Some water does come from volcanic eruptions, but it is now thought that most of the Earth's water came from comets which hit the Earth. Sin ce comets are made of ice, it is probable that a number of them melted and brought water to the Earth. Clouds act like insulation. After the sun has heated the Earth during the day, the clouds trap the heat near the Earth. On clear nights, the heat is able to dissipate faster.
Deserts are very bare.
This means that there is nothing to protect it from the sun, so it gets very hot in the day. During the night, there is nothing to hold the warm air near the ground, so the desert cools off very quickly. Anticlines are where layers of stratified rock bend away from each other. Synclines are troughs where the layers dip toward each other from either side. A plain is a large area of flat land.