ca. 4.4 million years agoca. 15,000 B.C.E.
Ardipithecus evolve in AfricaEarliest evidence of bows and atlatls; humans cross the Bering Strait land bridge to the Americas
ca. 2.5–4 million years agoca. 15,000–10,000 B.C.E.
Australopithecus evolve in AfricaFinal retreat of glaciers; megafaunal extinctions
ca. 500,000–2 million years agoca. 9000 B.C.E.
Homo erectus evolve and spread out of AfricaBeginning of the Neolithic; horticulture; domestication of sheep and goats
ca. 250,000–9000 B.C.E.ca. 7000 B.C.E.
Paleolithic eraDomestication of cattle; plow agriculture
ca. 250,000 years agoca. 5500 B.C.E.
Homo sapiens evolve in AfricaSmelting of copper
ca. 30,000–150,000 years agoca. 5000 B.C.E.
Neanderthals flourish in Europe and western AsiaInvention of pottery wheel
ca. 120,000 years agoca. 3200 B.C.E.
Homo sapiens migrate out of Africa to EurasiaEarliest known invention of writing
ca. 50,000 years agoca. 3000 B.C.E.
Human migration to AustraliaDevelopment of wheeled transport; beginning of bronze technology
ca. 20,000–30,000 years agoca. 2500 B.C.E.
Possible human migration from Asia to the AmericasBronze technology becomes common in many areas; beginning of the Bronze Age
ca. 25,000 B.C.E.
Earliest evidence of woven cloth and baskets

A note on dates: This book generally uses B.C.E. (Before the Common Era) and C.E. (Common Era) when giving dates, a system of chronology based on the Christian calendar and now used widely around the world. Scholars who study the very earliest periods of hominid and human history usually use the phrase “years ago” to date their subjects, as do astrophysicists and geologists; this is often abbreviated as B.P. (Before the Present). Because the scale of time covered in Chapter 1 is so vast, a mere 2,000 years does not make much difference, and so B.C.E. and “years ago” have similar meaning.