Examkin

Question

Difficulty: MediumExplicit Causal Relationships

Paleoclimatologists investigating the Cretaceous oceanic anoxic events (OAEs) have established a definitive causal sequence initiated by massive submarine volcanism. The formation of Large Igneous Provinces released vast quantities of carbon dioxide into the atmosphere. This sudden spike in greenhouse gases precipitated a period of intense, rapid global warming. Consequently, the elevated global temperatures accelerated the hydrological cycle, leading to a marked increase in the chemical weathering of continental silicate rocks. This accelerated weathering washed massive influxes of terrestrial nutrients, primarily phosphorus, into the ocean basins. The resulting nutrient surplus triggered unprecedented phytoplankton blooms in the photic zone. As these massive algal populations inevitably died and sank, their subsequent decomposition by aerobic bacteria in the water column consumed staggering amounts of dissolved oxygen. Ultimately, this severe oxygen depletion resulted in the widespread anoxic conditions that characterize the sediment record of these periods.

Based exclusively on the detailed mechanism described above, arrange the following phenomena in the chronological causal order of their occurrence, from the earliest catalyst to the final consequence:

  1. 1A significant increase in atmospheric greenhouse gas concentrations
  2. 2Enhanced chemical degradation of terrestrial silicate rocks
  3. 3A surge in oceanic phosphorus and other nutrient levels
  4. 4Unprecedented growth of photosynthetic marine organisms
  5. 5Extensive consumption of dissolved oxygen during biological decay

Answer

The correct causal order is: First, a significant increase in atmospheric greenhouse gas concentrations; second, enhanced chemical degradation of terrestrial silicate rocks; third, a surge in oceanic phosphorus and other nutrient levels; fourth, unprecedented growth of photosynthetic marine organisms; and finally, extensive consumption of dissolved oxygen during biological decay.
The passage lays out a rigid, linear causal chain. Submarine volcanism releases carbon dioxide, leading to a significant increase in greenhouse gases. This warming accelerates the hydrological cycle, causing enhanced degradation (weathering) of terrestrial silicate rocks. This rock weathering delivers phosphorus and other nutrients to the ocean. The nutrient surge triggers unprecedented growth of phytoplankton. Finally, when these organisms die, their biological decay by aerobic bacteria extensively consumes dissolved oxygen.

Step-by-Step Solution

1
Identify the initial catalyst described in the text.
A significant increase in atmospheric greenhouse gas concentrations.
The passage explicitly notes that the sequence was initiated by volcanism releasing 'vast quantities of carbon dioxide' (a greenhouse gas).
2
Determine the direct consequence of the initial greenhouse gas spike.
Enhanced chemical degradation of terrestrial silicate rocks.
The sudden spike in gases caused global warming, which accelerated the hydrological cycle and led directly to increased chemical weathering of rocks.
3
Trace the immediate effect of the accelerated rock weathering.
A surge in oceanic phosphorus and other nutrient levels.
The text states that accelerated weathering washed 'massive influxes of terrestrial nutrients, primarily phosphorus, into the ocean basins.'
4
Identify the outcome caused by the influx of nutrients.
Unprecedented growth of photosynthetic marine organisms.
The passage indicates that the resulting nutrient surplus 'triggered unprecedented phytoplankton blooms' (photosynthetic organisms).
5
Determine the final step that directly precedes the anoxic conditions.
Extensive consumption of dissolved oxygen during biological decay.
The text concludes that the decomposition of these dead algal populations by aerobic bacteria consumed massive amounts of dissolved oxygen.

Key Concept

Sequencing explicitly stated multi-step causal relationships in dense academic passages.
Estimated Time:2m 0s
Rate this question

Topics

Explicit Causal Relationships

More questions from this topic