Question
Oxygen production from photosynthetic cyanobacteria led to the deposition of these formations. For 10 points each:
[10m] Name these formations that record the oxygenation of Earth’s ancient oceans. These Precambrian formations are composed of alternating layers of chert and oxides of their namesake element.
ANSWER: banded iron formations [or BIFs; accept banded ironstone formations]
[10e] The absence of banded iron formations during the “Boring Billion” led Donald Canfield to theorize that its oceans had high sulfide levels and this property. Unlike a related condition, water with this property is completely depleted of dissolved oxygen.
ANSWER: anoxic [or anoxia; accept anaerobic; prompt on euxinic or euxinia; reject “hypoxic” or “hypoxia” or “dysoxic” or “dysoxia”]
[10h] Canfield proposed his namesake model by first considering a deep-ocean one of these constructs that interacts with two surface ones. Henry Stommel used two of these constructs to study the AMOC in his namesake model.
ANSWER: boxes [or reservoirs; accept Stommel box model or 2-box model or 3-box model; prompt on compartments]
<Other Science>
Summary
| 2025 ACF Nationals | 04/19/2025 | Y | 1 | 10.00 | 100% | 0% | 0% |
Data
| Columbia A | Minnesota | 0 | 10 | 0 | 10 |