Radiometric dating estimates ages from predictable isotope decay, using carbon-14 for relatively recent organic remains and potassium-40 for much older rocks associated with early life.
Coverage 2014–2014 · Updated 15 Jul 2026
Dates for the first cells and LUCA are estimates built by combining fossils, isotope signatures, molecular clocks and geological context.
Each method has assumptions: fossils require interpretable structures, isotope signals can have non-biological sources, and molecular clocks depend on mutation rates and calibration. Agreement across methods increases confidence.
Ask what a method actually dates:
A microfossil in a securely dated rock can constrain an early-cell minimum age, while a molecular clock estimates when lineages diverged rather than when the first cell existed.
The oldest evidence found is a minimum bound; absence of older evidence does not prove life was absent.
This objective is assessed through structured response, commonly using Outline / State / Describe.
Outline / State / Describe
Build the answer around this relationship: Radioactive isotopes decay at predictable rates expressed by half-life.
Using carbon-14 to date rocks or fossils billions of years old.
Representative question
Outline the use of two named radioisotopes for dating fossils.
A2.1 is usually tested as a connected argument, not as isolated facts. A strong answer builds a chain: early Earth conditions made abiotic organic synthesis plausible; origin models require small molecules, polymers, self-replication, and membranes; experiments and models support parts of the chain; LUCA, dating, and vents provide later evidence and constraints. The highest-scoring habit is to say “supports” when evidence supports, and avoid saying “proves” when it does not.
