Visions of the Cosmos

Life Among the Stars

The History of Earth - the Last 600 Million Years

THE STRATIGRAPHICAL COLUMN

ERA PERIOD EPOCH BEGAN Mya ENDED Mya COMMENTS
Pre-Cambrian Archaen Hadean 4,560 3,800 Moon formed about 4,500 Mya.  Age of bombardments and 3,9000Mya Age of Late Bombardments. Some suggest that Hadean ended earlier
    Isuan 3,800 3,500 Life probably began about 3,800 million years ago
    Swazian 3,500 2,800 First oxygen metabolising  organisms Stromatolites - Cyanobacteria
    Randian 2,800 2,500  
  Proterozoic Huronian 2,500 2,200  
    Mongolian 2,200 1,600  
    Riphean 1,600 800  Increase in Cyanobacteria - Increase in Free Oxygen
    Sturtian 800 610 Snowball Earth occurred during this time
    Vendian 610 540 Clear evidence of soft bodied fossils
Lower.Palaeozoic Cambrian   540 500 Cambrian Explosion  At end of Cambrian First Mass Extinction
  Ordovician   500 439 At end Second Mass Extinction
  Silurian   439 409  
Upper Palaeozoic Devonian   409 360 'Age of Fishes
  Carboniferous   360 290 Europe and North America were Equatorial / Coal formed
  Permian   290 250 End of Permian Third Mass Extinction - 'The Great Dying'
Mesozoic Triassic   250 206 Fourth Mass Extinction
  Jurassic   206 144 So warm that animals and plants could live in the polar regions.  No ice or snow
  Cretaceous   144 65 Fifth Mass Extinction
Cainozoic Tertiary Palaeocene 65 55  
    Eocene 55 34  Warm global climate.  Whales probably found their home in the water during this epoch, evolving from hoofed carnivores.
    Oligocene 34 23 Climate colder Antarctic freezing up
    Miocene 23 5 Indian Plate collides with Asia.  Himalayas Rockies and Appalachians form.  Climate gets even colder than in Oligocene. Antarctic Ice increases
    Pliocene 5 1.8 Additionally, the Panamanian Isthmus land-bridge between North and South America appeared during the Pliocene. Arctic starts to freeze
Quaternary Quaternary Pleistocene 1.8 0.01 It was during the Pleistocene that the most recent episodes of global cooling, or ice ages, took place. H sapiens and  Neanderthal Humans
    Holocene 0.01 present day HUMANS are separated from the rest of the animal kingdom in that we can change nature. During the late Holocene, a majority of the climate changes have been due to activity of humans.  Warmer than the Pliestocene

Almost every encyclopaedia and text book on geology provides a stratigraphical column.  Some choose to put the earliest time at the top from Pre-Cambrian to the present day (Holocene).  Others do the reverse.   Some divide geological time into eons, eras, periods and epochs -  others use eras, periods and epochs only.

There is general agreement as to when each period and epoch begins and ends .  However there are slight disagreements on these points.  The approximate ages on the above column are taken from an excellent chart published by Pan Terra Inc - PO Box 556 - Hill City -SD - 57745. USA and obtainable from HM Ordnance Survey Office in The Natural History Museum - South Kensington - London.

Our planet did not just start 4,650  million years ago nor did life begin around 3,800 million years ago.  They both started at the moment of the Big Bang and the information for their beginning was coded in the laws of nature and the properties of the quarks, electrons, gluons and photons which dictated the properties baryonic matter.  This is a question we shall refer to in much later sections of the web-site.

Only 50 years ago scientists knew little about the history of our planet.  The work of Arthur Holmes and his co-workers had already fixed the age of the Earth as about four and a half billion years old but little was known of the history of our planet before the beginning of the Cambrian period and everything before it was more or less consigned to one enormous era called the Pre-Cambrian which represented about 87% of the total age.  It was this that led to the term Cambrian Explosion since it appeared that advanced animal marine life suddenly erupted onto the scene about 544 million years ago.  Since then clear fossil evidence of soft animals who lived between 610 and 544 million years ago has been found in Australia and Russia and a period called the Vendian or Eriacarian has been assigned to this period.  The question of the Pre-Cambrian, the Vendian and the Cambrian Periods have been dealt with in the two previous pages of the web-site and now we are passing on to discuss the ages that began after the end of the Cambrian.

The Ordovician Period 

490 to 443 Million Years Ago

As the Cambrian came to an end there was a large mass extinction often referred to as the first mass extinction.  The Ordovician period began approximately 510 million years ago, with the end of the Cambrian, and ended around 445 million years ago, with the beginning of the Silurian At this time, the area north of the tropics was almost entirely ocean, and most of the world's land was collected into the southern super-continent Gondwanaland.  the world during Ordovician times During the Ordovician, Southern Europe, Africa, South America, Antarctica and Australia remained joined together into Gonwanaland, which had moved down to the South Polar regions.    North America straddled the equator, and was about 45 degrees clockwise from its present orientation.  Western and Central Europe were separated from the rest of Eurasia,  and were in the southern tropics.. Volcanoes went rampant during the Ordovician, causing many igneous rocks to form out of ash and lava. The Ordovician was marked by periods of continental submergence. This climaxed into the Late Ordovician Flood that was the most widespread ever recorded.  There was therefore less 'dry land ' than there is today and the globe was covered by a little over 80% of ocean.   A major transgression in the Middle Ordovician created widespread shallow, warm epicontinental seas.  Thus, most of the Ordovician was favourable for marine life, particularly around the continental shelves of the European and North American plates.

Because of the floods, Ordovician life was very different to Cambrian life.  The Ordovician is best known for the presence of its diverse marine invertebrates, including graptolites, trilobites, brachiopods, and the early vertebrates such as armoured, jawless fish,.  A typical marine community consisted of these animals, plus red and green algae, primitive fish, cephalopods, corals, crinoids, and gastropods.

Algae were abundant, and a lot of them formed reefs in the widespread ocean. It is unknown whether plants lived on land or not in this period. If they did, it would probably have been in the form of moss and lichens.  Recently, evidence has been found of tetrahedral spores that are similar to those of primitive land plants, suggesting that plants invaded the land at this time.

From the Early to Middle Ordovician, the earth experienced a milder climate in which the weather was warm and the atmosphere contained a lot of moisture. A major transgression in the Middle Ordovician created widespread shallow, warm epicontinental seas.  Thus, most of the Ordovician was favourable for marine life, particularly around the well-studied European and North American cratons

However, the Ordovician ended in a brief but very severe ice age.    During the Late Ordovician, massive glaciers formed over large parts of Gonwanaland covering the South Pole formed causing shallow seas to drain and sea levels to drop. This may have been the cause the mass extinctions that characterize the end of the Ordovician, in which 60% of all marine invertebrate genera and 25% of all families went extinct.   However, the Ordovician ended in a brief (300-500 ky), but severe, ice age.  Gonwanaland, particularly Africa, straddled the South Pole and became extensively glaciated.  There were even glaciers in what is now the Sahara.  Animals were severely effected. The end of the period is marked by an extinction event.  About 60% of animal genera became extinct, making this the second or third most deadly mass extinction of all time.

A spectacular success story were the nautiloid cephalopods.  Small and rare in the late Cambrian, the nautiloids evolved quickly along many different lines.  At least ten different orders flourished at this time, all but one appearing for the first time during the early or middle part of the Ordovician.    These intelligent carnivorous creatures replaced the Cambrian Anomalocarids as the dominant life form and top predator of the world's ocean.  The biggest, such as the endocerides attained huge size; with shells of up to 10 meters in length they were the largest animal that, up until that time, had ever lived. The tremendous evolutionary radiation of nautiloid cephalopods meant an increase in the level of consciousness in Paleozoic oceans.  Cephalopods are the most intelligent of all invertebrates, owing to the development of elaborate manipulative organs (tentacles for touching and grasping).  One researcher described the common octopus as like a sort of aquatic dog or cat.  Although Ordovician cephalopods were probably not equal to modern forms in intelligence, they were certainly superior to that of contemporary (non-cephalopod) life-forms.  It may be that the seas of the world would have to wait many millions of years until in relatively modern times the dolphins and whales surpassed the cephalopods in intelligence.

Illustration of Cephalopod attacking a trilobite in Ordovician times Credit for illustration to University of Michigan Exhibit Museum, Carl Wozniak. (Earth History Resources)  Credit for illustrations to  Earth History Resources Contact  Carl Wozniak  e-mail cwozniak@nmu.edu.

The Silurian Period

443 to 417 Million Years Ago

 

graphic from Naturmuseum Senckenberg (Centre for Biodiversity Research)

 

drawing shows Eurypterids, rhynchonelid brachiopods, and trilobites (left); primitive fish, more brachs, various types of corals, stalked crinoids, archaeogastropod, and drifting Jawless fish invade brackish and fresh water, as do eurypterids, xiphosurids, scorpions, which may have been semi-aquatic.  Rhyniophytes, primitive lycopods, and myriapods became the first proper land organisms.  At the end of the period Jawed fish appeared for the first time, but they remain insignificant.graptolites (center); and more corals, another trilobite, and several types of nautilod cephalopod (right)

 

Following the Ordovician extinction event there was a rapid recovery of invertebrate faunas during the Silurian.  The high sea levels and warm shallow continental shelf seas provided a hospitable environment for marine life of all kinds.    The Silurian (443 to 417 million years ago) was a time when the Earth underwent considerable changes that had important repercussions for the environment and life within it. The Silurian witnessed a relative stabilization of the earth's general climate, ending the previous pattern of erratic climatic fluctuations. One result of these changes was the melting of large glacial formations. This contributed to a substantial rise in the levels of the major seas

The ecology was basically still similar to that of the Ordovician, but was more diverse.  .

. Coral reefs made their first appearance during this time, and the Silurian was also a remarkable time in the evolution of fishes. Not only does this time period mark the wide and rapid spread of jawless fish, but also the highly significant appearances of both the first known freshwater fish as well as the first fish with jaws. Jawless fish and scorpions invaded brackish and fresh water. 

It is also at this time period that our first good evidence of life on land is preserved, including relatives of spiders and centipedes, and also the earliest fossils of vascular plants.  The most important evolutionary development of this period, was that of the first true terrestrial ecosystem.  The first fossil records of vascular plants, that is, land plants with tissue that carries food, appeared in the Silurian period. They were simple plants that had not developed separate stems and leaves.

The Devonian Period

417 to 354 Million Years Ago

To the left a cluster of crinoids wave in the shallow water currents.  Nearby are assorted corals and brachiopods.  Several types of armoured fish swim, or rest on the sandy bottom.  To the right are two eurypterids ("sea scorpions"), with an acanthodian fish just above.  On land the first primitive plants move ashore.
graphic from Naturmuseum Senckenberg (Centre for Biodiversity Research)

During the Devonian, there were three major continental masses: North America and Europe sat together near the equator, much of their current land was flooded by shallow seas.  To the north lay a portion of modern Siberia. A composite continent (Gonwanaland) consisting of South America, Africa, Antarctica, India, and Australia dominated the southern hemisphere.

As far as life was concerned the Devonian was a time of great transition.  In the sea many new kinds of ammonites and fish evolved.  The Devonian is sometimes referred to as 'The Age of Fishes'  . Crinoids and other echinoderms and rugose corals.

On land trees and forests appear for the first time.   During the Devonian, some major animal groups colonized the land. Most noteworthy were a group of land vertebrates - the tetrapods In addition the first terrestrial arthropods, including wingless insects and the earliest group of animals belonging to the spiders (arachnids) appeared on the scene.

The Carboniferous Period

354 to 290 Million Years Ago

During the Carboniferous Period the tectonic plates were moving towards the creation of the super-continent Pangae.  The map of the world during the Serpukhovian Period around 329 million years ago is shown below

ATW041219.  Map public domain.  No rights reserved.  An enormous, 2400 x 1200 pixel, unlabelled version of this map is available (free) in all the usual formats, including a Photoshop .psd file with each topographical type on a different layer.    Email augwhite@sbcglobal.net

 

Credit for coloured illustration of Carboniferous Forest to University of Michigan Exhibit Museum, Carl Wozniak. (Earth History Resources) e-mail cwozniak@nmu.edu

 

 

 

 

 

 

 

Illustration from a 19 century print by Hawkins in 1884

Dragonflies are regarded by many as the jewels of the insect world. For centuries, they have been revered by humans and celebrated in art, poetry and religion. The modern-day dragonflies are the descendants of giant insects that flew in the prehistoric forests of the Carboniferous era.

In addition to having the ideal conditions for the beginnings of coal, several major biological, geological, and climatic events occurred during this time. One of the greatest evolutionary innovations of the Carboniferous was the amniote egg, which allowed for the further exploitation of the land by certain tetrapods. The amniote egg allowed the ancestors of birds, mammals, and reptiles to reproduce on land by preventing the desiccation of the embryo inside. There was also a trend towards mild temperatures during the  Carboniferous, as evidenced by the decrease in lycopods and large insects and an increase in the number of tree ferns

By the Late Carboniferous the continents that make up modern North America and Europe had collided with the southern continents of Gondwana to form  the western half of Pangea.    By early Late Carboniferous, the South American-North African margin of Gondwanaland had collided with the northern Devonian super-continent of Euramerica (or Laurasia). .  There is regional subsidence of the East-European Platform (east Laurussia/Euramerica) due to compressional stresses at the platform's margins.  The northward drifting Gondwanaland then collided with Laurasia, resulting in a fold belt and mountain building from Poland through central Europe to the Appalachians.  Through the collision of these two super-continents arose the super-super-continent of Pangea.  Ice covered much of the southern hemisphere and vast coal swamps formed along the equator.  Europe and North America were close to the equator.   The lowlands were covered by huge tropical and equatorial forests.  Europe and North America were close to the equator.   So vigorous was the growth of these ancient trees that they seemed to have sucked much of the carbon dioxide out of the atmosphere, producing a surfeit of oxygen. Oxygen levels were higher during this time than at any other time in the history of the Earth  Oxygen constituted  about 35%.  The moist tropical climate produced a lush plant growth, which eventually becomes the great Coal Deposits (hence the name Carboniferous - "coal bearing")  Massive trees such as the Lepidodendrons and Siggalarians.During late Carboniferous times the great northern party of the southern continent of Gonwanaland and the continent of Laurasia now Northern America and Europe ground up against one another and a huge range of mountains was formed

Although the equatorial regions remained warm and wet and tropical, the poles became gripped in a massive ice age, one that lasted for many millions of years.  Vast sheets of ice covered southern Gondwanaland.

.On land, especially in the Euramerican part of Pangea, the equatorial regions are covered by forests. . The fern-like but seed-bearing pteridosperms, the huge green-stemmed Lepidodendron lycopods(Lepidodendron, Sigillaria, etc, 35 meters tall), the giant sphenopsid Calamites (20 meters in height), and the strap-leaved mangrove-rooted Cordaitales (Cordaites, up to 45 meters) are all abundant, and tied closely to water. The drier uplands were much more sparsely covered. Meanwhile, Gondwanaland, with its colder Antarctic climate, has its own very distinct flora, dominated by glossopterid pteridosperms.

The Permian Period

290 to 248 Million Years Ago

During the Permian Period all the world's land masses became welded together  into a single super-continent which has been given the name PANGEA meaning  ALL EARTH or ALL LAND.  Similarly the Ocean has been given the name PANTHALASSA meaning ALL SEA. In the region of present-day North America, the Appalachian Mountains were formed, along with the Urals in Asia and the Austrian Alps.

Pangea was shaped sort of like a giant "Pacman", with the mouth on the east.   There was a correspondingly large ocean, called  the Panthalassic Ocean.  The body of water enclosed by the pacman mouth constituted a smaller sea, the  Paleo-tethys Ocean or just Tethys which covered much of what is now southern and central Europe.

Those parts of the super-continent near the poles were heavily glaciated but most of the continent was warm and dry.

An excellent library of palaeogeographical maps has been compiled by Professor Chris Scotese of the University of Texas and many thanks are given to him for permission to show the map of the world in Permian times, 255 million years ago.  I have put in a  Hyperlink to Palaeogeographic  Maps

Credit"Plate tectonic maps and Continental drift animations by C. R. Scotese,
PALEOMAP Project (www.scotese.com)"

Pangea was shaped sort of like a giant "Pacman", with the mouth on the east.   There was a correspondingly large ocean, called  the Panthalassic Ocean.  The body of water enclosed by the pacman mouth constituted a smaller sea, the  Paleo-tethys Ocean or just Tethys which covered much of what is now southern and central Europe.

Due to the formation of the super-continent Pangea, the sea level dropped and the warm shallow seas declined in extent.  This is one of the factors that may have led to the extinction of many life-forms at the end of the period.

An excellent survey of the Mass Extinction which occurred at the end of the Permian Period is given in a web-site published by the Bristol University.  This website is one in a series of Palaeofiles produced by students following the palaeobiology programmes at Department of Earth Sciences in the University of Bristol -  Authors: Anna Goodwin, Jon Wyles and Alex Morley (2001)

 

Dimetrodons sunning themselves by Calamite Trees                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    A Permian reef, with spiny-shelled nautiloid

Credit for illustrations to University of Michigan Exhibit Museum, Carl Wozniak. (Earth History Resources)

In the late Permian, Europe was covered by a very salty inland sea, the Zechstein sea, which advanced and receded at least twice. This was home to an impoverished fauna, mainly brachiopods and bivalves, which were able to cope with the hypersaline conditions.

There were several periods in which salty inland seas evaporated to leave salt deposits which now represent valuable mineral deposits.  In particular the Stassfurt deposits in Germany have been extensively exploited.  Much valuable work was carried out by Professor v'ant Hoff, who is referred to in another part of this web site, on the Stassfurt deposits.

 The Mesozoic Era

The Mesozoic Era is Divided into Three Periods, The Triassic, The Jurassic and The Cretaceous

The Triassic Period

248 to 206 Million Years Ago

The Triassic was a hot-house word with no evidence of ice at the poles.  During the period the Super continent of Pangea expanded to it's maximum extent. The increased distance from the sea dried out the interior of the continent, producing increasingly arid conditions. Large inland seas formed and dried out leaving salt flats .  Many of the salt deposits  come not only from the Zechstein but also from the hypersaline seas of other periods.

The huge extinctions that occurred at he end of the Permian Period had cleared many of the evolutionary niches for new colonisers to evolve which led to an evolutionary race. This race led not only to the rise of the dinosaurs but also to many other important groups including, the crocodilians ( the crocodile group), the pterosaurs (a group of ancient flying reptiles), the turtles, and the mammals.

The mammal-like reptiles that dominated the Permian, were virtually wiped out by the Permian mass extinction.

The mammal-like reptiles are extensively described in web-site URL http://www3.telus.net/therapsid/index.htm

A branch of the therapsids called cynodonts survived the Permian, and in the Early Triassic radiated into herbivorous and carnivorous animals which achieved worldwide success.  Through the Triassic some reptiles became ever more mammal like..  There is evidence that during the Triassic the cynodonts, a large group of mammal-like reptiles, were warm blooded.  They had whiskers and the argument goes that, whiskers meant the animals had hair, and the presence of fur means they could keep the heat in.  This suggests that they were warm blooded, like mammals (including ourselves) today, rather than the reptilian method of absorbing body heat from the sun. 

Above all  the Triassic saw the rise of a group which would lead to some of the largest and most terrible animals ever to walk the earth, the Dinosaurs.

The Jurassic Period

206 to 144 Million Years Ago

During the Jurassic Period the giant continent Pangaea broke up into two landmasses known as Laurasia (in the north) and Gondwanaland (in the south). A channel separated Eurasia from North America which would one day become the huge Atlantic Ocean  A shallow sea, later to become the Mediterranean, flooded central Europe and separated it from Asia.

The Jurassic climate stayed warm and became very  humid. The great deserts of the Triassic were transformed into warm and life bearing places.  The polar areas were ice-free during this Period and plants grew in the polar regions.,

As the deserts shrank and more humid climate progressed, ferns cycads and ginkgoes flourished. The early traces of flowering plants started. They were to become the commanding plants during the Cretaceous Period

In the Jurassic Dinosaurs became larger and more varied. One group of these dinosaurs to evolve was the Sauropods, which included Brontosaurus, Diplodocus, and Brachiosaurus. Brachiosaurus was among the largest land animals to ever live. It was 80 feet (24 meters) long and weighed up to 50 tons. It could eat the branches of trees up to 40 feet high. Diplodocus was 90 feet long. One of the only predators capable of attacking the large herbivorous dinosaurs of attacking the  ferocious Allosaurus, which also appeared in the Jurassic. It was 30 feet long, and it would give rise to even larger carnivores, such as the infamous Tyrannosaurus Rex, in the Cretaceous. In the skies, the Pterosaurs, a large group of flying reptiles, reigned. But another flier also sprouted wings. The first known bird, Archaeopteryx, was probably descended from the dinosaurs and is first found  in the Jurassic.  The picture is taken from the book by Heinrich Harder (1858-1935)Tiere Der Umwelt published in 1916.

 

 

The first birds developed during the Jurassic.  They were in fact a type of dinosaur with feathers.  In fact one important group of them were the only dinosaurs to survive the mass extinction and are still with us.  The archaeopterix was one of the first birds and the Illustration is taken from

In the seas the sea reptiles flourished.  Their fossil remains were discovered in the early part of the nineteenth century by a remarkable woman whose discoveries play a major role in the Natural History Museum in London.  Her name was Mary Anning and a separate page is devoted to her and to her discoveries in this web-site.

 

The Cretaceous Period

144 to 65 Million Years Ago

The Cretaceous is usually noted for being the last portion of the "Age of Dinosaurs", but that does not mean that new kinds of dinosaurs did not appear then. It is during the Cretaceous that the first cerapopsian and pachycepalosaurid dinosaurs appeared. Also during this time, we find the first fossils of many insect groups, modern mammal and bird groups, and the first flowering plants. In the plant world ferns, horsetails, ginkgoes and cycads thrived.  One of the most significant changes however was the evolution of the angiosperms that is flowering plants.  This included grasses, fruits and vegetables.  Even before the great extinction the foundations of the modern world were laid

The break up of the world-continent Pangaea, which began in the Jurassic, continued in the Cretaceous This led to increased regional differences in floras and faunas between the northern and southern continents. Laurasia (Northern Continent) and Gondwanaland (Southern Continent) were finally separated in the early Cretaceous. Later, South America separated from Africa and Australia from Antarctica.   India also detached from Gondwanaland about 100 million years ago, establishing the first step of its 8000-km long journey to the rest of Asia.   Evolution took a very interesting  twist there.   The marsupials evolved and became predominate in Australia. in those separate places. Only in South Americas do we find the Edentates or 'toothless mammals' which includes armadillos, sloths, and anteaters. These animals formed in no other place in the world. India took its first step on its 8,400 kilometre journey to Asia.                                                                              

                                                                                                       The map shows the world in the Cretaceous 94 Million years ago

                                                          Credit" Plate tectonic maps and Continental drift 
                                                            by  C. R. Scotese,PALEOMAP Project (www.scotese.com)"
                                

A separate page of the web-site is devoted to Mass Extinctions which includes the extinction event at the end of the Cretaceous which changed the world forever.

 

Hyperlinks

Previous Page The Cambrian Extinction

In the next page we shall discuss the Triumph of the Mammals ending so far in the dominance of the human species

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Mary Anning

Mass Extinctions