As for water, even if all ice in Antarctica and Greenland melts, the level of the oceans will increase only by 68 meters. There would also be some minor additional increase due to melting of glaciers around the world. And of course, warmer water expands, so it could potentially rise higher. However, no matter how much we can stretch all those variables, a could hundred meters of water could not possibly cover most of the land (for example, about half the continental US is at height of 500 meters or more), not even mentioning mountains (Everest peaks out at 8848 meters).
As for ice, since the level would not need to be uniform like for liquid water, it could have covered all or most of the Earth during a few periods in its history. The hypothesis of “snowball Earth” refers to three periods between 650 and 750 million years ago when such an event likely occurred. There is much evidence for and against it. It is theoretically possible: as ice cover would reflect more sunlight and thus cool the Earth further creating more ice cover in a loop. Over millions of year, volcanic activity could accumulate enough greenhouse gases to warm the Earth enough for ice to melt.
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