Since the spore theory was first proposed in 1908, the hypothesis that life came to Earth from outer space has been debated among scientists. Even Crick, who discovered the double helix structure of DNA, argued for it, but concrete evidence of the origin of life is still lacking. Both the theory that meteorites brought life and the hypothesis that they wiped out life on Earth are still under debate, and no conclusive answers have been found.
In 1908, Svante Arrhenius was the first to propose the spore theory, a bold hypothesis that the seeds of life from outside the Earth flew in and became the origin of life on Earth. The idea that microorganisms could travel through outer space was scientifically revolutionary at the time, but it was not accepted as a scientific theory because there was no way to verify it. Nevertheless, spore theory has been mentioned intermittently among scientists ever since as one possibility to explain the origin of life. Although the spore theory fell out of favor due to the scientific limitations and lack of technology at the time, the questions it raised about the relationship between life and the universe still captured the attention of scientists.
Later, Francis Crick, who won the Nobel Prize for discovering the double helix structure of DNA, reasserted the spore theory in his 1981 book Life Itself. Crick seriously explored the possibility that life on Earth may have originated in space, and proposed the idea that life may have spread throughout the universe rather than originating only on Earth. However, these claims were highly controversial even at the time. Even his wife said that he had become a little strange after receiving the prize. This is an example of how scientific achievements and personal fame don’t necessarily translate into confidence in a scientific hypothesis.
There is still no clear reason to believe that there is life outside of Earth. Nevertheless, some scientists are willing to accept the existence of extraterrestrial life as a fact, which is driven by human curiosity about our origins and the spirit of exploration of the universe. They claim that when astronomers detected simple organic molecules like methanol in the nebulae between stars in their spectra, this was evidence of extraterrestrial life. However, the space between stars is almost a vacuum, making it difficult for life to exist. So while this discovery does not directly prove the existence of life, it is important in that it suggests that the universe is an environment that could provide the basic building blocks for life.
Another piece of evidence supporting the possibility of extraterrestrial life is the extraction of organic molecules from meteorites. It is clear that organic molecules come to Earth from outer space in meteorites, as evidenced by the detection of a total of 74 amino acids in a fragment of a meteorite that fell in Murchison, Australia in 1969. This discovery raises the possibility that life may have originated outside of Earth, leading scientists to explore how organic molecules formed on exoplanets and how they traveled to Earth through space. These studies straddle the boundaries between cosmochemistry and biology, and are contributing to a deeper understanding of the origin of life.
On the other hand, there is also a hypothesis that meteorites actually wiped out life on Earth. In 1980, Luis Walter Alvarez proposed that a meteorite impact was responsible for the sudden extinction of dinosaurs at the end of the Mesozoic era. This hypothesis was not mere speculation, but a proposal based on scientific evidence. He noted that the K-T layer, a sedimentary layer between the Mesozoic and Cenozoic eras, is found in many parts of the world because it contains a lot of iridium. Iridium is a rare element that is almost absent from the Earth’s surface, but is relatively abundant in meteorites. Based on this, he estimated that a meteorite about 10 kilometers in diameter hit the Earth at the end of the Mesozoic Era. The resulting massive cloud of dust blocked out sunlight for decades, causing the planet’s temperature to plummet, which, he argued, led to the extinction of most life, including dinosaurs.
Through the study of fossils, scientists have realized that there have been several large-scale extinctions in Earth’s history. For example, trilobites and fusulina suddenly disappeared at the end of the Paleozoic era. There are many theories about what caused these mass extinctions, and meteorite impacts are one of them. In addition to meteorite impacts, other factors such as large volcanic eruptions and climate change have been suggested as possible contributors to the extinction events, which may have acted in combination to cause drastic changes in the Earth’s ecosystems.
Today, many scientists are willing to accept the possibility that organic matter, the source of life, came from extraterrestrial sources via meteorites, and that meteorites caused the extinction of life on Earth. However, there is no consensus on how organic matter on Earth was created. Even if organic matter did arrive from extraterrestrial sources, the specific process of how it developed into life on Earth is still unclear. For this reason, Carl Edward Sagan proposed an eclectic view that both extraterrestrial organic matter and Earth-made organic matter may have contributed to the origin of life. This view attempts to unify the various theories of the origin of life, emphasizing that the origin of life is a complex and multidimensional process, not just a single event.
Until conclusive evidence is found, there will continue to be many different hypotheses to explain the origin of life. Scientists are constantly searching for new evidence, revising existing theories, and trying to solve the mystery of the origin of life. In the process, our understanding of life and the universe is growing deeper and deeper, and one day we may have the ultimate answer to the origin of life. Until then, however, many different hypotheses will coexist, and the journey of exploring the mysteries of life and the universe will continue.
