"IF one considers the origin of life to fall within the biological sciences (that's debatable), then the most-interesting unanswered question in the biological sciences would be, ""How did life arise?"" My favorites theories/hypotheses on that are a form of the iron-sulfur world and the RNA world. As for the modified form of the iron-sulfur world, the best candidate for a location for the origin of life is alkaline hydrothermal vents. These are NOT the ""black smoker"" hydrothermal vents many people are familiar with. Simple organisms there - methanogens - use proteins containing iron-sulfur catalytic cores to use hydrogen (H2) to reduce carbon dioxide into methane. Note that the proteins are not catalysts themselves - they just aid the mineral catalysts. So the abiotic conditions as alkaline hydrothermal vents may be able to produce organic molecules from inorganic ones. In addition, there could be mineral analogs to the biological process of obtaining energy from ion gradients across membranes. The RNA World theory has RNA serving the 2 primary functions of biomolecules today: information storage (as DNA does today) and catalysis (as proteins do today). We know RNA can store genetic information because some viruses have only RNA for their genetic material. And we know of many RNA molecules (called ribozymes) that can catalyze chemical reactions. So at least in principle, RNA would perform the duties now played by DNA and proteins. The two theories are not contradictory; they could explain different parts of the origin of life (the first, energetic, and the second, informational). The topic is very complex and the above does not do either of the hypotheses/theories justice."
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