Equation 1 · Part 4 · What a Biosignature Has to Rule Out
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
If no gas can be trusted individually, the natural move is to look for a property of the whole atmosphere. The most general candidate is thermodynamic disequilibrium: life is a persistent chemical engine, so a biosphere should hold its planet’s atmosphere away from the composition it would relax to if all permitted reactions ran to completion. The quantity is the available Gibbs energy — the difference between the free energy of the observed composition and that of its equilibrium state at the same elemental abundances, temperature and pressure: . Krissansen-Totton, Olson and Catling computed this across Earth history and reported values that make the appeal obvious and…
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
These citations provide research context; check each source for the exact claim it supports.