Earliest known life forms

Putative fossilized microorganisms

Evidence of possibly the oldest forms of life on Earth has been found in hydrothermal vent precipitates.[1]

Life timeline

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Earliest fossils

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Atmospheric oxygen

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Greening of Earth

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Ediacaran biota

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Cambrian explosion

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(million years ago)

The earliest known life forms on Earth may be as old as 4.1 billion years (or Ga) according to biologically fractionated graphite inside a single zircon grain in the Jack Hills range of Australia.[2] The earliest evidence of life found in a stratigraphic unit, not just a single mineral grain, is the 3.7 Ga metasedimentary rocks containing graphite from the Isua Supracrustal Belt in Greenland.[3] The earliest direct known life on Earth are stromatolite fossils which have been found in 3.480-billion-year-old geyserite uncovered in the Dresser Formation of the Pilbara Craton of Western Australia.[4] Various microfossils of microorganisms have been found in 3.4 Ga rocks, including 3.465-billion-year-old Apex chert rocks from the same Australian craton region,[5] and in 3.42 Ga hydrothermal vent precipitates from Barberton, South Africa.[1] Much later in the geologic record, likely starting in 1.73 Ga, preserved molecular compounds of biologic origin are indicative of aerobic life.[6] Therefore, the earliest time for the origin of life on Earth is at least 3.5 billion years ago and possibly as early as 4.1 billion years ago — not long after the oceans formed 4.5 billion years ago and after the formation of the Earth 4.54 billion years ago.[7]

## Biospheres

[edit]

Further information: Abiogenesis and Biosphere

Earth is the only place in the universe known to harbor life, where it exists in myriad environments.[8][9] The origin of life on Earth was at least 3.5 billion years ago, possibly as early as 3.8-4.1 billion years ago.[2][3][4] Since its emergence, life has persisted in several geological environments. The Earth's biosphere extends down to at least 10 km (6.2 mi) below the seafloor,[10][11] up to 41–77 km (25–48 mi)[12][13] into the atmosphere,[14][15][16] and includes soil, hydrothermal vents, and rock.[17][18] Further, the biosphere has been found to extend at least 914.4 m (3,000 ft; 0.5682 mi) below the ice of Antarctica[19][20] and includes the deepest parts of the ocean.[21][22][23][24] In July 2020, marine biologists reported that aerobic microorganisms (mainly) in "quasi-suspended animation" were found in organically poor sediment 76.2 m (250 ft) below the seafloor in the South Pacific Gyre (SPG) ("the deadest spot in the ocean").[25] Microbes have been found in the Atacama Desert in Chile, one of the driest places on Earth,[26] and in deep-sea hydrothermal vent environments which can reach temperatures over 400°C.[27] Microbial communities can also survive in cold permafrost conditions down to -25°C.[28] Under certain test conditions, life forms have been observed to survive in the vacuum of outer space.[29][30] More recently, studies conducted on the International Space Station found that bacteria could survive in outer space.[31] In February 2023, findings of a "dark microbiome" of microbial dark matter of unfamiliar microorganisms in the Atacama Desert in Chile, a Mars-like region of planet Earth, were reported.[32]

## Geochemical evidence

[edit]

The age of Earth is about 4.54 billion years;[7][33][34] the earliest undisputed evidence of life on Earth dates from at least 3.5 billion years ago according to the stromatolite record.[35] Some computer models suggest life began as early as 4.5 billion years ago.[36][37] The oldest evidence of life is indirect in the form of isotopic fractionation processes. Microorganisms will preferentially use the lighter isotope of an atom to build biomass, as it takes less energy to break the bonds for metabolic processes.[38] Biologic material will often have a composition that is enriched in lighter isotopes compared to the surrounding rock it's found in. Carbon isotopes, expressed scientifically in parts per thousand difference from a standard as δ13C, are frequently used to detect carbon fixation by organisms and assess if purported early life evidence has biological origins. Typically, life will preferentially metabolize the isotopically light 12C isotope instead of the heavier 13C isotope. Biologic material can record this fractionation of carbon.

Zircons in metaconglomerates from the Jack Hills in Australia show carbon isotopic evidence for early life.

The oldest disputed geochemical evidence of life is isotopically light graphite inside a single zircon grain from the Jack Hills in Western Australia.[2][39] The graphite showed a δ13C signature consistent with biogenic carbon on Earth. Other early evidence of life is found in rocks both from the Akilia Sequence[40] and the Isua Supracrustal Belt (ISB) in Greenland.[3][41] These 3.7 Ga metasedimentary rocks also contain graphite or graphite inclusions with carbon isotope signatures that suggest biological fractionation.

The primary issue with isotopic evidence of life is that abiotic processes can fractionate isotopes and produce similar signatures to biotic processes.[42] Reassessment of the Akilia graphite show that metamorphism, Fischer-Tropsch mechanisms in hydrothermal environments, and volcanic processes may be responsible for enrichment lighter carbon isotopes.[43][44][45] The ISB rocks that contain the graphite may have experienced a change in composition from hot fluids, i.e. metasomatism, thus the graphite may have been formed by abiotic chemical reactions.[42] However, the ISB's graphite is generally more accepted as biologic in origin after further spectral analysis.[3][41]

Metasedimentary rocks from the 3.5 Ga Dresser Formation, which experienced less metamorphism than the sequences in Greenland, contain better preserved geochemical evidence.[46] Carbon isotopes as well as sulfur isotopes found in barite, which are fractionated by microbial metabolisms during sulfate reduction,[47] are consistent with biological processes.[48][49] However, the Dresser formation was deposited in an active volcanic and hydrothermal environment,[46] and abiotic processes could still be responsible for these fractionations.[50] Many of these findings are supplemented by direct evidence, typically by the presence of microfossils, however.

## Fossil evidence

[edit]

Fossils are direct evidence of life. In the search for the earliest life, fossils are often supplemented by geochemical evidence. The fossil record does not extend as far back as the geochemical record due to metamorphic processes that erase fossils from geologic units.

### Stromatolites

[edit]

Main article: Stromatolite

Stromatolites are laminated sedimentary structures created by photosynthetic organisms as they establish a microbial mat on a sediment surface. An important distinction for biogenicity is their convex-up structures and wavy laminations, which are typical of microbial communities who build preferentially toward the sun.[51] A disputed report of stromatolites is from the 3.7 Ga Isua metasediments that show convex-up, conical, and domical morphologies.[52][53][54] Further mineralogical analysis disagrees with the initial findings of internal convex-up laminae, a critical criterion for stromatolite identification, suggesting that the structures may be deformation features (i.e. boudins) caused by extensional tectonics in the Isua Supracrustal Belt.[55][56]

Stromatolite fossil showing convex-up structures.

The earliest direct evidence of life are stromatolites found in 3.48 billion-year-old chert in the Dresser formation of the Pilbara Craton in Western Australia.[4] Several features in these fossils are difficult to explain with abiotic processes, for example, the thickening of laminae over flexure crests that is expected from more sunlight.[57] Sulfur isotopes from barite veins in the stromatolites also favor a biologic origin.[58] However, while most scientists accept their biogenicity, abiotic explanations for these fossils cannot be fully discarded due to their hydrothermal depositional environment and debated geochemical evidence.[50]

Most archean stromatolites older than 3.0 Ga are found in Australia or South Africa. Stratiform stromatolites from the Pilbara Craton have been identified in the 3.47 Ga Mount Ada Basalt.[59] Barberton, South Africa hosts stratiform stromatolites in the 3.46 Hooggenoeg, 3.42 Kromberg and 3.33 Ga Mendon Formations of the Onverwacht Group.[60][61] The 3.43 Ga Strelley Pool Formation in Western Australia hosts stromatolites that demonstrate vertical and horizontal changes that may demonstrate microbial communities responding to transient environmental conditions.[62] Thus, it is likely anoxygenic or oxygenic photosynthesis has been occurring since at least 3.43 Ga Strelley Pool Formation.[63]

### Microfossils

[edit]

Further information: Microfossil

Claims of the earliest life using fossilized microorganisms (microfossils) are from hydrothermal vent precipitates from an ancient sea-bed in the Nuvvuagittuq Belt of Quebec, Canada. These may be as old as 4.28 billion years, which would make it the oldest evidence of life on Earth, suggesting "an almost instantaneous emergence of life" after ocean formation 4.41 billion years ago.[64][65] These findings may be better explained by abiotic processes: for example, silica-rich waters,[66] "chemical gardens,"[67] circulating hydrothermal fluids,[68] and volcanic ejecta[69] can produce morphologies similar to those presented in Nuvvuagittuq.

Archaea (prokaryotic microbes) were first found in extreme environments, such as hydrothermal vents.

The 3.48 Ga Dresser formation hosts microfossils of prokaryotic filaments in silica veins, the earliest fossil evidence of life on Earth,[70] but their origins may be volcanic.[71] 3.465-billion-year-old Australian Apex chert rocks may once have contained microorganisms,[72][5] although the validity of these findings has been contested.[73][74] "Putative filamentous microfossils," possibly of methanogens and/or methanotrophs that lived about 3.42-billion-year-old in "a paleo-subseafloor hydrothermal vein system of the Barberton greenstone belt, have been identified in South Africa."[1] A diverse set of microfossil morphologies have been found in the 3.43 Ga Strelley Pool Formation including spheroid, lenticular, and film-like microstructures.[75] Their biogenicity are strengthened by their observed chemical preservation.[76] The early lithification of these structures allowed important chemical tracers, such as the carbon-to-nitrogen ratio, to be retained at levels higher than is typical in older, metamorphosed rock units.

### Molecular biomarkers

[edit]

Further information: Biosignature

Biomarkers are compounds of biologic origin found in the geologic record that can be linked to past life.[77] Although they aren't preserved until the late Archean, they are important indicators of early photosynthetic life. Lipids are particularly useful biomarkers because they can survive for long periods of geologic time and reconstruct past environments.[78]

Lipids are commonly used in geologic studies to find evidence of oxygenic photosynthesis.

Fossilized lipids were reported from 2.7 Ga laminated shales from the Pilbara Craton[79] and the 2.67 Ga Kaapvaal craton in South Africa.[80] However, the age of these biomarkers and whether their deposition was synchronous with their host rocks were debated,[81] and further work showed that the lipids were contaminants.[82] The oldest "clearly indigenous"[83] biomarkers are from the 1.64 Ga Barney Creek Formation in the McArthur Basin in Northern Australia,[84][85] but hydrocarbons from the 1.73 Ga Wollogorang Formation in the same basin have also been detected.[83]

Other indigenous biomarkers can be dated to the Mesoproterozoic era (1.6-1.0 Ga). The 1.4 Ga Hongshuizhuang Formation in the North China Craton contains hydrocarbons in shales that were likely sourced from prokaryotes.[86] Biomarkers were found in siltstones from the 1.38 Ga Roper Group of the McArthur Basin.[87] Hydrocarbons possibly derived from bacteria and algae were reported in 1.37 Ga Xiamaling Formation of the NCC.[88] The 1.1 Ga Atar/El Mreïti Group in the Taoudeni Basin, Mauritania show indigenous biomarkers in black shales.[89]

## Genomic evidence

[edit]

Main article: Last universal common ancestor

By comparing the genomes of modern organisms (in the domains Bacteria and Archaea), it is evident that there was a last universal common ancestor (LUCA). Another term for the LUCA is the cenancestor and can be viewed as a population of organisms rather than a single entity.[90] LUCA is not thought to be the first life on Earth, but rather the only type of organism of its time to still have living descendants. In 2016, M. C. Weiss and colleagues proposed a minimal set of genes that each occurred in at least two groups of Bacteria and two groups of Archaea. They argued that such a distribution of genes would be unlikely to arise by horizontal gene transfer, and so any such genes must have derived from the LUCA.[91] A molecular clock model suggests that the LUCA may have lived 4.477—4.519 billion years ago, within the Hadean eon.[36][37]

## RNA replicators

[edit]

Further information: Abiogenesis and RNA world

Model Hadean-like geothermal microenvironments were demonstrated to have the potential to support the synthesis and replication of RNA and thus possibly the evolution of primitive life.[92] Porous rock systems, comprising heated air-water interfaces, were shown to facilitate ribozyme catalyzed RNA replication of sense and antisense strands and then subsequent strand-dissociation.[92] This enabled combined synthesis, release and folding of active ribozymes.[92]

## Theories for the origin of life on Earth

[edit]

### Extraterrestrial origin for early life

[edit]

The theory of panspermia speculates that life on Earth may have come from biological matter carried by space dust[93] or meteorites.[94]

While current geochemical evidence dates the origin of life to possibly as early as 4.1 Ga, and fossil evidence shows life at 3.5 Ga, some researchers speculate that life may have started nearly 4.5 billion years ago.[36][37] According to biologist Stephen Blair Hedges, "If life arose relatively quickly on Earth ... then it could be common in the universe."[95][96][97] The possibility that terrestrial life forms may have been seeded from outer space has been considered.[98][99] In January 2018, a study found that 4.5 billion-year-old meteorites found on Earth contained liquid water along with prebiotic complex organic substances that may be ingredients for life.[94]

### Hydrothermal vents

[edit]

Hydrothermal vents have long been hypothesized to be the grounds from which life originated. The properties of ancient hydrothermal vents, such as the geochemistry, pressure, and temperatures, have the potential to create organic molecules from inorganic molecules.[100] In experiments performed by NASA, it was shown that the organic compounds formate and methane could be created from inorganics in the conditions of ancient hydrothermal vents.[101] The production of organic molecules could have led to the formation of more complex organic molecules, such as amino acids that can eventually form RNA or DNA.

### Darwin’s Hypothesis

[edit]

Charles Darwin is well-known for his theory of evolution via natural selection. His theory for the origin of life was a “warm little pond” that harbored necessary elements for the creation of life such as “ammonia and phosphoric salts, lights, heat, electricity … so that a protein compound was chemically formed ready to undergo still more complex changes.”[102] However, he mentioned that such an environment today would likely have been destroyed faster than it would take to form life. With this, Darwin’s ideas are generally regarded as the spontaneous generation hypothesis.[citation needed]

### Oparin-Haldane Hypothesis

[edit]

In 1924, Aleksander Oparin suggested that the early atmosphere on Earth was full of reducing components such as ammonia, methane, water vapor, and hydrogen gas.[103] This was proposed after atmospheric methane was discovered on other planets. Later in 1929, J.B.S. Haldane published an article that proposed the same conditions for early life on Earth as Oparin suggested. Their hypothesis was later supported by the Miller-Urey experiment.

### Miller Urey Experiment

[edit]

Schematic of the Miller-Urey experiment.

At the University of Chicago in 1953, a graduate student named Stanley Miller carried out an experiment under his professor, Harold Urey.[104] The method would allow for reducing gases to simulate the atmosphere early on Earth and a “spark” to simulate lightning. There was a reflux apparatus that would heat water and mix into the atmosphere where it would then cool and run into the “primordial ocean.” The gases that were used to mimic the reducing atmosphere were methane, ammonia, water vapor, and hydrogen gas. Within a day of allowing the apparatus to run, the experiment yielded a “brown sludge” which was later tested and found to include the following amino acids: glycine, alanine, aspartic acid, and aminobutyric acid. In the following years, many scientists attempted to replicate the results of the experiment and is now known as a fundamental approach to the study of “abiogenesis”. The Miller-Urey experiment was able to simulate the early conditions of Earth’s atmosphere and produced essential amino acids that likely contributed to the production of life.[105]

### Clay Hypothesis

[edit]

Cairns-Smith first introduced this hypothesis in 1966, where they proposed that any crystallization process is likely to involve a basic biological evolution.[106] Hartman then added on to this hypothesis by proposing in 1975 that metabolism could have developed from a simple environment such as clays. Clays have the ability to synthesize monomers such as amino acids, nucleotides, and other building blocks and polymerize them to create macromolecules. This makes it possible for nucleic acids like RNA or DNA to be created from clay, and cells could further evolve from there.

## Gallery

[edit]

Earliest known life forms

Life timeline

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Water

Single-celled life

Photosynthesis

Multicellular life

Plants

Arthropods Molluscs

Flowers

Dinosaurs

Mammals

Birds

Primates

Hadean

Archean

Proterozoic

Phanerozoic

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Earth formed

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Earliest water

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LUCA

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Earliest fossils

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Atmospheric oxygen

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Sexual reproduction

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Earliest fungi

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Greening of Earth

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Ediacaran biota

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Cambrian explosion

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Earliest tetrapods

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Earliest hominoid

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(million years ago)

* Stromatolites may have been made by microbes moving upward to avoid being smothered by sediment.[54][56]

* Stromatolites left behind by cyanobacteria are one of the oldest fossils of life on Earth.

* The cyanobacterial-algal mat, salty lake on the White Sea seaside

* Microbialites in the Lake Salda rocks of Turkey

* Wrinkled Kinneyia-type sedimentary structures formed beneath cohesive microbial mats in peritidal zones.[107]

* Kinneyia-like structure in the Grimsby Formation (Silurian) exposed in Niagara Gorge, NY

## See also

[edit]

* Abiogenesis
* Creation myth
* Extremophile
* First universal common ancestor
* Hypothetical types of biochemistry
* List of longest-living organisms
* Oldest dated rocks
* Outline of biology
* Outline of life forms
* Timeline of the evolutionary history of life
* Viroid
* Virus

## References

[edit]

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102. ^ Schopf, J. William (2024-10-21). "Pioneers of Origin of Life Studies-Darwin, Oparin, Haldane, Miller, Oró-And the Oldest Known Records of Life". Life (Basel, Switzerland). 14 (10): 1345. Bibcode:2024Life...14.1345S. doi:10.3390/life14101345. ISSN 2075-1729. PMC 11509469. PMID 39459645.
103. ^ Schopf, J. William (2024-10-21). "Pioneers of Origin of Life Studies-Darwin, Oparin, Haldane, Miller, Oró-And the Oldest Known Records of Life". Life (Basel, Switzerland). 14 (10): 1345. Bibcode:2024Life...14.1345S. doi:10.3390/life14101345. ISSN 2075-1729. PMC 11509469. PMID 39459645.
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106. ^ Kloprogge, Jacob Teunis Theo; Hartman, Hyman (2022-02-09). "Clays and the Origin of Life: The Experiments". Life (Basel, Switzerland). 12 (2): 259. Bibcode:2022Life...12..259K. doi:10.3390/life12020259. ISSN 2075-1729. PMC 8880559. PMID 35207546.
107. ^ Porada H.; Ghergut J.; Bouougri El H. (2008). "Kinneyia-Type Wrinkle Structures – Critical Review And Model Of Formation". PALAIOS. 23 (2): 65–77\. Bibcode:2008Palai..23...65P. doi:10.2110/palo.2006.p06-095r. S2CID 128464944.

## External links

[edit]

* Vitae (BioLib)
* Biota (Taxonomicon)
* Life (Systema Naturae 2000)
* Wikispecies — a free directory of life
* Life in the Universe — Stephen Hawking (1996)
* Video (24:32): "Migration of Life in the Universe" on YouTube — Gary Ruvkun, 2019.

* v
* t
* e

Biology

* Introduction (Genetics, Evolution)
* Outline
* History
* Timeline
* Index

Biology|

| Overview|

* Science
* Life
* Properties (Adaptation,  Energy processing, Growth, Order, Regulation, Reproduction (Self-replication), Response to environment)
* Hierarchy of life (Atom > Molecule > Organelle > Cell > Tissue > Organ > Organ system > Organism > Population > Community > Ecosystem > Biosphere)
* Reductionistic
* Emergent property
* Mechanistic
* Scientific method
* Taxonomic rank
* Theory
* Law
* Peer review
* Biology journals
* Common name

|

Chemical basis|

* Atoms
* Amino acids
* Carbohydrates
* Chemical bond
* Chemical element
* Lipids
* Matter
* Quantum
* Molecules
* Monomer
* Nucleic acids
* Organic compounds
* pH
* Polymer
* Proteins
* Water

Cells|

* ATP
* Cell cycle
* Cell theory
* Cell signaling
* Cellular respiration
* Energy transformation
* Enzyme
* Eukaryote
* Fermentation
* Metabolism
* Meiosis
* Mitosis
* Photosynthesis
* Prokaryote

Genetics|

* DNA
* Epigenetics
* Evolutionary developmental biology
* Gene expression
* Gene regulation
* Genomes
* Mendelian inheritance
* Post-transcriptional modification

Evolution|

* Adaptation
* Earliest known life forms
* Function
* Genetic drift
* Gene flow
* History of life
* Macroevolution
* Microevolution
* Mutation
* Natural selection
* Phylogenetics
* Speciation
* Taxonomy

Diversity|

* Archaea
* Bacteria
* Eukaryote
* Alga
* Animal
* Fungus
* Plant
* Protist
* Virus

Plant form
and function|

* Epidermis (botany)
* Flower
* Ground tissue
* Leaf
* Phloem
* Plant stem
* Root
* Shoot
* Vascular plant
* Vascular tissue
* Xylem

Animal form
and function|

* Breathing
* Circulatory system
* Endocrine system
* Digestive system
* Homeostasis
* Immune system
* Internal environment
* Muscular system
* Nervous system
* Reproductive system
* Respiratory system

Ecology|

* Biogeochemical cycle
* Biological interaction
* Biomass
* Biomes
* Biosphere
* Climate
* Climate change
* Community
* Conservation
* Ecosystem
* Habitat
* niche
* Microbiome
* Population dynamics
* Resources

Research
methods|

| Laboratory
techniques|

* Genetic engineering
* Transformation
* Gel electrophoresis
* Chromatography
* Centrifugation
* Cell culture
* DNA sequencing
* DNA microarray
* Green fluorescent protein
* vector
* Enzyme assay
* Protein purification
* Western blot
* Northern blot
* Southern blot
* Restriction enzyme
* Polymerase chain reaction
* Two-hybrid screening
* in vivo
* in vitro
* in silico

|

Field techniques|

* Belt transect
* mark and recapture
* species discovery curve

Branches|

* Abiogenesis
* Aerobiology
* Agronomy
* Agrostology
* Anatomy
* Anthropogeny
* Anthropology
* Astrobiology
* Bacteriology
* Biochemistry
* Biogeography
* Biogeology
* Bioinformatics
* Biological engineering
* Biomathematics
* Biomechanics
* Biophysics
* Biosemiotics
* Biostatistics
* Biotechnology
* Botany
* Cell biology
* Cellular microbiology
* Chemical biology
* Chronobiology
* Cognitive biology
* Computational biology
* Conservation biology
* Cryobiology
* Cytogenetics
* Dendrology
* Developmental biology
* Ecological genetics
* Ecology
* Embryology
* Epidemiology
* Epigenetics
* Evolutionary biology
* Freshwater biology
* Generative biology
* Genetics
* Genomics
* Geobiology
* Gerontology
* Herpetology
* Histology
* Human biology
* Ichthyology
* Immunology
* Lipidology
* Mammalogy
* Marine biology
* Microbiology
* Molecular biology
* Mycology
* Neontology
* Neuroscience
* Nutrition
* Ornithology
* Osteology
* Paleontology
* Parasitology
* Pathology
* Pharmacology
* Photobiology
* Phycology
* Phylogenetics
* Physiology
* Pomology
* Primatology
* Proteomics
* Protistology
* Quantum biology
* Relational biology
* Reproductive biology
* Sociobiology
* Structural biology
* Synthetic biology
* Systematics
* Systems biology
* Taxonomy
* Teratology
* Toxicology
* Virology
* Virophysics
* Welfare biology
* Xenobiology
* Zoology

Glossaries|

* Biology
* Botanical terms
* Ecological terms
* Plant morphology terms

* Biology portal
* Category
* Commons
* WikiProject

* v
* t
* e

Origin of life

History of research|

* Panspermia (5th century BC)
* Spontaneous generation (4th century BC)
* Primordial soup (19th century)

Prebiotic synthesis|

* Pseudo-panspermia
* Miller–Urey experiment
* Formamide-based prebiotic chemistry
* Alternative abiogenesis scenarios

Protocells|

* GADV-protein world
* Clay hypothesis
* Iron–sulfur world
* Primordial sandwich
* PAH world
* Peptide-RNA world
* Quasispecies model
* RNA world

Earliest organisms|

* Earliest known life forms
* Last universal common ancestor (LUCA)

Research|

* Astrobiology
* Paleobiology

* v
* t
* e

Astrobiology

Disciplines|

* Astrochemistry
* Astrophysics
* Atmospheric sciences
* Biochemistry
* Evolutionary biology
* Exoplanetology
* Geomicrobiology
* Microbiology
* Paleontology
* Planetary oceanography
* Planetary science

Main topics|

* Abiogenesis
* Allan Hills 84001
* Biomolecule
* Biosignature
* Drake equation
* Earliest known life forms
* Earth analog
* Extraterrestrial life
* Extraterrestrial sample curation
* Extremophiles
* Hypothetical types of biochemistry
* List of microorganisms tested in outer space
* Ocean planet
* Panspermia
* Planetary protection
* Search for extraterrestrial intelligence (SETI)
* Yamato meteorite

Planetary
habitability|

* Circumstellar habitable zone
* Earth analog
* Extraterrestrial liquid water
* Galactic habitable zone
* Habitability of binary star systems
* Habitability of natural satellites
* Habitability of neutron star systems
* Habitability of red dwarf systems
* Habitability of K-type main-sequence star systems
* Habitability of yellow dwarf systems
* Habitability of F-type main-sequence star systems
* Habitable zone for complex life
* List of potentially habitable exoplanets
* Tholin
* Superhabitable planet

Space
missions|

| Earth orbit|

* BIO
* BIOCORE
* Biolab
* Bion
* BIOPAN
* Biosatellite program
* E-MIST
* ERA
* Eu:CROPIS
* EXOSTACK
* EXPOSE
* Lunar Micro Ecosystem
* O/OREOS
* OREOcube
* Tanpopo
* VEGGIE

|

Mars|

* Beagle 2
* Fobos-Grunt
* Mars Science Laboratory
* Curiosity rover
* Mars 2020
* Perseverance rover
* Phoenix
* Tianwen-1
* Zhurong rover
* Trace Gas Orbiter
* Viking

Comets and
asteroids|

* Hayabusa2
* OSIRIS-REx
* Rosetta

Heliocentric|

* BioSentinel

Planned|

* Dragonfly
* Europa Clipper
* ExoMars
* Rosalind Franklin rover

Proposed|

* Breakthrough Enceladus
* BRUIE
* CAESAR
* Enceladus Explorer
* Enceladus Life Finder‎
* Enceladus Life Signatures and Habitability
* Enceladus Orbilander
* Europa Lander
* ExoLance
* Explorer of Enceladus and Titan
* Icebreaker Life
* Journey to Enceladus and Titan
* Laplace-P
* Life Investigation For Enceladus
* Mars sample return mission
* Oceanus
* THEO
* Trident

Cancelled and
undeveloped|

* Astrobiology Field Laboratory
* Beagle 3
* Biological Oxidant and Life Detection
* Kazachok
* Living Interplanetary Flight Experiment
* Mars Astrobiology Explorer-Cacher
* MELOS
* Northern Light
* Red Dragon
* Terrestrial Planet Finder

Institutions
and programs|

* Astrobiology Society of Britain
* Astrobiology Science and Technology for Exploring Planets
* Breakthrough Initiatives
* Breakthrough Listen
* Breakthrough Message
* Breakthrough Starshot
* Carl Sagan Institute
* Center for Life Detection Science
* European Astrobiology Network Association
* NASA Astrobiology Institute
* Nexus for Exoplanet System Science
* Ocean Worlds Exploration Program
* Spanish Astrobiology Center‎

* Category
* Commons

* v
* t
* e

Extraterrestrial life

Events and objects|

* Shergotty meteorite (1865)
* Nakhla meteorite (1911)
* Murchison meteorite (1969)
* Viking lander biological experiments (1976)
* Allan Hills 77005 (1977)
* Allan Hills 84001 (1984)
* Yamato 000593 (2000)
* CI1 fossils (2011)

Signals of interest|

| Misidentified|

* CP 1919 (misidentified pulsar)
* CTA-102 (misidentified quasar)

|

Stars|

* KIC 8462852 (unusual light fluctuations)
* EPIC 204278916 (unusual light fluctuations)
* VVV-WIT-07 (unusual light fluctuations)
* HD 164595 signal (unknown origin)

Other|

* SHGb02+14a (radio source)
* Wow! signal (inconclusive)
* Fast radio burst (unknown origin)
* BLC1 (radio signal)

Life in the Universe|

* Earliest known life forms
* Planetary habitability in the Solar System
* Life on Venus
* Life on Mars
* Life on Titan

Planetary
habitability|

* Catalog of Nearby Habitable Systems
* Circumstellar habitable zone
* Earth analog
* Extraterrestrial liquid water
* Galactic habitable zone
* Habitability of binary star systems
* Habitability of natural satellites
* Habitability of neutron star systems
* Habitability of red dwarf systems
* Habitability of K-type main-sequence star systems
* Habitability of yellow dwarf systems
* Habitability of F-type main-sequence star systems
* List of potentially habitable exoplanets
* Planetary habitability
* Superhabitable planet
* Tholin

Space missions|

* Beagle 2
* Biological Oxidant and Life Detection
* BioSentinel
* Curiosity rover
* Darwin
* Dragonfly
* Enceladus Explorer
* Enceladus Life Finder
* Europa Clipper
* ExoMars
* Rosalind Franklin rover
* ExoLance
* EXPOSE
* Foton-M3
* Icebreaker Life
* Journey to Enceladus and Titan
* Laplace-P
* Life Investigation For Enceladus
* Living Interplanetary Flight Experiment
* Mars Geyser Hopper
* Mars sample-return mission
* Mars 2020
* Northern Light
* Opportunity rover
* Perseverance rover
* SpaceX Red Dragon
* Spirit rover
* Tanpopo
* Titan Mare Explorer
* Venus In Situ Explorer
* Viking 1
* Viking 2

Interstellar
communication|

* Active SETI
* Allen Telescope Array
* Arecibo message
* Arecibo Observatory
* Berkeley SETI Research Center
* Bracewell probe
* Breakthrough Initiatives
* Breakthrough Listen
* Breakthrough Message
* Communication with extraterrestrial intelligence
* Gauss's Pythagorean right triangle proposal
* Astrolinguistics
* Lincos language
* NIROSETI
* Pioneer plaque
* Project Cyclops
* Project Ozma
* Project Phoenix
* SERENDIP
* Search for extraterrestrial intelligence
* SETI@home
* setiQuest
* Voyager Golden Record
* Water hole
* Xenolinguistics

Types of alleged
extraterrestrial beings|

* Energy beings
* Grey aliens
* Insectoids
* Little green men
* Nordic aliens
* Reptilian humanoids

Hypotheses|

* Cosmic pluralism
* Directed panspermia
* Drake equation
* Extraterrestrial hypothesis
* Fermi paradox
* Hypothetical types of biochemistry
* Interplanetary contamination
* Kardashev scale
* Mediocrity principle
* Non-planetary abiogenesis
* Panspermia

Fermi paradox solutions|

* Aestivation hypothesis
* Berserker hypothesis
* Dark forest hypothesis
* Firstborn hypothesis
* Great Filter
* Hart–Tipler conjecture
* Neocatastrophism
* Planetarium hypothesis
* Rare Earth hypothesis
* Zoo hypothesis

Related topics|

* Ancient astronauts
* Astrobiology
* Astroecology
* Biosignature
* Brookings Report
* Exotheology
* Extraterrestrials in fiction
* Extremophile
* Hemolithin
* History of the extraterrestrial life debate
* Nexus for Exoplanet System Science
* Noogenesis
* Planetary protection
* Potential cultural impact of extraterrestrial contact
* Post-detection policy
* San Marino Scale
* Technosignature
* UFO religion
* Xenoarchaeology

* v
* t
* e

Evolutionary biology

* Introduction
* Outline
* Timeline of evolution
* History of life
* Index

Evolution|

* Abiogenesis
* Adaptation
* Adaptive radiation
* Altruism
* Cheating
* Reciprocal
* Baldwin effect
* Cladistics
* Coevolution
* Mutualism
* Common descent
* Convergence
* Divergence
* Earliest known life forms
* Evidence of evolution
* Evolutionary arms race
* Evolutionary pressure
* Exaptation
* Extinction
* Event
* Homology
* Last universal common ancestor
* Macroevolution
* Microevolution
* Mismatch
* Non-adaptive radiation
* Origin of life
* Panspermia
* Parallel evolution
* Signalling theory
* Handicap principle
* Speciation
* Species
* Species complex
* Taxonomy
* Unit of selection
* Gene-centered view of evolution

Population
genetics|

* Artificial selection
* Biodiversity
* Evolutionarily stable strategy
* Fisher's principle
* Fitness
* Inclusive
* Gene flow
* Genetic drift
* Kin selection
* Inbreeding avoidance
* Kin recognition
* Parental investment
* Parent–offspring conflict
* Mutation
* Population
* Natural selection
* Sexual dimorphism
* Sexual selection
* Flowering plants
* Fungi
* Mate choice
* Social selection
* Trivers–Willard hypothesis
* Variation

Development|

* Canalisation
* Evolutionary developmental biology
* Genetic assimilation
* Inversion
* Modularity
* Phenotypic plasticity

Of taxa|

* Bacteria
* Birds
* origin
* Brachiopods
* Molluscs
* Cephalopods
* Dinosaurs
* Fish
* Fungi
* Insects
* butterflies
* Life
* Mammals
* cats
* canids
* wolves
* dogs
* hyenas
* dolphins and whales
* horses
* Kangaroos
* primates
* humans
* lemurs
* sea cows
* Plants
* pollinator-mediated
* Reptiles
* Spiders
* Tetrapods
* Viruses

Of organs|

* Cell
* DNA
* Flagella
* Eukaryotes
* symbiogenesis
* chromosome
* endomembrane system
* mitochondria
* nucleus
* plastids
* In animals
* eye
* hair
* auditory ossicle
* nervous system
* brain

Of processes|

* Aging
* Death
* Programmed cell death
* Avian flight
* Biological complexity
* Cooperation
* Color vision
* in primates
* Emotion
* Empathy
* Ethics
* Eusociality
* Immune system
* Metabolism
* Monogamy
* Morality
* Mosaic evolution
* Multicellularity
* Sexual reproduction
* Gamete differentiation/sexes
* Life cycles/nuclear phases
* Mating types
* Meiosis
* Sex-determination
* Snake venom

Tempo and modes|

* Gradualism/Punctuated equilibrium/Saltationism
* Micromutation/Macromutation
* Uniformitarianism/Catastrophism

Speciation|

* Allopatric
* Anagenesis
* Catagenesis
* Cladogenesis
* Cospeciation
* Ecological
* Hybrid
* Non-ecological
* Parapatric
* Peripatric
* Reinforcement
* Sympatric

History|

* Renaissance and Enlightenment
* Transmutation of species
* David Hume
* Dialogues Concerning Natural Religion
* Charles Darwin
* On the Origin of Species
* History of paleontology
* Transitional fossil
* Blending inheritance
* Mendelian inheritance
* The eclipse of Darwinism
* Neo-Darwinism
* Modern synthesis
* History of molecular evolution
* Extended evolutionary synthesis

Philosophy|

* Darwinism
* Alternatives
* Catastrophism
* Lamarckism
* Orthogenesis
* Mutationism
* Saltationism
* Structuralism
* Spandrel
* Theistic
* Vitalism
* Teleology in biology

Related|

* Biogeography
* Ecological genetics
* Evolutionary medicine
* Group selection
* Cultural evolution
* Cultural group selection
* Dual inheritance theory
* Hologenome theory of evolution
* Missing heritability problem
* Molecular evolution
* Astrobiology
* Phylogenetics
* Tree
* Polymorphism
* Protocell
* Systematics
* Transgenerational epigenetic inheritance

* Category
* Portal

* v
* t
* e

Molecules detected in outer space

Molecules|

| Diatomic|

* Aluminium monochloride
* Aluminium monofluoride
* Aluminium(II) oxide
* Argonium
* Carbon cation
* Carbon monophosphide
* Carbon monosulfide
* Carbon monoxide
* Cyano radical
* Diatomic carbon
* Fluoromethylidynium
* Helium hydride ion
* Hydrogen chloride
* Hydrogen fluoride
* Hydrogen (molecular)
* Hydroxyl radical
* Imidogen
* Iron(II) oxide
* Magnesium monohydride
* Methylidyne radical
* Nitric oxide
* Nitrogen (molecular)
* Oxygen (molecular)
* Phosphorus monoxide
* Phosphorus mononitride
* Potassium chloride
* Silicon carbide
* Silicon monoxide
* Silicon monosulfide
* Sodium chloride
* Sodium iodide
* Sulfanyl
* Sulfur mononitride
* Sulfur monoxide
* Titanium(II) oxide

|
|

Triatomic|

* Aluminium(I) hydroxide
* Aluminium isocyanide
* Amino radical
* Carbon dioxide
* Carbonyl sulfide
* CCP radical
* Chloronium
* Diazenylium
* Dicarbon monoxide
* Disilicon carbide
* Ethynyl radical
* Formyl radical
* Hydrogen cyanide (HCN)
* Hydrogen isocyanide (HNC)
* Hydrogen sulfide
* Hydroperoxyl
* Iron cyanide
* Isoformyl
* Magnesium cyanide
* Magnesium isocyanide
* Methylene
* Methylidynephosphane
* N2H+
* Nitrous oxide
* Nitroxyl
* Ozone
* Potassium cyanide
* Sodium cyanide
* Sodium hydroxide
* Silicon carbonitride
* c-Silicon dicarbide
* SiNC
* Sulfur dioxide
* Thioformyl
* Thioxoethenylidene
* Titanium dioxide
* Tricarbon
* Trihydrogen cation
* Water

Four
atoms|

* Acetylene
* Ammonia
* Cyanoethynyl
* Formaldehyde
* Fulminic acid
* HCCN
* Hydrogen peroxide
* Hydromagnesium isocyanide
* Isocyanic acid
* Isothiocyanic acid
* Ketenyl
* Methyl cation
* Methyl radical
* Methylene amidogen
* Propynylidyne
* Protonated carbon dioxide
* Protonated hydrogen cyanide
* Silicon tricarbide
* Thiocyanic acid
* Thioformaldehyde
* Tricarbon monosulfide
* Tricarbon monoxide

Five
atoms|

* Ammonium ion
* Butadiynyl
* Carbodiimide
* Cyanamide
* Cyanoacetylene
* Cyanoformaldehyde
* Cyanomethyl
* Cyclopropenylidene
* Formic acid
* Isocyanoacetylene
* Ketene
* Methane
* Methoxy radical
* Methylenimine
* Propadienylidene
* Protonated formaldehyde
* Silane
* Silicon-carbide cluster

Six
atoms|

* Acetonitrile
* Cyanobutadiynyl radical
* Cyclopropenone
* Diacetylene
* E-Cyanomethanimine
* Ethylene
* Formamide
* HC4N
* Ketenimine
* Methanethiol
* Methanol
* Methyl isocyanide
* Pentynylidyne
* Propynal
* Protonated cyanoacetylene

Seven
atoms|

* Acetaldehyde
* Acrylonitrile
* Vinyl cyanide
* Cyanodiacetylene
* Ethylene oxide
* Glycolonitrile
* Hexatriynyl radical
* Methyl isocyanate
* Methylamine
* Propyne
* Vinyl alcohol

Eight
atoms|

* Acetic acid
* Acrolein
* Aminoacetonitrile
* Cyanoallene
* Ethanimine
* Glycolaldehyde
* Hexapentaenylidene
* Methyl formate
* Methylcyanoacetylene

Nine
atoms|

* Acetamide
* Cyanohexatriyne
* Dimethyl ether
* Ethanethiol
* Ethanol
* Methyldiacetylene
* N-Methylformamide
* Octatetraynyl radical
* Propene
* Propionitrile

Ten
atoms
or more|

* Acetone
* Benzene
* Benzonitrile
* Buckminsterfullerene (C60, C60+, fullerene, buckyball)
* Butyronitrile
* C70 fullerene
* Cyanodecapentayne
* Ethyl formate
* Ethylene glycol
* Heptatrienyl radical
* Methyl acetate
* Methyl-cyano-diacetylene
* Methyltriacetylene
* Propionaldehyde
* Pyrimidine

Deuterated
molecules|

* Ammonia
* Ammonium ion
* Formaldehyde
* Formyl radical
* Heavy water
* Hydrogen cyanide
* Hydrogen deuteride
* Hydrogen isocyanide
* N2D+
* Propyne
* Trihydrogen cation

Unconfirmed|

* Anthracene
* Dihydroxyacetone
* Glycine
* Graphene
* H2NCO+
* Hemolithin
* Linear C5
* Methoxyethane
* Naphthalene cation
* Phosphine
* Pyrene
* Silylidyne

Related|

* Abiogenesis
* Astrobiology
* Astrochemistry
* Atomic and molecular astrophysics
* Chemical formula
* Circumstellar dust
* Circumstellar envelope
* Cosmic dust
* Cosmic ray
* Cosmochemistry
* Diffuse interstellar band
* Earliest known life forms
* Extraterrestrial life
* Extraterrestrial liquid water
* Forbidden mechanism
* Homochirality
* Intergalactic dust
* Interplanetary medium
* Interstellar medium
* Iron–sulfur world theory
* Kerogen
* Molecules in stars
* Nexus for Exoplanet System Science
* Organic compound
* Outer space
* PAH world hypothesis
* Photodissociation region
* Polycyclic aromatic hydrocarbon (PAH)
* Pseudo-panspermia
* RNA world hypothesis
* Spectroscopy
* Tholin

* Category:Astrochemistry
* Outer space portal
* Astronomy portal
* Chemistry portal

* v
* t
* e

Life, non-cellular life, and comparable structures

Cellular life|

| "Prokaryota"|

* Archaea
* Bacteria
* Mitochondrion
* Plastid
* LUCA

|

Eukaryota|

* Animalia
* Fungi
* Plantae
* "Protista"

Incertae sedis|

* Parakaryon
* Microbes with highly unusual DNA (?)

Non-cellular life|

| Virus

* * *

Viroid

* * *

Satellite|

| Realms|

* Adnaviria
* Duplodnaviria
* Monodnaviria
* Riboviria
* Ribozyviria
* Varidnaviria

|

Unassigned|

| Classes|

Naldaviricetes

|

Families|

* Alphasatellitidae
* Ampullaviridae
* Anelloviridae
* Avsunviroidae
* Bicaudaviridae
* Clavaviridae
* Finnlakeviridae
* Fuselloviridae
* Globuloviridae
* Guttaviridae
* Halspiviridae
* Ovaliviridae
* Plasmaviridae
* Polydnaviridae
* Portogloboviridae
* Pospiviroidae
* Spiraviridae
* Thaspiviridae
* Tolecusatellitidae

Genera|

* Dinodnavirus
* Rhizidiovirus

Other|

* Nanobe (?)
* Obelisk

Comparable
structures|

* Bio-like structure
* Cancer cell
* HeLa
* Clonally transmissible cancer
* Cosmid
* Defective interfering particle
* Endogenous viral element
* Fosmid
* Integrative and conjugative element
* Jeewanu
* "Nanobacterium"
* Phagemid
* Plasmid
* Prion
* Fungal prion
* Proteinoid microsphere
* Retroelements not elsewhere classified
* Retron
* Diversity-generating retroelement
* Telomerase reverse transcriptase
* Reverse transcriptase-related cellular gene
* Ribozyme
* Spiegelman's Monster
* Tandem repeat
* Transposable element
* Retroposon
* Transpoviron
* Xenobot

Portals:

* Astronomy
* Biology
* Evolutionary biology
* Geology
* Paleontology
* Science
* World

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