1. Ordovician-Silurian Extinction event
By Symone Hopkins

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

3. 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

4. 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

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

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

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

9. 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

11. 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

12. 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

13. 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

14. Works cited http://www.ucmp.berkeley.edu/ordovician/ordovician.php
_an_introduction