Earth and Space Sciences Regents, January 2026, question 10
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What the figure shows
The passage says cyanobacteria in the oceans made oxygen by photosynthesis starting around 2.7 Ga (billion years ago). The oxygen escaped into the atmosphere and reacted with methane, so methane levels decreased and oxygen levels increased between about 2.4 and 2.1 Ga, an event called the Great Oxidation Event. Two models, Before Event and During Event, show sunlight reaching Earth, energy reflected from Earth's surface (straight arrows) and energy absorbed by the atmosphere (curved arrows). Before Event shows two reflected arrows and four absorbed arcs; During Event shows four reflected arrows and two absorbed arcs. The table in the question has columns for Change to Atmospheric Gas, Response to Change, and Effect on Climate.
How to think about it
Work across the row one column at a time. Use the passage to decide which way each gas changed. Then count the reflected and absorbed arrows in the two models to see how the energy changed. A row is right only if all three columns agree with the information and with each other.
Which row in the table below correctly describes the evidence for the coevolution of Earth systems as a result of the Great Oxidation Event? Row Change to Atmospheric Gas Response to Change Effect on Climate
Row 1 is right. The passage says methane decreased and oxygen increased. Methane is a greenhouse gas, so with less methane the atmosphere absorbed less energy, as the During Event model shows with fewer curved arrows. The same model shows more energy reflected, and a planet that keeps less energy cools, which fits the start of the earliest ice age.
Row 2 reverses every column. The passage says methane decreased and oxygen increased, and the During Event model shows less energy absorbed and more energy reflected. Less reflection with more absorbed energy would warm Earth, not start an ice age.
Row 3 has the right energy and climate columns but the gas changes are backwards. The passage states that oxygen reacted with methane, so methane went down and oxygen went up.
Row 4 has the gas changes right, but the energy and climate columns are reversed. The During Event model shows fewer absorbed arcs and more reflected arrows than the Before Event model. This row may come from reading the two models in the wrong order.
