Question

earth’s spheres and interactions (concept 1 and 2 quiz)
chart: x - axis labeled millions of years before present (ranging from 1000 to 0), y - axis with a value up to 5
today, oxygen makes up about 21% of earth’s atmosphere, but for most of our planet’s history, o₂ levels in the atmosphere and ocean were much less than they are today and could not support human life. there was very little o₂ in the atmosphere 3.8–2.4 billion years ago as evidenced by iron oxides not being found within earth’s crust and mantle. then cyanobacteria began to photosynthesize, producing o₂ as a by - product. o₂ that was used by organisms for aerobic cellular respiration. a balance between the two processes resulted in no net release of oxygen into the atmosphere. based on carbon dating, scientists proposed that around 2.4 billion years ago, organic matter became buried in ocean sediments. the burial of organic matter destabilized the photosynthesis - respiration equilibrium, making it possible for o₂ to accumulate in the oceans and be released into the atmosphere. about 320–275 million years ago, during the carboniferous and permian periods, o₂ levels may have surpassed present - day levels, perhaps reaching as much as 35% of the atmosphere. all but one is an explanation for this dramatic increase in atmospheric oxygen.

• massive volcanic activity at the permian - triassic transition resulted in the largest mass extinction in geological history
• global burial of organic matter also made it possible for o₂ to accumulate in the atmosphere.
• all oxygen sinks were finally saturated resulting of continued outgassing of oxygen.
• evolution of large vascular land plants may have brought about an increase in o₂ production.

Explanation:

To solve this, we analyze each option:

Option 1:

Massive volcanic activity at the Permian - Triassic transition caused the largest mass extinction. Mass extinctions involve the death of organisms. If organisms die, processes like respiration (which consumes O₂) and the burial of organic matter (which is related to O₂ accumulation) would be disrupted. This event is about extinction, not directly about the increase in atmospheric O₂. So this is not an explanation for the O₂ increase.

Option 2:

Global burial of organic matter. When organic matter is buried, it doesn't decompose (decomposition would consume O₂). So less O₂ is used in decomposition, and more O₂ can accumulate in the atmosphere. This explains the O₂ increase.

Option 3:

All oxygen sinks were saturated. Oxygen sinks are components (like certain chemical compounds or processes) that absorb O₂. If they are saturated, they can't absorb more O₂, and with continued outgassing (release) of O₂, the atmospheric O₂ level would increase. This explains the O₂ increase.

Option 4:

Evolution of large vascular land plants. These plants perform photosynthesis, which produces O₂. More photosynthesis means more O₂ production, leading to an increase in atmospheric O₂. This explains the O₂ increase.

Answer:

A. Massive volcanic activity at the Permian - Triassic transition resulted in the largest mass extinction in geological history