Definition of Abiogenesis
Abiogenesis is the creation of organic molecules through forces other than living organisms. While living organisms can easily form carbon-carbon bonds using enzymes, doing so inorganically requires significant energy. Early in scientific history, this fact was used to challenge evolutionary theory, as it was unclear how organic molecules could arise from inorganic sources. The theory of abiogenesis gained credibility when Stanley Miller conducted his famous experiment aimed at proving the inorganic origin of life.
Miller combined gases thought to have existed in the early Earth atmosphere. These gases were placed in a chamber and subjected to high doses of electricity over several weeks. Afterward, Miller analyzed the samples, discovering that the molecules had started combining into more complex forms. He theorized that over billions of years, these molecules could evolve into self-replicating structures like RNA and DNA. Later laboratory experiments confirmed these findings, showing that many molecular structures found in cells could be synthesized from inorganic solutions when energy is supplied. Proteins and RNA have been synthesized in this way.
The lab-based synthesis of proteins and RNA provides critical evidence supporting abiogenesis. These processes could lead to self-replicating RNA molecules, and it is known that both proteins and RNA molecules can act as catalysts. These abiogenically-produced molecules could have catalyzed important reactions, leading to the replication of RNA and the production of complex structures like ribosomes, which translate RNA messages into proteins. The formation of these molecules through abiogenesis supports the early steps of the theory. However, some scientists argue that the theory underestimates the amount of lightning and other energy sources present in the primitive atmosphere.
Abiogenesis Theory
The theory of abiogenesis posits that all life began from inorganic molecules that recombined due to energy inputs. These various recombinations eventually formed a self-replicating molecule, which could have used other abiogenically-produced molecules to start building the basic structures of life, such as the cell.
Just as populations of organisms evolve over time, the evolution of molecules involves changes in molecular structures over time. Scientists speculate that the first self-replicating molecules were likely RNA. Some RNA molecules have the known ability to catalyze the formation of new RNA molecules, as seen in ribosomes found in nearly all Earthly creatures. One of these early RNA molecules formed perfectly, enabling it to create an identical RNA molecule. Its concentration increased dramatically in the prebiotic soup, interacting with itself and forming proteins around it, also through abiogenesis.
Eventually, this RNA molecule mutated, enabling it to synthesize a protein that could produce more RNA. Further mutations allowed proteins to synthesize DNA from RNA, leading to the birth of the modern organism’s genome. Over millions of years, evolutionary changes accumulated in these molecules, giving rise to the complexity of life today. Scientists studying abiogenesis often debate when abiogenesis transitions into biogenesis. Similar arguments arise regarding whether viruses are living organisms. Abiogenesis, by definition, refers to the creation of organic molecules from inorganic sources and does not necessarily pinpoint the origin of life.
Related Biology Terms
- Evolution: The process that changes populations of organisms over time, adapting them to their environment.
- Inorganic: Molecules that contain little carbon and are not produced by living organisms.
- Organic: Molecules synthesized by living organisms, typically containing many carbon-carbon bonds.
- Ribosome: One of the earliest cellular machines, capable of producing proteins from RNA and amino acids.