Question

Why are the Miller-Urey experiments essential to the theory of evolution?
They showed that life can only come from life.
They showed that electricity can create life.
They showed how organic molecules could be made from Earth's early atmosphere.

Answer 1

Correct answer: "They showed how organic molecules could be made from Earth's early atmosphere."

What the Miller–Urey experiment actually did
- In 1953 Stanley Miller and Harold Urey circulated a mixture of simple gases thought to resemble early Earth (water, methane, ammonia, hydrogen) and applied electrical sparks to simulate lightning. After running the experiment they recovered a variety of organic molecules, including amino acids.
- The experiment showed that energy sources available on early Earth could drive formation of biologically important building blocks from inorganic chemicals.

What it did not do
- It did not create living organisms. It produced small organic molecules, not cells.
- It did not prove that electricity "creates life" in a direct sense—electricity was only one plausible energy source that can drive prebiotic chemistry.

Why it matters to evolution
- Miller–Urey addresses abiogenesis (how the first biomolecules and, ultimately, first living systems could arise), not the mechanism of evolution (natural selection and descent with modification) that explains how life changes after it exists.
- Having a plausible pathway for making organic building blocks is a necessary piece of the larger picture: without a source of biomolecules, there would be nothing for evolution to act on.

Caveats
- Later work has shown other plausible sources and pathways (different early-atmosphere compositions, hydrothermal vents, meteorites), and the exact early-atmosphere composition is still debated. The experiment is historically and scientifically important because it showed that prebiotic synthesis is plausible, not because it settled all questions about the origin of life.