Among the theories about the origin of life on Earth , the panspermia hypothesis occupies a special place. This concept is quite exotic. It says that life on our planet has a cosmic nature. Its embryos were brought to Earth from another celestial body (such as a comet) or even an alien ship. Panspermia is an idea whose appearance is associated with the name of the ancient thinker Aristotle. A supporter of the theory was living in the XVII-XVIII centuries. Gottfried Leibniz. However, it was only at the beginning of the 20th century that panspermia ceased to be only philosophical reasoning and acquired various scientific justifications and models.
Radiation panspermia
In 1908, the Swedish scientist Svante Arrhenius put forward a concept called the theory of radiation panspermia. The physicist suggested that the first bacterial spores appeared on Earth after migration from the far corners of the universe. The reason for this "relocation" Arrhenius considered the pressure of sunlight (or the light of another large star).
This hypothesis of panspermia has many supporters. These scientists call Venus the most probable ancestral home of life, from where heat-resistant bacteria could get to the Earth at the moment when two planets were at the shortest distance from each other.
Light pressure factor
The existence of light pressure even before Arrhenius was experimentally proved by the Russian physicist Peter Lebedev. In addition, he analyzed the effect of this phenomenon on spores of lycopodia (plauna). In this regard, in the XIX century, the theory of panspermia was supported by Ferdinand Kohn, Justus Liebig, Hermann Helmholtz and other eminent scientists of his time.
However, in the XX century, this concept was criticized by a variety of researchers. Among them were Joseph Shklovsky, Karl Sagan and many others. Opponents refute the evidence of panspermia on the grounds that long-term space migration cannot do without receiving a dose of radiation that is harmful to spores.
Space guests
In a generalized form, the theory of panspermia states that the vacuum in which bacteria can remain during a long journey should not interfere with their vital functions, since at extremely low temperatures the cells are in a frozen state (suspended animation). Theoretically, such guests could "wake up" immediately after their arrival on Earth, where, thanks to a combination of circumstances, comfortable climatic conditions have developed.
The above ideas have been refuted by modern scholars. Studies in laboratories have shown that in a cosmic vacuum, a cell simply explodes due to the ultrafast evaporation of its own water. As a result of this process, microorganisms are destroyed by excessive internal pressure. This is the main argument of experts who believe that radiation panspermia is a myth.
Lithopanspermia
Another type of panspermia is lithopanspermia. The founder of the theory, Melvin Calvin, believed that the rudiments of life could fall on our planet with a meteorite. Until now, this concept of panspermia has not been supported by the corresponding texture.
Tiny remnants of meteorites burnt in the atmosphere really do fall to Earth. Such materials have been studied by a variety of scientists, but no one has yet managed to detect traces of life on them or in them. Scientists have recorded only some biological substances (for example, fatty acids and amino acids).
Comet concept
Another hypothesis about the emergence of life on Earth associated with panspermia is the so-called comet theory set forth in the book “The Cloud of Life” by Fred Hoyle. In this publication, the author tried to prove the validity of his concept on the example of global viral epidemics (including the example of Spaniards from the beginning of the 20th century). Hoyle suggested that such massive diseases (pandemics) can be explained by their cometary origin. In the same way as viruses, life could have come to Earth, the author claimed.
Opponents of the theory of the cometary origin of bacteria have their own arguments. Most virologists agree that, for example, the influenza epidemic in Hong Kong in 1968-1969. it is much more logically explained by the transmission of infection from person to person and its evolution in the fight against the immune system, than by the idea of its cosmic roots. In addition, lithopansermia is a hypothesis that cannot explain how a meteorite with bacteria got into the solar system from another star system, where there may be signs of life.
Directional panspermia
In the 1970s Another bold theory of the origin of life on Earth appeared in the scientific community - directed panspermia. This hypothesis would not exist if it were not for the then popularity of the topic of an alien mind. According to the directed panspermia, the first embryos of life appeared on Earth by the will of a certain civilization that exists somewhere in the depths of space. Perhaps the spores and bacteria were sent on a special apparatus, and all this was done to create a colony or conduct a scientific experiment.
Supporters of the idea of directed panspermia remind us that all terrestrial organisms have rare metals for our planet, including molybdenum, in their structure. Another argument is the nature of the genetic code. The origins of this phenomenon are still not fully understood. Because of the many white spots, the most incredible assumptions appear, in particular the hypothesis of directed panspermia. Its apologists believe that all terrestrial organisms descended from a common ancestor (microorganism), which appeared here thanks to an alien civilization. Meanwhile, there is still no clear evidence about the existence of aliens and their visits to Earth.
Space dust
Another panspermic hypothesis comes down to the assumption that the Earth was formed from cosmic dust, which already had the embryos of life. In this case, bacteria could only survive while maintaining a stable temperature on the new planet. However, studies by scientists have shown: in the early stages of its existence, the Earth was a hot ball that continued to cool for many millions of years.
Nevertheless, cosmic dust as a carrier of life could get to our planet much later. This is another hypothesis that panspermia offers. In short, these assumptions are untenable in the 1970s. proved including the Soviet scientist Lev Mukhin. Any complex organic compounds, before appearing on Earth, must overcome the dense layers of the atmosphere, where they burn together with meteorites and other space objects.
Live rainfall
New disputes about the cosmic nature of earthly life began in 2001, when a unique red rain fell in the Indian state of Kerala. The exclusivity of this natural phenomenon was not only in the unexpected color of precipitation. Eyewitnesses to the rain reported that before the rain they witnessed an unusual thunderstorm and powerful flashes of light.
The phenomenon of red rain has attracted the attention of scientists and amateurs from around the world. Further studies showed that particles that were suspended in water became the real cause of the unnatural color. The culprits of the sensation were disputes. For proponents of panspermia, this fact was another argument in favor of the concept of the cosmic sources of earthly life.
Could billions of years ago the first such rain from the spores that had never been on the planet before passed over the Earth? Most experts interpreted the events in India differently. Scientists have found that the spores that fell with the red rain belonged to epiphytes - a common plant species that grows everywhere in this part of the world. Thus, precipitation was only an episode of the cycle of organic substances in nature. Nevertheless, the red rain episode in Kerala demonstrated how, hypothetically, the population of the Earth could have happened.
Search continues
To date, no one has been able to detect signs of life outside the Earth (including in meteorite matter that hit the third planet of the solar system from space). Sensational information about such finds periodically appears in the media, but in reality it turns out to be an incorrect interpretation of facts or intentional lies. Inorganic compounds like bacterial are often taken as organisms. In addition, getting to Earth, cosmic matter is “polluted” by earthly life, which further confuses observers.
All these arguments show that panspermia is a dubious hypothesis that has no evidence base. However, scientific skepticism does not prevent a significant number of enthusiasts from continuing to search for arguments supporting such theories.