The Evolution of Earth: 35 Remarkable Facts From Its Past

31Human Endangerment

Human Endangerment

Humans were once an endangered species. About 1.2 million years ago, at a time when our ancestors were spreading through Africa, Europe, and Asia, there were probably only around 18,500 individuals capable of breeding. Humans faced another population bottleneck where the human population was reduced to less than 1000 people total around 70,000 years ago due to a supervolcano explosion in Indonesia that triggered a nuclear winter.


32Magnetic Pole

Magnetic Pole

The Earth's magnetic poles move. About 780,000 years ago the Earth's magnetic poles flipped and we could be in the early stages of another. The magnetic North Pole moves in loops of up to 50 miles per day. It is slowly moving west and in the last 150 years, the pole has wandered a total of about 685 miles.


33Mammoth Steppe

Mammoth Steppe

The mammoth steppe was the Earth’s most extensive biome. It spanned from Spain eastwards across Eurasia to Canada and from the arctic islands southwards to China. It thrived for approximately 100,000 years without major changes and then suddenly became all but extinct about 12,000 years ago. Vegetation was dominated by high-productivity grasses, herbs and willow shrubs and the animal biomass was dominated by bison, horses, and the woolly mammoth.


34Milankovitch Cycles

Milankovitch Cycles

A wobble of Earth’s axis causes the Sahara to cycle between desert and grassland every 23,000 years. The last cycle started 7,000 – 10,000 years ago and Sahara will turn back into vast grassland in around 16,000 years. These are known as Milankovitch cycles, which are caused by variation in orbit and tilt of the Earth. These cycles have a great effect on the earth’s climate and are a leading cause of periodic ice ages.


35Big Freeze

Big Freeze

The Younger Dryas was a time period occurring about 12,000 years ago when the Earth’s temperature dropped 2 to 6 degrees Celsius within decades, which is amazingly fast in geological terms. It is debated to have been caused by asteroid impacts and volcanic eruptions. Humans developed light skin as a balance between vitamin D production and UV protection, likely in response to the Big Freeze that followed.

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