ERAS OF THE EARTH
It wasn’t long ago that our Earth was thought to be only a few thousand years old and having been created in a matter of days. However during the scientific revolution that was taking place in the 18th and 19th centuries, minds like Darwin, Hutton and Lyell were challenging these age old theories. It was Charles Lyell that pioneered the theory that the forces of physics have remained the same throughout history, James Hutton also expressed that we can interpret the ancient past by studying modern day natural processes because the past and present are governed by the same laws. His findings reported that layers of sediment accumulated at around 2cm per year, he deduced that since mountains are sedimentary formations and thousands of metres high that the planet is more than a few thousand years old, but hundreds of millions.
Our Earth is actually 4600 million years old, this staggeringly long time is almost impossible for the human mind to comprehend. As far as we know, life emerged as single celled organisms around 3800 million years ago, for the next 3 billion years it would remain as these minute unicellular organisms. This is the Precambrian, 4600 - 570 million years ago.
To help us grasp the immense history of the Earth, a geological timescale was developed with each period marking a milestone in evolution and life.
CAMBRIAN 540 - 488 million years ago
Named after Cambria, an ancient name for Wales where rocks of this age are greatly exposed.
The Cambrian period sees explosive development of multicellular life with all the main modern phyla being established. Complex eyes and food chains evolve as well as active predation. Life is confined to the sea.
ORDOVICIAN 488 - 440 million years ago
Named for an ancient welsh tribe, the ordovices who lived in areas where rocks of this age are well exposed. Th oceans flourish with huge diversity of jawless fish, trilobites and gastropods and arthropods begin to dominate. The period ends with arthropods taking the first steps onto land. The end of the ordovician is marked by the first of the five major mass extinctions to hit the planet.
SILURIAN 444 - 416 million years ago
Named for another welsh tribe, the silures, who inhabited areas where rocks of this age are abundant. Life in the oceans recovered from extinctions, magnificent coral reefs thrive in warm seas. Small plants begin to colonise the land and jawed fishes evolve.
DEVONIAN 416 - 359 million years ago
Named after the English county of Devon which is rich in Devonian age rocks and fossils. The Devonian period is also known as the age of the fishes. Jawed fish and placoderm fish rule the oceans, trilobites still thrive. Plants move from the coastal areas deep into land and the first forests spring up. Shark species increase in numbers and early forms of amphibian begin to spend more time on land.
CARBONIFEROUS 359 - 299 million years ago
Known as the age of amphibians and named for the ancient coal deposits which were laid down during this time. The land is overrun with lush forests and swamps, The two main continents of the time, Eurasia and Gondwana are colliding to form the supercontinent Pangea. Winged insects take over the skies, oxygen content is much higher that today allowing insects to reach great sizes and the first true reptiles evolve, these are the first truly terrestrial vertebrates.
PERMIAN 299 - 251 million years ago
Named after Perm in Russia where rocks of the age are well exposed. Pangea is covered in harsh deserts, the number of species goes into decline, eventually 95% of them are wiped out in the worst mass extinction ever seen. Mammal like reptiles evolve. The first dinosaurs evolve towards the end of the Permian, they start as a few isolated groups and begin to increase rapidly in numbers.
TRIASSIC 251 - 200 million years ago
Named after the word “Trias” referring to 3 rock divisions in Germany called bunter, muschelkalk and keuper. The climate of Pangea is warm and dry and dinosaurs have gradually assumed dominance in the land, skies and oceans. Mammals only exist as a few small species. Ichthyosaurs and plesiosaurs reign in the sea and reach phenomenal size.
JURASSIC 200 - 146 million years ago
Named for the Jura mountains. Dinosaurs still dominate the land and the oceans flourish with marine reptiles and ammonites. The first bird start to appear towards the end of the Jurassic.
CRETACEOUS 146 - 65 million years ago
Named for the latin “creta” meaning chalk which is laid down during this period and found widely now. Dinosaurs continue to dominate, the first flowering plants evolve. Sea levels are up to 300m higher than today in some areas, much of the land is covered in shallow seas. Carbon dioxide concentrations rise, slowly choking the atmosphere. The end of the cretaceous is marked by the extinction of the dinosaurs due to possible meteor impact.
PALEOGENE 65 - 23 million years ago
The world begins to recover, mammals and birds begin to flourish and exploit the vacant niches left behind by the dinosaurs, in doing so they grow to incredible sizes. The climate is gradually cooling and will continue to do so bringing the earth into an ice age. In these cooler conditions the first grasses evolve.
NEOGENE 23 - 2.5 million years ago
The climate is still cooling, ice sheets begin to spread down from the poles, as a result sea levels slowly drop. The size of forests reduce and grasslands take over resulting in vast open planes. Mammals dominate the earth due to their ability to adapt to changing environments and harsh conditions. Towards the end of the period early hominids begin to appear.
QUATERNARY 2.5 million years ago to present
With an enduring ice age much of the mammalian megafauna have become extinct. Hominids have continued to evolve, only the homo sapiens survive as they are able to adapt.