Ordovician-Silurian Extinction event By Symone Hopkins

Periods when earths history when abnormally large numbers of species die out simultaneously or within a given time frame.

It is the second largest extinction in Earth’s history losing 86% of species.60% of which were marine invertebrates The most affected being Brachiopod Corals Bryozoans

Ordovician period Lasted 45 my North of tropics was mostly ocean, with most of land (Gondwana) in the southern hemisphere, which shifted to the south pole and submerged through this period. life was confined to the ocean and this period boasted high invertebrate diversity especially conodonts The shallow seas covering Gondwana made great breeding grounds for new forms of trilobites, but this time boasted extremely high sea levels There is evidence that plants invaded land at this time (through tetrahedral spores) and terrestrial arthropods Large glaciers formed lowering see levels and draining shallow seas

Gondwana starts moving southward and is covered by clear shallow seas over continental shelves which encourages calcium depositing organism growth

Abundant life forms CONODOTS JAWLESS FISH As well as trilobites and some algae CONODOTS JAWLESS FISH

The extinction Lost 60% of marine life forms Oceans and seas were significantly cooler than the earlier greenhouse climate Sea levels dropped significantly

Silurian period Latitude climates similar to today Earths general climate was stable for the first time, entered a greenhouse phase Coral reefs appeared Evidence of fish evolution, life on land (plant and animal). Slight continental movement Rapid invertebrate recovery Branchipods are the most common hard shelled organism Corals and algae flourish while trilobites start to decline

Abundant life forms of Silurian platyceras The planet started to warm causing ice to melt and sea levels to rise This rapid change did not allow for life to adapt quickly enough leading into the second part of the extinction, this time losing 20% of life

What Happened? It is called the Ordovician-Silurian extinction because it happened between the end of Ordovician and the begging of the silurian with two peaks in extinctions separated by 4 million years. Gondwana settles in south pole Huge glaciers formed draining shallow seas, and lowering sea level, changing chemistry and habitats of marine life This is most likely the cause of the great extinction which marked the end of the Ordovician The ice age was short lived which gives cause to believe their were other contributing factors Though life flourished after the Ordovician the rapidly warming of the planet by the middile of the silurian caused another extinction this time wiping out 20% of life together with habitat destruction caused by plate tectonic movements, suggesting that the end Ordovician mass extinctions were a product of the coincidence of a number of contributing factors. Moreover, when the deteriorating climate intensified, causing widespread glaciation, a tipping point was reached resulting in catastrophe

As gondwana starts to move north the glaciers that were over the south pole begin to melt The second phase is more clearly linked to near-global anoxia associated with a marked transgression during the Late Hirnantian, killing off the survivors and more complex verisons from the first pulse who have now been adapted to cooler shallower environments

Works cited http://www.ucmp.berkeley.edu/ordovician/ordovician.php https://cosmosmagazine.com/earth-sciences/big-five-extinctions http://earthwise.bgs.ac.uk/index.php/Carboniferous_of_the_Southern_Uplands_- _an_introduction http://plate-tectonic.narod.ru/photo22.png http://madan.org.il/en/node/8864 http://science.nationalgeographic.com/science/prehistoric-world/ordovician/ http://www.uky.edu/OtherOrgs/KPS/pages/fossilphoto.html http://www.britannica.com/animal/lamp-shell http://palaeos.com/paleozoic/silurian/silurian.htm#Silurian