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← Theoretical A

Q26 — Mass Extinctions and Carbon Cycle Perturbations

Theoretical A Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Macroevolutionary Patterns & Mass Extinctions

Mass extinctions occur when environmental changes outpace rates of species adaptation. One way to quantify this change is by measuring the addition of inorganic carbon to oceans over time. Significant changes in the flux between inorganic and organic carbon reservoirs are termed carbon cycle perturbation events. Mass change measures the magnitude of change in inorganic carbon mass in oceans. Another quantifying metric of a carbon cycle, isotopic shift measures the change in carbon isotopic composition during the event.

In the last 220 million years, the biological pump, which transports organic carbon and calcium carbonate from the ocean’s surface to the deep sea, has significantly strengthened.

Four scatter plots of carbon-cycle perturbation events: isotopic shift vs event duration, mass change vs event duration with a threshold line separating mass extinctions from other events, mass change vs date, and event duration vs date, with red dots marking mass extinctions and blue dots marking other events. Figure 1. Carbon-shifting processes plots. A Isotopic shift vs Event duration. B Mass change vs Event duration. Gray shaded area around the line represents error margin of the fit line. C Mass change vs Date. D Event duration vs Date; my - million years, a.u. - arbitrary units; Red dots: events considered as mass extinctions. Blue dots: other carbon perturbation events. Units may differ between graphs. Note that mass extinction events are not included in graph D.

On your answer sheet, indicate “T” for true statements and “F” for false ones.

A. One of the mass extinction events is likely caused by mechanisms distinct from those seen in other events.
B. The lack of information about minor events that happened early in Earth's history alone can explain the trend in Graph C.
C. The line in Graph B represents a critical threshold, above which a carbon perturbation event is likely to be associated with extinction catastrophe.
D. A more efficient biological pump results in smaller and shorter carbon perturbation events.
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Question reproduced from IBO 2024, Theoretical Exam Part A, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)