The "universal germ theory" on the origin of life means that life comes from the universe. One of the most favorable evidences for this hypothesis is that life on earth originated from the common ancestor "Luca" (abbreviated as Luca) about 3.7 billion years ago, which was only hundreds of millions of years later than the formation of the solar system. How did a large number of complex molecules related to the formation of life form primitive cells from scratch in just a few hundred million years?
A very reasonable guess is that the organic molecules required for life and even life itself follow countless comets and asteroids to spread around in space. The life on earth comes from the "extraterrestrial visitors" who hit the earth 4billion years ago. As early as the 19th century, some people imagined that "microbial spores with special shells were floating in space", but then the scientific community found that the cosmic radiation in space was enough to kill spores, and the early "theory of cosmic germ" disappeared.
However, since the 1990s, scientists from all over the world have found evidence of the existence of organic matter in space, which has revived the idea that life originated from space. According to the technical times, scientists' analysis and Research on the Murchison meteorite sample in Australia found that it contains a large number of relatively complex organic molecules, including amino acids that can synthesize proteins and even more complex polypeptides. Scientists have found similar organic molecules in other meteorites.
In addition, with the help of advanced detection equipment, astronomers have proved that there are a wide range of organic matter in the universe. For example, according to the paper published in the British journal Nature astronomy in 2021, Spanish astronomers found the spectrum of ethanolamine, an important molecule constituting the biological cell membrane, in the cold molecular cloud near the center of the Milky Way galaxy. Researchers believe that the collision between a large amount of gas and dust is enough to produce complex organic molecules such as ethanolamine. When meteorites hit the earth, they may transfer a large amount of ethanolamine from space to the earth, thus providing the basis for the birth of early life on earth. "It also shows that the possibility of life being born elsewhere may be greater than we previously thought."
Therefore, before Japan obtained samples from the "Dragon Palace" asteroid, scientists had confirmed that there was indeed organic matter outside the earth, but they did not get direct evidence. In 2018, a paper from Massachusetts Institute of technology even speculated that amino acids, nucleotides and other key molecules constituting life had appeared as early as 168million years after the big bang, "they were born 8billion-9billion years earlier than life on earth".
According to the discovery channel of the United States, the early Earth encountered a large number of asteroids and comets during the "late heavy bombing period" between 4.1 billion and 3.8 billion years ago. They not only brought in a large number of life-related organic substances, but also the violent impact itself can quickly promote the transformation of organic molecules.
In addition, recent research by the European Space Agency has proved that the water bear can survive for more than 10 days in the extreme environment of space. The tenacious vitality of this microorganism reminds people of whether the primitive life on earth really came directly from space? However, the "theory of cosmic germ seeds" still cannot explain how the organic matter in the universe evolved into life.