Abiotic Synthesis
Cells contain a lot of organic molecules, which are carbon-based compounds that help do things for the cells. Fats and carbohydrates can store energy, for example, while proteins help reactions happen, and nucleic acids hold the cell's information. These components are made by cells and make up cells. Before cells evolved, however, organic molecules would've had to have been made via abiotic synthesis.
'Abiotic' means without life, and 'synthesis' means to make. Abiotic synthesis is, therefore, making things without life. The atmosphere on the early earth most likely contained water vapor, methane gas, ammonia, and carbon dioxide. These gases contain the major elements found in organic molecules: carbon, oxygen, nitrogen, and hydrogen. Scientists hypothesized that these gases could join up together to make organic molecules, just like taking Lego blocks from a small house and combining them to build a bigger, more elaborate house.
If these building blocks of life could be made without cells, then it's possible that they combined together to eventually form larger molecules. Amino acids could join together to form proteins. Nucleic acids could join together to form small genes, or pieces of information that could be passed on. As these organic molecules became more complex over millions of years, the very first cells could have been formed. This would be like all of the pieces of the factory coming together to make the final product.
Miller-Urey Experiment
Like any good scientists, two men named Stanley Miller and Harold Urey decided to test the hypothesis that organic molecules could be formed without cells on the early earth. They set up an apparatus and pumped in the gases found in Earth's atmosphere billions of years ago. They then sent a spark through the gases, to mimic lightning. When the Miller-Urey experiment was completed, the scientists found many organic molecules in the apparatus, including amino acids and nucleic acids, that had formed from the non-living gases and the spark.
While this experiment showed that abiotic synthesis of organic molecules is possible, it isn't definitive proof that this was how life evolved. Still, along with many other experiments, it provides evidence that might someday help explain where life came from.
Lesson Summary
The origin of life on Earth is still an unanswered question. One hypothesis, based on the notion of abiotic synthesis, or the process of making things without life, suggests that small organic molecules, like the amino acids that build proteins, were formed before life existed. These small molecules joined together, becoming more and more complex, until the first cells were formed. The Miller-Urey experiment, which found that organic molecules (including amino and nucleic acids) could be produced from non-living materials, provides some evidence to support this hypothesis.
