What is the evidence for a liquid water ocean on Europa, and why is this interesting to scientists searching for extraterrestrial life?

Europa has a crust of water ice and atmosphere with oxygen. When you observe the Europa carefully you will notice that it has a lot of cracks and streaks on its surface. Such cracks have been observed on the Earth as well and liquid water had been found beneath those areas. Also, micro organisms were found over there which survived even without any Sun light.

That is the reason scientists think that there can be liquid water beneath the icy crust and Europa may have life.

Salt water ocean below the continent

Explanation:

One discovery was salt water below the continent. The ocean can cover the whole surface of continent. The water is so much, much more than the earth's two thirds.

However, the oceans under continent are solid ice.