Are the life forms on earth still developing?
Who we are and where we come from, people have been asking since time immemorial. We used to look for answers in religion. Today we know that the earth and everything that can be found on it is made of stardust. But the big riddle still remains unsolved: How did life develop from a pile of dead matter? And when?
In search of answers to these questions, scientists have followed the path of evolution back in time, to the earliest history of our planet. And today they know exactly what that form of earthly life must have looked like from which all living beings today descended.
"Luca" (Last Universal Common Ancestor) - this is the name of this "last common ancestor". It must have existed about 3.6 billion years ago, a genetic analysis of organisms living today has shown. Luca consisted of a single cell and liked it hot - preferably around 100 degrees Celsius.
His description sounds like a simple organism, but the impression is deceptive: Luca was already a highly complex living being with a few hundred genes. There must have been simpler forms before him. But how they looked, how and why they appeared on the young planet Earth, is still largely in the dark.
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However, researchers have developed some theories about it. Their search has led them into the depths of the primeval ocean, to pools on the barren, rocky beach of the first land masses and into the depths of space, to distant, perhaps long-burnt solar systems.
Starting point: a hell four billion years ago
The formation of our earth begins about five to 4.6 billion years ago: A cloud of dust and gas condenses to form the sun and the planets - including our earth. Over the course of millions of years, the earth's surface solidifies into a stony crust, the planet envelops itself in a hot atmosphere of methane, ammonia and other poisonous gases that slowly cool down. Water vapor condenses to form the primeval sea.
Light and darkness, moisture and dryness, heat and cold - the constantly changing conditions fuel chemical reactions. At that time, complex molecules must have formed from simple carbon compounds, from hydrogen, nitrogen, sulfur and other substances - which ultimately came to life. And at a speed that still puzzles scientists.
The earliest known fossils to suggest the existence of life have recently been discovered in the Nuvvuagittuq greenstone belt in northern Canada on Hudson Bay. They are tubes and filament structures that are similar in structure to bacterial colonies. The age of the rock is estimated to be 3.77 to 4.3 billion years. This would mean that the life forms here would have been at least 700 million years older than the bacteria that presumably left behind the stromatolites that were discovered in Greenland in 2015.
In a zirconium crystal from Western Australia, researchers at the University of California have discovered evidence of organisms that may even have lived 4.1 billion years ago. The minerals contain a ratio of carbon isotopes that is commonly found in living things.
The findings suggest that life already existed soon after the planet's surface froze: the "infernal" Hadaikum, named after the Greek underworld Hades, is drawing to a close. The following age of the Archean is heralded by the "Great Bombardment". Meteorites hit the earth in huge numbers. And it is precisely under these extreme conditions that the first basic forms of life suddenly appear.
For the development of the first life forms, therefore, only a few hundred million years were necessary - a short time in geological terms. By contrast, it takes one to two billion years, a much longer time, until multicellular organisms such as green algae appear.
Aliens as ancestors?
Some researchers therefore suspect that there was not enough time for the creation of the first life on earth. Your hypothesis that Panspermia, states that building blocks of life or even simple forms of organisms from much older celestial bodies came to earth somewhere in space via asteroids or comets.
In fact, organic molecules have been identified on comets and asteroids, and even in clouds of cosmic gas and dust, that are considered to be the building blocks of life - including forms as complex as amino acids. Nonetheless, panspermia is extremely controversial. And it ultimately leaves the question open as to how life could have originated elsewhere. This puzzle is only shifted to another time and place.
Chemical kits in seething pools
Most researchers therefore continue to search for the origin of life on the young earth. One of the most important questions is whether the conditions back then were even suitable for creating the necessary building blocks.
Stanley Miller and Harold Urey wanted to answer this question at the University of Chicago in 1952. With an experiment that is still famous today: Miller created a "primordial atmosphere" of water vapor, ammonium, methane and hydrogen in a glass flask and created electrical flashes in it. Amino acids and sugar molecules were formed within a few days. The "primordial soup" experiment showed that the step from the inorganic to the organic world was actually possible in prehistoric times with simple ingredients.
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