The earth condenses into a solid sphere, with an inner core which is extremely dense and hot

The earth's surface settles into a heaving turmoil of rock and water

Single-celled water creatures, such as algae, begin the 2-billion-year process of evolving into slightly more complex forms of life

Sponges and jellyfish drift in the sea, to be joined later by more purposeful shrimps and lobsters

The earliest known creature with a skeleton evolves as a form of fish

Plants, previously living only in the seas and rivers, begin to establish themselves on land

Insects become the first creatures capable of living their full life span out of the water - and the first to master flight

Amphibians develop lungs, enabling them to live on land as well as in the water

Reptiles develop evolutionary advantages for adaptation to a wide range of environments

The entire land surface of the earth merges into a single continent, known as Pangaea, which after about 50 million years splits in two

The dinosaurs dominate the planet in a way that no previous creature has been able to

The process of continental drift, beginning 200 million years ago, results eventually in our present arrangement of six continents

Mammals begin to make their appearance

Primitive birds begin to feature in the fossil record

In a very short space of time the dinosaurs die out, for reasons as yet uncertain

Mammals evolve in many new forms on land and in the water, using opportunities made possible by the extinction of the dinosaurs

Australia becomes a separate land mass, isolating its living creatures. They evolve into many species unique to the area

Primates evolve, from lemur-like animals to monkeys

A primate of this period, at ease both in the trees and on the ground, is probably the common ancestor of gorillas, chimpanzees and humans

Various species of ape develop the habit of walking upright on two feet

Certain primates, in eastern and southern Africa, are by now sufficiently like humans to be classed as hominids

A female of the species Australopithecus Afarensis (nicknamed Lucy when her skeleton is found), lives in the Afar Depression in Ethiopia within 50 miles of where her predecessor Ardi was unearthed

Creatures of the genus Homo, classified as early modern humans, are living in east Africa

The ice ages set in, to continue throughout most of human history

Anaximander, a pupil of Thales, develops bold theories about the formation of the earth and the beginning of life