[A] PHANEROZOIC AEON: ("abundant or evident life"): the last 570 Mya of Earth history, made up of three Eras, the Palaeozoic (570 to 225Mya), Mesozoic (225 to 65Mya) and Cenozoic (65 Mya to present). A global sea level change over this period reflects mostly continental drift.
 CENOZOIC ERA ("recent life") zero
65 Mya.: [ see map and
Geological data . Climate
change over this period is also critical to human evolution.] The
Cenozoic Era is divided into the Tertiary (65 to 2Ma) and Quaternary
(2 Mya to present) periods. For the past 10 Mya, the
has cooled in a long-term ice age. This ice age started during the
Quaternary, and is in evidence today, as ice caps remain at both
poles. During this period, climate has fluctuated between times of
relative warmth and frigidity.
[1.1] QUATERNARY PERIOD (includes present time [ see map ])
HOLOCENE EPOCH ("recent") zero to 10,000:
First civilisations with cities, agriculture and domesticated animals emerge. Humans reduce biological diversity to the lowest level since the end of the Mesozoic era, 65 million years ago (Wilson, 1989). Humans use metals, coal, oil and other natural resources.
The warmest period of the Holocene, a thermal maximum, was attained by 6,000 to 7,000 years ago. Between 2,500 and 4,500 years ago, global climates cooled, a period known as the Iron Age neoglaciation. A slight warming then occurred, followed by a return to cooler climates after 500 A.D. (the Dark Ages). Around 900 to 1300 A.D. (Medieval Optimum), European temperatures attained the warmest levels of the last 4,000 years. After 1450 A.D., there was steady return to colder conditions (called the " Little Ice Age ") through further glacial advance. Human activities may have stopped this and started a phase of global warming .
PLEISTOCENE EPOCH ("the most recent") 10,000 to 1.8 Mya:
The last glacial maximum (coolest period) occurred 18,000 years ago.
Northern Hemisphere ice sheets had retreated by 14,000 years
ago. At the transition from the Pleistocene to the Holocene
Epochs, about 10,000 to 11,000 years ago, a rapid cooling, called
Younger Dryas Cooling , occurred. This was followed by a
rapid rise in temperatures and the end of the ice age.
Evolution of Homo sapiens from primitive Homo species. Use of fire, tools, weapons. Increase in human brain volume. Mammoths and woolly rhinoceros flourish. Homo erectus emerges 1.6 Mya and uses fire by 1 Mya. Homo neanderthalensis emerges by 300,000 years ago. and other large mammals become extinct 11,000 years ago, possibly through a combination of climate change and human hunting. From 130,000 years ago to 20,000 years ago , our global climate has progressively cooled and then warmed rapidly back to the temperatures of the interglacial period of 130,000 years ago. Within the past 2.5 million years (http://www.doc.mmu.ac.uk/aric/gccsg/), the climate has varied between six degrees Celsius.
[1.2] UPPER TERTIARY PERIOD:
Origin of early human ancestor, Australopithecus afarensis
Mya), in Africa. Many large mammals now roam the earth.
Birds and mammals similar to modern forms. Sea life similar to
today's. Hominid bipedalism emerges
4 Mya and use of stone tools by 2 Mya.
Modern animals, flowering plants and trees. Grazing animals. Hoofed
animals and primates diversify. Apes are found in Asia and
Africa. A new group of primates, the dryomorphs evolves (Dryopithecus
fontani). Proconsul africanus is a very early dryomorph, or
the immediate dryomorph ancestor. This small primate had a
skull, jaws and teeth that were apelike. Its long trunk, arms and
finger bones were monkeylike. Middle Miocene dryomorph descendants
are possibly ancestral to both modern African apes and the first
homonids, the australopithecines. It lived from
approximately 23 to 14 million years ago. The chimpanzee and
hominid lines evolve 12 to 20 Mya. A significant cooling transition
occurrs 10 to15 Mya). This is reflected in an increase in the
d18 O record between 14 and 15Ma, caused by the rapid growth of the
Antarctic ice sheet (Shackleton & Kennet, 1975) and a deep water
cooling event (4 to 5°C) (Moore et al., 1987).
[1.3] LOWER TERTIARY PERIOD:
Climates cooled during the Oligocene. Origin of tailless anthropoid ape, Aegyptopithecus 28-33 mya (Gribbin and Cherfas, 2001). (Aegyptopithecus zeuxis, dated from 33 to 34 mya). Three-toed horse ancestors, Mesohippus . Birds plentiful (eg. parrots and pigeons). Cats and dogs present. Rapid continental ice formation took place at this time. Prosimian ranges are reduced to the warmer climates of Asia, Africa and the East Indies. Another ape fossil is Propliopithecus.
Eocene (55 to 50Ma) was the warmest period during the Cenozoic. First primates (50 Mya) that would eventually lead to humanity. Eosimias evolves about 45 million years ago as (a posssible) ancestor to both prosimians and anthropoids. Early horse ancestor, Hyracotherium (Eohippus). It had a four toed forefoot and three-toed hind foot. Abundant modern mammals and angiosperms. Most of the living placental orders emerge. Rabbits and hares have evolved by 55 Mya. Tarsiers and lemurs (primates within the sub-order Prosimii) are found throughout the continents of the northern hemisphere. Notharctus sp., is a possible prosimian descendant from which monkeys and apes are derived. Lemur-like creatures evolve 50 mya. Sub-order Strepsirhini (Omomyidae sp.) has nails on digits and excellent eyesight. The first monkeys, infra-order Catarrhini, with great binocular vision, and higher intelligence, evolves 40 mya (Apidium and Catopithecus browni)
Small mammals emerge (rats, mice, and squirrels by 60 Mya) that have
changed from egg laying to viviparity (placental), modern tooth
forms, the stapes bone of the middle ear for improved hearing,
improved visual system and hoof instead of claws or nails.
Flowering plants plentiful (image of fossil Vitis olriki leaf). Plesiadapis
sp., a highly specialized primate with rodentlike
incisors claws instead of nails evolves.
 MESOZOIC ERA ("middle life") (240 to
63 MYA or 225 to 65Mya) [2: mesozoic
During this Era, birds, mammals and flowering plants emerged. True
primates, Order Primates evolve 85 mya. See article
Dominance by Dinosaurs, but with rapid extinction at the end of this period during the Cretaceous mass extinction a meteorite impact. Tyrannosaurus (& last dinosaurs). Early mammals with primitive characteristics (eg. primitive kangaroos 135 Mya) and first primates. First modern birds and modern fishes. Insectivore mammals like Plesiadapis and Purgatorius evolve as tree dwelling creatures 125 mya.
| (image of
|©1 .This is a duckbilled dinosaur (hadrosaur). Its breathing passages passed through its unusual head crest and it is believed that they made various trumpeting noises to communicate. Males and females had different crest shapes, so a form of sexual selection may have been involved inthe evolution of these breathing structures.|
| (image of 9 - 11 metres
long dinosaur Iguanodon.)
|©1 An early Cretaceous bipedal, ornithopod that had efficient plant chewing teeth. Ornithopods were a successful, abundant and diverse group found across musch of Europe.|
| (image of
|©1 A bipedal dinosaur from the Gobi desert in Mongolia|
| (image of
|©1 This is the skull of a young duck-billed dinosaur, showing herbivore dentition and a small crest.|
| (image of
|©1 These herbivorous dinosaurs looked a bit like giant chameleons, but with parrot beaks and a crest around the neck.|
Angiosperm or FLOWERING PLANTS with covered seeds emerge 125 to130 mya and increase in dominance! See article Ants, bees (Trigona sp.), wasps, butterflies, and other pollinating insects emerge. Evolution of social insects such as bees and ants.
Emergence of two groups of dinosaurs amongst a diversity of reptiles. Bony fish called teleosts rise in dominance. Cycad and conifer plants common. Very first warm-blooded mammals emerge 210-230 Mya. Kuehneutherium is warm blooded and the size of a rat. It may have laid eggs like monotremes. Diverse and plentiful insect types. Therapsids (mammal-like reptiles) dominant. Protosuchia, crocodile ancestor (Buffetaut, 1979) around 230 mya. Cone bearing trees plentiful.
A mass extinction event occurs around 210 mya. Seed production by
gymnosperms and seed ferns proved an adaptive advantage over
other plant types. Frogs and turtles evolve. Frightening fish
like predator reptiles with paddle-like limbs frequent the ocean.
Pangea, the super-continent breaks up to form the continents that
we know today. Bees evolve 225 Mya.
In this Era most of the major living groups of plants and animals
evolved. However, birds, mammals and flowering plants had not
yet evolved! A mammal-like reptile, Thrinaxodon evolves
Reptiles such as Dimetrodon and many others (click to see image of the reptile, Mesosaurus
brasiliensis , from Permian period) ©1 begin to dominate and replace amphibians.
Fish and amphibians still plentiful. Insects diversify. Many plant
& animal groups. Reptile-like therapsid ancestors to mammals
evolve. The oldest mammal fossil, 260 million years old,
evolve in the Karoo region of Southern Africa. Their fossil
record reflects six mass extinction events in eight million years as
evidence of large climatic fluctuations. This process of
natural selection led to small warm-blooded animals better
adapted to cold conditions. They also evolved more complicated
and specialised teeth and jaws and more efficient respiratory systems.
Pelycosaurs dominant. Cycads and conifers common. A mass
extinction event occurs 250 mya at the end of the Permian, killing 90
to 96% of all species! Mammal-like reptiles survive, eventually to
evolve into true mammals. Two groups evolve from diapsid reptiles,
the lepidosaurs (includes lizards and snakes), and the archosaurs
(dinosaurs and crocodiles). Coniferous flora of the Northern
Hemisphere survive into the Triassic.
PERIOD (the coal strata formerly called the Coal Measures)
to 360 Mya:
[ see map and Geological data ]
Mississippian period (360 to 320 Mya); Pennsylvanian period (320 to 286 Mya).
First reptiles appear, becoming the first vertebrates to live fully independent of water (310 m.y.a.). These early reptiles gave rise to the synapsid reptiles (e.g. Dimetrodon), which became abundant by the Permian. Amphibians emerge and diversify (300-350 Mya), producing creatures more than 20 feet long. Seed ferns, primitive conifers, scale trees and other seed bearing plants flourished. Coal beds typify this period. These resulted from the huge tropical and subtropical forests that covered the massive continent of Pangea. Primitive insects, ancient grasshoppers, mayflies and roaches were common (winged insects, 300 Mya).
By this time five digit hands and feet, hinge like ankle bones and skull features typical of modern forms had evolved. No birds or mammals roamed the earth! Climax of shell crushing sharks. Amphibians dominate land.
Features that had evolved by 350 Mya includes jaws, internal
pectoral and pelvic girdles, bony skeletons, lobed fins and a pattern
of bony skull plates the same as in terrestrial animals. Coelacanths
appeared about 350 million years ago.
A great variety of fish species are represented in the fossil
record. Fish such as Dipterus, trilobites (click to see image) ©1 , plants, first amphibians (following a
doubling in the number of chromosomes of fish) (Wills, 1991), snails,
many fish species. First Amphibians such as Ichthyostega
evolve 400 mya. First bony fish and shark (375 Mya) species emerge.
Terrestrial life becomes abundant and diverse. Springtails are
among the first land insects that evolve (350-360 Mya). The second
mass extinction event (the late Frasnian) occurs toward the end if this
period (370 m.y.a.), killing off most fish (Gore, 1989).
Tetrapods emerge, such as the 370 million year old Elginerpeton
and the 365 million year old Hynerpeton. Earliest Reptiles likeHylonomusemerge
First traces of land life as plants and animals. By 430 Mya,
waxy-coated algae begin to live on land. Lung fish with jaws,
coral. Land plants include scale trees and ferns that reproduce
by spores. There are no seed bearing plants. Millipedes emerge 420
Mya as one of the first land animals. Instects appear on the land.
Lobed fin, jawed fish such as Cheirolepis evolve.
First fish such as armoured ostracoderm fishes. Dominance by a
diversity of invertebrates. The first recorded mass extinction event occurs,
destroying about 75% of animal species. Trilobites (click to see image of Cybele coronata from Early
ordovician period) ©1
, corals and molluscs common.
No terrestrial life! Spriggina (an annelid). Grazing by burrowing
animals leads to a decline of Stromatolites. Marine invertebrate
groups and Protozoa. All modern phyla evolved by this time.
Foundation plans for higher animals include true tissues, a form
of embryo development called gastrulation, three tissue layers,
body cavities, blood circulatory systems and segmentation. Most
ancient vertebrates emerge, i.e., first fish & chordates
(Valentine, 1978). The most ancient chordate yet discovered is
the 525 million year-old Yunnanozoon lividum (Nash, 1995).
Macroscopic fossils first appear, first as shells of calcium
carbonate and then as bones of calcium phosphate (Mason, 1992).
Trilobites (click to see image of Asaphus sp. ) ©1 dominate fossil
545 Mya sees the Cambrian explosion of hard-bodied organisms. 517
Mya - Burgess Shale formation. Early Vertebrates- jawless
fish such as Arandaspis 510 mya.
[B] PRECAMBRIAN AEON:(4500 to 544 mya)
This aeon had a warm climate, shown by few evident glaciations in this period, as opposed to the frequent glaciations of the Phanerozoic aeon. Glacial deposits are found 2.5 to 2.0 (or 2.7 to 2.3) billion and 1.0 to 0.57 (or 0.9 to 0.6 (Frakes, 1979)) billion years ago. The two eras of this aeon cover about 80 percent of the earth's history and about four billion years. The first Chordates-Pikaiaevolve around 570 mya.
 PROTEROZOIC ERA ("earlier life") 550 to 2500 Mya: [2: proterozoic ]
2.3 billion years ago most of the planet's seven continents, then concentrated around the equator, were glaciated. Similar glaciations are found 600 and 750 million years ago ( Neoproterozoic Era). Stromatolites are common in this era. By 800 Mya, many features that persist today had already evolved. Collagen proteins for binding cells. Eukaryotes (cells with a nucleus) appear (similar to green algae, with chloroplasts and aerobic photosynthesis), perhaps as early as 2100 Mya, but definitely by 1400 Mya. Mitochondria (metabolic organelles) and meiosis (cell division for sexual reproduction) evolve. In the, the Cambrian there is the "sudden" appearance of diverse invertebrate animals, with representatives of all the living phyla. Traces of soft bodied relatives of modern coelenterates, annelids and arthropods have been dated at 1000 Mya old, but no intermediate forms linking these to the diversity of the Cambrian period have been found! At the beginning of this period, oxygen levels rapidly rise (Allegre & Schneider, 1994). Accompanying this oxygen production is the deposition of banded iron formations as reduced, soluble iron is precipitated out of the oceans. Oxygen begins to rise in the atmosphere by 2 billion years ago after the oxygen sinks are saturated. Atmospheric oxygen reaches present day level by1600 Mya and then stabilizes. Increased consumption of carbon dioxide by photosynthesizing creatures and increased oxygen levels lead to a period of cold and glaciation 2.5 to 2.0 billion years ago. 0.6 billion years ago, the present day continents of Antarctica, Africa, South America, India, China and Australia and the units of Laurasia (North America, Siberia and Europe) form the super continent of Gondwanaland. Invertebrates and vertebrates diverge shortly before the beginning of the Cambrian period.
 ARCHAEAN (ARCHAEOZOIC) 2500 TO
3800 Mya: [2: archean ]
The origin of life is still a mystery (Horgan, 1991). Unicellular prokaryotes (no nucleus) such as bacteria and photosynthetic blue-green algae appear. Anaerobic bacterial photosynthesis evolves (Schopf, 1978). Somewhat later, blue-green algae released oxygen molecules into the atmosphere, steadily strengthening the ozone layer and changing the Earth's atmosphere from being chemically reducing to chemically oxidizing. Already at the foundation of life was RNA, DNA, sexual reproduction & protein synthesis. Earliest fossils of undisputed age are 3.5 billion years old (Allegre & Schneider, 1994). 3.3 to 3.5 billion years old stromatolite structures are found in Australia and South Africa. 40 classes of micro fossils have been found in sediments from this period. Major continent formation events take place between 3.0 and 2.5 billion years ago. 75 percent of existing continental crust was formed by 2.5 billion years ago.
 HADEAN 3800 Mya to 4800 Mya:
[2: hadean ]
Formation of solar system around 4.55 billion years ago (Allegre & Schneider, 1994). Oldest known sedimentary rocks are about 3800 million years old (Mason, 1992), but examples are few, the mean age of the continental crust being 1.8 to 1.5 billion years old. Earth's heat production is four times that of today's, allowing only a thin proto-crust. Oceans and continents form (Schopf, 1978). Oceans of water and an atmosphere rich in carbon dioxide covered the earth by 3.8 billion years ago. Solar radiation from the sun four billion years ago is 25 percent lower than today, but the earth was hot due to the greenhouse effect of high CO 2 levels. By 4.3 billion years ago, an ozone layer is being formed through the photodissociation of atmospheric water by ultraviolet light.
 Five billion years. Origin of the sun (Kirshner, 1994).
 12 billion years ago:
Supernova explosions of dying stars, creates elaborate atoms such as carbon, oxygen, calcium and iron (Kirshner, 1994). Much of the material that forms the sun and planet was dust and gas ejected by supernovas over a period of several billion years (Schramm & Clayton, 1978). A particular supernova explosion near our developing solar system, may have helped in its formation. The collapse of a cloud of gas and dust into our solar system may have been caused by the shock waves of a supernova explosion.
 13.7 billion years ago:
Big Bang and origin of universe! Before the big bang, no time or space exists. Within 3 minutes of the big bang, there is still no light and no atoms, but only a superhot fog (108 oC) of protons and electrons. In the next 300,000 years, hydrogen and helium atoms are formed and light starts to shine. Another 700,000 years is needed for the force of gravity to have its influence, forming clouds of hydrogen and helium and the beginnings of stars. These stars turn on 200 million years after the big bang. As these stars form and die over the next 15 billion years to the present, they produce the heavy elements that form our planet. This is in a universe made up of 4% ordinary matter, 23% dark matter and 73% dark energy (Lemonick, 2003)
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