By Trisha Rangaraju
How Did Life on Earth Begin?
Or, more specifically, how did non-living molecules combine to create a living one?
This has been a long standing debate for scientists for an extremely long time and there's still no clear-cut answer. We are very knowledgeable about the complexities of the building blocks of life (DNA, RNA, Amino Acids, etc), yet we still don’t truly understand what turning point in evolution caused life to emerge.
Extraterrestrial Organism
Francis Crick believes the only possible way a life form could have existed is if it was from another planet. Even so, this poses many new questions. How did this “alien” organism form in the first place? How and why did it make its way to Earth? There is no conclusive evidence to any of these questions yet.
Chemical Reactions in Early Earth
Some believe that early Earth was much like a biological chemical factory full of chemicals waiting to interact with each other. To truly understand this theory, we must know what constitutes life as living. Life can be defined as something that responds to the environment, reproduces, adapts, develops, practices homeostasis, processes energy, and goes through the process of evolution. So, according to this theory, all the chemicals of life Earth consisted of at the time, created complex chemical and genetic interactions (especially ones involving proteins as proteins form readily and often in nature) to instill all these traits of life in a once non-living cell. The only evidence we have of this theory is chemical traces of life we’ve found in early rocks that can point to a chemical reaction occurring. For example, in Greenland, a rock was found 3.8 billion years ago. It carries traces of carbon isotope signatures that may have been created by organisms that lived at the time.
Bacteria
A type of bacteria called cyanobacteria evolved 2.4 billion years agoand may have marked the beginning transition to life on Earth. They were the first photosynthesizers, using the sun as energy to make food and water. They increased the oxygen on Earth and may have helped transform Earth into a suitable environment for most life forms.
Multicellular Life
Many scientists speculate that clusters of multicellular cooperating cells turned into the first animals. Since the oxygen levels in the water were still not as high as they should have been for most life forms to exist, molecular evidence points to sea sponges being the first animals to exist, as sponges can survive in areas with lower levels of oxygen.
When we look around today, we see a vast, complex, interconnected web of animals and plants that make up the vivid diversity of life on Earth. Where this all started from, though, is still one of the largest scientific mysteries.
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