Tuesday, January 1, 2008

The Earth's history is one of my favourite subjects, it's still mind boggling to think that if you flew past the earth in a spaceship even a few hundred million years ago, the Earth would look like an alien planet. And the way the earth only had single cell life for an extremely long time, and the crust has gotten "wrinklier" as it has thickened over time with more land area and deeper oceans. About a billion years ago the whole earth was basically like a scaled-up Polynesia with shallow oceans and some small flat landmasses. And about 250m years from now the crust will have thickened enough for the continents to be locked in place (by then Australia will be around where Japan is now and collide with asia, similar to India). And whether we're here or not life will still be going on, the sun will still rise and set for billions of years. Mein Gott.

I thought This site was interesting as had mapped the continents as far back as 650 million years using the latest data (the site is now getting a little old). What set it apart what that he used the originating parts of the continents rather than drawing modern continental shapes fitted together like a jigsaw.

I found an overlay for Google Earth that lets you look at continental drift on a 3D globe but the creator has a different set of projections, it looks like he's used roughly the same amount of land area throughout the ages which does not appear to reflect reality.

Here is a series of stills allowing you to imagine what landmasses might have been around a familiar part of the earth (for Australasians). You can simply load it into Google Earth yourself but I thought it would be interesting to post them on a page and add some background information to the epochs, borrowed liberally from other sites. Keep in mind that the landmasses and dates are all educated guesswork at best, and the climate displayed in the pictures doesn't always match up with the descriptions.

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Hadean 4500 million years ago

Because collisions between large planetesimals release a lot of heat, the Earth and other planets would have been molten at the beginning of their histories. Solidification of the molten material into rocks happened as the Earth cooled. The oldest Earth rocks currently known are 3.8 billion years old. Sometime during the first 800 million or so years of its history, the surface of the Earth changed from liquid to solid. Once solid rock formed on the Earth, its geological history began. The beginning of the rock record that is currently present on the Earth is the inception of a time known as the Archaean.

It was early in the Archaean (3800-2500 MYA) that life first appeared on Earth. Our oldest fossils date to roughly 3.5 billion years ago, and consist of bacteria microfossils. Stromatolites, colonies of photosynthetic bacteria increased in abundance throughout the Archaean, but began to decline during the Proterozoic. They are not common today.

The period of Earth's history that began 2.5 billion years ago and ended 543 million years ago is known as the Proterozoic. Many of the most exciting events in the history of the Earth and of life occurred during the Proterozoic -- stable continents first appeared and began to accrete, a long process taking about a billion years. Also coming from this time are the first abundant fossils of living organisms, mostly bacteria and archaeans, but by about 1.8 billion years ago eukaryotic cells appear as fossils too.

With the beginning of the Middle Proterozoic comes the first evidence of oxygen build-up in the atmosphere. This global catastrophe spelled doom for many bacterial groups, but made possible the explosion of eukaryotic forms. These include multicellular algae, and toward the end of the Proterozoic, the first animals.


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Ediacaran 600m

Life:
The first organisms that existed are believed to have been unicellular. However, unlike some other milestones in evolution, multicellularity is thought to have evolved many times independently - plants, animals and fungi had independent evolution paths, and several other clades have evolved multicellularity; multicellularity exists in both prokaryotes and eukaryotes, and first appeared several billion years ago in cyanobacteria. In eukaryotes, it appeared several times starting from around a billion years ago, in algae, kelp, fungi - several independent paths, and in the animal kingdom.


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Ediacaran 560 MYA

Life:
The Ediacaran biota represent the earliest known complex multicellular organisms. They appeared soon after the Earth thawed from the Cryogenian period's extensive glaciers, and largely disappeared soon before the rapid appearance of biodiversity known as the Cambrian explosion, which saw the first appearance in the fossil record of the basic patterns and body-plans that would go on to form the basis of modern animals. Little of the diversity of the Ediacaran biota would be incorporated in this new scheme, with a distinct Cambrian biota arising and usurping the organisms that dominated the Ediacaran fossil record.

Climate:
The post-glacial Ediacaran was warm to hot and relatively arid at low and most middle latitudes. Even at high latitudes in the south, there is evidence of a warm, humid climate. The latest Ediacaran and earliest Cambrian were marked by a return to colder conditions, with some glaciation at high latitudes.

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Early Cambrian 540MYA

Life:
At the beginning of the Cambrian period, about 540 million years ago, life was entirely confined to the oceans. During the 53 million years that the Cambrian period lasted there was the sudden appearance and diversification of almost every major group (phylum) of animal life, as well as many types that later died out. Animals with shells and exoskeletons appeared for the first time, including trilobites, brachiopods, molluscs, and many other groups. This sudden evolutionary burst was so spectacular that it has been termed the "Cambrian explosion". There hasn't been anything like it on Earth before or since.

Climate:
The Cambrian climate was generally warm, wet and mild. As there were no continental landmasses located at the poles, ocean currents were able to circulate freely, hence there was no significant ice formation. As a result temperatures worldwide were mild. The Cambrian constituted a benign spell between two great ice ages - Snowball Earth and the Late Ordovician Ice Age.


Geography:
Continental drift rates in the Cambrian may have been anomalously high. Laurentia, Baltica and Siberia remained independent continents since the break-up of Pannotia. Gondwana started to drift towards the South Pole. Panthalassa covered most of the southern hemisphere, and minor oceans included the Proto-Tethys Ocean, Iapetus Ocean, and Khanty Ocean, all of which expanded by this time.


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Late Cambrian 510MYA

Life:
The Cambrian–Ordovician extinction event occurred approximately 488 million years ago. It was the first major extinction event in the Phanerozoic eon and it eliminated many brachiopods and conodonts, and severely reduced the number of trilobite species
In the Early Ordovician, many new types of organism appaeared alongside the trilobites, including tabulate corals, strophomenid, rhynchonellid, and many new orthid brachiopods, bryozoans, planktonic graptolites and conodonts, and many types of molluscs and echinoderms, including the ophiuroids ("brittle stars") and the first sea stars. Nevertheless the trilobites remained abundant, with all the Late Cambrian orders surviving, and being joined by the new group Phacopida.


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Middle Ordivician 470MYA

Life:
The Ordovician Period is the second period of the Paleozoic Era. This important period saw the origin and rapid evolution of many new types of invertebrate animals which replaced their Cambrian predecessors. Primitive plants colonised the land, until then totally barren. The supercontinent of Gondwana drifted over the south pole, initiating a great Ice Age that gripped the earth at this time. The end of the period is marked by an extinction event.
The first evidence of plants on land comes from trilete spores,[3] from the Middle Ordovician (~470 million years ago). The microstructure of the earliest spores resembles that of modern liverwort spores.

In the Middle Ordovician, the trilobite-dominated Early Ordovician communities were replaced by generally more mixed ecosystems, in which brachiopods, bryozoans, molluscs and echinoderms all flourished, tabulate corals diversified and the first rugose corals appeared; trilobites were no longer predominant. The planktonic graptolites remained diverse, with the Diplograptina appearing. Bioerosion became an important process, particularly in the thick calcitic skeletons of corals, bryozoans and brachiopods, and on the extensive carbonate hardgrounds which appear in abundance at this time. The earliest known armoured agnathan ("ostracoderm") vertebrate, Arandaspis, dates from the Middle Ordovician of Australia.

Climate:
Sea levels were high during the Ordovician; in fact during the Tremadocian, marine transgressions worldwide were the greatest for which evidence is preserved in the rocks.

Geography:
Southern Europe, Africa, South America, Antarctica and Australia remained joined together into the supercontinent of Gondwanaland, which had moved down to the South Pole. North America straddled the equator, and was about 45 degrees clockwise from its present orientation. Western and Central Europe were separate from the rest of Eurasia, rotated about 90 degrees counterclockwise from their present orientation and in the southern tropics. The Iapetus Ocean continues to shrink as Baltica and North America converge. Where the Iapetus was, mountains are thrust up, remnant strata of which remain today in Greenland, Norway, Scotland, Ireland and north-eastern North America. Scotland and England are united into a single landmass.

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Late Ordivician 450MYA

Geography:
Baltica began to move towards Laurentia later in the period, causing the Iapetus Ocean to shrink between them. Also, Avalonia broke free from Gondwana and began to head north towards Laurentia. The Rheic Ocean was formed as a result of this.

Life:
For most of the Late Ordovician, life continued to flourish, but at and near the end of the period there were mass-extinction events that seriously affected planktonic forms like conodonts, graptolites, and some groups of trilobites (Agnostida and Pytchopariida, which completely died out, and the Asaphida which were much reduced). Brachiopods, bryozoans and echinoderms were also heavily affected, and the endocerid cephalopods died out completely, except for possible rare Silurian forms. The Ordovician-Silurian Extinction Events may have been caused by an ice age that occurred at the end of the Ordovician period as the end of the Late Ordovician was one of the coldest times in the last 600 million years of earth history.

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Silurian 430 MYA

Climate:
During this period, the Earth entered a long warm greenhouse phase, and warm shallow seas covered much of the equatorial land masses. Early in the Silurian, glaciers retreated back into the South Pole until they almost disappeared in the middle of Silurian. The period witnessed a relative stabilization of the Earth's general climate, ending the previous pattern of erratic climatic fluctuations. Layers of broken shells (called coquina) provide strong evidence of a climate dominated by violent storms generated then as now by warm sea surfaces. Later in the Silurian, the climate cooled slightly, but in the Silurian-Devonian boundary, the climate became warmer.

Life:
Coral reefs made their first appearance during this time, built by extinct tabulate and rugose corals. The first bony fish, the Osteichthyes appeared, represented by the Acanthodians covered with bony scales; fishes reached considerable diversity and developed movable jaws, adapted from the supports of the front two or three gill arches. A diverse fauna of Eurypterids (Sea Scorpions) - some of them several meters in length - prowled the shallow Silurian seas of North America. Leeches also made their appearance during the Silurian Period. Brachiopods, bryozoa, molluscs, hederelloids and trilobites were abundant and diverse.

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early devonian 400m

Geography:

The Devonian period was a time of great tectonic activity, as Laurasia and Gondwanaland drew closer together.

The continent Euramerica (or Laurussia) was created in the early Devonian by the collision of Laurentia and Baltica, which rotated into the natural dry zone along the Tropic of Capricorn. Near the equator, Pangaea began to consolidate from the plates containing North America and Europe.

The southern continents remained tied together in the supercontinent of Gondwana. The remainder of modern Eurasia lay in the Northern Hemisphere. Sea levels were high worldwide, and much of the land lay submerged under shallow seas, where tropical reef organisms lived. The deep, enormous Panthalassa (the "universal ocean") covered the rest of the planet.

Life:
Sea levels in the Devonian were generally high. Marine faunas continued to be dominated by bryozoa, diverse and abundant brachiopods, the enigmatic hederelloids, and corals. Lily-like crinoids were abundant, and trilobites were still fairly common, but less diverse than in earlier periods due to the abundance of mobile swimming predators such as early sharks and predatory bony fish. The ostracoderms were joined in the mid-Devonian by the first jawed fishes, the great armored placoderms, as well as the first sharks and ray-finned fish.

By the Devonian Period, life was well underway in its colonization of the land. The moss forests and bacterial and algal mats of the Silurian were joined early in the period by primitive rooted plants that created the first stable soils. By the Middle Devonian, shrub-like forests of primitive plants existed: lycophytes, horsetails, ferns, and progymnosperms had evolved.

A great barrier reef, now left high and dry in the Kimberley Basin of northwest Australia, once extended a thousand kilometers, fringing a Devonian continent. Unlike modern reefs they were composed of calcareous algae and coral-like stromatoporoids, and tabulate and rugose corals.

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Late devonian370m

Life:
In the late Devonian the lobe-finned fish appeared, giving rise to the first tetrapods. The developments of fish, and the great diversity of fish around at the time, have led to the Devonian being given the name "The Age of Fish" in popular culture.

In the Late Devonian, the tree-like ancestral fern Archaeopteris and the giant cladoxylopsid trees grew with true wood. These are the oldest known trees of the world's first forests. Prototaxites was the fruiting body of an enormous fungus that stood more than 8 meter tall. By the end of the Devonian, the first seed-forming plants had appeared.

Primitive arthropods co-evolved with this diversified terrestrial vegetation structure. The evolving co-dependence of insects and seed-plants that characterizes a recognizably modern world had its genesis in the Late Devonian. The rapid evolution of a terrestrial ecosystem containing copious animals opened the way for the first vertebrates to seek out a terrestrial living. By the end of the Devonian, early amphibians and arthropods were solidly established on the land.

The 'greening' of the continents acted as a carbon dioxide sink, and atmospheric levels of this greenhouse gas may have dropped. This may have cooled the climate and led to a massive extinction event about 364 million years ago. The Devonian extinction crisis primarily affected the marine community, mainly shallow warm-water organisms including brachiopods, trilobites, ammonites, conodonts, acritarchs, jawless fish, and all placoderms.


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Carboniferous 340m

Climate:
A global drop in sea level at the end of the Devonian reversed early in the Carboniferous There was also a drop in south polar temperatures; southern Gondwanaland was glaciated throughout the period, though it is uncertain if the ice sheets were a holdover from the Devonian or not. These conditions apparently had little effect in the deep tropics, where lush coal swamps flourished within 30 degrees of latitude of the northernmost glaciers

A mid-Carboniferous drop in sea-level precipitated a major marine extinction, one that hit crinoids and ammonites especially hard.

Geography:

As the supercontinent Pangaea came together, the southern continents remained tied together in the supercontinent Gondwana, which collided with Laurussia along the present line of eastern North America. In the same time frame, much of present eastern Eurasian plate welded itself to Europe along the line of the Ural mountains. Most of the Mesozoic supercontinent of Pangea was now assembled, although North China (which would collide in the Latest Carboniferous), and South China continents were still separated from Laurasia. The Late Carboniferous Pangaea was shaped like an "O".

There were two major oceans in the Carboniferous—Panthalassa and Paleo-Tethys, which was inside the "O" in the Carboniferous Pangaea. Other minor oceans were shrinking and eventually closed - Rheic Ocean (closed by the assembly of South and North America), the small, shallow Ural Ocean (closed by the collision of Baltica and Siberia continents, creating the Ural Mountains) and Proto-Tethys Ocean (closed by North China collision with Siberia/Kazakhstania).

Life:

In the oceans coral reefs and invertebrate life flourish, with groups such as brachiopods, echinoderms, ammonites, bryozoa, and corals diversify and are common. Among brachiopods, Productids, Spiriferids and Rhynchonellids are abundant. Terebratulids are also very common. Ammonoids are common and Trilobites are rare, represented only by the proetids. Among echinoderms, blastoids and crinoids are extremely common, especially in the Early Carboniferous (Mississippian)

Among fish, the armoured placoderm and ostracoderm and marine lobe-finned fish that so dominated the Devonian seas are all gone, to be replaced by an amazing diversity of sharks (Chondrichthyes).

In the water and water margins the tetrapods flourish, and many different types inhabit the rivers, ponds, and swamps of the Carboniferous tropics, including many crocodile, eel, and salamander-like forms.

Inhabiting the great forests were many types of insects, spiders, and other types of arthropods. Encouraged by the oxygen-rich atmosphere, the abundance of food in the decaying forest leaf-litter, and the absence of large terrestrial vertebrates, many reach huge sizes. The dragonfly-like Meganeura, an aerial predator, had a wingspan of 60 to 75 cm. The inoffensive stocky-bodied and armoured millipede-like Arthropleura was 1.8 meters long, and the semi-terrestrial Hibbertopterid eurypterids were perhaps as large, while some scorpions reached 50 or 70cm. Alongside these giants were more conventionally sized invertebrates.

Meanwhile, the first reptiles appear, adapted to life lived totally on land, but remain insignificant until at least the very end of the Carboniferous.

In the Euramerican part of Pangea especially, the equatorial regions are covered by forests. The moist tropical climate produces a lush plant growth, which eventually becomes the great Coal Deposits. The fern-like but seed-bearing pteridosperms, the huge green-stemmed Lepidodendrale 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.

So vigorous is 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



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pennsylvanian300m

The early part of the Carboniferous was mostly warm; in the later part of the Carboniferous, the climate cooled. Glaciations in Gondwana, triggered by Gondwana's southward movement, continued into the Permian and because of the lack of clear markers and breaks, the deposits of this glacial period are often referred to as Permo-Carboniferous in age.

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earlypermian280m
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latepermian260m
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middletrassic240m
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latetriassic220m
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earlyjurassic200m
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middlejurassic170m
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latejurassic150m
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earlycreataceous120m
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middlecretaceous105m
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latecretaceous90m
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tertiarycretaceous65m
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eocene50m
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oligocene35m
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miocene20m
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present

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