An Introduction to Environmental Chemistry

The source of water for the formation of the hydrosphere is problematical.

Some meteorites contain up to 20% water in bonded hydroxyl (OH) groups,

while bombardment of the proto-Earth by comets rich in water vapour is another

possible source. Whatever the origin, once the Earth’s surface cooled to 100°C,

water vapour, degassing from the mantle, was able to condense. Mineralogical

evidence suggests water was present on the Earth’s surface by 4.4 billion years

6 Chapter One

Oxygen 46.6%

Others 1.4%

Magnesium 2.1%

Potassium 2.6%

Sodium 2.8%

Calcium 3.6%

Iron 5.0%

Aluminium 8.1%

Silicon 27.7%

Fig. 1.3Percentage of major elements in the Earth’s crust.

Table 1.1Inventory of water at the Earth’s surface. After Speidel and Agnew (1982).

Reservoir Volume (10^6 km^3 ) Percentage of total

Oceans 1350 97.41

Ice-caps and glaciers 27.5 1.98

Groundwater 8.2 0.59

Inland seas (saline) 0.1 0.007

Freshwater lakes 0.1 0.007

Soil moisture 0.07 0.005

Atmosphere* 0.013 0.001

Rivers 0.0017 0.0001

Biosphere 0.0011 0.00008

Total 1385.9 100

* As liquid equivalent of water vapour.