The Origin of Water on Earth

20 Apr 2010

At April 18th ... we have a post by Steven Goddard, 'Volcanoes and Water' ... with a series of stunning images. Water vapour is consistently the most abundant of volcanic gases - normally comprising some 60 per cent of total emissions. C02 accounts for between 10 to 40 per cent. Around 70 per cent of the surface of the earth is covered with water - but where did all that water come from? At steam from the interior of the earth, rising from the hot mantle into a cool atmosphere, caused the early oceans to form. Today, one can observe gases escaping from active volcanoes and these too contain water and in such a scenario oceans are continuing to increase in size all the time, an ongoing process that will never end. Other theories for the origin of water are, i) the ocean condensed out of an early atmosphere - repudiated as it could not have contained adequate water vapour. The ii) theory is often stated by scientists, an origin in comets. However, the hydrogen isotope active in the oceans seems to differ from those of Comet Halley and Hale-Bopp. This has therefore cast some doubt on the comet theory. So, how then did the oceans originate - and water created during volcanic episodes is one possibility according to Goddard. Is he referring to water that is locked inside rock - in the crust of the earth or the mantle? Is he referring to water subducted at plate boundaries during major events involving ocean floor slipping beneath crust (forming mountain chains as along the west coast of the Americas) - but would that not be recycling of water?

Steam pressure is the primary driver of explosive eruptions. Mount St Helens in 1980 was a prime example - almost all steam, some ash, and virtually no smoke. A volcano in Alaska in 2006 was virtually 100 per cent steam. Non-explosive volcanoes also exist, such as Mauna Loa on Hawaii. It was virtually all lava. Steam was absent. Mauna Loa had very little water mixed into the magma as it is not near a subduction  zone or covered in snow or ice. Explosive volcanoes appear to always involve water - and steam is what makes them blow. Steam is liquid water until it comes into contact with very hot magma - and becomes vapour.