Visions of the Cosmos

Life Among the Stars

The Triumph of the Mammals

With the demise of the dinosaurs and the other vast changes that occurred at the end of the Cretaceous a new world was born.  The Mass Extinction left the field free for the evolution of a totally new flora and fauna but the most significant change of all was the rapid evolution of the most intelligent land animals of all time - the mammals - culminating in the coming of the human species. 

It is a strange thought that perhaps if the dinosaurs had not been killed in the mass extinction event sixty five million years ago we might not be here.

The Cainozoic

The Period after the demise of the dinosaurs is known as the Cainozoic which is sub-divided into the Tertiary which includes the Palaeocene, Eocene, Oligocene, Miocene and Pliocene epochs and the Quaternary which includes the Pleistocene and the Holocene

The table below shows these epochs together with the main events occurring during each epoch.

The Palaeocene, Eocene and Oligocene are collectively called the PALAEOGENE.  The Miocene and Pliocene are together called the NEOGENE.  The Cenozoic was an important period in Earth's climatic history, since it records the change from greenhouse climates during the early Palaeogene to icehouse climates in the Neogene. In particular, the record of this major climate transition in the Southern Hemisphere is important because it involves the initiation and development of the Antarctic ice sheet, which now exerts a major control on our global climate.

 
Epoch Meaning of Name Time Period Mya Events
Palaeocene Ancient Recent Life 65 - 55 million years ago epoch ended in a large global warming event
Eocene Dawn of Recent Life 55 - 34 million years ago  
Oligocene Slightly Recent Life 34 - 24 million years ago  
Miocene Less Recent Life 24 -.5.3 million years ago The Indian plate finally collided with Asia. The  Himalayas formed
Pliocene More Recent Life 5.3 - 1.8 million years ago Isthmus of Panama formed land-bridge as the North and South American Plates collided
Pleistocene Most Recent Life 1.8 - 0.01 million years ago  Ice Ages.Emergence of Homo Sapiens and Homo Neanderthalis  The Tobe Volcano
Holocene Completely  Recent Life The last 10,000 years Ice retreats . Development of Agriculture. Rise of Civilisation. Domination of humans over all other animals

Palaeocene and Eocene Epochs

During these time the climate was much warmer than it is to-day.  A recent paper published in Nature (1 Jun 2006) discusses Arctic Ocean temperatures during the Palaeocene/Eocene thermal maximum.  The paper deals with the warm seas of the Arctic Ocean round about 55 million years ago.  The Palaeocene/Eocene thermal maximum, about 55 million years ago, was a brief period of widespread, extreme climatic warming.  Sea surface temperatures near the North Pole increased from around 18 C to over 23 C during this event. which was associated with massive atmospheric greenhouse gas concentrations.

At the same time, at the other end of the world there were forests in Antarctica.  Evidence for the flora in Antarctica  during the Palaeocene and early Eocene have been extensively investigated on Seymour  Island, which is about 65 degrees south, by Professor Jane Francis, Dr David Cantrill and Dr Anne-Marie Tosolini who have kindly given permission for the inclusion of the two pictures of Seymour Island below.  The presence of temperate vegetation at palaeolatitudes of approximately 65S (approximately the same latitude as snow-covered Seymour Island is to-day) indicates that the Antarctic experienced much warmer climates during the early Cenozoic.   Fossil plants from Palaeogene strata on Seymour Island, Antarctica, are being investigated to determine the nature of vegetation response to climate change in southern high latitudes. The fossil assemblages represent vegetation which once grew so close to the south polar regions.

The picture shows the exposure of Palaeocene and Eocene Deposits where evidence of Plant Life in the Palaeocene/Eocene times is to be found

Principal Investigator: Professor Jane Francis University of Leeds
Co-Investigator: Dr David Cantrill (British Antarctic Survey)
Post Doctoral Research Associate: Dr Anne-Marie Tosolin

Professor Jane Francis kindly gave permission for the inclusion of the photographs

Ice Ice-packs near Stewart Island to-day

A note on Sharks Teeth from the Eocene in Abbey Wood

Abbey Wood is probably the most fossil bearing site in London.  The area dates from the Eocene period, around 55 million years ago, during which time water covered this area of the country.  The site is an excellent place to find fossils, in particular a variety of sharks teeth, shells and vertebrae.  

 

Abbey wood is located in East London, close to the Woolwich car ferry.  The fossil beds are exposed within the woods themselves and are easily found.  Visitors to the site are required to seek the permission of the local council before removing any specimens.  The best way to explore the site is through organised trips.  The Tertiary Research Group (TRG) arrange annual visits to the site and provide all the necessary equipment to maximize the number of finds. More information about the group can be read on their website at www.trg.org.

UKFossils.co.uk includes further information on this location

The Oligocene and Miocene

The climate of the Cainozoic got much cooler during the Oligocene, and the Antarctic was freezing up. The tropics diminished, giving way to cooler grasslands and woodlands.   Tropical forests diminished, and grasslands spread around the earth.

The Miocene was a time of warmer global climates than those in the preceding Oligocene, or the following Pliocene. It is particularly notable in that two major ecosystems first appeared at this time: kelp forests and grasslands. The expansion of grasslands is correlated to a drying of continental interiors as the global climate first warmed and then cooled.

Global circulation patterns changed as Antarctica became isolated and the circum-polar ocean circulation became established. This reduced significantly the mixing or warmer tropical water and cold polar water, and permitted the build up of the Antarctic polar cap. The African-Arabian plate joined to Asia, closing the seaway which had previously separated Africa from Asia, and a number of migrations of animals brought these two faunas into contact.

 The Himalayas: Two continents collide

Plates were very much on the move during the Cainozoic. The subcontinent of India was on its way to Asia. Australia and Antarctica parted and cruised away from each other. South America was on its own.

About 225 million years ago, India was a large island still situated off the Australian coast.

A vast ocean (called the Tethys) separated India from the Asian continent. When Pangaea broke apart about 200 million years ago, India began to forge northward. By studying the history -- and ultimately the closing-- of the Tethys, scientists have reconstructed India's northward journey.

About 80 million years ago, India was located roughly 6,400 km south of the Asian continent, moving northward at a rate of about 9 m a century. When India began to ram into Asia about 40 to 50 million years ago, its northward advance slowed by about half. The collision and associated decrease in the rate of plate movement are interpreted to mark the beginning of the rapid uplift of the Himalayas.  The final collision of the two land masses occurred in the Miocene epoch.

 

Among the most dramatic and visible creations of plate-tectonic forces are the lofty Himalayas, which stretch 2,900 km along the border between India and Tibet. This immense mountain range began to form between 40 and 50 million years ago, when two large landmasses, India and Eurasia, driven by plate movement, collided. Because both these continental landmasses have about the same rock density, one plate could not be subducted under the other. The pressure of the impinging plates could only be relieved by thrusting skyward, contorting the collision zone, and forming the jagged Himalayan peaks.

India was once situated well south of the Equator, near the continent of Australia.

The progress of the last 6,000-km part of the journey of the India landmass (Indian Plate) before its collision with Asia (Eurasian Plate) about 40 to 50 million years ago is shown in the illustration.   Map Courtesy United States Geological Service

The Miocene was a time of warmer global climates than those in the preceding Oligocene, or the following Pliocene. It is particularly notable in that two major ecosystems first appeared at this time: kelp and grasslands. The expansion of grasslands is correlated to a drying of continental interiors as the global climate first warmed and then cooled.

Many new mountain ranges were formed during the Miocene. When the African plate pushed against Europe and Asia, the Alps formed. The Rocky Mountains and the Appalachians formed, along with the Himalayas, which where just beginning to form as the subcontinent of India crashed into Asia. Australia and South America remained separated from the rest of the world.

In South America, since it was separated from the rest of the world, strange developments evolved. Edentates commonly known as "toothless animals" emerged. They were animals like sloths , armadillos and anteaters.

Likewise in Australia the Marsupial mammals held sway.

Due to the increase in grasses, more herbivores appeared. Grasses called for advanced digestive systems, called rumens . Pigs, cattle, deer, and camels were only a few of the mammals that evolved to take advantage of the expanding food source. Cats and dogs evolved as predators during the Oligocene to feast on the new abundance of herbivores.

Global circulation patterns changed as Antarctica became isolated and the circum-polar ocean circulation became established. This reduced significantly the mixing or warmer tropical water and cold polar water, and permitted the build-up of the Antarctic polar cap. Likewise, the African-Arabian plate joined to Asia, closing the seaway which had previously separated Africa from Asia, and a number of migrations of animals brought these two faunas into contact.

The more grassland there was, the more herbivores roamed the earth. Ruminant herbivores had developed a strategy against the carnivorous mammals that were evolving. They were able to store large amounts of "spare" food inside themselves. In doing this, they could run away from any predator, and feast on their reserve of food in a safer place. Many other safeguards were developed by these herbivores during the Miocene epoch

New species included some birds: parrots, woodpeckers, pigeons, and pelicans, falcons, and crows. Mammal newcomers were mice, rats, porcupines, and guinea pigs.

Apes also evolved during the Miocene. They are believed to have evolved from monkeys, which had evolved since the Palaeocene. African primates, scientists say, developed into apes, and eventually into us.

The Pliocene Epoch

During the Pliocene, most landmasses arrived in their present-day positions. The world was also getting a lot colder. Not only had the Antarctic ice cap grown bigger yet, but an ice cap dominated the northern Arctic, too.

New and diverse ruminant herbivores appeared during this epoch. Some animals that were following the forest-to-grass trend were the newly evolved hippopotamuses, gazelles, antelopes, and giraffes that still had short necks.

A major advancement of the mammalian carnivores in this epoch was the "idea" of hunting in packs. This provided many benefits. An obvious advantage is that a very large prey could be killed, even if it was twice the size of any individual pack member.  Also, a hierarchy could be organized in each of the social packs. This gave better communication, so the prey could be more easily killed.

The Pleistocene

1.8 million to ~10,000 years ago

It was during the Pleistocene that the most recent episodes of global cooling, or ice ages, took place. Much of the world's temperate zones were alternately covered by glaciers during cool periods and uncovered during the warmer interglacial periods when the glaciers retreated.  The large mammals of the Pleistocene weathered several climate shifts.

 Pleistocene plants and animals were extremely close to modern ones many genera and even species of Pleistocene conifers and flowering plants were present.  Among the animals many molluscs, birds and mammals survive to this day. Yet the Pleistocene was also characterized by the presence of distinctive large land mammals and birds. Mammoths and their close cousins the mastadons, long horned bison, sabre toothed tigers, giant ground sloths, and many other large mammals characterized Pleistocene habitats in North America, Asia, and Europe.  A mammoth, found in deposits in Russia, was one of the largest land mammals of the Pleistocene, the time period that spanned from 1.8 million to ~10,000 years ago.  Native horses and camels galloped across the plains of North America. Great teratorn birds with 25-foot wingspans stalked prey. Around the end of the Pleistocene, all these creatures went extinct (the horses living in North America today are all descendants of animals brought from Europe in historic times).

Many paleontologists study Pleistocene fossils in order to understand the climates of the past. The Pleistocene was not only a time during which climates and temperatures shifted dramatically; Pleistocene fossils are often abundant, well-preserved, and can be dated very precisely. Some, such as diatoms, foraminifera and plant pollen, are both abundant and highly informative about paleoclimates. Today, there is concern about future climate change (e.g. global warming) and how it will affect us. Paleontologists who work on Pleistocene fossils are providing a growing amount of data on the effect of climate change on the Earth's biota, making it possible to predict the effects of future climate change.

The Triumph of the Mammals

After the demise of the dinosaurs the whole world saw the blossoming of a totally new flora and fauna.  The mammals who had been minor players on the stage of life became the dominant land animals and even in the forms of whales, dolphins, seals and walruses returned partially or completely to the sea.   The outstanding characteristic of the mammals was their increased intelligence over all other life forms at least on land.   On land the mammals were the monarchs of the Earth.  

The Pleistocene saw the evolution and expansion of our own species, Homo sapiens, and by the close of the Pleistocene, humans had spread through most of the world. According to a controversial theory, first proposed in the 1960s, human hunting around the close of the Pleistocene caused or contributed to the extinction of many of the Pleistocene large mammals. It is true that the extinction of large animals on different continents appears to correlate with the arrival of humans, but questions remain as to whether early human hunters were sufficiently numerous and sufficiently technologically advanced to wipe out whole species. It has also been hypothesized that some disease wiped out species after species in the Pleistocene. The issue remains unsolved; perhaps the real cause of the Pleistocene extinction was a combination of these factors.  Among the humans was another species different to our own although no doubt closely related.   They were the Neanderthal people who seemed from the evidence of skull remains to have had slightly larger brains than ourselves.  They seemed to have been more resistant to the cold than our own species but died out for unknown reasons about 30 thousand years ago.  The reasons for their demise are not known but are under investigation.  Among all the millions of life forms on the planet this left one human species to rule the Earth.. 

We have accomplished wonderful things and produced some wonderful people like the Buddha and the Christ who have pointed the way to a beautiful and peaceful world.  We have also produced the most appalling nightmares.   Why such a strange species arose we do not know - anymore than we can answer that final question why does anything exist - why is there something and not nothing?

We have the power to make a paradise on Earth or to be the authors of our own destruction.

 

Hyperlinks

The History of the Earth - the last 600 million years

The Search for Extra-terrestial Intelligence  -  SETI

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