978-0-19-988839-9. Archivedfrom the original on 4 September 2016.
- ^ a b Wilkinson, Ian (1998). "History of Clinical Chemistry – Wöhler & the Birth of Clinical Chemistry" (PDF). The Journal of the International Federation of Clinical Chemistry and Laboratory Medicine. 13 (4). Archived from the original (PDF) on 5 January 2016. Retrieved 27 December 2015.
- from the original on 10 January 2012.
- ISBN 978-0-520-07827-7. Archivedfrom the original on 4 September 2016.
- ISBN 978-8437-033280.
- ^ "NCAHF Position Paper on Homeopathy". National Council Against Health Fraud. February 1994. Archived from the original on 25 December 2018. Retrieved 12 June 2012.
- ^ "Age of the Earth". U.S. Geological Survey. 1997. Archived from the original on 23 December 2005. Retrieved 10 January 2006.
- S2CID 130092094.
- .
- ^ a b Tenenbaum, David (14 October 2002). "When Did Life on Earth Begin? Ask a Rock". Astrobiology Magazine. Archived from the original on 20 May 2013. Retrieved 13 April 2014.
- ^ a b c d Borenstein, Seth (19 October 2015). "Hints of life on what was thought to be desolate early Earth". Associated Press. Archived from the original on 6 April 2019. Retrieved 9 October 2018.
- ^ (PDF) from the original on 6 November 2015. Retrieved 20 October 2015. Early edition, published online before print.
- ^ a b Courtland, Rachel (2 July 2008). "Did newborn Earth harbour life?". New Scientist. Archived from the original on 14 November 2016. Retrieved 14 November 2016.
- ^ a b Steenhuysen, Julie (20 May 2009). "Study turns back clock on origins of life on Earth". Reuters. Archived from the original on 14 November 2016. Retrieved 14 November 2016.
- .
- PMID 16754604.
- ISBN 978-0-07-112261-0. Retrieved 7 July 2013.
- ISBN 978-1-4051-9336-8. Archivedfrom the original on 4 September 2016.
- ^ doi:10.1038/ngeo2025.
- ^ a b Borenstein, Seth (13 November 2013). "Oldest fossil found: Meet your microbial mom". Associated Press. Archived from the original on 29 June 2015.
- ^ PMID 24205812.
- S2CID 2777386.
- S2CID 2777386.
- ^ Dreifus, Claudia (2 December 2014). "Much-Discussed Views That Go Way Back – Avi Loeb Ponders the Early Universe, Nature and Life". The New York Times. Archived from the original on 3 December 2014. Retrieved 3 December 2014.
- ^ S. B. Hedges. Life. Pp. 89–98 in The Timetree of Life, S. B. Hedges and S. Kumar, Eds. (Oxford University Press, 2009).
- ^ ISBN 978-0-412-63380-5. Archivedfrom the original on 5 September 2015. Retrieved 26 May 2015.
- ^ ISBN 978-0-300-08469-6. Archivedfrom the original on 17 July 2017. Retrieved 30 May 2017.
- ^ a b Novacek, Michael J. (8 November 2014). "Prehistory's Brilliant Future". The New York Times. Archived from the original on 29 December 2014. Retrieved 25 December 2014.
- .
- ^ ISBN 978-1-133-70787-5. Archivedfrom the original on 18 March 2015. Retrieved 27 December 2014.
We do not know how many species there are on the earth. Estimates range from 8 million to 100 million. The best guess is that there are 10–14 million species. So far, biologists have identified almost 2 million species.
- ^ PMID 21886479.
In spite of 250 years of taxonomic classification and over 1.2 million species already catalogued in a central database, our results suggest that some 86% of existing species on Earth and 91% of species in the ocean still await description.
- ^ a b Staff (2 May 2016). "Researchers find that Earth may be home to 1 trillion species". National Science Foundation. Archived from the original on 4 May 2016. Retrieved 6 May 2016.
- LiveScience. Archivedfrom the original on 7 June 2017. Retrieved 7 June 2017.
- ^ from the original on 18 July 2015. Retrieved 18 July 2015.
- ^ a b "The Biosphere: Diversity of Life". Aspen Global Change Institute. Basalt, CO. Archived from the original on 10 November 2014. Retrieved 19 July 2015.
- ^ Wade, Nicholas (25 July 2016). "Meet Luca, the Ancestor of All Living Things". The New York Times. Archived from the original on 28 July 2016. Retrieved 25 July 2016.
- PMID 16849185.
- ^ "Habitability and Biology: What are the Properties of Life?". Phoenix Mars Mission. The University of Arizona. Archived from the original on 17 April 2014. Retrieved 6 June 2013.
- ISBN 978-0-9641304-0-1. Archivedfrom the original on 5 September 2016.
- ISBN 978-0-19-854751-8. Archivedfrom the original on 31 March 2021. Retrieved 25 August 2020.
- ^ a b Barazesh, Solmaz (13 May 2009). "How RNA Got Started: Scientists Look for the Origins of Life". U.S. News & World Report. Archived from the original on 23 August 2016. Retrieved 14 November 2016.
- ^ Watson, James D. (1993). Gesteland, R. F.; Atkins, J.F. (eds.). Prologue: early speculations and facts about RNA templates. The RNA World. Cold Spring Harbor, New York: Cold Spring Harbor Laboratory Press. pp. xv–xxiii.
- S2CID 8026658.
- PMID 2424025.
- PMID 21441585.
- S2CID 4412117.
- S2CID 205046409.
- ^ PMID 23733935.
- PMID 19131595.
- PMID 19667013.
- PMID 21836052.
- ^ Steigerwald, John (8 August 2011). "NASA Researchers: DNA Building Blocks Can Be Made in Space". NASA. Archived from the original on 23 June 2015. Retrieved 10 August 2011.
- ^ "DNA Building Blocks Can Be Made in Space, NASA Evidence Suggests". ScienceDaily. 9 August 2011. Archived from the original on 5 September 2011. Retrieved 9 August 2011.
- S2CID 96659714.
- ^ Marlaire, Ruth (3 March 2015). "NASA Ames Reproduces the Building Blocks of Life in Laboratory". NASA. Archived from the original on 5 March 2015. Retrieved 5 March 2015.
- ^ Rampelotto, P.H. (2010). "Panspermia: A Promising Field Of Research" (PDF). Archived (PDF) from the original on 27 March 2016. Retrieved 3 December 2014.
- ^ Reuell, Peter (8 July 2019). "Harvard study suggests asteroids might play key role in spreading life". Harvard Gazette. Archived from the original on 25 April 2020. Retrieved 16 September 2019.
- ^ a b c d e Rothschild, Lynn (September 2003). "Understand the evolutionary mechanisms and environmental limits of life". NASA. Archived from the original on 29 March 2012. Retrieved 13 July 2009.
- S2CID 23615028.
- ISBN 978-0-7538-0785-9.
- ISBN 978-0-19-507623-3.
- ^ "Bioshere". The Columbia Encyclopedia, Sixth Edition. Columbia University Press. 2004. Archived from the original on 27 October 2011.
- Science Daily. Archivedfrom the original on 10 November 2014. Retrieved 10 November 2014.
- ^ Hadhazy, Adam (12 January 2015). "Life Might Thrive a Dozen Miles Beneath Earth's Surface". Astrobiology Magazine. Archived from the original on 12 March 2017. Retrieved 11 March 2017.
- BBC online. Archivedfrom the original on 25 November 2016. Retrieved 11 March 2017.
- ^ Dvorsky, George (13 September 2017). "Alarming Study Indicates Why Certain Bacteria Are More Resistant to Drugs in Space". Gizmodo. Archived from the original on 14 September 2017. Retrieved 14 September 2017.
- ^ Caspermeyer, Joe (23 September 2007). "Space flight shown to alter ability of bacteria to cause disease". Arizona State University. Archived from the original on 14 September 2017. Retrieved 14 September 2017.
- PMID 11542696.
- PMID 11542695.
- ^ LiveScience. Archivedfrom the original on 2 April 2013. Retrieved 17 March 2013.
- ^ doi:10.1038/ngeo1773.
- ^ LiveScience. Archivedfrom the original on 2 April 2013. Retrieved 17 March 2013.
- ^ Morelle, Rebecca (15 December 2014). "Microbes discovered by deepest marine drill analysed". BBC News. Archived from the original on 16 December 2014. Retrieved 15 December 2014.
- PMID 25143097.
- ^ Mack, Eric (20 August 2014). "Life Confirmed Under Antarctic Ice; Is Space Next?". Forbes. Archived from the original on 22 August 2014. Retrieved 21 August 2014.
- ISBN 978-0-13-250882-7. Archived from the originalon 2 November 2014. Retrieved 15 June 2016.
- ^ Zimmer, Carl (3 October 2013). "Earth's Oxygen: A Mystery Easy to Take for Granted". The New York Times. Archived from the original on 3 October 2013. Retrieved 3 October 2013.
- from the original on 8 September 2017. Retrieved 2 March 2017.
- ^ Zimmer, Carl (1 March 2017). "Scientists Say Canadian Bacteria Fossils May Be Earth's Oldest". The New York Times. Archived from the original on 2 March 2017. Retrieved 2 March 2017.
- ^ Ghosh, Pallab (1 March 2017). "Earliest evidence of life on Earth 'found". BBC News. Archived from the original on 2 March 2017. Retrieved 2 March 2017.
- ^ Dunham, Will (1 March 2017). "Canadian bacteria-like fossils called oldest evidence of life". Reuters. Archived from the original on 2 March 2017. Retrieved 1 March 2017.
- ^ "Meaning of biosphere". WebDictionary.co.uk. WebDictionary.co.uk. Archived from the original on 2 October 2011. Retrieved 12 November 2010.
- ^ "Essential requirements for life". CMEX-NASA. Archived from the original on 17 August 2009. Retrieved 14 July 2009.
- ^ ISBN 978-0-7637-1316-4.
- ^ a b Chang, Kenneth (12 September 2016). "Visions of Life on Mars in Earth's Depths". The New York Times. Archived from the original on 12 September 2016. Retrieved 12 September 2016.
- .
- from the original on 31 March 2021. Retrieved 8 March 2021.
- ^ Baldwin, Emily (26 April 2012). "Lichen survives harsh Mars environment". Skymania News. Archived from the original on 28 May 2012. Retrieved 27 April 2012.
- Bibcode:2012EGUGA..14.2113D. Archived from the original(PDF) on 4 May 2012. Retrieved 27 April 2012.
- Wall Street Journal. Dow Jones & Company, Inc. Archivedfrom the original on 17 August 2017.
Until now, however, they were all thought to share the same biochemistry, based on the Big Six, to build proteins, fats and DNA.
- ISBN 978-0-309-66906-1. Archivedfrom the original on 10 May 2012. Retrieved 3 June 2012.
- PMID 15556414. Archived from the original(PDF) on 16 October 2012. Retrieved 3 June 2012.
- ^ Purcell, Adam (5 February 2016). "DNA". Basic Biology. Archived from the original on 5 January 2017. Retrieved 15 November 2016.
- ISBN 978-0-8053-4553-7.
- S2CID 915930.
- S2CID 8845393.
- ^ "Aristotle". University of California Museum of Paleontology. Archived from the original on 20 November 2016. Retrieved 15 November 2016.
- PMID 15253348.
- S2CID 84634277.
- PMID 5762760.
- ^ PMID 2112744.
- S2CID 8060916.
- PMID 16713373.
- ^ Linnaeus, C. (1735). Systemae Naturae, sive regna tria naturae, systematics proposita per classes, ordines, genera & species.
- ^ Haeckel, E. (1866). Generelle Morphologie der Organismen. Reimer, Berlin.
- ^ Chatton, É. (1925). "Pansporella perplexa. Réflexions sur la biologie et la phylogénie des protozoaires". Annales des Sciences Naturelles - Zoologie et Biologie Animale. 10-VII: 1–84.
- S2CID 84634277.
- PMID 5762760.
- S2CID 6557779.
- PMID 25923521.
- ISBN 978-0-19-515619-5.
- PMID 11543344. Archived from the original(PDF) on 6 April 2013. Retrieved 2 June 2012.
- PMID 9618454.
- S2CID 4431143. Archived from the original(PDF) on 16 October 2012. Retrieved 2 June 2012.
- ^ "Scientific background". The Nobel Prize in Chemistry 2009. Royal Swedish Academy of Sciences. Archived from the original on 2 April 2012. Retrieved 10 June 2012.
- PMID 20605430.
- ISBN 978-0-8160-6736-7. Archivedfrom the original on 4 September 2016.
- ISBN 978-0-8153-1620-6. Retrieved 12 June 2012.
- ^ Zimmer, Carl (7 January 2016). "Genetic Flip Helped Organisms Go From One Cell to Many". The New York Times. Archived from the original on 7 January 2016. Retrieved 7 January 2016.
- ISBN 978-0-8153-3218-3. Archivedfrom the original on 4 September 2015. Retrieved 12 June 2012.
- ISSN 0273-1177.
There is growing scientific confidence that the discovery of extraterrestrial life in some form is nearly inevitable
- ^ Cantor, Matt (15 February 2009). "Alien Life 'Inevitable': Astronomer". Newser. Archived from the original on 23 May 2013. Retrieved 3 May 2013.
Scientists now believe there could be as many habitable planets in the cosmos as there are stars, and that makes life's existence elsewhere "inevitable" over billions of years, says one.
- from the original on 31 March 2021. Retrieved 13 December 2019.
- Wired. Archivedfrom the original on 27 January 2015. Retrieved 27 January 2015.
- ^ Strain, Daniel (14 December 2009). "Icy moons of Saturn and Jupiter may have conditions needed for life". The University of Santa Cruz. Archived from the original on 31 December 2012. Retrieved 4 July 2012.
- ISBN 978-3-540-33692-1. Archivedfrom the original on 3 September 2016.
- from the original on 31 May 2020. Retrieved 30 August 2018.
- ISBN 978-0-85745-211-5. Archivedfrom the original on 31 March 2021. Retrieved 25 August 2020.
- from the original on 1 November 2021. Retrieved 1 November 2021.
- ^ Fuge, Lauren (30 October 2021). "NASA proposes playbook for communicating the discovery of alien life – Sensationalising aliens is so 20th century, according to NASA scientists". Cosmos. Archived from the original on 31 October 2021. Retrieved 1 November 2021.
- ^ "Artificial life". Dictionary.com. Archived from the original on 16 November 2016. Retrieved 15 November 2016.
- ^ Chopra, Paras; Akhil Kamma. "Engineering life through Synthetic Biology". In Silico Biology. 6. Archived from the original on 5 August 2008. Retrieved 9 June 2008.
- ^ Definition of death. Archived from the original on 3 November 2009.
- ^ a b "Definition of death". Encyclopedia of Death and Dying. Advameg, Inc. Archived from the original on 3 February 2007. Retrieved 25 May 2012.
- National Geographic. Archivedfrom the original on 1 November 2017. Retrieved 23 October 2017.
- ^ "How the Major Religions View the Afterlife". Encyclopedia.com. Archived from the original on 4 February 2022. Retrieved 4 February 2022.
- ^ Extinction – definition. Archived from the original on 26 September 2009.
- ^ "What is an extinction?". Late Triassic. Bristol University. Archived from the original on 1 September 2012. Retrieved 27 June 2012.
- from the original on 29 February 2020. Retrieved 29 June 2019.
- ^ "Frequently Asked Questions". San Diego Natural History Museum. Archived from the original on 10 May 2012. Retrieved 25 May 2012.
- ^ Vastag, Brian (21 August 2011). "Oldest 'microfossils' raise hopes for life on Mars". The Washington Post. Archived from the original on 19 October 2011. Retrieved 21 August 2011.
- ^ Wade, Nicholas (21 August 2011). "Geological Team Lays Claim to Oldest Known Fossils". The New York Times. Archived from the original on 1 May 2013. Retrieved 21 August 2011.
Further reading
- Walker, Martin G. (2006). LIFE! Why We Exist ... And What We Must Do to Survive. Dog Ear Publishing. ISBN 978-1-59858-243-7. Archived from the originalon 24 July 2011.
External links

- Life (Systema Naturae 2000)
- Vitae (BioLib)
- Biota (Taxonomicon)
- Wikispecies – a free directory of life
- Resources for life in the Solar System and in galaxy, and the potential scope of life in the cosmological future
- "The Adjacent Possible: A Talk with Stuart Kauffman"
- Stanford Encyclopedia of Philosophy entry
- The Kingdoms of Life