ORDOVICIAN PERIOD 488 - 435 Million Years Ago Edit
This is a period that arose after a terrible extinction event at the end of the Cambrian Period. Despite having a variety of newly evolved animals and plants in the Cambrian, famous for the new abundance of that appeared, the extinction event saw off many ancient families. Those that survived were much weaker. Then survivors fought it out for dominance, and the survivors that had been least affected, exploited the niches left by the previous top predators. Evolving from small molluscs, the Orthocones, and then Giant Orthocones affirmed their dominance for almost 90 million years. Beneath them, were the Sea Scorpions, though some forms, such a Pterygotus of the Silurian Period, were big enough to fend off most Giant Orthocones. This was a time of large scale glaciations, and the sea level fell to a very low level, creating land surface that had once been seabed. The Carbon Dioxide level was much, much higher than today, and as there was no plants yet on land, Oxygen could not be released into the atmosphere. If we were to stay in the Ordovician for any more than a few hours, we would probably die of oxygen deprivation, and the progress symptoms that would be caused by it. Nausea would turn to black out, and black out, would turn to death. Very interestingly, the speed of the rotation of the earth is much faster in this period, which causes the day to last only 21 hours, instead of the 24 hours that we are all familiar with.
The Hadean Eon The Archaean Eon The Proterozoic Eon The Phanerozoic Eon The Palaeozoic Era The Cambrian Period The Ordovician Period The Silurian Period The Devonian Period The Carboniferous Period The Permian Period The Mesozoic Era The Triassic Period The Jurassic Period The Cretaceous Period The Cenozoic Era The Tertiary Period The Palaeocene Epoch The Eocene Epoch The Oligocene Epoch The Miocene Epoch The Pliocene Epoch The Quaternary Period The Pleistocene Epoch The Holocene Epoch