Theories about the origin of life on Earth

Life on Earth is believed to have originated about 4 billion years ago, but until now scientists still have no exact evidence of the origin that promoted life to "sprout" on this planet.

Earth formed about 4.6 billion years ago and for several hundred million years afterward, because the planet's surface was so hot and was constantly impacted by comets and asteroids, no life form could form. .

 The origin of life on Earth is still a question without an exact answer. (Source: NASA Ames Research Center).

Yet, about a billion years later, life not only exists but has left evidence of its presence in the form of fossilized microbial mats.

So what happened during that time to cause life to arise? Scientists have proposed a number of hypotheses about how life emerged amid such harsh conditions.

1. Life originated from lightning

Jim Cleaves, chair of the chemistry department at Howard University and co-author of 'A Brief History of Creation: Science and the Search for the Origins of Life,' notes that atmospheric conditions at the time life emerged were very different compared to current conditions.

In the 1950s, Nobel Prize-winning chemist Harold Urey noted that most of the solar system's atmosphere is dominated by nitrogen and methane, he explains.

Urey believes that the early Earth also had this type of atmosphere and this was the premise for creating organic compounds, which could be the origin of life.

Cleaves tasked research student Stanley Miller with developing an experiment to test this theory, creating a closed system in which water is heated and combined with hydrogen, methane and ammonia molecules. .

The chemical reaction is then activated by electricity (representing lightning) and cooled so that the mixture condenses and falls back, like rain.

The results were astonishing. Within a week , the experimental 'ocean' had turned a reddish-brown color as molecules joined together to create amino acids, the foundation of life.

 The origin of life on Earth can originate from many causes. (Source: National Geographic).

Subsequent research has shown that Earth's early atmosphere was slightly different from the experiment conducted by Miller and that the main components were nitrogen and carbon dioxide, with hydrogen and methane present in smaller quantities.

However, the principles implemented by Miller in the experiment are generally sound, with lightning combining with meteorite impacts and ultraviolet radiation from the Sun to produce hydrogen cyanide, which then reacts. with iron brought up by water from the Earth's crust to form chemicals such as sugar.

These chemicals can combine to create strands of ribonucleic acid, or RNA, a key component of life that helps store information; At some point, RNA molecules began to copy themselves and life became possible.

2. Life was originally brought to Earth from outer space

According to another theory, amino acids, as well as some other important components of life such as carbon and water, may have been brought to early Earth from outer space.

Comets and meteorites have been found to contain some organic molecules, and their impact with Earth may have increased the availability of amino acids.

According to Nobel Prize-winning chemist Jack Szostak of the University of Chicago, asteroid and comet impacts were almost certainly indispensable.

He noted that an initial atmosphere containing nitrogen and carbon dioxide would be less conducive to some of the chemical reactions in Miller's combination of hydrogen, methane, and ammonia; however, a moderate-scale impact could temporarily produce hydrogen and methane in the atmosphere, allowing for a temporary change in compound-forming conditions suitable for life.

3. Life is hidden in the oceans on Earth

Another theory is that life may have begun deep in the ocean, around undersea hydrothermal vents, but Szostak rejects this theory.

According to him, many chemical reactions to create nucleotides and RNA - factors for the formation of life - require a catalyst from ultraviolet radiation from the Sun.

Therefore, life cannot originate from the deep ocean - where sunlight cannot penetrate. However, it is almost certain that life began in water.

Szostak argues that it is more likely that life formed 'on the surface, perhaps in shallow ponds or hot springs: the type of environment that is very common around meteorite impact sites or volcanic regions. ".

 Until now, Earth is a rare planet where life appears in the universe. (Source: Earth)

It's possible that all life on Earth today shares a common ancestor, an unknown form of microbial life that has probably long since disappeared, but life itself may have begun at various times. through different pathways, destroyed by comet impacts or simply unable to adapt, until the RNA-based molecule that is the ancestor of us all was formed.

Early life remains mysterious

If that really happens - if life begins and dies many times before it takes root - then we will almost certainly never know what might have happened, because hypothetical life forms thus leaving no trace of their existence.

Life could have followed a very different evolutionary path, one that would not have led to the formation of trees, dinosaurs or humans.

This scientist commented: 'Life is such a complex system that the simplest bacteria or virus has thousands of parts. It is difficult to understand how such a complex process could appear suddenly. And the answer is no. It happens step by step '.