Origin of life: from water or from space?

A stone, a crawling beetle, an artificial toy – apparently these objects are significantly different from each other. They belong to three realms of reality, which philosophers also call “layers” (Nicolai Hartmann) or “forms of movement” (Friedrich Engels) or something else – namely inanimate nature, animate nature and the human (the human, insofar as it is nature exceeds). The layers are also stages of development in the cosmos. Despite the knowledge accumulated to date, the transitions between stages still pose a mystery.

100 years ago, a theory of the origin of life on Earth that met scientific standards was presented for the first time. The Russian-Soviet biochemist Alexander Ivanovich Oparin (1894–1980) published one in his book “The Origin of Life” (in Russian) in 1924. A translation into English appeared in 1936, and one into German only in 1957. In subsequent writings, Oparin explained his theory in more detail. This is outlined here using today’s terms:

The relevant development began about four billion years ago, when the early Earth cooled enough for liquid water to remain on the surface.

The atmosphere at that time consisted of hydrogen, water vapor, methane, ammonia, carbon dioxide and other gases in smaller quantities, but did not contain any oxygen. Solar radiation, volcanism, meteorites and electrical discharges caused powerful energy flows. The Earth’s atmosphere became a large chemical reactor. Reaction products rained down onto the surface.

The chemical processes leading to living matter took place in aqueous solutions. Oparin was thinking of the “primordial ocean,” but other bodies of water can also be considered. Dissolved minerals and mineral surfaces promoted the reactions. From the given mixture of substances, first simple and then increasingly complex organic compounds emerged, and finally the building blocks of life – proteins, RNA and DNA.

At a crucial stage, small bubbles floating in the water – Oparin calls them coacervates – acted as miniature reactors and miniature depots. Organic chemistry actually knows bubbles with the properties assumed by Oparin.

Already in the pre-biological stage of the coacervates, evolution according to Darwin’s rules – shortened to natural selection – took place. Chemical evolution preceded biological evolution. To put it clearly: Nature undertook an unimaginable number of “experiments”; only a tiny fraction of them contributed to the emergence of life.

The emergence of life from inanimate matter was Oparin’s major theme. The biologist and biochemist studied and worked at Moscow University from 1912. His various functions, directorships and others, gave him enough freedom to do this. Stays abroad broadened his horizons. From 1934 Oparin was a member of the Soviet Academy of Sciences, and from 1937 a professor of biochemistry. Of the many honors, Oparin was a member of the Leopoldina since 1956 and the Academy of Sciences in Berlin since 1966.

Experimental confirmation

Oparin’s theory received delayed attention abroad; the basic features were also independently rediscovered. This is particularly true of the versatile English biologist John BS Haldane (1892–1964) and his 1929 book “The Origin of Life.” He later recognized Oparin’s priority. Confirmation also came from the American chemist Harold C. Urey (1893–1981), among other things in his 1952 book “The Planets”. Urey as the idea generator and his colleague Stanley L. Miller (1930–2007) as the practitioner carried out the famous experiment named after them in 1953, which was intended to recreate processes on the early Earth.

The experimental setup of the Miller-Urey experiment looks like this: A large glass vessel contains hydrogen, methane, ammonia, and sometimes also carbon monoxide or carbon dioxide and/or nitrogen, but no oxygen. A water circuit is connected to the reaction vessel; Water alternately evaporates and condenses. Finally, an arc in the reaction space simulates a thunderstorm. The result exceeded the experimenters’ expectations: numerous organic compounds – alkanoic acids, amino acids and much more – were ultimately found in the vessel. Experiments of the Miller-Urey type were later often repeated, varied and refined. They were always in line with the Oparin-Haldane scenario. This paradigm persists to this day; Gaps were filled and details were explored. However, opinions differ about the scene in which life came into being. The ocean, tide pools, ponds, and other locations are being considered. A particular candidate are so-called hot spots in the deep sea – cracks in the earth caused by volcanic activity from which hot gases and minerals emerge.

The discussion today is influenced by the fact that the possibility of life on other celestial bodies has become more concrete. From this point of view, it is noticeable that the living world on earth is fairly uniform. The diversity of organisms is more external; Biochemically and genetically, all earthlings are quite similar to one another. One goes so far as to assume a single “ancestor”; he has already been given a name: Luca. This stands for “last universal common ancestor”. If Luca existed, it was a bacterium or similar microbe (not an individual, but a population).

Meteorites as a bringer of life

It could have been completely different, say some researchers. Perhaps life did not originate (or not only) on Earth, but germs of life fell from space onto our planet and initiated biological evolution there. What’s more – perhaps the cosmic migration of life germs is not a singular event, but a widespread natural process called panspermia. This hypothesis is also based on facts.

Small bodies (collective term for everything from dust to boulders to asteroids and comets) travel around in our solar system, sometimes out of it, and occasionally fall on a celestial body (planet or moon). They can transport germs of life – that is, spores or organisms in a resting and waiting state, called latency. Some have been proven to survive space travel, especially when protected by surrounding material.

Meteorites sporadically knock chunks out of a celestial body, which can then reach escape velocity. For example, pieces of rock from Mars have been found on Earth. In this way, germs of life could travel from one celestial body to another.

Contrary to all expectations, organic chemical reactions can take place on small bodies in cold space. Numerous organic compounds have been detected on asteroids and comets, including many known from biochemistry.

Epidemics caused by alien germs

A prominent representative of the panspermia hypothesis was the famous Swedish physical chemist Svante Arrhenius (1859–1927). In his 1908 book The Making of the Worlds, he depicts panspermia, emphasizing radiation pressure from the sun (or another star) as a cause of movement.

The astrophysicists Fred Hoyle (1915–2001) and Chandra Wickramasighe (born 1939) become more specific; they provide a link between epidemiology and panspermia. They believe that global epidemics are repeatedly triggered by pathogens that reach Earth from space.

So-called transspermia is a weaker variant of panspermia, namely the migration of life germs between neighboring celestial bodies. Mars and Earth are serious candidates for this. Life on Earth could come from Mars. There are two reasons for this: Some researchers believe that relics of life appear relatively suddenly in Earth’s history – as far as it can be reconstructed – as if they had no predecessors on Earth. In addition, life could have emerged on Mars much earlier than on Earth. Because it cooled faster because it is significantly smaller, it then offered conditions conducive to life, especially water and an atmosphere that was denser than today.

Of course, panspermia and transspermia only postpone the basic problem; they do not explain how life originally emerged. If you rely on such an alternative, the big question is put back to the beginning.

Prof. Dr. Rainer Schimming taught mathematics at the University of Greifswald and conducted research in the fields of mathematical physics, differential geometry and mathematical biology. Since his retirement in 2010 he has turned to philosophy.