Earth and Space Sciences Regents, January 2026, question 12
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What the figure shows
The passages describe cyanobacteria (stromatolites) making oxygen in the oceans, the Great Oxidation Event, and the Huronian ice ages between 2.4 and 2.1 Ga (billion years ago). A further passage says banded iron formations are sedimentary rocks that formed in oceans containing some of Earth's first free oxygen. The Model of Earth's Early Ocean and Atmosphere shows iron from black smokers at hydrothermal vents entering the ocean (4.0 Ga), the concentration of iron ions in the ocean, oxygen released by stromatolites in shallow water, the label "Iron ions + Oxygen" with an arrow down to a banded iron formation in deep water, and a curve for oxygen in the atmosphere labelled Great Oxidation Event. A timeline below runs from 4.6 Ga (formation of Earth) to today.
How to think about it
The claim has a cause and an effect. The cause must be a change in the hydrosphere (the oceans), and the effect must be a change in the geosphere (rock). Look for a statement where something in ocean water leads to new rock, and check that the model or passage shows it.
Which statement correctly uses information from the model and passages as evidence to support the claim that, during the end of the Huronian ice age, changes in Earth’s hydrosphere caused a change in Earth’s geosphere?
Choice 4 is right. Oxygen made by stromatolites entered seawater that already held dissolved iron ions. The model shows iron ions and oxygen combining and settling as banded iron formations on the deep ocean floor. A change in ocean chemistry (hydrosphere) produced new layers of rock (geosphere).
The model shows the iron coming from black smokers at hydrothermal vents, not from microfossils. Microfossils are traces of early life found in rock; they are not a source of iron.
Stromatolites carried out photosynthesis, which uses energy from sunlight and releases oxygen. The model shows them giving off oxygen, not taking in iron for energy.
The model shows black smokers forming at hydrothermal vents around 4.0 Ga, long before the Huronian ice age, and it links them to iron, not to carbon dioxide and methane. This choice may come from mixing up the gases in the atmosphere passage with the vents shown in the model.
