A
hydrosphere (from
Greek ?d?? -
hydor, "
water" +
sfa??a -
sphaira, "
sphere") in
physical geography describes the collective mass of water found on, under, and over the surface of a
planet.
The Earth's hydrosphere consists of water in all forms the ocean (which is the bulk of the hydrosphere), other surface waters including inland seas, lakes, and rivers; rain; underground water; ice (as in glaciers and snow); and atmospheric water vapor (as in clouds). The average depth of the oceans is 3,794 m (12,447 ft), more than five times the average height of the continents. The mass of the oceans is approximately 1.35 × 1018 tonnes, or about 1/4400 of the total mass of the Earth (ranges reported 1.347 × 1021 to 1.4 × 1021 kg.[1] )
The abundance of water on Earth is a unique feature that distinguishes our "Blue Planet" from others in the solar system. Approximately 70.8[2] percent (97% of it being sea water and 3% fresh water[3]) of the Earth is covered by water and only 29.2 percent is landmass. Earth's solar orbit, volcanism, gravity, greenhouse effect, magnetic field and oxygen-rich atmosphere seem to combine to make Earth a water planet.
Earth is actually beyond the outer edge of the orbits which would be warm enough to form liquid water. Without some form of a greenhouse effect, Earth's water would freeze. Paleontological evidence indicates that at one point after blue-green bacteria (Cyanobacteria) had colonized the oceans, the greenhouse effect failed, and Earth's oceans may have completely frozen over for 10 to 100 million years in what is called a snowball Earth event.
