The Permian period of time started around 299 million years ago when the Earth was in the deep freeze of an ice age. Most of the land on Earth was joined together into one huge continent that geologists call Pangea. Huge glaciers fed off massive ice sheets and moved towards the oceans. As they moved they ground up rock which was caught up in the ice. These glaciers reached the oceans and broke off chunks of ice that floated away from the continents as icebergs. When these icebergs melted, any rocks caught up in the ice dropped through the ocean and landed on the sea floor. Animals living on the ocean floor at this time had to survive the deluge of these 'drop stones'. In some places, those animals with thick shells survived better than those with thin shells.
Evidence for the Permian period of time can be found in the rocks that made up the sea floor during the Permian. Layers of mud with drop stones and fossil animals with thick shells can be found around the world.
Over the next tens of millions of years (we are still in the Permian) the planet started to warm. The ice sheets and glaciers melted away from most of the globe. Then, after a few more tens of millions of years the ice ages returned and receded a few more times. So the Permian was a time of very varied climates...but overall it is considered to be a cold time in the history of the planet.
Permian - the catastrophic death of life
What is remarkable about the Permian...or at least the end of the Permian around 25o million years ago...is that something catastrophic happened to Earth. Exactly what happened is not really known - but it was so dramatic that 96% or more of sea life and 70% or more of land-dwelling life became extinct. It is the only know time on Earth in which most of the insects became extinct. For life on Earth, this catastrophic event was so major that it took the Earth over 10 million years to recover....and when it did it ushered in the world of the dinosaurs!
Scientists have put forward a number of possible causes for these mass extinctions during the end of the Permian. They include:
A. Earth being hit by a large meteorite or comet (that happened later in the history of the Earth and wiped out the dinosaurs). There is just a little evidence for this in the Permian - but being so old (250 million years ago) it is hard to find a definitive impact site etc.
B. A massive outpouring of basaltic lava. There are two places of Earth that are made up of vast amounts of lava that poured out during the end of the Permian. One place is the Siberian Traps where 2 million square kilometers was covered by lava right at the end of the Permian. The amount of volcanic gases and material released during these events could dramatically change Earth's climate.
C. Methane hydrate release in the oceans. The Earth's oceans contain vast amounts of 'frozen' methane gas found in an ice-like substance in sediments in the sea floor. Under the right conditions, these hydrates can be rleased in the ocean water, making the oceans toxic to life. The methane can also reach the atmosphere, changing climate.
D. Oceans anoxia - where the oceans lose most of their dissolved oxygen making if toxic for life. This may be triggered by massive amounts of carbon dioxide in the atmosphere - which in turn may be caused by huge volcanic eruptions (see above).
There are some other theories, including microbes and other gases. It may have been a combination of two or more of these things. Gathering scientific evidence and coming up with plausible explanations is the role of geologists who know (and love) rocks deposited in this time period.
Understanding these types of events can help us to understand the way our planet reacts to catastrophic changes as well as more subtle changes, either naturally occurring events (like increased volcanism) or human induced (like burning fossil fuels).
So the Permian was a time considerably different in climate as our own - but certainly was a time of some massive upheaval that shook life on Earth to it's very foundations. For me, it provides a lesson to all of us that our planet is so very dynamic that we can expect change to occur even over the short lifespans of humans. How we be adapt to those changes is really up to us as a society.