The Earth formed about 4.6 billion years ago. In the hundreds of millions of years that followed, our planet was completely uninhabitable. The Earth's surface was extremely hot and was bombarded by comets and asteroids. However, the first life forms were a reality a billion years later. how is that possible? There are various scientific theories about this matter.
1. He was struck by lightning
In the 1950s, chemist and Nobel Prize winner Harold Urey observed that most of the atmosphere in the solar system consisted primarily of nitrogen and methane. Yuri saw that the Earth once had a similar atmosphere. Only with the arrival of new life was more oxygen added.
His student Stanley Miller was tasked with developing an experiment to test Urey's theory. In the now-famous Miller-Urey experiment, hot water was mixed with molecules of hydrogen, methane, and ammonia. This mixture was then subjected to electrical discharges – designed to mimic lightning on early Earth – and then cooled until it condensed and returned to water as rain.
The results were amazing. Within a week, the experimental ocean turned reddish-brown because the molecules formed complex amino acids, the building blocks of life. Subsequent research showed that our planet's early atmosphere was little different from that seen in Miller's experiment. However, the results of his research remain important to this day.
2. Taken from blue
According to another theory, life came to us from space. We now know that amino acids – and some other essential elements important for life, such as carbon and water – are frequently found on meteorites and comets. It is therefore possible that the meteorite impact increased the presence of amino acids on early Earth.
According to chemist and Nobel Prize laureate Jack Szostak from the University of Chicago (USA), asteroids and comets were almost certainly of great importance for the origin of life.
In the early atmosphere, which was dominated by nitrogen and carbon dioxide, the chemical reactions in Miller's experiment may not have started so quickly. But Szostak shows that a meteorite impact could have temporarily supplied the atmosphere with hydrogen and methane. At that very moment, life might have been briefly given a chance.
3. Stagnant water
Another hypothesis is that life arose in the depths of the ocean, around hydrothermal vents on the sea floor. But according to Szostak, this theory is outdated.
“If you look at what it takes to convert simple starting materials into nucleotides and RNA, you're dealing with a lot of chemical reactions that require ultraviolet radiation from the sun,” he explains. “The sun is by far our most important source of energy, and this was also the case on early Earth. If you knew you needed that energy, you wouldn't be able to find the answer at the bottom of the sea.
Szostak says it is likely that life originated on Earth. “In shallow ponds or where there are hot springs: the type of environment that often occurs around impact sites or in volcanic areas.”
Moreover, it cannot be excluded that life found its way in different locations and in different ways at the same time. What is certain however: one form of life will eventually evolve into everything we know today.
