Drops of a nutrient solution containing radioactive carbon-14 were added to Martian soil, and a stream of radioactive carbon dioxide was detected rising out of the soil.
When the organism dies, no new radioactive carbon is assimilated.
A living organism would take in the radioactive carbon and convert it to organic material.
Food grains, scraps of cloth, bits of wood and so on can thus be dated by finding out how much radioactive carbon is left in them: the less there is, the older they are.
Using carbon-dating techniques, archaeologists can determine the age of many ancient objects by measurement the amount of radioactive carbon they contain.
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