Equation 6 · Part 9 · Radioactive Clocks: How Nuclear Physics Gave Evolution Its Time
subtraction
subtraction
What this part means
Subtract the following term or group from the preceding one. A leading minus marks a negative quantity.
Its job in the formula
Subtract the following term or group from the preceding one. A leading minus marks a negative quantity.
Full expression→subtraction→Article meaning
The passage around this formula
Uranium’s usefulness as a clock is doubled by an accident of nuclear structure: natural uranium consists of two isotopes, uranium-238 and uranium-235, which decay through separate chains to two different stable lead isotopes, lead-206 and lead-207 respectively, at two different, independently measured rates. Uranium-238’s half-life is about four point four seven billion years and uranium-235’s is about seven hundred four million years, values fixed by direct laboratory counting experiments [ 6 ] and formally adopted as the field’s working convention shortly after [ 7 ] . Because both chains run inside the same mineral grain simultaneously, from the same crystallization event, a single zircon…
Learn the underlying idea
Addition combines quantities; subtraction measures the signed difference between them. Parentheses show what is combined before the rest of the expression is evaluated.
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Sources cited in the surrounding passage
- [6] Precision Measurement of Half-Lives and Specific Activities of U235 and U238 ↗
- [7] Subcommission on Geochronology: Convention on the Use of Decay Constants in Geo- and Cosmochronology ↗
- [17] Uranium–lead dating ↗
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