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Recent separate findings indicate that plant leaves receiving more light have a higher density of veins, as well as a higher ratio of a naturally occurring isotope called carbon 13.

So researchers compare the amount of carbon 14 with the levels of carbon 12 and carbon 13 to determine how much time has passed since an organism perished.

Carbon 13 usually comes from inorganic sources, such as volcanoes, while carbon 12 is tied to living things.

There’s carbon 12 and its ever-so-slightly-heavier sibling, carbon 13.

The key is in the rock’s atomic composition; organisms that use sunlight for energy incorporate a lighter version of carbon, called carbon 12, over the heavier carbon 13.