Origin of life

It still is a challenge for scientists and philosophers to define life, since the definition must include all life we are familiar with, but at the same time not exclude life forms that might be fundamentally different from life we know on earth.

Life can be defined as:

• A network of regulatory mechanisms (negative feedbacks) inferior to the potential of expansion and reproduction (positive feedback).

• Living things that are self-organising and autopoietic (they produce and maintain without help).

• Living beings that are themodynamic systems and have an organized molecular structure.

• Things with the capacity for metabolism and motion.

• A way to hydrogenate carbon dioxide.

• Matter that can reproduce itself and evolve as survival dictates.

NASAs definition states that life is a self sustained chemical system capable of undergoing Darwinian evolution.

Yes, extraterrestrial life could be possible.

• Carbon based life: it is frequently assumed in astrobiology, that if life exists somewhere else it will also be carbon based, like earth.

• Sufficient quantities of carbon and the other major life-forming elements (Hydrogen Oxygen, Nitrogen, Phosphorus and Sulphur), along with water, may enable the formation of living organisms on other planets with a chemical make-up and temperature range similar to Earth.

• Terrestrial planets, such as Earth, are formed from "stardust" in a process that allows for the possibility of other planets having formed with compositions similar to Earth’s.

• Another possibility would be silicon based life, since silicon has many properties similar to carbon (not soluble below 1600 degrees Celsius, highly reactive with water, can’t form chemical bonds with many elements).

Terrestrial life is carbon based:

• 95% of the elements life is built on are CHNOPS

• Water is required as solvent for biochemical reactions

• Structural elements for life (ribos, DNA, RNA) are all based on carbohydrates

The habitable zone is the region around a star where conditions are just right for liquid water to exist on a planet’s surface, not too hot and not too cold.

This is important because liquid water is essential for life as we know it.

If a planet is:

• Too close to its star, it would be to hot and water would evaporate

• Too far from its star, it would be too cold and water would freeze

The Kepler Project was a NASA space mission launched in2009 to discover Earth-like planets by monotoring the brightness of stars and detecting planets through the transit method.

It revolutionized our understanding of exoplanets by identifying thousands of planets, many of them potentially habitable.

The Miller-Urey experiment aimed to recreate the atmosphere of primitive Earth to test whether it could support the formation of amino acids and other organic molecules. At that time, oxygen was not present, because it is produced by plants, which didn’t yet exist. In addition, the cosmos was full of hydrogen, which reacted with and removed any free oxygen. Earth’s low gravity also allowed most hydrogen to escape into space, leaving behind a reducing atmosphere.

Miller and Urey simulated this early atmosphere using methane (CH₄), ammonia (NH₃), hydrogen (H₂), and water vapor (H₂O), and recreated the early water cycle by heating water to produce steam and adding electric sparks to mimic lightning.

After several days, the experiment resulted in the formation of amino acids, showing that biomolecules can form naturally in Earth-like conditions. This supported the idea that chemical reactions on the early Earth could have led to the origin of life.

The origin of DNA-based life is still uncertain, since genes need proteins, and proteins need genes to form. Earth is about 4.4 billion years old, and life appeared roughly 3.95 billion years ago. All known life shares a common molecular mechanism, pointing to a single-celled ancestor.

One main hypothesis suggests that early life was based on RNA, which can both store information and replicate. Some RNA components, like adenine, may have formed in space and arrived on Earth.

Experiments show that:

• Organic molecules and nucleotides existed on early Earth.

• Fatty acids formed vesicles that could grow and take in small molecules.

• Monomers entered vesicles, polymerized, and replicated.

• Heat split the strands, and growth pressure caused vesicles to divide.

• Faster-replicating sequences spread — a first step toward evolution.

• 1665: Cell discovered (Robert Hooke)

• 1892: Virus discovered (Dmitri Ivanovsky)

• 1928: Penicillin discovered

• 1972: First DNA molecule created in Lab

Deep-sea hydrothermal vents are key to origin-of-life studies because they offer a unique environment where early life could have started.

These vents release mineral-rich fluids that drive chemical reactions, potentially powering the first metabolic cycles.

Amino acids may have formed deep inside Earth’s crust, then moved into cooler waters where clay minerals facilitated the formation of peptides and protocells—primitive cell-like structures.

Interestingly, methane and ammonia, common in the early atmosphere, are absent in vents, indicating a different chemistry that might have favored life’s emergence in this setting.