How did life first appear on Earth?
Genesis of Life: Is it a divine force or an alien presence? Scientists believe that life began not on Earth, but in space. The earliest known ancestor of all living organisms is called LUCA (Last Universal Common Ancestor), a single-celled microbe that lived approximately 3.7 billion years ago. Interestingly, humans share 60% of their DNA with bananas, proving that all life forms, including plants, animals, fungi, and bacteria, evolved from a common ancestor.
However LUCA was not the first living organism. There were others before it. But their exact nature is not yet known. The bigger question is how did life arise from non living matter? Previously, scientists had believed that living things had a special “life force”, but this theory changed in 1780 when French chemist Antoine Lavoisier showed that living and non living matter follow the same chemical principles. He measured a guinea pig’s body heat and carbon dioxide production and compared them to the burning of coal, finding striking similarities. Later, in 1790, the Italian scientist Luigi Galvani discovered that the dead frog legs twitched when touched by a steel blade, suggesting the role of electricity in life. These discoveries have helped shape our understanding of the origin of life.
The discovery of “animal electricity” began when a scientist saw the legs of a dead frog twitching and assumed that a life force was present. However, Alessandro Volta challenged this and showed that the reaction was caused by the interaction of two metals, leading to the invention of the first electric battery. The term “excitation” comes from his name.
Scientists had long believed that organic compounds found in living things could not be made from nonliving matter. This idea led to the birth of organic chemistry. The turning point came in 1828, when German chemist Friedrich Wöhler accidentally synthesized urea, an organic compound, using inorganic chemicals. This experiment challenged the idea of a life force and proved that organic compounds could be created artificially. In 1850, Marcelin Berthelot further demonstrated that organic compounds such as hydrocarbons, al-kohols, esters, and organic acids could be synthesized, leading to the realization that life was not inherent to these compounds.
Genesis of Life: What defines life?
Movement, reproduction, and metabolism were considered, but exceptions such as mules (which cannot reproduce) complicated the definition. In 2011, biophysicist Edward Trifon identified 123 different definitions of life, all agreeing on the idea of “self-reproduction with variation.” But metabolism how organisms use energy and release waste remains an important characteristic that distinguishes life from nonlife. Understanding these differences is essential to solving the mystery of how inanimate matter becomes living.
What is the difference between living and non-living organisms?
The difference between living and non-living organisms lies in their ability to maintain a boundary that separates them from their environment, a function performed by skin cells in humans, cell walls in plants, and protective layers in bacteria and viruses. Another important criterion for life is reproduction or ‘replication’, which even the smallest microbes accomplish by copying DNA. The transition from non-living to living forms was not sudden, but gradual and evolved by complex processes.
The early solar system was a cloud of material that eventually formed the Sun and Earth. After the formation of the Earth, there were frequent impacts of comets and meteorites in a period known as the Late Heavy Bombardment. Some scientists hypothesize that these celestial bodies brought the building blocks of life to Earth, a theory called Panspermia. Spectroscopy provides evidence that these essential molecules exist in the universe. By analyzing the light spectra of distant stars and galaxies, scientists can determine their chemical composition.
Advances in spectroscopy from the 1930s to the present have revealed complex organic molecules in the Universe, such as cyanide, ammonia, water and formaldehyde. The 1969 Murchison meteorite contained more than 20 amino acids, while later discoveries included urea, glycine and ethanol. In 2014, scientists found isopropyl cyanide in a cloud 25,000 light-years away, confirming the presence of chiral molecules, a fundamental property of life on Earth. These findings suggest that the basic ingredients of life may have come from outer space. This supports the idea that life on Earth has an extraterrestrial origin.
Scientists have discovered all 20 amino acids, the basic building blocks of life, in the universe. Additionally, the building blocks of DNA and RNA, such as ribose, have been found in interstellar clouds such as Sagittarius B2. This suggests that the universe functions as a chemical factory, with Earth filled with pre-synthesized molecules. The original soup hypothesis postulates that these organic compounds accumulated in Earth’s early environment, where lightning and volcanic heat triggered the emergence of life.
What is Clay Mineral Hypothesis?
In 1953, Stanley Miller and Harold Urey conducted an experiment to simulate early Earth conditions, producing amino acids from simple gases. Another key theory, the Clay Mineral Hypothesis, suggests that charged clay surfaces facilitated the formation of RNA, which could store genetic information and replicate itself. The RNA World Hypothesis states that RNA emerged first, eventually leading to proteins and DNA.
The origin of cellular structures is explained by the role of fatty acids in the formation of lipid membranes, RNA capture, and the formation of protocells. The hydrothermal vent theory suggests that life may have begun near deep-sea vents, where chemical energy fueled metabolism. Over time, bacteria and archaea merged to form complex life. This was confirmed in the 1960s by studies of mitochondria, which retain the properties of ancient bacteria. They conducted a DNA study and found out that the cell has its own DNA and mitochondria have their own DNA.
What is Typhus?
The DNA of mitochondria is similar to the DNA of a bacteria called Typhus, which causes fever, headache and rash in humans. So the conclusion from this was that mitochondria and the rest of the cell must have been two different organisms at one point of time. And today there is solid evidence that the merger of archaea and bacteria took place and bacteria became mitochondria and archaea remained the rest of the cell. And since mitochondria are not found only in eukaryotes, all multicellular organisms were born due to this. Without mitochondria, no multicellular organism was possible. All eukaryotes provide an average eukaryote with a genome that is 2 lacs times larger.
It can support life and can command 2 lacs times more energy. It is because of this extra energy that eukaryotic cells started to form, genes started to form and the process of natural selection started. So, if we look at it overall, this transformation from a non-living thing to a living bean is not something that happened suddenly in one go. Many different things happened for this, which took a very long time. Specifically, it took at least 2 billion years for this transformation to happen. The age of the first life is estimated to be 3.7 billion to 4 billion years ago and the age of the first multicellular organism is estimated to be at least 1.5 billion years ago. It takes so much time. So many different processes have to be correct, that too with the right conditions and the right raw material, only then the transformation can happen. But in all this it will not be wrong to say that we are all made of stardust. All the things required for the formation of all of us are present in space.
DNA studies have shown that mitochondria have their own DNA, separate from the rest of the cell. Interestingly, mitochondrial DNA is very similar to the DNA of the bacteria that cause typhoid. This suggests that the mitochondria and the cell were once separate organisms. Scientific evidence confirms that archaea and bacteria merged, with the bacteria evolving mitochondria while the archaea formed the rest of the cell.
Mitochondria are found exclusively in eukaryotes, making multicellular life possible. Eukaryotic genomes are much larger and generate 200,000 times more energy than prokaryotes, allowing complex life. This extra energy allowed the evolution of genes and the process of natural selection, which led to the development of multicellular organisms.
This transformation from non-living to living was not instantaneous, but took place over billions of years. Life appeared around 3.7 to 4 billion years ago, while the first multicellular organisms appeared around 1.5 billion years ago. The right conditions and raw materials were necessary for this development.
