12. The Great Oxidation Event

More than two billion years ago, oxygen began building up in Earth’s atmosphere and oceans, creating a crisis for many organisms that couldn’t tolerate it. This catastrophe led to our ozone layer, but it also resulted in a huge extinction of organisms.

NOAA on Unsplash

13. Late Ice Age Sea-Level Rise

As Ice Age glaciers melted, seas rose, and low-lying coastlines changed. People who lived near shorelines would’ve watched useful land, travel routes, and food-gathering places disappear under 20 meters of water in just 500 years.

Thomas Vimare on Unsplash

14. Eemian Interglacial Heat

Around 130,000 to 115,000 years ago, the last interglacial brought warmer conditions to the northern hemisphere, so much so that forests expanded into the Arctic Circle. It’s possible that, on top of population bottlenecks, early humans may have also engaged in cannibalism just to stay alive.

Donald Giannatti on Unsplash

15. African Humid Period Collapse

Thousands of years ago, parts of the Sahara supported lakes, grasslands, cattle herding, fishing, and human communities. As that wetter period faded between roughly 6,000 and 5,000 years ago, people moved toward more dependable water, including the Nile Valley and other livable corridors.

Andrzej Kryszpiniuk on Unsplash

16. Laacher See Eruption

About 13,000 years ago, the Laacher See volcano in what’s now western Germany erupted and spread ash across parts of Europe. The worst effects were local and regional, but nearby communities would’ve faced damaged hunting grounds, altered plant life, and years of environmental stress.

Abiyyu Zahy on Unsplash

17. Middle Paleolithic Climate Swings

During the later Ice Age, Europe shifted again and again between colder and somewhat milder phases. Neanderthals and early modern humans had to track animals, adjust to changing vegetation, and survive in smaller usable pockets of land while the climate changed around them.

Jack White on Unsplash

18. MIS 6 Glaciation

From about 191,000 to 130,000 years ago, a major glacial stage lowered sea levels and changed African environments. Early Homo sapiens persisted through this stretch, likely using scattered refuges, coastal resources, inland waterways, and whatever workable habitats were available.

James St. John on Wikimedia

19. Campi Flegrei Caldera Eruption

Around 39,000 years ago, the Campanian Ignimbrite eruption from the Campi Flegrei volcanic area near present-day Naples spread ash widely across parts of Europe. Its role in Neanderthal decline is debated, but it added another serious environmental shock during an already difficult period.

Jesse Allen and Robert Simmon on Wikimedia

20. Toba Ash-Fall Survival Zones

The Toba eruption left ash in parts of South Asia, including areas where stone tools show people were present before and after the event. That doesn’t mean the aftermath was easy; it means humans were able to survive the damaged landscapes, disrupted food sources, and massive volcanic fallout.

NASA/METI/AIST/Japan Space Systems, and U.S./Japan ASTER Science Team on Wikimedia