4.5 billion years ago Earth condenses as hot solid sphere
The earth condenses into a solid sphere, with an inner core which is extremely dense and hot

4 billion years ago Earth's rock-and-water surface
The earth's surface settles into a heaving turmoil of rock and water

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

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

500 million years ago Fishes get skeletons
The earliest known creature with a skeleton evolves as a form of fish

400 million years ago Plants get out of the water
Plants, previously living only in the seas and rivers, begin to establish themselves on land

350 million years ago Insects are up and away
Insects become the first creatures capable of living their full life span out of the water - and the first to master flight

340 million years ago Amphibians get lungs
Amphibians develop lungs, enabling them to live on land as well as in the water

300 million years ago Reptiles rule
Reptiles develop evolutionary advantages for adaptation to a wide range of environments

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

225 million years ago Dinosaurs inherit the earth
The dinosaurs dominate the planet in a way that no previous creature has been able to

200 million years ago Single continent begins to crumble
The process of continental drift, beginning 200 million years ago, results eventually in our present arrangement of six continents

170 million years ago First tiny mammals
Mammals begin to make their appearance

125 million years ago Birds appear on the scene
Primitive birds begin to feature in the fossil record

65 million years ago Dinosaurs die out
In a very short space of time the dinosaurs die out, for reasons as yet uncertain

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

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

45 million years ago Primates in the trees
Primates evolve, from lemur-like animals to monkeys

15 million years ago Large primates happy at ground level
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

6 million years ago Apes walk tall
Various species of ape develop the habit of walking upright on two feet

4.5m. years ago First hominids
Certain primates, in eastern and southern Africa, are by now sufficiently like humans to be classed as hominids

3.2 million years ago Lucy in Ethiopia
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

2.2 million years ago First humans in east Africa
Creatures of the genus Homo, classified as early modern humans, are living in east Africa

1.7 million years ago Chilly times ahead
The ice ages set in, to continue throughout most of human history

570 BC Anaximander on how it all began
Anaximander, a pupil of Thales, develops bold theories about the formation of the earth and the beginning of life

380 BC Four humours in human body say Greeks
A Greek text, attributed to Polybus, argues that the human body is composed of four humours

300 BC Earliest work on botany
The Greek author Theophrastus writes On the History of Plants, the earliest surviving work on botany

1530 Printed illustrations of botany
German botanist Otto Brunfels publishes Living images of plants, the first serious work of natural history with printed illustrations

1560 Tobacco good for you - official
Tobacco is grown in Europe's physic gardens for its medicinal qualities

1596 Swiss botanist classifies plants
Swiss botanist Gaspard Bauhin begins work classifying 6000 plants on a new binomial system of nomenclature

1661 Malpighi sees smallest blood vessels
Italian doctor Marcello Malpighi discovers the capillaries, thus completing the evidence for the circulation of the blood

1674 Leeuwenhoek observes red blood corpuscles
The Dutch scientist Anton van Leeuwenhoek builds a microscope powerful enough for him to observe and describe the red corpuscles in blood

1677 Spermatozoa sighted
With his powerful new microscope Leeuwenhoek observes spermatozoa in the semen of a dog

1686 Ray classifies plants
English naturalist John Ray begins publication of his Historia Plantarum, classifying some 18,600 plants in 'mutual fertility' species

1735 Linnaeus provides a system
Swedish naturalist Carolus Linnaeus publishes a 'system of nature', capable of classifying all living things

1769 Banks and Solander seek specimens
Captain Cook's distinguished passengers, Joseph Banks and Daniel Solander, collect valuable specimens of Pacific flora

1785 James Hutton describes Scottish rocks
James Hutton describes to the Royal Society of Edinburgh his studies of local rocks , launching the era of scientific geology

1799 Smith studies rock strata
English surveyor William Smith compiles a manuscript, Order of the Strata, revealing chronology through fossils in rocks

1809 Lamarck on evolution
French biologist Jean-Baptiste Lamarck argues in Zoological Philosophy that creatures can inherit acquired characteristics

1811 Mary Anning discovers giant fossil
A 12-year-old Dorset child, Mary Anning, discovers at Lyme Regis a 21 ft (6.4m) fossil of an icthyosaur

1812 Cuvier launches science of palaeontology
French scientist Georges Cuvier introduces scientific palaeontology with his Research on the Fossil Bones of Quadrupeds

1831 Voyage of the Beagle
HMS Beagle sails from Plymouth to survey the coasts of the southern hemisphere, with Charles Darwin as the expedition's naturalist

1835 Protoplasm revealed
French zoologist Félix Dujardin identifies protoplasm, the viscous translucent substance common to all forms of life

1836 Darwin brings home specimens
HMS Beagle reaches Falmouth, in Cornwall, after a voyage of five years, and Charles Darwin brings with him a valuable collection of specimens

1836 Scientific proof that glaciers move
Louis Agassiz builds a hut on the Aar glacier in Switzerland and succeeds in recording gradual movement of the ice

1840 Theory of ice ages proposed
Swiss scientist Louis Agassiz argues, in his Study on Glaciers, that much of Europe was recently in the grip of an ice age

1843 Fossil fish classified
Swiss naturalist Louis Agassiz completes his pioneering Poissons Fossiles ('Fossil Fish'), classifying more than 1500 categories

1851 Clergyman discovers bee space
An American clergyman, L.L. Langstroth, discovers the 'bee space', which becomes a standard feature of the modern beehive

1854 Mendel studies peas
Austrian monk Gregor Mendel begins his study of pea plants in the garden of the Abbey of St Thomas in Brno

1854 John Snow links cholera and water
English physician John Snow proves that cholera is spread by infected water (from a pump in London's Broad Street)

1856 Neanderthal man found in quarry
The first Neanderthal man to be discovered is unearthed by quarry workers in the Neander valley, near Düsseldorf

1857 Pasteur discovers micro-organisms
French chemist Louis Pasteur proves the existence of micro-organisms by showing that a liquid will only ferment if exposed to contamination from the air

1858 Darwin receives shock in morning post
Charles Darwin is alarmed to receive in his morning post a paper by Alfred Russell Wallace, outlining very much his own theory of evolution

1859 On the Origin of Species
Charles Darwin puts forward the theory of evolution in On the Origin of Species, the result of twenty years' research

1865 Mendel launches science of genetics
Gregor Mendel reads a paper to the Natural History Society in Brno describing his discoveries in the field of genetics

1883 Galton pioneers eugenics
English polymath Francis Galton publishes Inquiries in Human Faculty, developing the theme of eugenics and coining the term

1903 Pavlov and the conditioned reflex
In a paper to a congress in Madrid, on the 'psychology and psychopathology of animals', Ivan Pavlov announces his discovery of the conditioned reflex

1905 Micro-organism causing syphilis is identified
German biologists Fritz Schaudinn and Erich Hoffmann discover the micro-organism Treponema pallidum which causes syphilis

1905 The word 'hormone' is coined
English physiologists William Bayliss and Ernest Starling coin the word 'hormone' for glandular secretions into the bloodstream

1906 The term 'genetics' is coined
English biologist William Bateson uses the word 'genetics' to describe the phenomenon of heredity and variation

1909 Human blood groups identified
Karl Landsteiner classifies the main human blood groups as A, B, AB and O

1910 Fruit fly reveals genetic secrets
US geneticist Thomas Hunt Morgan establishes the chromosome theory of heredity through his study of the fruit fly Drosophila melanogaster

1912 Theory that continents are drifting
German scientist Alfred Wegener, impressed by the neat fit between the coasts of Africa and South America, proposes the theory of continental drift

1913 Age of earth revised
English geologist Arthur Holmes publishes The Age of the Earth, offering evidence that the planet is at least 1.6 billion years old

1914 Last passenger pigeon
Martha, 29 years old and the last passenger pigeon in the world, dies in the Cincinnati zoo in Ohio

1922 Banting and Best discover insulin
Canadian physiologists Frederick Banting and Charles Best isolate insulin from the pancreas for the treatment of diabetes

1925 Scopes Monkey Trial
Biology teacher John Scopes is prosecuted for breaking state law by teaching evolution to his class of children in Dayton, Tennessee

1927 Discovery of the bee dance
Austrian zoologist Karl von Frisch demonstrates that bees communicate the whereabouts of food by means of a dance

1928 Fleming discovers penicillin
Scottish bacteriologist Alexander Fleming accidentally discovers a mould that selectively kills bacteria, and calls it penicillin

1935 Richter Scale
US seismologist Charles Richter devises a scale for measuring the magnitude of earthquakes

1935 Konrad Lorenz and his geese
The Austrian zoologist Konrad Lorenz describes his experiments on young geese, with their capacity to imprint on human beings

1937 Krebs cycle
German-born British scientist Hans Krebs discovers the biochemical cycle that becomes known by his name

1946 Mechanism of genetic transfer discovered
Joshua Lederberg and Edward Tatum announce their discovery of bacterial conjugation, meaning that in effect bacteria mate and transfer genes

1948 Rats in the Skinner box
US psychologist B.F. Skinner trains laboratory rats to use their brains in his 'Skinnner box'

1949 Inbuilt compass of bees
Karl von Frisch demonstrates that bees make use of the polarized light of the sun to calculate direction

1953 DNA unravelled
Molecular biologists Francis Crick and James Watson announce their discovery of the double-helix structure of DNA

1963 Silent Spring
US environmentist Rachel Carson publishes Silent Spring, an impassioned warning of ecological disaster

1966 Plate tectonics
Scientists at the US Geological Survey develop the theory of plate tectonics as the explanation of continental drift

1983 HIV virus described
Luc Montagnier, at the Pasteur Institute in Paris, discovers a new human retrovirus that he names LAV (later changed to HIV)

1984 Genetic fingerprinting
Genetic (or DNA) fingerprinting is invented and developed by British geneticist Alec Jeffreys

1985 Human Genome Project
The Human Genome Project begins in the US Department of Energy, with the aim of sequencing the whole of human DNA

1986 Mad Cow Disease
Mad Cow Disease (BSE, or bovine spongiform encephalopathy ) is identified and described in Britain

1990 Goodall reveals dark side of primate life
British primatologist Jane Goodall publishes Through a Window, exposing violence and brutality in chimpanzees

1996 CJD variant of BSE
A fatal variant CJD (Creutzfeldt-Jacob disease) is first identified in Britain, linked to BSE but capable of infecting humans

1996 Dolly cloned
Dolly the Sheep is cloned in an epoch-making experiment at the Roslin Institute in Edinburgh

1999 Human genome sequenced
Chromosome 22 becomes the first human genome to be fully sequenced, at the Sanger Institute in Cambridge, England

2000 Human genome draft completed
A White House ceremony celebrates a full draft of the human genome completed by two rival projects

2001 Nobel prize for cell cycle discoveries
Leland Hartwel, Paul Nurse and Tim Hunt win the Nobel Prize for their discoveries of key regulators of the cell cycle

2015 October 23 Strongest hurricane ever in the Western Hemisphere
Hurricane Patricia becomes the most intense hurricane ever recorded in the Western Hemisphere with winds of 215 mph

2017 November 2 New species of ape discovered
A new species of orangutan is identified in Indonesia, becoming the third known species of orangutan as well as the first great ape to be described for almost a century

2018 March 19 Last white rhinoceros dies
The world's last male northern white rhinoceros dies in Kenya, making the subspecies functionally extinct

2018 June 3 Guatemala volcano countries deadliest
At least 109 people are killed and hundreds wounded by the eruption of Volcán de Fuego, Guatemala's deadliest volcanic eruption in over a century

2019 April 28 Deepest human undersea dive in history
Victor Vescovo achieves the deepest dive of any human in history as he reaches Challenger Deep within the Mariana Trench, at a depth of 10,928 m (35,853 ft)