Life on Earth emerged about 3 billion years ago. The 1st inhabitants on the planet were ancient microbes that gradually evolved into the rich diversity of living organisms that surround us.
But how exactly life arose from the primordial soup is a question that's been plaguing generations of scientists and still does not have an answer. Here some of the most likely theories for the origins of life on Earth:
It's known that electrical sparks can generate amino acids and simple sugars in an environment containing water, methane, ammonia and hydrogen. This was observed for the 1st time in the Miller–Urey experiment in 1953.
According to scientists it is proof that one lightning strike was capable of laying the foundations for life in the early days of the planet, from which molecules, cells and so on can later develop.
The only problem with this theory is the fact that Earth's primordial atmosphere was poor in hydrogen, according to scientists. Still they allow the possibility for the divine spark to have flashed among clouds formed after a volcanic eruption, ones that were abundant in methane, ammonia and hydrogen.
Another group of scientists believes that the molecules of life may have been born in the clay covering the young planet. Supporter of this theory is the scientist Alexander Graham Cairns-Smith from the University of Glasgow, according to whom the primordial clay helped organize the amino acids into a protein matrix.
He gives credit of this to the minerals in clay, which 1st organized the amino acids and then later in the process of evolution, organic molecules took over this function.
Life in the freezer
Based on other theories, life did not appear from hot thermal vents but deep under the ice. Eric Rignot from NASA believes that approximately 3 billion years ago our planet was covered with a thick ice sheet.
It was the ice that protected and preserved the 1st sparks of life, far away from the harmful ultraviolet radiation of the sun.
Deep-sea geysers on the ocean floor eject hot water, rich in minerals, and still even today stun scientists with the strange and unique underwater ecosystems that they create around them.
It's possible that billions of years ago the hydrothermal vents catalyzed a chemical reaction which led to the formation of the 1st amino acids, then from there to life as well.
This is one of the most popular theories about the origins of life on Earth. It states that life did not at all originate from our own planet but came from space, carried by debris ripped away from another planet and eventually crashing to Earth. In fact, rocky debris is ripped away from Mars all the time, some of it ultimately ending up on Earth.
Scientists allow that some of the debris might have had colonies of bacteria that had survived the journey in the vacuum of space and then crash landed on Earth's surface. Some scientists go even further and theorize that life might have been brought from the other end of the galaxy by comet.