Earth The Earth is a little over 4.5 billion years old, its oldest materials being 4.3 billion-year-old zircon crystals. Its earliest times were geologically violent, and it suffered constant bombardment from meteorites. When this ended, the Earth cooled and its surface solidified to a crust - the first solid rocks. There were no continents as yet, just a global ocean peppered with small islands. Erosion, sedimentation and volcanic activity - possibly assisted by more meteor impacts - eventually created small proto-continents which grew until they reached roughly their current size 2.5 billion years ago. The continents have since repeatedly collided and been torn apart, so maps of Earth in the distant past are quite different to today's. The history of life on Earth began about 3.8 billion years ago, initially with single-celled prokaryotic cells, such as bacteria. Multicellular life evolved over a billion years later and it's only in the last 570 million years that the kind of life forms we are familiar with began to evolve, starting with arthropods, followed by fish 530 million years ago (Ma), land plants 475Ma and forests 385Ma. Mammals didn't evolve until 200Ma and our own species, Homo sapiens, only 200,000 years ago. So humans have been around for a mere 0.004% of the Earth's history. Geological time periods Geologists have organised the history of the Earth into a timescale on which large chunks of time are called periods and smaller ones called epochs. Each period is separated by a major geological or palaeontological event, such as the mass extinction of the dinosaurs which occurred at the boundary between the Cretaceous period and the Paleocene epoch. My dinosaur ate your Jesus fish........
Archean era Began:3.8 billion years ago Ended:2.5 billion years ago It was during the Archean era that life first arose on Earth. At this time there were no continents, just small islands in a shallow ocean. There was a vast amount of carbon dioxide in the atmosphere, but since the sun was much fainter back then, the combined effect did not raise Earth's temperature to an extreme. Such levels of carbon dioxide would be toxic to the majority of animals alive today - as would the low oxygen levels.
Cryogenian period Began:850 million years ago Ended:635 million years ago A succession of incredibly harsh ice ages waxed and waned during the Cryogenian. It is nicknamed Snowball Earth as it's been suggested that the glaciation was so severe it may even have reached the equator. Life during the Cryogenian consisted of tiny organisms - the microscopic ancestors of fungi, plants, animals and kelps all evolved during this time.
Ediacaran period Began:635 million years ago Ended:545 million years ago Known also as the Vendian, the Ediacaran was the final stage of Pre-Cambrian time. All life in the Ediacaran was soft-bodied - there were no bones, shells, teeth or other hard parts. As soft bodies don't fossilise very well, remains from this period are rare. The world's first ever burrowing animals evolved in the Ediacaran, though we don't know what they looked like. The only fossils that have been found are of the burrows themselves, not the creatures that made them. This period gets its name from the Ediacara Hills in Australia, where famous fossils of this age were found.
Cambrian period Began:545 million years ago Ended:495 million years ago The Cambrian is famed for its explosion of abundant and diverse life forms. Life had diversified into many forms and many ways of living: animals now swam, crawled, burrowed, hunted, defended themselves and hid away. Some creatures had evolved hard parts such as shells, which readily fossilised and left a clear record behind. However, sometimes geologists get lucky and find beautiful fossils of soft and squishy creatures - as at the Burgess Shale site. In Cambrian times there was no life on land and little or none in freshwater - the sea was still very much the centre of living activity.
Ordovician period Began:495 million years ago Ended:493 million years ago During the Ordovician, a few animals and plants began to explore the margins of the land, but nothing colonised beyond these beachheads, so the majority of life was still confined to the seas. The Ordovician began with shallow, warm seas but the end of the period experienced a 500,000 year long ice age, triggered by the drift of the supercontinent, Gondwana, to the south polar regions. The Ordovician ended with a mass extinction. Ordovician-Silurian mass extinction: The third largest extinction in Earth's history, the Ordovician-Silurian mass extinction had two peak dying times separated by hundreds of thousands of years. During the Ordovician, most life was in the sea, so it was sea creatures such as trilobites, brachiopods and graptolites that were drastically reduced in number. In all, some 85% of sea life was wiped out. An ice age has been blamed for the extinctions - a huge ice sheet in the southern hemisphere caused climate change and a fall in sea level, and messed with the chemistry of the oceans.
Silurian period Began:443 million years ago Ended:417 million years ago ( Ordovician-Silurian mass extinction also occurred starting Ordovician ending Silurian) The Silurian period was the time when reefs got their act together, grew really big and created a completely new type of ecosystem for marine life. Silurian reefs weren't built by the same types of coral around now, but by a host of tabulate and rugose corals, crinoids and sponges. As the Ordovician ice ages ended, sea levels rose, making the Silurian a period of extensive seas. Bony fish made their first appearance. Meanwhile, on land, plants became more established, and grew in a zone along the edges of rivers and lakes to give Earth its first riverine and wetland habitats.
Devonian period The Devonian is also known as the Age of Fishes, since several major fish lineages evolved at this time. Sea levels were high and the global climate was warm. Sea surface temperatures in the tropics averaged 30 Celsius, much like the warmer parts of the Pacific today. Growth rings from corals living during the Devonian period have provided evidence that there were more than 365 days in the year back then - about 404 at the start of the period, falling to 396 by the end. Began:417 million years ago Ended:354 million years ago Flood basalt eruptions: Flood basalt eruptions are a type of large-scale volcanic activity, both in terms of extent and duration, that can occur on land or on the ocean floor. A flood basalt may continue to erupt for tens of thousands - possibly millions - of years and the lava can cover hundreds of thousands of kilometres. Large plateaux and mountains can result from the huge volume of newly surfaced rock. The huge volume of lava is accompanied by a similarly large release of volcanic gases such as sulphur dioxide and carbon dioxide. These can affect climate and cause acid rain, so flood basalts are thought to be a potential cause of mass extinctions. Impact events: Impact events, proposed as causes of mass extinction, are when the planet is struck by a comet or meteor large enough to create a huge shockwave felt around the globe. Widespread dust and debris rain down, disrupting the climate and causing extinction on a global, rather than local, scale. The demise of the dinosaurs at the end of the Cretaceous has been linked to an impact that left a crater in the seabed off the Yucatan peninsula of Mexico. Impacts have also been blamed for other mass extinctions, but the timing and links between cause and effect for these is still debated by scientists.
Still more to do only half way through, have a look at the LHC post for how hot they take that thing to
Don't want to ruin bills great threads love this stuff. The meat heads will not disappear, we are all preprogrammed to say hii look at this. The basic instinct is to reproduce and attract the opposite sex It's intelligence that moves us on from that stage, sadly does not happen to everyone.
That they are indeed. So every time you see a baboons with their bright red bums it's a meathead time. It's everywhere.
Carboniferous period The Carboniferous is famed for having the highest atmospheric oxygen levels the Earth has ever experienced and for the evolution of the first reptiles. Plants grew and died at such a great rate that they eventually became coal. The period was originally called the Coal Measures after its proliferation of coal-bearing rocks. Though the Carboniferous started off warm - hence its lush coal forests - the temperature began to drop and the polar regions were plunged into an ice age that lasted millions of years. In North America, the Carboniferous is divided into two epochs, the Mississippian and the Pennsylvanian. Began:354 million years ago (Late Devonian mass extinction) Ended:290 million years ago Late Devonian mass extinction: Three quarters of all species on Earth died out in the Late Devonian mass extinction, though it may have been a series of extinctions over several million years, rather than a single event. Life in the shallow seas were the worst affected, and reefs took a hammering, not returning to their former glory until new types of coral evolved over 100 million years later. In fact, much of the sea bed became devoid of oxygen, rendering it effectively out of bounds for anything except bacteria. Changes in sea level, asteroid impacts, climate change and new kinds of plants messing with the soil have all been blamed for these extinctions. This happened:359 million years ago End of the Devonian period Start of the Carboniferous period
Permian period The Permian started with an ice age and ended with the most devastating mass extinction the Earth has ever experienced. In fact, at least two mass extinctions occurred during this time. It's also when all the continents of the world finally coalesced into one supercontinent, named Pangaea (meaning 'the entire Earth'). As the globe warmed up and the ice retreated, many areas of Pangaea became very arid. The oxygen level plummeted too, from a high of 35% of the total atmosphere to around 15%. For comparison, today's oxygen content is 21%. Began:290 million years ago Ended:248 million years ago (Permian mass extinction) Permian mass extinction: The Permian mass extinction has been nicknamed The Great Dying, since a staggering 96% of species died out. All life on Earth today is descended from the 4% of species that survived. The event turns out to have been complex, as there were at least two separate phases of extinction spread over millions of years. Marine creatures were particularly badly affected and insects suffered the only mass extinction of their history. Many causes have been proposed for the event: asteroid impact, flood basalt eruptions, catastrophic methane release, a drop in oxygen levels, sea level fluctuations or some combination of these. This happened:248 million years ago End of the Permian period Start of the Triassic period
