By the time when Arrhenius proposed this theory he did not really have any argument supporting it.
Now, there exists only one argument supporting it.
The last common ancestor of all cellular living beings that exist on Earth was already a quite complex bacterium.
There is no doubt that it was the product of an already very long evolution process. For instance the genetic code that is used, with very small variations, by all living beings on Earth must have succeeded a long sequence of simpler genetic codes, with an increase of each step of the complexity of the code and of the number of amino-acids that could be encoded.
The oldest versions of the genetic code are likely to have encoded only between 4 and 6 amino-acids instead of 20 to 22, like today.
Based on the probable bacterial fossils that are quite old, it seems like the time from the apparition of life on Earth might have been too short to explain the complexity of the last common ancestor of the present living beings.
So this supports the idea that life could have appeared elsewhere, but then some bacteria and viruses have reached Earth and then they have evolved further.
Even in the unlikely case when this supposition were true, this changes nothing about the appearance of life, it just pushes it to another place that must have had a pretty much identical environment with the primitive Earth, in order to make possible the apparition of life.
Life cannot appear without a continuous source of energy for it. There exists only one known source of energy that can be used by the simplest possible forms of life, and this source of energy is the internal heat of a relatively big planet or of a very large satellite, like Titan or the big satellites of Jupiter.
The internal planetary heat can provide the energy for sustaining life indirectly, through volcans or hydrothermal vents. When volcanic rocks are ejected from the hotter inside of a planet, they consist of chemical substances that are no longer in chemical equilibrium at the lower temperature of the planet surface. This causes chemical reactions that result in substances like free dihydrogen, which, in the presence of catalysts, make possible the continuous synthesis of the complex organic molecules required for life.
As far as we know, Earth had ideal conditions for the appearance of life right here. It did not need to be colonized by bacterial spores coming for elsewhere.
The only reason why there is a very small chance for Arrhenius to have been right, is that the bigger Earth has remained very hot for a longer time than smaller planets like Mars, delaying the apparition of life here.
So it might have been possible for a place like Mars to have conditions suitable for the appearance of life before Earth. Life could have been appeared there and it could have been transported by one of the many meteorites that are known to have come from Mars to Earth as a consequence of big impacts.
Then Mars has lost most of its atmosphere and it became very cold, so if it ever had life, that could have disappeared.
For now this scenario that would match the theory of Arrhenius cannot be considered as 100% excluded, but in any case it is far-fetched and it does not change anything about the evolution of the living beings known on Earth, even if the initial part of that evolution could have taken place elsewhere, but in conditions not really different from those of the primitive Earth.
It is indeed a cool idea, but it is likely completely wrong.
For life, it is not enough for the ambient temperature at the surface of a planet to be acceptable.
For life to appear, it is necessary that the interior of the planet is much hotter than the surface, so that this thermal non-equilibrium will be converted into chemical non-equilibrium by volcanism.
When the universe had cooled to a habitable temperature after the Big Bang, if any celestial bodies existed they were in thermal equilibrium, so they could not provide any energy for the appearance of life.
The internal heat of a planet normally has 2 sources, the radioactive decay of heavy elements that have been produced only in catastrophic events that have happened late in the history of Universe, e.g. supernova explosions or neutron star impacts, and the residual heat produced from collisions with other planets.
For satellites close to big planets or for planets close to stars there may be also heat produced by tidal deformations.
Such sources of heat are unlikely to have existed in the early Universe, and even supposing that collisions could have existed, in that case the environment with a life-enabling temperature would not have been correlated with the epoch when the entire Universe had a temperature that now is suitable for life.
Moreover life cannot appear without chemical elements up to the iron-cobalt-nickel group, which are the chemical catalysts on which life depends as much as on the structural elements HCNOS.
The iron group elements are generated only late in the lifetime of a star, so life can appear only in celestial bodies that recycle matter from explosions of the first generation stars, billions of years after the Big Bang and long after the Universe had cooled.
The discussion on the origin of life often focuses on where and how it began, but I believe it is just as important to consider the fundamental role of life in the universe. What purpose does life serve in a cosmic context? What physical effects does it have on planetary systems? Rather than analyzing the current state of life, we may gain deeper insights by working backward from the necessary conditions for life’s existence.
One possible hypothesis is that life functions as a thermal regulation system. Just as in the story of Goldilocks, where conditions must be "just right" for life to emerge, the presence of life itself may play a role in maintaining this balance. If life only arises under optimal thermal conditions, then its role might include sustaining those conditions over time.
At the same time, life has evolved from single-celled to multicellular organisms, from plants to animals, continuously increasing in complexity and mobility. This suggests that life is not meant to remain confined to one place but is naturally inclined to spread, even beyond planetary boundaries. If this hypothesis holds, life inherently seeks movement and expansion —consciously or unconsciously— and has the potential to terraform multiple habitable planets.
From an entropy perspective, life plays a dual role: it disperses across space while simultaneously reducing local entropy through intelligence-driven processes. This cycle of diffusion, local convergence, and further expansion could be a fundamental aspect of life’s function. In simpler terms, life may be an entropy regulation mechanism, which makes the possibility of life existing and thriving beyond Earth highly plausible.
Much like how ancient Earth’s organisms were unaware of each other’s existence across vast distances, it is entirely possible that extraterrestrial life operates within a similarly fractal pattern, remaining beyond our current recognition.
