The Ends of the World: Volcanic Apocalypses, Lethal Oceans, and Our Quest to Understand Earth's Past Mass Extinctions

by Peter Brannen

Plankton has gotten bulkier and heavier over time—with huge implications for the ocean and for life on earth. Today’s single-celled, armored drifters—creatures like foraminifera, and the more plant-like diatoms, and coccolithophores—are microscopic to our eyes but are still enormous compared to the single-celled plankton of the Paleozoic, a suite that was dominated by bacteria and green algae. This sort of modern plankton is also freighted with mineral ballast, an extra load that, combined with its size, allows it to sink much further into the deep ocean before being consumed again by life. This has huge consequences, as consumption of this biological snowfall in the oceans uses up oxygen. If plankton can sink deeper into the ocean before being consumed, then so too will the ocean’s Oxygen Minimum Zone (OMZ), the layer at which dissolved oxygen in the ocean is at its lowest. Today the OMZ is at about 600 meters down. But in the earth’s past—when plankton particles were tinier and sank more slowly—the OMZ might have been much, much shallower, with devastating consequences for life.