The Origin of Life: Is it Possible and Could It Have Happened Multiple Times?

Category Science

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The origin of life is a central question in biology. Scientists believe that life emerged from non-living molecules through a natural process called abiogenesis. Multiple lively beginnings have been suggested, and some experiments such as the Miller-Urey experiment, have shown how molecules can be naturally formed under conditions similar to early Earth. Abiogenesis could have happened more than once, leading to multiple distinct lineages of living organisms.

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From its humble origin(s), life has infected the entire planet with endless beautiful forms. The genesis of life is the oldest biological event, so old that no clear evidence was left behind other than the existence of life itself. This leaves many questions open, and one of the most tantalizing is how many times life magically emerged from non-living elements.

Has all of life on Earth evolved only once, or are different living beings cut from different cloths? The question of how difficult it is for life to emerge is interesting, not least because it can shed some light on the likelihood of finding life on other planets.

Life first emerged on Earth about four billion years ago

The origin of life is a central question in modern biology, and probably the hardest to study. This event took place four billion years ago, and it happened at a molecular level, meaning little fossil evidence remains.

Many lively beginnings have been suggested, from unsavory primordial soups to outer space. But the current scientific consensus is that life emerged from non-living molecules in a natural process called abiogenesis, most likely in the darkness of deep-sea hydrothermal vents. But if life emerged once, why not more times? .

The Miller-Urey experiment showed how simple molecules could form under natural conditions similar to early Earth

What Is Abiogenesis? .

Scientists have proposed various consecutive steps for abiogenesis. We know that Earth was rich in several chemicals, such as amino acids, a type of molecules called nucleotides or sugars, which are the building blocks of life. Laboratory experiments, such as the iconic Miller-Urey experiment, have shown how these compounds can be naturally formed under conditions similar to early Earth. Some of these compounds could also have come to Earth riding meteorites.

RNA molecules can self-replicate, making them ideal to serve as an information system in early life forms

Next, these simple molecules combined to form more complex ones, such as fats, proteins, or nucleic acids. Importantly, nucleic acids—such as double-stranded DNA or its single-stranded cousin RNA—can store the information needed to build other molecules. DNA is more stable than RNA, but in contrast, RNA can be part of chemical reactions in which a compound makes copies of itself—self-replication.

The "RNA world" hypothesis suggests that early life may have used RNA as material for both genes and replication before the emergence of DNA and proteins.

Through a process called natural selection, the most equipped molecules for replication won the primitive evolutionary race

Once an information system can make copies of itself, natural selection kicks in. Some of the new copies of these molecules (which some would call "genes") will have errors, or mutations, and some of these new mutations will improve the replication ability of the molecules. Therefore, over time, there will be more copies of these mutants than other molecules, some of which will accumulate further new mutations, making them even faster and more abundant, and so on.

The fat molecules bound the internal and external environment together, producing protocells

Eventually, these molecules probably evolved a lipid (fatty) boundary separating the internal environment of the organism from the exterior, forming protocells. Protocells could concentrate and organize better the molecules needed in biochemical reactions, providing a contained and efficient metabolism.

Life on Repeat? .

Abiogenesis could have happened more than once. Earth could have birthed self-replicating molecules several times, and maybe early life for thousands or million of years. This could explain why there are multiple distinct lineages of living organisms, some of them so different that even share some of the molecular machinery.

Life on Earth could have originated more than once, independently

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