Reading Time in Ancient Wood
Written by Studio AM.
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A growing tree uses atmospheric carbon to form new wood. That carbon includes a small amount of radioactive carbon-14, which decays at a known rate. A tree ring largely retains the carbon incorporated as it formed. Measuring what remains can therefore help estimate when that ring grew, not simply when the whole tree died.
The measurement is not a clock with a printed calendar date. Laboratories compare carbon-14 with stable carbon and report an age with uncertainty. Contamination from newer roots, conservation glue, or older carbon can shift a result. Researchers clean samples and choose material tied closely to the event they want to date.
Atmospheric carbon-14 has varied over time. A raw radiocarbon age must therefore be calibrated against records with independently known dates. Tree rings are valuable because their calendar years can be counted and matched across overlapping wood. Other archives extend parts of the calibration record.
Calibration can turn one measured range into an irregular set of possible calendar ranges. Greater numerical precision in the laboratory does not remove every ambiguity in the curve. Archaeological context also matters. A beam cut from an old tree may be reused centuries later, so the wood's age need not equal the building's age. Radiocarbon dating is powerful because physical decay supplies a measurable connection to time. Sampling, chemistry, calibration, context, and uncertainty all shape the final interpretation.
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Question 1 of 4
What is the main idea of the passage?
The answer is A: Radiocarbon dating can estimate when wood formed, but sampling, calibration, contamination, context, and uncertainty shape the result.
The passage explains the decay basis while emphasizing the steps required to turn measurement into a historical date.
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Question 2 of 4
Why might a timber date be older than a building?
The answer is B: Wood from an old tree or earlier structure may have been reused later.
The fourth paragraph distinguishes when wood grew from when people used it in the current structure.
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Question 3 of 4
What does “calibrated” mean here?
The answer is C: adjusted by comparison with independently dated records
Raw radiocarbon ages are compared with tree-ring and other dated archives to relate them to calendar time.
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Question 4 of 4
What independently dated archive is especially valuable?
The answer is D: tree rings
The third paragraph identifies countable and matchable tree rings as especially valuable.
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