In another chapter I suggested that all the water on Earth has been produced as a
waste product by trillions of methanogens, an ancient form of life, over a 3.5 billion
year period. This water synthesis is still ongoing and is attributable to the annual
increase in sea-level. It has been noted from tide gauges that sea levels have increased
by 18 cm over the past 100 years (Warrick and Oerlemans ). Many other indicators
show that this sea-level increase has been consistent since the times of the earliest
civilisations. We can extrapolate further into geological time, if we consider that
the production of water is, like it’s producer, increasing exponentially over time.
It is estimated that there are 1.2 trillion, trillion litres of water in the oceans
(Wikipedia). If we place this figure at the top of the curve on an exponential graph,
we can extrapolate for quantities of water which may have existed at different stages
up to 500 million years ago. We can also see how this sits with the amount calculated
from ocean level increase over the past 30 million years. We must also allow for
the increase in ocean-bed area as the Earth’s radius gets larger over time and we
can take this information from my small Earth models.
By dividing the total quantity of water at a given time by the surface area of the
Earth, at the same time, we can gather some idea of the depth of water, if the water
were to cover the whole surface, and if that surface were the same level throughout.
These are only crude figures and the amount of glaciation is not included in the
calculations. However, glaciation has less significance in the equation than one
may consider at first. This is because glaciation is cyclical; water vapour from
the oceans freezes on high ground at the cooler polar regions. A mass of ice accumulates
which gradually moves down to lower ground and eventually to the ocean where it melts
back into sea water. Ice which forms over sea water (pack ice) merely displaces the
water and when it melts (such as during a post major glacial) the water level is
not altered. Greenland, for example, is an archipelago of high mountainous terrain
and many of its glaciers already exist over water.
Similarly, there is a cycle for water on land; water vaporises from the oceans’ surface,
forms rain clouds which deposit water on land, and this water gravitates into aquifers
and rivers and eventually returns to the oceans.