what caused this decline but those changes had

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Unformatted text preview: O2] has changed substantially ... What caused this decline? ... but those changes had massive consequences Greenhouse conditions Glaciations along history of Earth, [CO2] has changed substantially ... Problem now: current rate of change How do we know that it is the burning of fossil fuels? & 13C: - stable isotopes 14C: - radioactive isotope: - decays (to 12C) - half-life of 5730 yrs 14C], Fossil fuels: very low [ because it has been decaying for millions of years Carbon isotopes: 12C burning fossil fuels adds CO2 to atmosphere that has little measure past atmospheric [14C] from 14C-content of growth rings of wood: Hypothesis: Burning fossil fuels is major cause of increased atmospheric [CO2] Prediction: over time, relative [14C] in atmosphere should ... decline 1 4C determine year when growth ring was laid down (dendrochronology) Cross-date trees of successively older ages to produce a chronology How do we know that it is the burning of fossil fuels? & 13C: - stable isotopes 14C: - radioactive isotope: - decays (to 12C) - half-life of 5730 yrs 14C], Fossil fuels: very low [ because it has been decaying for millions of years Carbon isotopes: 12C burning fossil fuels adds CO2 to atmosphere that has little measure past atmospheric [14C] from 14C-content of growth rings of wood: Hypothesis: Burning fossil fuels is major cause of increased atmospheric [CO2] Prediction: over time, relative [1...
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