We currently live in an icehouse where large continental ice sheets exist at both poles. The onset of this icehouse started in Antarctica 34 ma and in the Arctic 2ma. At least 3 times during earths history, the planet has been in a 'deep freeze', when ice sheets extended from the poles to the tropics.
Icehouse events are characterised by lower temperatures, ice caps and glaciers. The ice sheets from the last period of glaciation are still present. The huge increase in ice coverage then increases the drop in in global temperatures by reflecting more of the suns radiation back into space.
Greenhouse events are characterised by a lack of ice coverage and an overall increase in global temperatures. They can be caused by an increase in the amount of solar radiation reaching the Earth or a change in the concentration of gases in the atmosphere.
The extinction of species can be influenced by climate change. Most organisms thrive in a relatively limited range of conditions, and if the conditions in an area change then the species living there will alter. If the changes happen on a global scale then whole species or groups could be wiped out. An example of this is the mass extinction at the Permian-Triassic boundary where 96% of marine life extinct and 70% of terrestrial life became extinct. This followed a major glaciation that affected Antarctica, Africa and South America when they all joined as Gondwanaland. It was similar to the current icehouse, with continental ice sheets in the southern hemisphere and low atmospheric carbon dioxide concentrations.