How Al-Biruni predicted unknown lands beyond Afro-Eurasia

Al-Biruni reasoned that unknown inhabited lands could exist

About Two-Fifths Of Earth’S Circumference

Al-Biruni calculated that the known lands of Africa, Europe, and Asia covered only about two-fifths of Earth's circumference. From the empty space left over, he reasoned that other inhabited land could exist between Asia and Europe, centuries before Europeans reached the Americas.

A giant black hole can have the average density of water

≈ density of water

A black hole can contain an enormous mass while having a surprisingly low average density inside its event-horizon-sized region. For a black hole with 100 million times the Sun's mass, that average density is roughly similar to water.

A high-altitude gene variant spread quickly among Tibetans

≈3,000 years

Over roughly 3,000 years, a gene variant that helps people live at high altitude became very common among Tibetans. It is an example of how quickly natural selection can change a human population when the environment strongly favors a trait.

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How Al-Biruni predicted unknown lands beyond Afro-Eurasia

Al-Biruni reasoned that unknown inhabited lands could exist

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