This was hard to pick because it is difficult to determine which origins of life hypotheses are the most uncommon, as different theories have varying levels of acceptance within the scientific community. Here are a few examples of origins of life hypotheses that are less well-known or less widely accepted:
Panspermia: The theory of panspermia proposes that life on Earth originated from seeds of life that were transported to our planet through comets, meteorites, or other means. According to this theory, life may have originated elsewhere in the universe and was then transported to Earth, where it could thrive and evolve. There are many versions of this; you can read ours here: the journal version and the arxiv version.
Directed panspermia: The theory of directed panspermia proposes that life on Earth was intentionally seeded by an intelligent extraterrestrial civilization. This theory is considered less likely than the common panspermia, as it requires the existence of an advanced extraterrestrial civilization capable of sending life to other planets. This can still be true if we–as us humans–are the advanced extraterrestrial civilization that might someday seed life on another planet, i.e., human-directed Panspermia.
Origin of life in ice: Some scientists have proposed that life may have originated in ice rather than in a liquid environment such as water. According to this theory, ice’s structural and chemical properties may have facilitated the synthesis of complex organic molecules and the emergence of life.
Origin of life through quantum mechanics: A few scientists have proposed that the origins of life may be related to the principles of quantum mechanics, which govern the behavior of subatomic
There are many different theories and hypotheses about the origins of life, and the specific mechanisms responsible for the emergence of life are still not fully understood. However, some origins of life hypotheses are more widely accepted or popular than others.
One of the most widely accepted hypotheses about the origins of life is the RNA world hypothesis. This theory proposes that RNA, a molecule that plays a central role in the synthesis and regulation of proteins, was the first form of genetic material and the precursor to DNA. According to this theory, RNA may have been able to replicate and evolve on its own, leading to the emergence of more complex life forms.
Another widely accepted hypothesis about the origins of life is the metabolic theory of the origin of life. This theory proposes that the first living organisms were simple metabolic systems that could extract energy from their environment and use it to synthesize complex organic molecules. According to this theory, the emergence of life resulted from a series of chemical reactions that occurred in the presence of energy sources such as UV radiation or lightning.
Overall, the origins of life are a complex and ongoing area of scientific research, and there are many different hypotheses about the specific mechanisms responsible for the emergence of life on Earth.
How do scientists study and gain new knowledge about our biological past?
There are many different approaches that scientists use to study the origins of life. Here are a few examples:
Experimental simulations (what I do): Scientists can conduct experiments to simulate the conditions that may have existed on early Earth and study the chemical reactions that may have led to the emergence of life. These experiments can be conducted in the laboratory using various techniques, such as chemical synthesis or irradiation with UV radiation.
Analysis of meteorites and comets (what I like): Scientists can study meteorites and comets to understand the types of chemical reactions that may have occurred in the early solar system and to search for evidence of the building blocks of life.
Astrobiological exploration (what I am curious about): Scientists can explore other planets and moons in our solar system and beyond to search for evidence of past or present life and understand the conditions necessary for life to emerge and evolve. For example, the recent James Webb Space Telescope.
Theoretical modeling (what I can’t do): Scientists can use computer simulations and mathematical models to understand the conditions and processes that may have been necessary for the emergence of life on Earth and to test different hypotheses about the origins of life.
Overall, the study of the origins of life is a multidisciplinary field that combines elements of biology, chemistry, physics, and other scientific disciplines to understand the conditions and processes necessary for the emergence of life on Earth.
The SCWFR at Kensei Kobayashi’s lab at Yokohama National University
Kensei Kobayashi’s group with the help of Takeo Kanaeko (a brilliant man) came up with another design where they named it Super Critical Water Flow Reactor (SCWFR) utilizing an infrared (IR) gold image furnace (Figure above). This enables the fluid in this system to heat up to 400 °C (or any desired temperature) within seconds (without pre-heating). This one specification is important as most autoclave and other flow reactors utilized an electrical heater which takes time to heat up to the desired temperature. This is undesirable as this “pre-heating” is also making the initial chemicals to react (or altered) to lower and rising temperature, which is not very realistic to a real vent. In other case, this is one of the slightly more realistic simulators i have worked to date.
Kobayashi’s ex-student, Nazrul Islam performed the survivability experiment using several amino acids (aspartic acid, threonine, serine, sarcosine, glutamic acid, α-aminobutyric acid, β- alanine, γ-aminobutyric acid, 5-aminovaleric acid and 6- aminohexanoic acid), 10 mM each) by heating them up at four different temperatures (250, 300, 350 and 400°C ) at 25 MPa for 2 min (that’s pretty fast). They showed that amino acids tend to show better recovery when it is hydrolyzed, suggesting some kind of aggregation and/or condensation is happening within the system. Additionally they also showed oligomerization of glycine (100mM) with the same temperature. At 400°C, no oligomerization was found. However, at 200-350°C, diketopiperazine, diglycine, triglycine and tetraglycine were formed. It was suggested that the glycine reactions in a supercritical fluid (300°C to 400°C) are quite different from those in the liquid phase (at 200–350°C). There were many other peaks of unknown compounds in all of the chromatograms of the unhydrolyzed products. Most of those peaks disappeared after acid hydrolysis. This particular findings however remains a mystery.
Another of Kensei’s sudent, Hironari Kurihara, used the SCWFR to test the stability of complex compounds produced from simulated primitive atmosphere (similar to Miller and Urey’s work). He then tested these compounds to assess the stability of some known amino acids. The complex-combined amino acids (from the primitive atmosphere simulation) preserved more amino acids (including amino acid precursors that give amino acids after acid hydrolysis) than free amino acids after heating in simulated SHS environments. In other words, these complex chemicals which could come from atmosphere (or space) could be better preserved if they are come into contact with the hot hydrothermal system which could have existed during the prebiotic-earth setting. This also hints that “clean or perfect” chemicals like amino acids used in many kinds of experiments are not necessarily showing the right picture when comes to chemical evolution on early earth. More on this in the future.
Many critics of hydrothermal vent simulators often argues that, simulators mentioned on this post and previous ones have a rather short flow-rate and short flow-length (showing low residence time, meaning how long the sample stays in the system). Critics usually cite studies that refer to residence time of fluids in axial hydrothermal environments range from years to decades, while those in lower temperature off-axis diffuse flow systems may be on the order of thousands of years. The problem with these studies about residential axial time of fluids is that, they’re are based on models and calculation only, no work has been done so far in regards to real time sampling or measuring the length of vent system (although, there are work in measuring the velocity of fluid emitting from a vent which looks promising for future measuring). Despite this limitation, i believe the future of simulators will be done using computer simulators, where experimental data from physical simulators (like the ones mentioned in this blog) could be used as parameters. The biggest advantage in this, is that, we do experiments on a larger scale which is could make the origin of life more complicated, interesting and not so straightforward, which I believe is a good problem to have in the future.
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Their first paper which made it to Nature (big thing for scientist), reported that oligomerization of glycine could occur at 200-250°C, where a monomer glycine solution was circulating for 2 hours or so. Oligomers up to Hexaglycine was reported when metal (Cu2+) and controlled pH was introduced. Without them, only oligomers up to triglycine could be obtained. They also tried the same experiment using glycine and alanine. They observed oligomerzation products such as
Schematic diagram of the HCFR system from Nagaoka Institute of Technology
diketopiperaxine, gly-ala, ala-gly, gly-ala-ala, ala-ala, ala-ala-ala and ala-ala-ala- ala was created when the solution was heated with similar conditions. What i described abover is a big thing in origin of life studies. This land-mark discovery, was the first to show that oligomerization (a shorter version of polymerization) could occur using basic amino acid (gly), without the help of DNA and RNA molecules which are crucial in making proteins in life.
In their other works, oligomerization of nucleotide up to trimers (basic monomer of DNA) was also observed when 20mM of adenosine monophosphate was used with 1mM ZnCl2 were reflowed at 110°C.
Despite the findings made by HCFR, the system is rather hypothetical, since we know that real live vents don’t really circulate in that manner (shown below) however, this kind of reactor is useful when it comes to monitor chemical changes in the system. In my next post, i will review another kind of flow-reactor in Japan which i have also worked on in the past.
HCFR mimicking a hypothetical circulatory system in a real life vent.
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Miller and Urey both designed their experiment assuming that the primitive atmosphere was reducing. This was a valid assumption at that time, and organic compounds are formed better in a reducing conditions. However, this reducing atmosphere scenario has changed, most scientist nowadays would envision a more redox neutral atmosphere. This is because there are no evidences of a reducing atmosphere documented in the rocks[1,2,3]. However, there is a small chance that a reduced atmosphere could happen for a short period of time in the presence of a meteorites impact or vapors from an erupting volcano[4]. Also it is worth noting, because there is lack of ozone layers during those periods, UV rays could have destroyed the biomolecules in the atmosphere as soon as they are formed. All this leads that the prebiotic atmosphere is limited in the sense of origins; moreover this biomolecules needs to be protected by the UV rays [5]; hence a SHSs’ reducing powers and its UV cloaking ability makes them an ideal spot for origins. The reducing conditions in hydrothermal vents (before the discovery of Lost City Hydrothermal field) is fueled by it reduced minerals which could act as a template for various catalytic activity [6,7,8,9,10] including polymerization.
SHS is also the only place that primitive life forms could have been protected during an event of meteorite shower and/or partial vaporization of the ocean[5]. Although, SHS could well be a spot for origins, critics often cite that residence times in axial hydrothermal environments range from years to decades, ( in other word, the time spent by fluid in the hydrothermal vents is long) while those in lower temperature off-axis diffuse flow systems may be on the order of thousands of years. These residence times are impossible to model experimentally, the effects of long residence times in SHSs are not generally considered in SHS experiments. This is one of the major limitation for experiments on SHS simulation.
1. Lambert, I.B, Donnelly, T.H, Dunlop, J.S.R and Groves, D.I (1978) Stable Isotope Compositions of Early Archaean Sulphate Deposits of Probable Evaporitic and Volcanogenic Origins: Nature, v.276,p.808.
2. Dimroth, E and Kimberley, M.M (1976) Precambrian Atmospheric Oxygen: Evidence in the Sedimentary Distributions of Carbon, Sulfur, Uranium and Iron: Canadian Journal Earth Science, v.13,1976, pp.1161-l185.
3. Zeschke, G (1960) Transportation of Uraninite in the Indus River, Pakistan: Geological Society of South Africa v.63, p.87.
4. Johnson, A. P, Cleaves, H. J, Dworkin, J. P, Glavin, D. P, Lazcano, A and Bada, J. L. (2008). The Miller volcanic spark discharge experiment. Science, 322(5900), 404–404.
5. Sleep, N. H, Zahnle, K. J, Kasting, L F and Morowitz, H.J (1989) Annihilation of ecosystems by large asteroid impacts on the early Earth, Nature 342, 139-142.
6. Wachtershauser, G (1988) Before enzymes and templates: Theory of surface metabolism, Microbiology Review. 52, 452-484.
7. Wachtershauser, G (1988) Pyrite formation, the first energy source for life: A hypothesis, Systematic and Applied Microbiology 10, 207-210.
8. Wachtershauser, G (1990) The case for the chemoautotrophic origin of life in an iron- sulfur world, Origins of Life and Evolution of the Biosphere 20, 173-176
9. Russell, M. J, Hall, A. J and Turner, D (1989) In vitro growth of iron sulphide chimneys: Possible culture chambers for origin-of-life experiments, Terra Nova 1, 238-241
10. Kadko, D and Butterfield, D.A (1998) The relationship of hydrothermal fluid composition and crustal residence time to the maturity of vent fields on the Juan de Fuca Ridge. Geochimica et Cosmochimica Acta 62:1521– 1533
11. Turekian, K.K, Cochran, J.K (1986) Flow-rates and reaction-rates in the Galapagos Rise spreading center hydrothermal system as inferred from Ra-228/Ra-226 in vesicomyid clam shells. Proceedings of the National Academy of Sciences of the United States of America, 83:6241–6244
12. Johnson, H.P, Pruis, M.J (2003) Fluxes of fluid and heat from the oceanic crustal reservoir. Earth and Planetary Science Letters 216:565–574
In the last post, i discussed briefly about SHS, here i will be posting some details on why SHS is suitable for life to start. I will be going one by one to help sell the idea on why SHS is good for origins and will show their shortcoming as well
Some of the accepted hypothesis on hyperthermophilles phylogenetic tree. The positions are based on 16S/18S rRNA phylogenic positions29. The root for trees A and B are placed in the bacterial branch30, hence making LUCA a hyperthermophile. In C, the root is placed under the eukaryotic branch making the hyperthermophile a last common prokaryotic ancestor (LCPA)31. D is unrooted, making the LCPA a mesophile. Adapted from DeLong, E.F, Wu, K.Y, Prezelin, B.B and Jovine, R.V.M (1994) Abundance of Archaea in Antarctic Marine Picoplankton. Nature 371, 695–697
One of the biggest reason associated with origins and SHS, is related to hyperthermophiles. They are microorganism that strive at extreme heat. These organism cultivated from the vents areas could strive at 110 ℃ of heat, which could flourish at temperature up to 110℃. Several authors1,2,3, have proposed that these microbes could have close relation to LUCA. This hypothesis derives from the construction of archaeal and bacterial phylogenetic trees based on 16S rRNA sequence comparisons4. Hyperthermophiles are clustered at the base of these trees and many of their branches are short, suggesting that they have conserved ancestral phenotypic characters3. However, there are also contradicting studies, which indicate that these microbes posses “missing” enzymes, that uses other energy co-factors, instead of conventional ATP molecule. In other words, this finding shows that these enzymes have adapted to function at high temperature thus indicating that these microbes are more recent than suggested5.
A limitation to this finding is that it assumes that ATP have existed long in time; this argument can be refuted if one also imagine that ATP is also a recent and high adapted energy co-factor in life. This hyperthermophiles, was the first hint which made SHS suitable for origins; however the theory is not limited to this reasons only.
Baross, J.A, and Hoffman, S.E (1985) Submarine hydrothermal vents and associated gradient environments as sites for the origin and evolution of life. Origins of Life and biosphere 15, 327–345.
Pace, N.R (1991) Origin of life–Facing up to the physical setting. Cell 65, 531–533.
Forterre, P (1996) A hot topic: the origin of hyperthermophiles. Cell, 85(6), 789–792.
Stetter, K.O (1994) In Early Life on Earth, S. Bengston, ed. (New York: Columbia University Press), pp. 143–151
Siebers, B and Hensel, R (1993) Glucose catabolism of the hyperthermophilic archaeum Thermoproteus tenax Microbiology Letters. 111, 1–8.
Forterre, P, Confalonieri, F, Charbonnier, F and Duguet, M (1995) Speculations on the origin of life and thermophily: review of available information on reverse gyrase suggests that hyperthermophilic procaryotes are not so primitive. Origins of Life and biosphere. 25, 235–249.
Plate tectonic is the theory which unified on how the earth worked. The theory has always been there (since 1879)1,2 and was only accepted in the 1950‘s. The theory also predicted the existence of hydrothermal vents; a deep-sea hot springs is formed when cold seawater seeps into magma-emitting cracks on the oceanic surface, heats up, and rises. Although scientists had been actively searching for vents since the early 1960s, it wasn’t until the 1977; when the Galápagos Hydrothermal Expedition led by Richard Von Herzen and Robert Ballard of the Woods Hole Oceanographic Institution, that confirmed their existence using the famous submersible, Alvin ,3,4.
The relationship between SHS and origin of life on the other hand, first came out through Jack Corliss, John Baross and Sarah Hoffman5. They claimed that the conditions surrounding the vent area provided all the conditions for life’s creation on earth. Over time this idea has sprouted and have been elaborated with many in-situ integration with simulation data. I will elaborate more on this in the next post.
Darwin, G.H (1879) On the procession of viscous spheroid, and on the remote History of the Earth.Philosophical Transactions of the Royal Society of London Vol. 170, 447-538
McKenzie, D. P (1969) Speculations on the consequences and causes of plate motions. Geophysical Journal International, 18(1), 1–32.
Corliss, J. B. J, Baross, J.A and Hoffman, S.E (1981) An hypothesis concerning the relationship between submarine hot springs and the origin of life on Earth. Oceanologica Acta 4, 59-69.
Corliss, J.B, Lyle, M, Dymond. J and Crane, K (1978) The chemistry of hydrothermal mounds near the Galapagos Rift. Earth and Planetary Science Letters, Volume 40, Issue 1,12–24.
Corliss, J.B, Baross, J.A. and Hoffman, S.E (1981) An hypothesis concerning the relationship between submarine hot springs and the origin of life on Earth, Oceanologica Acta 4, 59–69
I first knew about the geological time scale during my college years, back then the only geological time i knew was “Jurassic” due to a certain Hollywood movie. Learning it was fun but memorizing it for exams was horrible. The lecturers will first show the scale like the one here (very very boring btw), and they will explain one by one what happened with pictures of dinosaurs, plants, ancient humans and etc. It was remarkable, but how did geologists came to this scale always puzzled me, it still does, as we have loopholes in it too. The scale is basically a convention agreed by geologists based on research which were agreeable from time to time.
Here i will briefly explain some key events and how they got there. Most importantly i will put emphasis on how and when life started, the rest is evolution which you can read/view elsewhere. I will be also breaking this topic to a few parts for easy understanding.
Lets start,
After the big bang, the HADEAN period named after Hades begin. The sun was already formed and the rise of giant planets (Jupiter and Saturn) could have happened during this time. This is based on “numerical models“. After the formation of Mars, earth was finally formed in it’s hottest state (hot as hell). It is also postulated that the moon was also formed right after this, and her origins came from earth. Check out the video below on how this could have happened
From here on, our primitive atmosphere begin to arise, which is absolutely hypothetical in case you were wondering. After this particular sequence of events, the building of the habitable earth begins. The first proto ocean were already in play after the cool down effects on earth . There are some speculation that life could have started here; but right after this, the late heavy bombardment (LHB) of comets and meteorite came showering on earth, the planet was destroyed, water evaporated completely and it was a mess. This phenomena is also observable on the moon .If you have wondered why the moon has craters, its because of LHB (despite not having tectonic plates etc).
Now, The ARCHEAN period begins, which is generally the post HLB. Earth during this time has a lot of minerals and more water because of the LHB. In other words, she has received more materials to allow life to flower.
The rest of story is to be continued in the near future, stay tuned
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The fossils records were the only prove when it comes to origin of life and its evolution, that was the past. With radioisotopes dating we have known more
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Kuhan Chandru 
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