Geological timeline in fossils
By Ian Wilkinson
When we speak about geological time, we refer to hundreds or even thousands of millions of years – vast periods of time. To aid in our understanding of this long timeline, the time equivalents of the rocks are divided up into a number of eras and periods each of which is given a name. Perhaps the most famous is the Jurassic featured in the film “Jurassic Park”. Absolute ages can be assigned to these eras and periods by a number of methods, including the measurement of radioactive decay of certain minerals. This Pathfinder moves through geological time explaining Britain’s environment at each time-slice and showing examples of the animal or plant life fossilised in the rock succession.
- Periods/subperiods Periods/subperiods P549448.jpg A Pleistocene bivalve, Pholas, preserved in its burrow 0–2 Millions of years Quaternary (Holocene and Pleistocene epochs) Rapid climatic cooling which had begun in the Neogene continued into the Pleistocene, when four major glaciations occurred. During periods of ice retreat, the climate was quite warm and animals such as mammoths, ‘Irish Elk’, woolly rhinoceras, hyenas, bears, wolves and even hippopotamus and lions migrated to Britain (Britain was connected to mainland Europe due to the fall in sea level). Eventually humans reached Britain, the earliest species being Homo erectus. Around the coasts of Britain, marine sediments dating to this time are found. Fossils include bivalves, gastropods, fish, ostracods, brachiopods and echinoids. Britain during the Holocene times (the last 10 thousand years), has been mainly free from ice. P549520 A Pliocene coral, Flabellum woodi, that lived in the North Sea 2–23 Millions of years Neogene (Pliocene and Miocene epochs) The Miocene was a time of cooling and the evolution and spread of grasslands, steppes and savannas. However, withdrawal of the sea during Miocene times has left a gap in the succession in Britain (there are one or two small patches of rock that may be of this age and they are known to occur in the North Sea and off northern Scotland). In Britain the Neogene is represented by shallow marine Pliocene rocks (1.8 to 5 million years old). Those in East Anglia contain corals, bryozoa, bivalves, gastropods, terebratulids, brachiopods and ostracods. P550283 The Oligocene gastropod, Filholia elliptica, from the Isle of Wight 23–34 Millions of years Late Palaeogene (Oligocene epoch) In the Isle of Wight shallow marine conditions were sometimes replaced by freshwater environments. Pulmonate gastropods such as Planorbina, Galba and Filholia are often found, and leaves and insects may also be present. P549463 An Eocene leaf of Lauracaea, from Southern England 34–65 Millions of years Early Palaeogene (Eocene and Palaeocene epochs) Palaeocene and Danian rocks do not occur in Britain, although they both occur offshore. Rocks of Eocene age (34-55 million years old) are best preserved in southern England. Here shallow marine clays contain fossil plants such as mangroves on the coast, pines, cinnamon, ferns and flowering plants such as magnolia and blackberry. Reptiles like crocodiles lived in the warm waters, birds are occasionally found and invertebrate fossils abound including bivalves and gastropods. By the close of the Eocene, cooler climatic conditions were starting to be felt. P550271 A late Cretaceous echinoid, Temnocidaris sceptrifera 65–99 Millions of years Late Cretaceous This was a period characterised by the Chalk of Britain. Over 90% of this very pure limestone comprises the skeletons of microscopic single-celled algae. However many other marine organisms are also found, including echinoids, crinoids, ammonites, belemnites, bivalves and gastropods, together with a number of crustaceans and fish (including the coelocanth Macropoma). However, the end of the Cretaceous saw the extinction of the Dinosaurs, ammonites, belemnites, and most of the large marine reptiles. P549465 An early Cretaceous fern, Cladophlebis, that lived in the Wealden woodlands 99–142 Millions of years Early Cretaceous The Wealden woodlands covered southern England at this time. Cycads, conifers and treeferns abound and small ferns, horsetails, clubmosses and liverworts form the undergrowth. Flowering plants began to evolve at this time, although none has been recognised in Britain. It was in this area that most of the dinosaurs of Britain have been recorded. In the north, sediments yield early Cretaceous ammonites, bivalves, ostracods and other marine organisms. By Aptian and Albian times (??? million years ago, the land of southern England had been covered by the sea. P549559 A late Jurassic ammonite, Rasenia uralensis 142–205 Millions of years Jurassic Beginning in the latest Triassic and throughout most of the Jurassic, much of Britain was submerged beneath the sea. Islands formed during the mid-Jurassic in places and plants (including ginkgos) and dinosaur remains are found. The Jurassic is characterised more by its marine animals including the newly evolved ammonites, brachiopods, bivalves, crinoids, fish and marine reptiles. The extinction of the Palaeozoic rugose and tabular corals had taken place at the end of the Permian, and newly evolved scleractinian corals began to proliferate and build reefs. 205 Millions of years Permo-Triassic This was a time when most of Britain was land. Britain had moved further north away from the equator where its climate became arid. Although fish, reptilian footprints and plant spores are found in different parts of the rock sequence, compared to the Palaeozoic and Jurassic this was a time of few fossils. Elsewhere mass extinction events saw the disappearance of trilobites, rugose and tabulate corals and many other groups of animal. In Triassic times dinosaurs and mammals evolved. P549466 A late Carboniferous seed fern, Neuropteris 290–316 Millions of years Late Carboniferous Britain was on the equator where the climate was humid. The basins in which the marine animals proliferated in the early Carboniferous were filled by sands and muds as the rivers created massive deltas. The earliest forests grew here with giant clubmosses and horsetails; ferns, tree ferns and seed ferns; and in the drier areas, conifers. It is from this forest that Britain’s coal formed. Large insects and spiders inhabited the forests, amphibians lived on the waterside and the first reptiles had evolved (Westlothiana from East Kirkton, Scotland). P549523 An early Carboniferous coral, Siphonodendron junceum, from Ecclefechan, Scotland 316–354 Millions of years Early Carboniferous Much of southern Britain was covered by a warm tropical sea in which corals, brachiopods, crinoids, gastropods etc. lived with a variety of fish. This was the time when the last of the dendroid graptolites eventually went into extinction. P550306 A Devonian lungfish, Dipterus, from northern Scotland 354–417 Millions of years Devonian Much of Britain was a hot, barren land at this time, although south-western England and parts of Scotland were covered by the sea. Scottish waters were rich in fish including lungfish, whereas goniatites, ostracods, bivalves, brachiopods, corals are found in south-west England. It was during the Devonian that the last of the planktonic graptolites became extinct, although benthic dendroids continued into the early Carboniferous. P550304 A Silurian crinoid, Periechocrinus from the Welsh Marches 417–443 Millions of years Silurian This was a time when much of Britain was covered by the sea (Iapetus Ocean). Scotland was separated from England and Wales, and graptolites and trilobites lived in the deep waters. England and Wales were situated near the equator where shallow warm water contained corals, sponges, trilobites, gastropods, brachiopods and crinoids. In the deeper waters, graptolites, straight nautiloids and trilobites lived. In a few places (e.g. Wales) land emerged through the waves and the earliest vascular plants grew. They were small and lacked leaves. P549553 An Ordovician graptolite, Didymograptus murchisoni 443–495 Millions of years Ordovician This was a time of continued evolutionary radiation. Trilobites reached their peak of diversity, brachiopods were the dominant form amongst the shelly animals, one of the straight types of nautiloids grew to over 4.5 m. long, a giant of its day, and corals began a phase of diversification. Amongst the planktonic species, graptolites were hugely successful and evolved rapidly. Late in the period, spores of non-vascular plants (distant relatives of moss and liverworts) were just beginning to colonise the land. P550301 Cambrian triliobite, Paradoxides davidis from Wales 495 Millions of years Cambrian Rocks of this age occur in Scotland, Wales and a few places in England. They are mainly marine sediments, with animals such as trilobites, brachiopods, gastropods and worms. Biomineralisation resulted in shells and skeletons for the first time P550159 Late Precambrian Charnia, the earliest multicelled animal known in Britain 545–4600 Millions of years Late Precambrian Britain has relatively few Precambrian rocks, but there are river-lain and marine deposits in some places. Although fossil bacteria and rocks known to have formed through the action of bacteria (Banded Ironstone Formations) are known in some parts of the world, there are none known in Britain. However, about 600 million years ago, some of the earliest multi-celled organisms lived in Britain, including soft-bodied sea pens. Burrows are also found.| Era | Fossil | Millions of years | Period/subperiods |
| Cainozoic | 0-2 | Quaternary (Holocene and Pleistocene epochs): Rapid climatic cooling which had begun in the Neogene continued into the Pleistocene, when four major glaciations occurred. During periods of ice retreat, the climate was quite warm and animals such as mammoths, ‘Irish Elk’, woolly rhinoceras, hyenas, bears, wolves and even hippopotamus and lions migrated to Britain (Britain was connected to mainland Europe due to the fall in sea level). Eventually humans reached Britain, the earliest species being Homo erectus. Around the coasts of Britain, marine sediments dating to this time are found. Fossils include bivalves, gastropods, fish, ostracods, brachiopods and echinoids. Britain during the Holocene times (the last 10 thousand years), has been mainly free from ice. | |
| Cainozoic | 2-3 | Neogene (Pliocene and Miocene epochs): The Miocene was a time of cooling and the evolution and spread of grasslands, steppes and savannas. However, withdrawal of the sea during Miocene times has left a gap in the succession in Britain (there are one or two small patches of rock that may be of this age and they are known to occur in the North Sea and off northern Scotland). In Britain the Neogene is represented by shallow marine Pliocene rocks (1.8 to 5 million years old). Those in East Anglia contain corals, bryozoa, bivalves, gastropods, terebratulids, brachiopods and ostracods. | |
| Cainozoic | 23-34 | Late Palaeogene (Oligocene epoch): In the Isle of Wight shallow marine conditions were sometimes replaced by freshwater environments. Pulmonate gastropods such as Planorbina, Galba and Filholia are often found, and leaves and insects may also be present. | |
| Cainozoic | 34-65 | Early Palaeogene (Eocene and Palaeocene epochs) : Palaeocene and Danian rocks do not occur in Britain, although they both occur offshore. Rocks of Eocene age (34-55 million years old) are best preserved in southern England. Here shallow marine clays contain fossil plants such as mangroves on the coast, pines, cinnamon, ferns and flowering plants such as magnolia and blackberry. Reptiles like crocodiles lived in the warm waters, birds are occasionally found and invertebrate fossils abound including bivalves and gastropods. By the close of the Eocene, cooler climatic conditions were starting to be felt. | |
| Cainozoic | 65-99 | Late Cretaceous: This was a period characterised by the Chalk of Britain. Over 90% of this very pure limestone comprises the skeletons of microscopic single-celled algae. However many other marine organisms are also found, including echinoids, crinoids, ammonites, belemnites, bivalves and gastropods, together with a number of crustaceans and fish (including the coelocanth Macropoma). However, the end of the Cretaceous saw the extinction of the Dinosaurs, ammonites, belemnites, and most of the large marine reptiles. | |
| Cainozoic | 99-142 | Early Cretaceous: The Wealden woodlands covered southern England at this time. Cycads, conifers and treeferns abound and small ferns, horsetails, clubmosses and liverworts form the undergrowth. Flowering plants began to evolve at this time, although none has been recognised in Britain. It was in this area that most of the dinosaurs of Britain have been recorded. In the north, sediments yield early Cretaceous ammonites, bivalves, ostracods and other marine organisms. By Aptian and Albian times (??? million years ago, the land of southern England had been covered by the sea. | |
| Cainozoic | 142-205 | Jurassic: Beginning in the latest Triassic and throughout most of the Jurassic, much of Britain was submerged beneath the sea. Islands formed during the mid-Jurassic in places and plants (including ginkgos) and dinosaur remains are found. The Jurassic is characterised more by its marine animals including the newly evolved ammonites, brachiopods, bivalves, crinoids, fish and marine reptiles. The extinction of the Palaeozoic rugose and tabular corals had taken place at the end of the Permian, and newly evolved scleractinian corals began to proliferate and build reefs. | |
| Cainozoic | 205-290 | Permo-Triassic: This was a time when most of Britain was land. Britain had moved further north away from the equator where its climate became arid. Although fish, reptilian footprints and plant spores are found in different parts of the rock sequence, compared to the Palaeozoic and Jurassic this was a time of few fossils. Elsewhere mass extinction events saw the disappearance of trilobites, rugose and tabulate corals and many other groups of animal. In Triassic times dinosaurs and mammals evolved. | |
| Cainozoic | 290-316 | Late Carboniferous: Britain was on the equator where the climate was humid. The basins in which the marine animals proliferated in the early Carboniferous were filled by sands and muds as the rivers created massive deltas. The earliest forests grew here with giant clubmosses and horsetails; ferns, tree ferns and seed ferns; and in the drier areas, conifers. It is from this forest that Britain’s coal formed. Large insects and spiders inhabited the forests, amphibians lived on the waterside and the first reptiles had evolved (Westlothiana from East Kirkton, Scotland). | |
| Cainozoic | 316-354 | Early Carboniferous: Much of southern Britain was covered by a warm tropical sea in which corals, brachiopods, crinoids, gastropods etc. lived with a variety of fish. This was the time when the last of the dendroid graptolites eventually went into extinction. | |
| Cainozoic | 354-417 | Devonian: Much of Britain was a hot, barren land at this time, although south-western England and parts of Scotland were covered by the sea. Scottish waters were rich in fish including lungfish, whereas goniatites, ostracods, bivalves, brachiopods, corals are found in south-west England. It was during the Devonian that the last of the planktonic graptolites became extinct, although benthic dendroids continued into the early Carboniferous. | |
| Cainozoic | 417-443 | Silurian: This was a time when much of Britain was covered by the sea (Iapetus Ocean). Scotland was separated from England and Wales, and graptolites and trilobites lived in the deep waters. England and Wales were situated near the equator where shallow warm water contained corals, sponges, trilobites, gastropods, brachiopods and crinoids. In the deeper waters, graptolites, straight nautiloids and trilobites lived. In a few places (e.g. Wales) land emerged through the waves and the earliest vascular plants grew. They were small and lacked leaves. | |
| Cainozoic |  |
443-495 | Ordovician: This was a time of continued evolutionary radiation. Trilobites reached their peak of diversity, brachiopods were the dominant form amongst the shelly animals, one of the straight types of nautiloids grew to over 4.5 m. long, a giant of its day, and corals began a phase of diversification. Amongst the planktonic species, graptolites were hugely successful and evolved rapidly. Late in the period, spores of non-vascular plants (distant relatives of moss and liverworts) were just beginning to colonise the land. |
| Cainozoic | 495-545 | Cambrian: Rocks of this age occur in Scotland, Wales and a few places in England. They are mainly marine sediments, with animals such as trilobites, brachiopods, gastropods and worms. Biomineralisation resulted in shells and skeletons for the first time. | |
| Cainozoic |  |
545 4600 | Late Precambrian: Britain has relatively few Precambrian rocks, but there are river-lain and marine deposits in some places. Although fossil bacteria and rocks known to have formed through the action of bacteria (Banded Ironstone Formations) are known in some parts of the world, there are none known in Britain. However, about 600 million years ago, some of the earliest multi-celled organisms lived in Britain, including soft-bodied sea pens. Burrows are also found. |
