fuck I think we'd be best served by developing some sort of neurotoxin.

(http://www.autoadmit.com/thread.php?thread_id=3492187&forum_id=2#32379286)

Maybe it was not 100% ice covered, maybe there were gaps (slushball earth) and after great extinction some lifeforms would survived, but you are taking chances with lowering the chance of evolving more complex life forms. We know that Tardigrade can survive freezing and space vacuum, more complex life is separate question.

Even with today's climate, if ice sunk to ocean bottom (where it is colder, and summer warmth is harder to get). Such ice would not melt for millennia, creating perma-ice (similar to permafrost). Life would be possible only in shallow layer of water between perma-ice and surface. This layer would be very cold, cooled from the bottom by perma-ice.

As a result, oil fields would not form, or if formed, they would be between layers of perma-ice. Same with other geological forms created from sediments of sea bottoms, like chalk, limestone, sandstone. These will be mixed with perma-ice. Possibly limestome would never form, because pressure to created it would heat and melt ice layers.

Such ice frozen under pressure transforms to hexagonal columns. Very pretty. Columns can be separated intact - ice shatters on impact into hexagonal columns.

After compressed in bigger depth, or uplifted by geological processes above sea level, ice would melt and layer above would collapse. Would create very different geology on such planet.

Interesting effects on such planet:

•No tsunami after earthquake, because liquid ocean is shallow.

•More volcanoes, because more water (perma-ice) would be subducted in subduction zones in continental drift.

•Frequent smaller tsunami, when mixed layers of ice and sediment crack.

•Bigger changes in weather between summer and winter, because temperature stabilizing effect of oceans would be substantially decreased (less volume of water).

•Interesting effects with near-ocean volcanoes like Hawaii and Iceland. Or underwater volcanoes, melting perma-ice and messing up geologic layers, creating more tsunamis.

•Warm ocean currents would melt underwater canyons in perma-ice. Would have interesting effects on oceans, especially as continental drift would move such canyons.

•such canyons in perma-ice would have surprising ways to focus tsunami. After thinking about it, tsunamis on such planet would be frequent and more localized, more focused, because energy of tsunami would dissipate less (wave would travel down the canyon with little decrease in devastating power or dispersion).

•this canyons would have similar effect like bends in river delta: instead of sediments, layers of ice higher than the "banks" of "canyons" would be deposited by tsunamis, and quickly frozen, creating "walls" between polders where water in summer would be fresh melt (little salt), but darker bottom because of sediments. Those polders would be freshwater lakes on perma-ice (not on dry land).

•Liquid parts of oceans would by much saltier because salt "freezes out" from ice.

•It is quite possible that in some areas closer to poles, salt would centralize in few areas, creating very salty lakes (which would not freeze even in winter, warming them up

•because of accumulation of glaciers in Arctic (2 miles thick above sea level like Antarctic), sea level in tropical areas would be much lower (some 100-300 meter less) because all that water would be solid in thick polar glaciers. Glaciers would extend much farther from poles, and climate would be colder (more sun energy would be reflected back to space).

•ice reflects more sun energy than water, positive feedback). Effect in Arctic Ocean would be perma-ice all the way to the surface, even way above sea level in tropics, with occasional very salty lakes high in the parma-ice/glacier mountains. So perma-ice would be like solid land, supporting glaciers and salt lakes (with possibly addition of layers of dust brought by winds).

•in snowball phase of Earth, oceans would freeze completely (bottom to top in winter) except near underwater volcanoes. As a result: Life would adapt to to survive occasional freezing, and be able to continue after thawing.

•Re @Taemyr comment about lover albedo of ice. As @David Richerby correctly notes, if ice fell to bottom, if cold lasts long enough, body of water would freeze bottom to top. Then, even during summer it might not melt all the way to the bottom (ice being protected by cold water on top of it), and ice would accumulate until frozen solid bottom to top. Not good for complex life.

•Effect on plant life on continents would be minimal. Seasons would be more pronounced, but plants can handle that. So coal should be possible - and also industrial revolution.

•Such adaptation to survive many freeze/thaw cycles would be boost for slower-than-light travel.

•So if advanced life and space-faring civilization could develop on such planet, they would have great advantage in space travel.

(http://www.autoadmit.com/thread.php?thread_id=3492187&forum_id=2#32379237)

we certainly wouldn't exist

(http://www.autoadmit.com/thread.php?thread_id=3492187&forum_id=2#36273792)