SO HOW DID LIFE BEGIN IN THE FIRST PLACE?*
First of all, what is life?
This question forms the title of a book written in 1944 by the Nobel Prize winning theoretical physicist Erwin Schrödinger – he of the 1926 probability wave equation describing the essence of quantum mechanics, and the 1935 simultaneously-alive-and-dead-cat - "until you look" demolition of the Copenhagen interpretation of quantum mechanics [1] fame.
Schrödinger[2] viewed even the most basic form of cellular life as requiring of necessity two attributes: the ability to draw chemical elements and energy from the environment, and the ability to replicate itself. These qualities have since been the subject of elaboration, and it is now accepted that life as we know it is endowed with four qualities[3]:
* For a succinct analysis of this most fundamental of all questions, part of "The Biggest Questions In Science" series in Nature magazine, and containing an excellent illustration by Matthew Twombly, see https://www.nature.com/articles/d41586-018-05098-w
[1] Both at http://elwynsbigbangpage.weebly.com/schrodingers-probability-wave-equation.html
[2] Mesler and Cleaves, op cit, 194-5.
[3] See the Big History site at https://www.bighistoryproject.com/chapters/3#the-tremendous-diversity-of-living-things
Modern Darwinian theory can explain how modern organisms have evolved from the simple life forms present on the early Earth. But how did life get going in the first place?
The answer is that we don’t really know. One theory is that it developed spontaneously as a result of chemical reactions. Living organisms are constructed for the most part from compounds of carbon and hydrogen. Throw in nitrogen, oxygen, phosphorus and sulphur and we can account for some 99% of the dry weight of all living organisms[1]. When conditions are right and these chemicals are abundant, it is easy to construct simple organic molecules[2], including amino acids, the building blocks of proteins, the basic structural materials of all organisms, and nucleotides (the molecules from which the genetic code is constructed). This metamorphosis or catalytic reaction is unlikely to occur in today’s atmosphere where there is too much oxygen with its capacity to generate heat (combustion) when it is chemically reactive.
The Miller Urey experiment[3]
But in an oxygen-free atmosphere that allowed simple organic molecules to survive long enough in the complex, slow-motion chemistry for chemical evolution to take place, things may have been different. In 1952, two American scientists, graduate student Stanley Miller and his Ph D supervisor the Nobel Prize winning chemist Harold Urey, created a model of the early atmosphere by filling a retort (a large closed container) with methane, water and ammonia. They warmed the mixture and provided shots of free energy similar to lightning. After seven days, a dark red sludge appeared in their retort, containing several of the most important amino acids, particularly glycine and alanine - simple organic molecules containing about 20 to 40 atoms that link up in different patterns to form the proteins that dominate the chemistry and the structure of all living organisms. Subsequent experiments have revealed that all 20 amino acids can be created in this way. Here we have the basis for the construction of proteins, the fundamental building blocks of life.
The Miller-Urey experiment also created in smaller quantities other important organic molecules including sugars and the main components of nucleotides. Although the earth’s early atmosphere may have been somewhat different to that which Miller and Urey supposed, the Miller-Urey experiment showed that the creation of the basic building blocks of life may not have been too difficult on the early earth. Amino acids have since been identified in dust clouds in interstellar space, and subsequent observations tend to suggest that the basic chemicals from which life is formed were abundant in the early solar system. The question then is to explain how these simple organic materials were assembled into the vast and complex structures necessary for life to exist, that is how proteins, tens of thousands of them, each fulfilling an allotted task: respiring, eating, reproducing, each having to be arranged in a precise sequence came to be formed from amino acids.
A “warm little pond” or archaebacteria?[4]
There are in fact different views as to where life first began. It seems unlikely that life could have originated in space where both energy and raw materials are in short supply thereby ensuring that chemical processes are very slow. Besides, many of the chemical reactions vital to life seem to require water in liquid form which cannot be found in space.
Darwin suggested that life might have begun “in some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity etc”[5], and ever since biologists have tried to figure out how natural chemical and physical processes could have assembled these chemicals into simple organisms somewhere in the seas or in the seashores of the early earth. Water plays a crucial role. Amino acids and nucleotides once formed could have been protected to some extent as long as they stayed in water.
A quite plausible speculation is that after millions of years, the seas of the early earth may have been full of simple organic chemicals, which could have then joined together into more complex organisms. However they were created, early organic molecules could have formed a weak organic “soup” of simple proteins, nucleic acids and other organic molecules. So along the shores and in the warm seas of the earth 4 billion years ago there may have already existed organic molecules that duplicated many of the activities of life, forming into cell-like globules with an outer skin, absorbing or “eating” other chemicals and then splitting into separate globules as if reproducing. All of these theories are quite plausible, but at this stage none can explain all the steps leading from nonlife to life.
There is also recent evidence to suggest that the earliest living organisms appeared before 3.8 billion years ago when the earth’s surface was still being bombarded regularly by extraterrestrial material. These forms of bacteria are called archaebacteria that evolved well below the surface of the earth, “feeding” on chemical energy produced within the earth itself from iron, sulphur, hydrogen and other chemicals buried in rocks or dissolved in seawater. In the 1990s, archaebacteria were found living inside rocks more than a kilometre below the earth’s surface; and they have also been found living at temperatures well above boiling point in volcanic vents on the seafloor, as well as in porous rocks below the seabed. In 2000, the existence of these hydrothermal vents was confirmed by the discovery of a network of active underwater chimneys caused by volcanic activity below the ocean floor in an area halfway between Europe and North America[6]. Archaebacteria have also been found living in huge quantities at the earth’s surface.
Archaebacteria may offer a better model than most other modern organisms for the earliest forms of life on earth. They live in environments that have changed little since the Hadean era, and their ability to live well below the surface means that they would have been less affected by the meteoric impacts that were common early in the earth’s history and may have periodically wiped out life near the surface. If these arguments are right, then life may have first appeared from beneath the surface of the earth and its seas, before producing new species that could survive in the cooler environments near or at the surface.
Fostering this line of research, scientists at University College London recently (2017) claim to have found the remnants of structures made by micro-organisms that are said to be the oldest fossils on Earth, dating to to between 3.8 and 4.3 billion years old. [7] These so-called "putative microfossils" were found in quartz layers within the Nuvvaugittuq suprastructural belt in Quebec, Canada, thought to be one of the world’s oldest rock formations. The authors say the fossils are not remnants of the single-celled organisms, but rather the tubes and filaments they formed as they fed on hydrogen sulphide and iron around hot vents on the ocean floors in conditions probably similar to where life on Earth began. If correct, the discovery would support the idea that cellular life emerged from hot, sea-floor vents shortly after planet Earth formed, implying that the steps from the molecular evolution to the RNA world, lipids, and peptides to membrane-bound cellular life with DNA may have happened within only a few million years after the earth formed.
However, the significance of the discovery is heavily disputed by others who assert that it is not proved the structures are of biological origin, and that the rocks in which they have been found are unusually badly preserved and strongly recrystalised and altered, having been cooked deep in the crust at more than 500 degrees, destroying their original structures. The study’s authors respond: “one, the structures were formed in a submarine environment; two, there are thermal springs; and three, we have these tubular features. What else could they be?”
Another backing the research has compared the Canadian findings with established fossilised stromatolite structures in the 1.8 billion-year-old Earaheedy structures and the 3.5 billion-year-old Pilbara structures in Western Australia, and found that they have exactly the same structure.
[1] Christian, Maps of Time, 95-96.
[2] The scientific meaning of ‘organic’ refers to a class of molecules that contain carbon, especially those involved in the chemistry of life.
[3] The Miller-Urey experiment is fully documented and its mechanics explained in Mesler and Cleaves, A brief History of Creation, WW Norton, New York, 2016, Chapter 9 "A laboratory earth", pp 172 ff. Urey graciously allowed his student to take prime position in the nomenclature publicising the experiment.
[4] Source for this material: Christian, Maps of Time, 93-99.
[5] Cited in Paul Davies, The Fifth Miracle: The Search for the Origin of Life, Hammondsworth, Penguin, 1999, p 54.
[6] Recounted in Mesler and Cleaves, op cit, Preface, xi-xii.
[7] See www.smh.com.au/technology/sci-tech/controversy-breaks-out-over-claims-that-worlds-oldest-fossils-have-been-found-20170301-gunu0j.html where the original article in Nature, accepted 9 January 2017, is referenced.
First of all, what is life?
This question forms the title of a book written in 1944 by the Nobel Prize winning theoretical physicist Erwin Schrödinger – he of the 1926 probability wave equation describing the essence of quantum mechanics, and the 1935 simultaneously-alive-and-dead-cat - "until you look" demolition of the Copenhagen interpretation of quantum mechanics [1] fame.
Schrödinger[2] viewed even the most basic form of cellular life as requiring of necessity two attributes: the ability to draw chemical elements and energy from the environment, and the ability to replicate itself. These qualities have since been the subject of elaboration, and it is now accepted that life as we know it is endowed with four qualities[3]:
- Metabolism (the software of chemical activity): the ability to take in energy from surroundings to keep going
- Self-regulation: also known as "homeostasis," an organism's ability to regulate itself to maintain stability
- Reproduction/replication (the hardware of the genetic code): the ability to create copies, allowing life to preserve itself and go on
- Adaptation: the ability to change from generation to generation and become better suited to environments.
* For a succinct analysis of this most fundamental of all questions, part of "The Biggest Questions In Science" series in Nature magazine, and containing an excellent illustration by Matthew Twombly, see https://www.nature.com/articles/d41586-018-05098-w
[1] Both at http://elwynsbigbangpage.weebly.com/schrodingers-probability-wave-equation.html
[2] Mesler and Cleaves, op cit, 194-5.
[3] See the Big History site at https://www.bighistoryproject.com/chapters/3#the-tremendous-diversity-of-living-things
Modern Darwinian theory can explain how modern organisms have evolved from the simple life forms present on the early Earth. But how did life get going in the first place?
The answer is that we don’t really know. One theory is that it developed spontaneously as a result of chemical reactions. Living organisms are constructed for the most part from compounds of carbon and hydrogen. Throw in nitrogen, oxygen, phosphorus and sulphur and we can account for some 99% of the dry weight of all living organisms[1]. When conditions are right and these chemicals are abundant, it is easy to construct simple organic molecules[2], including amino acids, the building blocks of proteins, the basic structural materials of all organisms, and nucleotides (the molecules from which the genetic code is constructed). This metamorphosis or catalytic reaction is unlikely to occur in today’s atmosphere where there is too much oxygen with its capacity to generate heat (combustion) when it is chemically reactive.
The Miller Urey experiment[3]
But in an oxygen-free atmosphere that allowed simple organic molecules to survive long enough in the complex, slow-motion chemistry for chemical evolution to take place, things may have been different. In 1952, two American scientists, graduate student Stanley Miller and his Ph D supervisor the Nobel Prize winning chemist Harold Urey, created a model of the early atmosphere by filling a retort (a large closed container) with methane, water and ammonia. They warmed the mixture and provided shots of free energy similar to lightning. After seven days, a dark red sludge appeared in their retort, containing several of the most important amino acids, particularly glycine and alanine - simple organic molecules containing about 20 to 40 atoms that link up in different patterns to form the proteins that dominate the chemistry and the structure of all living organisms. Subsequent experiments have revealed that all 20 amino acids can be created in this way. Here we have the basis for the construction of proteins, the fundamental building blocks of life.
The Miller-Urey experiment also created in smaller quantities other important organic molecules including sugars and the main components of nucleotides. Although the earth’s early atmosphere may have been somewhat different to that which Miller and Urey supposed, the Miller-Urey experiment showed that the creation of the basic building blocks of life may not have been too difficult on the early earth. Amino acids have since been identified in dust clouds in interstellar space, and subsequent observations tend to suggest that the basic chemicals from which life is formed were abundant in the early solar system. The question then is to explain how these simple organic materials were assembled into the vast and complex structures necessary for life to exist, that is how proteins, tens of thousands of them, each fulfilling an allotted task: respiring, eating, reproducing, each having to be arranged in a precise sequence came to be formed from amino acids.
A “warm little pond” or archaebacteria?[4]
There are in fact different views as to where life first began. It seems unlikely that life could have originated in space where both energy and raw materials are in short supply thereby ensuring that chemical processes are very slow. Besides, many of the chemical reactions vital to life seem to require water in liquid form which cannot be found in space.
Darwin suggested that life might have begun “in some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity etc”[5], and ever since biologists have tried to figure out how natural chemical and physical processes could have assembled these chemicals into simple organisms somewhere in the seas or in the seashores of the early earth. Water plays a crucial role. Amino acids and nucleotides once formed could have been protected to some extent as long as they stayed in water.
A quite plausible speculation is that after millions of years, the seas of the early earth may have been full of simple organic chemicals, which could have then joined together into more complex organisms. However they were created, early organic molecules could have formed a weak organic “soup” of simple proteins, nucleic acids and other organic molecules. So along the shores and in the warm seas of the earth 4 billion years ago there may have already existed organic molecules that duplicated many of the activities of life, forming into cell-like globules with an outer skin, absorbing or “eating” other chemicals and then splitting into separate globules as if reproducing. All of these theories are quite plausible, but at this stage none can explain all the steps leading from nonlife to life.
There is also recent evidence to suggest that the earliest living organisms appeared before 3.8 billion years ago when the earth’s surface was still being bombarded regularly by extraterrestrial material. These forms of bacteria are called archaebacteria that evolved well below the surface of the earth, “feeding” on chemical energy produced within the earth itself from iron, sulphur, hydrogen and other chemicals buried in rocks or dissolved in seawater. In the 1990s, archaebacteria were found living inside rocks more than a kilometre below the earth’s surface; and they have also been found living at temperatures well above boiling point in volcanic vents on the seafloor, as well as in porous rocks below the seabed. In 2000, the existence of these hydrothermal vents was confirmed by the discovery of a network of active underwater chimneys caused by volcanic activity below the ocean floor in an area halfway between Europe and North America[6]. Archaebacteria have also been found living in huge quantities at the earth’s surface.
Archaebacteria may offer a better model than most other modern organisms for the earliest forms of life on earth. They live in environments that have changed little since the Hadean era, and their ability to live well below the surface means that they would have been less affected by the meteoric impacts that were common early in the earth’s history and may have periodically wiped out life near the surface. If these arguments are right, then life may have first appeared from beneath the surface of the earth and its seas, before producing new species that could survive in the cooler environments near or at the surface.
Fostering this line of research, scientists at University College London recently (2017) claim to have found the remnants of structures made by micro-organisms that are said to be the oldest fossils on Earth, dating to to between 3.8 and 4.3 billion years old. [7] These so-called "putative microfossils" were found in quartz layers within the Nuvvaugittuq suprastructural belt in Quebec, Canada, thought to be one of the world’s oldest rock formations. The authors say the fossils are not remnants of the single-celled organisms, but rather the tubes and filaments they formed as they fed on hydrogen sulphide and iron around hot vents on the ocean floors in conditions probably similar to where life on Earth began. If correct, the discovery would support the idea that cellular life emerged from hot, sea-floor vents shortly after planet Earth formed, implying that the steps from the molecular evolution to the RNA world, lipids, and peptides to membrane-bound cellular life with DNA may have happened within only a few million years after the earth formed.
However, the significance of the discovery is heavily disputed by others who assert that it is not proved the structures are of biological origin, and that the rocks in which they have been found are unusually badly preserved and strongly recrystalised and altered, having been cooked deep in the crust at more than 500 degrees, destroying their original structures. The study’s authors respond: “one, the structures were formed in a submarine environment; two, there are thermal springs; and three, we have these tubular features. What else could they be?”
Another backing the research has compared the Canadian findings with established fossilised stromatolite structures in the 1.8 billion-year-old Earaheedy structures and the 3.5 billion-year-old Pilbara structures in Western Australia, and found that they have exactly the same structure.
[1] Christian, Maps of Time, 95-96.
[2] The scientific meaning of ‘organic’ refers to a class of molecules that contain carbon, especially those involved in the chemistry of life.
[3] The Miller-Urey experiment is fully documented and its mechanics explained in Mesler and Cleaves, A brief History of Creation, WW Norton, New York, 2016, Chapter 9 "A laboratory earth", pp 172 ff. Urey graciously allowed his student to take prime position in the nomenclature publicising the experiment.
[4] Source for this material: Christian, Maps of Time, 93-99.
[5] Cited in Paul Davies, The Fifth Miracle: The Search for the Origin of Life, Hammondsworth, Penguin, 1999, p 54.
[6] Recounted in Mesler and Cleaves, op cit, Preface, xi-xii.
[7] See www.smh.com.au/technology/sci-tech/controversy-breaks-out-over-claims-that-worlds-oldest-fossils-have-been-found-20170301-gunu0j.html where the original article in Nature, accepted 9 January 2017, is referenced.
Another theory on life’s origins
Hydrothermal vents at the bottom of the Pacific Ocean pumping out minerals such as iron and sulphur and gases such as methane and hydrogen sulphide are one thing. Volcanic hot springs and pools on land, about 3.5 billion years ago are quite another, yet this forms the basis of an evocative theory about where life got started by two geologists and a biomolecular engineer [1], who theorise that land pools that repeatedly dry out and then get wet again could be a much better places for life to get started than hydrothermal vents deep within the ocean where the molecules might spread out too quickly to interact and form cell membranes and primitive metabolisms.
Land pools, the product of hot springs and geysers, “have heat to catalyse reactions, dry spells in which complex molecules called polymers can be formed from simpler units, wet spells that float these polymers around and further drying periods that maroon them in tiny cavities where they can interact and even become concentrated in compartments of fatty acids – the prototypes of cell membranes”.[2] Shades of Darwin’s “warm little ponds!
The necessary ingredients for kick-starting the conditions necessary for life to begin in this way encompass seven steps beginning with chemical synthesis thereafter moving through cycles of increasing complexity. First we have synthesis – many of life’s basis building blocks, such as amino acids, form in space and fall to earth. These accumulate in hydrothermal pools and are then concentrated within tiny vesicles called lipids. Their close proximity plus heat and chemical energy form the spring system that links them together to form more complex molecular chains. The pools then go through repeated cycles of wet, dry and moist gels. The primordial communal phase in which surviving polymers crowd together in a moist gel, a so-called “progenote”, facilitating the mixing together and exchange of polymers and nutrient molecules across the barriers of lipid membranes, is critical.[3] In this process, the polymers used to carry information such as chains of nucleic acids are synthesised; protocells form and then pack together and exchange sets of polymers, selecting those that enhance survival during repetitive cycles.
The best adapted protocells spread to other pools or streams, moving by wind and water. Some develop the ability to use carbon dioxide for photosynthesis. One photocell eventually develops the machinery that enables it to divide into daughter cells. Some of these early microbes are pushed into saltwater estuaries beyond their native saltwater ponds. “Sea storms and tugging tides” enable them to cement themselves together, piling themselves up into stacks called stromatolites. After billions of years, these organisms evolve into complex multicellular plants and animals.[4]
The Dresser Formation in the Pilbara region of Western Australia is an ideal “origin analogue site” [5] for all this to have occurred. It was once filled with thermal hot springs in a geothermal system, and then contained many of the key ingredients and organisational structures required for the origin of life: circulating hydrothermal fluids, boron (a crucial ingredient in the synthesis of ribose necessary for nucleic acids such as RNA, a variety of other minerals and clays functioning as catalysts for creating complex organic molecules, and its immense variety in its ecosystem with wet and dry cycles occurring multiple times each day, variable pool chemistries and the ability to exchange components as geysers splash their contents around and an interconnected fluid filled subterranean network.[6]
The deep-sea hydrothermal vent hypothesis still has its adherents, but the land-based hot springs pool model is a compelling rival, demanding worthy consideration in its own right. [7]
[1] Martin J Kranendonk, David Deamer and Tara Djokic, “Life Springs”, Scientific American, August 2017, 28-35. What follows is an edited version of their article.
[2] Ibid, 30-31.
[3] The ideas and experiments of Bruce Damer, a computer scientist, are noted at ibid, 30)
[4] Ibid, 32-3.
[5] Ibid 34.
[6] Ibid, 32, 34-5.
[7] Ibid, 35.
Hydrothermal vents at the bottom of the Pacific Ocean pumping out minerals such as iron and sulphur and gases such as methane and hydrogen sulphide are one thing. Volcanic hot springs and pools on land, about 3.5 billion years ago are quite another, yet this forms the basis of an evocative theory about where life got started by two geologists and a biomolecular engineer [1], who theorise that land pools that repeatedly dry out and then get wet again could be a much better places for life to get started than hydrothermal vents deep within the ocean where the molecules might spread out too quickly to interact and form cell membranes and primitive metabolisms.
Land pools, the product of hot springs and geysers, “have heat to catalyse reactions, dry spells in which complex molecules called polymers can be formed from simpler units, wet spells that float these polymers around and further drying periods that maroon them in tiny cavities where they can interact and even become concentrated in compartments of fatty acids – the prototypes of cell membranes”.[2] Shades of Darwin’s “warm little ponds!
The necessary ingredients for kick-starting the conditions necessary for life to begin in this way encompass seven steps beginning with chemical synthesis thereafter moving through cycles of increasing complexity. First we have synthesis – many of life’s basis building blocks, such as amino acids, form in space and fall to earth. These accumulate in hydrothermal pools and are then concentrated within tiny vesicles called lipids. Their close proximity plus heat and chemical energy form the spring system that links them together to form more complex molecular chains. The pools then go through repeated cycles of wet, dry and moist gels. The primordial communal phase in which surviving polymers crowd together in a moist gel, a so-called “progenote”, facilitating the mixing together and exchange of polymers and nutrient molecules across the barriers of lipid membranes, is critical.[3] In this process, the polymers used to carry information such as chains of nucleic acids are synthesised; protocells form and then pack together and exchange sets of polymers, selecting those that enhance survival during repetitive cycles.
The best adapted protocells spread to other pools or streams, moving by wind and water. Some develop the ability to use carbon dioxide for photosynthesis. One photocell eventually develops the machinery that enables it to divide into daughter cells. Some of these early microbes are pushed into saltwater estuaries beyond their native saltwater ponds. “Sea storms and tugging tides” enable them to cement themselves together, piling themselves up into stacks called stromatolites. After billions of years, these organisms evolve into complex multicellular plants and animals.[4]
The Dresser Formation in the Pilbara region of Western Australia is an ideal “origin analogue site” [5] for all this to have occurred. It was once filled with thermal hot springs in a geothermal system, and then contained many of the key ingredients and organisational structures required for the origin of life: circulating hydrothermal fluids, boron (a crucial ingredient in the synthesis of ribose necessary for nucleic acids such as RNA, a variety of other minerals and clays functioning as catalysts for creating complex organic molecules, and its immense variety in its ecosystem with wet and dry cycles occurring multiple times each day, variable pool chemistries and the ability to exchange components as geysers splash their contents around and an interconnected fluid filled subterranean network.[6]
The deep-sea hydrothermal vent hypothesis still has its adherents, but the land-based hot springs pool model is a compelling rival, demanding worthy consideration in its own right. [7]
[1] Martin J Kranendonk, David Deamer and Tara Djokic, “Life Springs”, Scientific American, August 2017, 28-35. What follows is an edited version of their article.
[2] Ibid, 30-31.
[3] The ideas and experiments of Bruce Damer, a computer scientist, are noted at ibid, 30)
[4] Ibid, 32-3.
[5] Ibid 34.
[6] Ibid, 32, 34-5.
[7] Ibid, 35.