Geological time is usually divided into two unequal divisions determined by the emergence of many shelled fossils at the beginning of the Cambrian. For many years the Cambrian ➚ was considered to be devoid of life, but it is now known that life existed for many hundreds of millions of years before the start of the Cambrian. The rarity of fossils means that radiometric ages are needed to correlate rocks of PreCambrian (from the formation of the Earth approximately 4000Mya to the start of the Cambrian 570Mya ago). The name Cambrian was given by Adam Sedgwick ➚ after the Roman name for Wales.
The time line shows a mixture of geological events both tectonic and biological since the later stages of the Precambrian (meaning before Cambrian). The age in million years before present is shown in the first column.
|700||Pre-Cambrian. Plenty of life but only trace fossils were left. For a long time the PreCambrian was thought to be lifeless as no clear fossil remains could be found.|
580 Start of break up of vast supercontinent which formed most of the Earth's continental landmass. The South American
plate breaks away from the East coast of North America and begins its long journey South.
Antarctica/India rifts away from Africa.
570 Start of Cambrian and Palaeozoic Era. End of late PreCambrian glaciations
Start of shelly fossils. Life already divided into five main groups ➚ : Monera (Bacteria, some algae); Protoctista (Protozoans, algae with nucleii, slime moulds); Fungi ; Plantae ; Animalia (including sponges). Transitional development over 30Mya best seen in rocks of Yunnan, China.
|550||Cambrian. Diversification of many fossil groups. Trilobites abundant and in many forms.|
492 Start of Ordovician
First Chordata (Animals with backbones) in the form of fish that eventually evolved into amphibians, reptiles and mammals.
480 A small plate bearing Spain, Southern UK, Scandinavia and Eastmost USA breaks away from Northern Gondwanaland
443 Massive extinction event, probably related to extensive Ice Age.
440 Start of Silurian
Ice recedes and a lot of land inundated by shallow seas under warm conditions.
Life flourishes again
First land plants (including ancestors of ferns and horsetails) and probably land animals.
405 Start of Devonian
Collision of Northern Europe and Eastern America, formation of Caledonian and Appalachian mountains.
First Gymnosperm land plants in form of seed ferns and conifers
|350||335 Start of Carboniferous
Land plants extremely prolific
Laying down of coal measures over wide areas
290 Start of Permian
260 Closure of ocean separating Africa/South America with North America, formation of the vast 'supercontinent' of Gondwanaland ➚.
250 Start of Triassic System and Mesozoic Era.
240 Creation of Urals by collision of the two halves of Siberia.
205 Start of Jurassic. Heyday of dinosaurs
|200||170 Start of Break up of the vast supercontinent of Gondwanaland. North America/Northern Europe/Asia breaks away from Africa/South America/Antarctica.|
150-70 Start of long process of plate accretion on the Western seaboard of
North America forming the Rockies in a series of intense volcanic episodes
140 Collision of N. China and North/Eastern Asia
135 Start of Cretaceous
First flowering seed plants (Angiosperms). The Cretaceous takes its name from the 'Chalk' that is the characteristic rock of the period. The chalk that forms the White cliffs of Dover was deposited in vast quantities over a large area of shallow sea. Chalk is formed from the remains of tiny calcareous algae called coccoliths.
130Break away of India from Gondwanaland
|100||100 Break away of Australian plate from Gondwanaland
66 Start of Tertiary System and Caenozoic Era
The famous K-T (Cretaceous-Tertiary) boundary marking the demise of the dinosaurs is now thought to relate to the impact of a meteorite in the Yucatan peninsular. Other evidence suggests that life was already stressed by the global atmospheric effect of the eruption of the massive Deccan basalt lava flows in India.
60 Rifting apart of the North Atlantic between Greenland and Scandinavia.
24 Start of Miocene Epoch within NeoGene
20 Collision of India and Asia to form Himalayas, a process still in operation today
10 Closure of Eastern Mediterranean when Africa collided with Europe, Creation of mountain ranges through Iraq and Iran. Formation of Alps by collision of Italy (part of African plate) and Europe
5 Formation of Central American barrier to separate the Pacific and Atlantic Oceans.
2 Pleistocene mass glaciation
1 Emergence of Homo Sapiens