7MYA: Oceans
Oceans Cool: The Pulse Beneath the Surface
When the Depths Responded to the Skies
As the skies cooled and the forests above began their slow retreat, the oceans — vast, silent, ancient — began to feel the chill. Unlike the surface, where winds and forests visibly shifted, the oceans responded in ways that were quieter but no less profound. The deep sea, sensitive to even the subtlest changes in temperature and chemistry, began a transformation that would ripple across the planet.
It was not a sudden freeze. But the great blue basins, which had been warm and tropical for much of the Miocene, were entering a new mood. The pulse of the Earth’s climate was slowing, cooling. And the oceans, as the Earth’s true climate regulators, absorbed that shift deeply.
Marine life evolved or vanished.
Scientific Interlude: How Ocean Cooling Happens
Oceans hold about 93% of Earth’s heat. When global CO₂ levels drop, surface temperatures decrease, and this leads to:
Stronger thermohaline circulation — the ocean’s “conveyor belt,” where cold, dense water sinks at the poles and drives deep-sea currents.
Cooler surface waters near the equator, which impacts evaporation rates and rainfall globally.
Reduced stratification, allowing nutrients from deeper layers to rise, altering marine ecosystems.
These processes began slowly, but their effects accumulated like drops into a tide.
Whale ancestors began long migrations in sync with cooler flows.
The Cascading Changes Beneath
As temperatures dipped, the warm surface layers of the oceans began mixing more with the colder, nutrient-rich waters from below. This change sparked an explosion of plankton blooms in some areas, feeding entire chains of marine life — from tiny fish to massive baleen whales.
But cooling also meant change in sea levels, salinity, and migration patterns. Coral reefs, sensitive to even slight shifts, began to retreat from their long-established homes. The ocean’s great hunters — ancient sharks, dolphins, and predatory fish — had to follow their prey to new routes and shallower waters.
In coastal zones, currents shifted. Sediment patterns changed. Some shallow seas shrank, while others became breeding grounds for marine life experimenting with new strategies for survival.
Altered Rainfall Accelerated Forest Fragmentation
Connections to Life on Land
These aquatic shifts echoed far inland. Rainfall patterns were altered. With less evaporation from cooler seas, certain regions received less precipitation, pushing forests into stress and accelerating their fragmentation.
In Africa, the heartland of primate evolution, this meant fewer rainy seasons and longer dry spells. Forests became isolated islands. Waterholes became more crucial. And life — from elephants to early primates — began to migrate more often in search of sustenance.
The Oceans Set The Stage For Evolution
Nowsense Realization: The Ocean’s Whisper to the Future
From the outside, the ocean seemed unchanged. Its waves still rolled, its tides still pulled. But within, it was stirring something deep — not just currents, but destinies. The cooling of the oceans didn’t just shift marine ecosystems. It helped set the stage for how and where the first hominins would walk.
When we speak of evolution, we often forget the sea. But here, at the dawn of walking apes, the oceans were more than background. They were part of the script.