Panspermia: The Extraterrestrial Hypothesis - On Human Origins

The chemicals, found in a giant cloud of gas about 25, light-years from Earth in ISM, may be a precursor to a key component of DNA and the other may have a role in the formation of an important amino acid. Researchers found a molecule called cyanomethanimine, which produces adenine , one of the four nucleobases that form the "rungs" in the ladder-like structure of DNA.

The other molecule, called ethanamine , is thought to play a role in forming alanine , one of the twenty amino acids in the genetic code. Previously, scientists thought such processes took place in the very tenuous gas between the stars.

The new discoveries, however, suggest that the chemical formation sequences for these molecules occurred not in gas, but on the surfaces of ice grains in interstellar space. In March , a simulation experiment indicate that dipeptides pairs of amino acids that can be building blocks of proteins , can be created in interstellar dust. PAHs seem to have been formed shortly after the Big Bang , are widespread throughout the universe, and are associated with new stars and exoplanets.

In March , NASA scientists reported that, for the first time, complex DNA and RNA organic compounds of life , including uracil , cytosine and thymine , have been formed in the laboratory under outer space conditions, using starting chemicals, such as pyrimidine , found in meteorites. Pyrimidine, like polycyclic aromatic hydrocarbons PAHs , the most carbon-rich chemical found in the Universe , may have been formed in red giants or in interstellar dust and gas clouds, according to the scientists. The chemistry of life may have begun shortly after the Big Bang , It is generally agreed that the conditions required for the evolution of intelligent life as we know it are probably exceedingly rare in the universe, while simultaneously noting that simple single-celled microorganisms may be more likely.

The extrasolar planet results from the Kepler mission estimate — billion exoplanets, with over 3, as candidates or confirmed exoplanets. It is estimated that space travel over cosmic distances would take an incredibly long time to an outside observer, and with vast amounts of energy required. However, there are reasons to hypothesize that faster-than-light interstellar space travel might be feasible. This has been explored by NASA scientists since at least Hoyle and Wickramasinghe have speculated that several outbreaks of illnesses on Earth are of extraterrestrial origins, including the flu pandemic , and certain outbreaks of polio and mad cow disease.

For the flu pandemic they hypothesized that cometary dust brought the virus to Earth simultaneously at multiple locations—a view almost universally dismissed by experts on this pandemic. Hoyle also speculated that HIV came from outer space. The Lancet subsequently published three responses to this letter, showing that the hypothesis was not evidence-based, and casting doubts on the quality of the experiments referenced by Wickramasinghe in his letter.

A separate fragment of the Orgueil meteorite kept in a sealed glass jar since its discovery was found in to have a seed capsule embedded in it, whilst the original glassy layer on the outside remained undisturbed. Despite great initial excitement, the seed was found to be that of a European Juncaceae or Rush plant that had been glued into the fragment and camouflaged using coal dust. The outer "fusion layer" was in fact glue.

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Whilst the perpetrator of this hoax is unknown, it is thought that they sought to influence the 19th century debate on spontaneous generation — rather than panspermia — by demonstrating the transformation of inorganic to biological matter. Until the s, life was thought to depend on its access to sunlight. Even life in the ocean depths, where sunlight cannot reach, was believed to obtain its nourishment either from consuming organic detritus rained down from the surface waters or from eating animals that did.

This chemosynthesis revolutionized the study of biology by revealing that terrestrial life need not be Sun-dependent; it only requires water and an energy gradient in order to exist. It is now known that extremophiles , microorganisms with extraordinary capability to thrive in the harshest environments on Earth, can specialize to thrive in the deep-sea, [] [] [] ice, boiling water, acid, the water core of nuclear reactors, salt crystals, toxic waste and in a range of other extreme habitats that were previously thought to be inhospitable for life.

In order to test some these organisms' potential resilience in outer space, plant seeds and spores of bacteria , fungi and ferns have been exposed to the harsh space environment. These structures may be highly resilient to ultraviolet and gamma radiation , desiccation , lysozyme , temperature , starvation and chemical disinfectants , while metabolically inactive.

Extraterrestrial Origin of Life

Spores germinate when favourable conditions are restored after exposure to conditions fatal to the parent organism. The discovery of deep-sea ecosystems , along with advancements in the fields of astrobiology , observational astronomy and discovery of large varieties of extremophiles, opened up a new avenue in astrobiology by massively expanding the number of possible extraterrestrial habitats and possible transport of hardy microbial life through vast distances. The question of whether certain microorganisms can survive in the harsh environment of outer space has intrigued biologists since the beginning of spaceflight, and opportunities were provided to expose samples to space.

The first American tests were made in , during the Gemini IX and XII missions, when samples of bacteriophage T1 and spores of Penicillium roqueforti were exposed to outer space for Thus, the plausibility of panspermia can be evaluated by examining life forms on Earth for their capacity to survive in space. After the approximately month mission, their responses were studied in terms of survival, mutagenesis in the his B.

The data were compared with those of a simultaneously running ground control experiment: Experiments developed for BIOPAN are designed to investigate the effect of the space environment on biological material after exposure between 13 and 17 days.

Panspermia

Of the 6 missions flown so far on BIOPAN between and , dozens of experiments were conducted, and some analyzed the likelihood of panspermia. Some bacteria, lichens Xanthoria elegans , Rhizocarpon geographicum and their mycobiont cultures, the black Antarctic microfungi Cryomyces minteri and Cryomyces antarcticus , spores, and even one animal tardigrades were found to have survived the harsh outer space environment and cosmic radiation.

If shielded against solar UV , spores of B. The data support the likelihood of interplanetary transfer of microorganisms within meteorites, the so-called lithopanspermia hypothesis. Results from the orbital missions, especially the experiments SEEDS [] and LiFE , [] concluded that after an month exposure, some seeds and lichens Stichococcus sp.

The Tanpopo mission is an orbital astrobiology experiment by Japan that is currently investigating the possible interplanetary transfer of life, organic compounds , and possible terrestrial particles in low Earth orbit. The Tanpopo experiment is taking place at the Exposed Facility located on the exterior of Kibo module of the International Space Station.

The mission will collect cosmic dusts and other particles for three years by using an ultra-low density silica gel called aerogel. The purpose is to assess the panspermia hypothesis and the possibility of natural interplanetary transport of life and its precursors. Panspermia is often criticized because it does not answer the question of the origin of life but merely places it on another celestial body. It was also criticized because it was thought it could not be tested experimentally. Wallis and Wickramasinghe argued in that the transport of individual bacteria or clumps of bacteria, is overwhelmingly more important than lithopanspermia in terms of numbers of microbes transferred, even accounting for the death rate of unprotected bacteria in transit.

These results clearly negate the original panspermia hypothesis, which requires single spores as space travelers accelerated by the radiation pressure of the Sun, requiring many years to travel between the planets. However, if shielded against solar UV , spores of Bacillus subtilis were capable of surviving in space for up to 6 years, especially if embedded in clay or meteorite powder artificial meteorites. The data support the likelihood of interplanetary transfer of microorganisms within meteorites , the so-called lithopanspermia hypothesis. From Wikipedia, the free encyclopedia.

List of microorganisms tested in outer space. Uses authors parameter link CS1 maint: Explicit use of et al. International Journal of Astrobiology. A promising field of research" PDF. Madhusoodanan, Jyoti May 19, Retrieved November 6, Retrieved 28 February Retrieved 31 October Monthly Notices of the Royal Astronomical Society. Retrieved 10 November Dent and Son, London , ch3 pp. Comets and the Origin of Life. Retrieved 25 July Proceedings of the National Academy of Sciences.

Twentieth Century Physics 2nd ed. Anaxagoras and the Origin of Panspermia Theory. Liebigs Annalen der Chemie und Pharmacie. Archived from the original on 13 October Worlds in the Making: The Evolution of the Universe. Astrophysics and Space Science. Viruses from Space and Related Matters.

University College Cardiff Press. Archived from the original on July 24, Retrieved 11 February Bacillus subtilis spores in artificial meteorites". Toxic gas holds hints". Retrieved 9 March Retrieved 1 August Planetary and Space Science. News at Princeton, September 24, Seeding the Universe with Life: A technical evaluation of seeding nearby planetary systems" PDF. Journal of the British Interplanetary Society. Strategies and motivation for seeding star-forming clouds" PDF.

Retrieved 24 August Archived from the original on January 11, Retrieved December 8, Held 16—23 July Published in Die Umschau. Microbiology and Molecular Biology Reviews. Intelligent Life in the Universe. Origins of Life and Evolution of the Biosphere: Schuerger; Peter Setlow 21 January Archived from the original PDF on 28 December Retrieved 2 August Probability Factors and Implications". Origins of Life and Evolution of the Biosphere. Journal of Microbiological Methods. Origins of Life and Evolution of Biospheres. First Phase of Lithopanspermia Experimentally Tested". Jay; Nicholson, Wayne L.

Some past speculations on the origin of life: Planetary microcosm bioessays of Martian and meteorite materials: Resources, biomass and populations" PDF. Renewing Our Search for Alien Intelligence. The New Reddit Journal of Science. Life Sciences in Space Research. Retrieved 16 April Earth and Planetary Science Letters. Archived from the original on June 17, Retrieved 8 November Retrieved 6 March Retrieved 10 August Retrieved 9 August Retrieved 26 October Retrieved 27 October Retrieved August 31, Geologists estimate that the Earth formed around 4.

Formation of Earth and early life

For many millions of years, early Earth was pummeled by asteroids and other celestial objects. Temperatures also would have been very high with water taking the form of a gas, not a liquid. The first life might have emerged during a break in the asteroid bombardment, between 4.

However, a second bombardment happened about 3. The earliest fossil evidence of life.

The earliest evidence of life on Earth comes from fossils discovered in Western Australia that date back to about 3. These fossils are of structures known as stromatolites , which are, in many cases, formed by the growth of layer upon layer of single-celled microbes, such as cyanobacteria. Stromatolites are also made by present-day microbes, not just prehistoric ones. The earliest fossils of microbes themselves, rather than just their by-products, preserve the remains of what scientists think are sulfur-metabolizing bacteria. The fossils also come from Australia and date to about 3.

Bacteria are relatively complex, suggesting that life probably began a good deal earlier than 3. How might life have arisen? Haldane both separately proposed what's now called the Oparin-Haldane hypothesis: Oparin and Haldane thought that the early Earth had a reducing atmosphere, meaning an oxygen-poor atmosphere in which molecules tend to donate electrons. Under these conditions, they suggested that:. Simple inorganic molecules could have reacted with energy from lightning or the sun to form building blocks like amino acids and nucleotides, which could have accumulated in the oceans, making a "primordial soup.

The building blocks could have combined in further reactions, forming larger, more complex molecules polymers like proteins and nucleic acids, perhaps in pools at the water's edge. The polymers could have assembled into units or structures that were capable of sustaining and replicating themselves.

The details of this model are probably not quite correct. For instance, geologists now think the early atmosphere was not reducing, and it's unclear whether pools at the edge of the ocean are a likely site for life's first appearance. But the basic idea — a stepwise, spontaneous formation of simple, then more complex, then self-sustaining biological molecules or assemblies — is still at the core of most origins-of-life hypotheses today. From inorganic compounds to building blocks. They found that organic molecules could be spontaneously produced under reducing conditions thought to resemble those of early Earth.

Cartoon depiction of the apparatus used by Miller and Urey to simulate conditions on early Earth. After letting the experiment run for a week, Miller and Urey found that various types of amino acids, sugars, lipids and other organic molecules had formed. Large, complex molecules like DNA and protein were missing, but the Miller-Urey experiment showed that at least some of the building blocks for these molecules could form spontaneously from simple compounds.

Were Miller and Urey's results meaningful? So, it's doubtful that Miller and Urey did an accurate simulation of conditions on early Earth. A nucleotide is a relatively complex, three-part molecule with a sugar ring, a nitrogenous base, and one or more phosphate groups. As such, it's less likely to form through simple chemical reactions than a typical amino acid.

From these experiments, it seems reasonable to imagine that at least some of life's building blocks could have formed abiotically on early Earth. However, exactly how and under what conditions remains an open question. From building blocks to polymers. How could monomers building blocks like amino acids or nucleotides have assembled into polymers, or actual biological macromolecules, on early Earth? In cells today, polymers are put together by enzymes.

But, since the enzymes themselves are polymers, this is kind of a chicken-and-egg problem! Monomers may have been able to spontaneously form polymers under the conditions found on early Earth. Fox suggested that, on early Earth, ocean water carrying amino acids could have splashed onto a hot surface like a lava flow, boiling away the water and leaving behind a protein.

The clay acts as a catalyst to form an RNA polymer. More broadly, clay and other mineral surfaces may have played a key role in the formation of polymers, acting as supports or catalysts. The image above shows a sample of a type of clay known as montmorillonite. What was the nature of the earliest life? If we imagine that polymers were able to form on early Earth, this still leaves us with the question of how the polymers would have become self-replicating or self-perpetuating, meeting the most basic criteria for life.

This is an area in which there are many ideas, but little certainty about the correct answer. One possibility is that the first life forms were self-replicating nucleic acids, such as RNA or DNA, and that other elements like metabolic networks were a later add-on to this basic system.

This is known as the RNA world hypothesis. Perhaps the most important is that RNA can, in addition to carrying information, act as a catalyst. A catalytic RNA could, potentially, catalyze a chemical reaction to copy itself. Such a self-replicating RNA could pass genetic material from generation to generation, fulfilling the most basic criteria for life and, potentially, undergoing evolution. In fact, researchers have been able to synthetically engineer small ribozymes that are capable of self-replication. Some highly conserved molecules found in the cells of many organisms are structurally related to RNA.

In addition, functional RNA molecules play key roles in protein synthesis: These networks might have formed, for instance, near undersea hydrothermal vents that provided a continual supply of chemical precursors, and might have been self-sustaining and persistent meeting the basic criteria for life. Eventually, the metabolic networks might have been able to build large molecules such as proteins and nucleic acids. What might early cells have looked like? A basic property of a cell is the ability to maintain an internal environment different from the surrounding environment.

In principle, this type of compartment could surround a self-replicating ribozyme or the components of a metabolic pathway, making a very basic cell. Though intriguing, this type of idea is not yet supported by experimental evidence — i. Organic molecules from outer space.

But could they instead have come from space? The idea that organic molecules might have traveled to Earth on meteorites may sound like science fiction, but it's supported by reasonable evidence.

Hypotheses about the origins of life (article) | Khan Academy

We also know that some organic compounds are found in space and in other star systems. Most importantly, various meteorites have turned out to contain organic compounds derived from space, not from Earth. One meteorite, ALH, came from Mars and contained organic molecules with multiple ring structures.

Another meteorite, the Murchison meteorite, carried nitrogenous bases like those found in DNA and RNA , as well as a wide variety of amino acids. One meteorite that fell in in Canada contained tiny organic structures dubbed "organic globules.

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There's no way for us to exclude the possibility that simple life forms were delivered to Earth on meteorites or other celestial objects early in Earth's history. However, so far, there hasn't been clear evidence for this hypothesis. Also, even if this turned out to be the case, we would effectively be "kicking the can down the road" on our question of how life arose. Even if life came to Earth from elsewhere in the universe, we would still be left wondering how it arose to begin with wherever it did arise. How life originated on our planet is both a fascinating and incredibly complex question.

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We know roughly when life began, but how remains a mystery. Miller, Urey, and others showed that simple inorganic molecules could combine to form the organic building blocks required for life as we know it. Once formed, these building blocks could have come together to form polymers such as proteins or RNA. Other ideas include the pre-RNA world hypothesis and the metabolism-first hypothesis. Organic compounds could have been delivered to early Earth by meteorites and other celestial objects.

These are not the only scientific ideas about how life might have originated, nor are any of them conclusive. Keep your ears and your mind open as new information becomes available and new scientific ideas are proposed concerning life's origins.