Urban worldsOur World

Cities

Walk through settlements that concentrated culture, trade, and invention.

Subject guide · scope, chapters & sources ↗

Origin depth

Official Earth time scaleSelect an eon on the road to reveal its eras.ICS 2026/06 ↗

Cosmic Originsbefore Earth’s geological eons

c. 13.8 billion years agoUniverse

The Big Bang

The universe expands and cools from a hot, dense early state.

Oval map of small temperature differences in the cosmic microwave background. — ESA and the Planck Collaboration / NOIRLab · CC BY 4.0

Within the first few hundred million yearsEarly Universe

The first stars ignite

Gravity gathers primordial gas and the cosmic dark ages begin to lift.

Illustrated cosmic timeline marking the dark ages, first stars and galaxies. — NASA, ESA, CSA, STScI · NASA editorial media-use permission

c. 4.54 billion years agoSolar System

Earth takes shape

Rock and metal gather around the young Sun.

Dark, crusted Allende meteorite fragment. — Jon Taylor · CC BY-SA 2.0

At least 3.5 billion years agoEarth

Microbial life leaves evidence

Ancient rocks preserve traces of a living planet.

Layered Paleoarchean stromatolite specimen. — Didier Descouens · CC BY-SA 4.0

c. 2.4 billion years agoAtmosphere & oceans

Oxygen transforms the atmosphere

Microbial photosynthesis changes the chemistry of Earth.

Blue-grey banded iron-formation specimen on a museum stand. — Kjoonlee · CC BY 4.0

c. 1.8 billion years agoEarth

Complex cells diversify

Cells with internal structures establish a new branch of life.

Light-microscope view of modern Paramecium caudatum cells. — Fritzmann2002 · CC BY-SA 4.0

c. 600 million years agoGlobal oceans

Large multicellular life spreads

Complex bodies become a visible part of the fossil record.

Oval, segmented Dickinsonia fossil impression in rock. — cprevot (https://www.geodiversite.net/auteur193) · CC BY-SA 3.0

By c. 200 million years agoEarth

Early mammals live alongside dinosaurs

Small mammals and their close relatives are part of Mesozoic ecosystems.

Small Morganucodon fossil remains preserved in a reddish rock fragment. — Ghedoghedo · CC BY-SA 3.0

c. 56 million years agoAsia, Europe & North America

Early primates diversify

Small tree-dwelling primates spread through warm forests.

Small fossil remains of Teilhardina belgica in a museum display. — Ghedoghedo · CC BY-SA 3.0

c. 7 million years agoAfrica

The hominin story begins

A lineage of African apes starts following its own evolutionary path.

Side view of a cast of the Toumaï cranium. — Oryctes · CC BY-SA 3.0

c. 2.8 million years agoAfrica

Early Homo enters the fossil record

A jaw from Ethiopia preserves evidence attributed to our genus.

Two views of a fossil lower jaw and its teeth. — Brian Villmoare · CC BY 4.0

c. 300,000 years agoAfrica

Homo sapiens emerge

Our species appears within a diverse human world.

Front view of a Jebel Irhoud 1 skull cast in a museum display. — Jonathan Chen · CC BY-SA 4.0

c. 60,000–40,000 years agoGlobal

Humans journey beyond Africa

Later waves of migration expand our species’ global presence.

c. 10,000 BCEGlobal

The agricultural turn

Communities reshape land, food, and settlement.

Stone sickle displayed in a museum case. — Gary Todd · CC0

c. 9,000 BCEMiddle East

Jericho

A settlement endures near a desert spring.

Excavated circular stone tower within an archaeological trench. — Reinhard Dietrich · Public domain

c. 3,500 BCEMiddle East

Uruk

One of the first great cities grows in Mesopotamia.

Weathered brick and earth remains of a ziggurat in an arid landscape. — tobeytravels · CC BY-SA 2.0

508–507 BCEEurope

Athens

Political participation is radically reimagined.

762 CEMiddle East

Baghdad

A new capital becomes a center of learning.

15th–16th centuries CEAfrica

Timbuktu

Trade and scholarship meet at the Sahara’s edge.

c. 2007–2008 CEGlobal

An urban planet

Humanity approaches a majority living in urban areas.

Dense Tokyo skyline under a dawn sky. — KimonBerlin · CC BY-SA 2.0

Road complete

You’ve reached the end of Cities

Return to “The agricultural turn” and continue along The Human Story, or search for another origin below.