Permafrost: Permafrost is defined on the basis of temperature, as soil or rock that remains below 0°C throughout the year, and forms when the ground cools sufficiently in winter to produce a frozen layer that persists throughout the following summer.The thickness and temperature of permafrost depends on the temperature on the ground surface.

Liquids: Liquids is in between the solid and gas state. A characteristic of an liquid is that they could take any shape of an object, it could take in a shape of a cup if you pour some liquids in it. When you try to compress something you force the atoms together but it is difficult to compress liquids because the atoms are already together. Liquids has a cohesive force that is that holds the molecules together. Liquids could remain in a fairly constant density, 

Liquid Oxygen: http://en.wikipedia.org/wiki/Liquids Don't have enough time so I post the link.......