Posted by: Prospector PJ24 OCT 2012
A raft of pumice larger than the surface area of Israel, and thought to have originated from an underwater volcanic eruption, was recently spotted floating in the Pacific Ocean. But this is not the first sighting of such an enormous floating boulder. Similar rafts drifted around the Pacific for up to 20 years after Krakatoa erupted in 1883.
This lightweight pumice is a solidified form of frothy lava created by simultaneous rapid cooling and depressurisation. The depressurisation creates bubbles by lowering the solubility of gases such as steam and carbon dioxide that are dissolved in the lava, while the cooling “freezes” the bubbles in the rock’s matrix. The density of pumice depends on the thickness of the solid material between the bubbles but, with an average porosity of 90 per cent, many samples float.
It has been suggested that floating pumice rafts could have played an important role in the origins of life on Earth. Pumice has the highest surface area to volume ratio of any rock. It has the ability to adsorb metals, organic materials and phosphates, as well as hosting organic catalysts such as zeolites (microporous crystalline solids that generally contain silicon, aluminium and oxygen in their framework and cations, water and/or other molecules within their pores).
And, because of these attributes, it could have formed an ideal “floating laboratory” for the development of the earliest micro-organisms.
During its life cycle pumice is exposed to lightning associated with volcanic eruptions, oily hydrocarbons and metals produced by thermal vents, and ultraviolet light from the sun as it floats on water. All these conditions foster the kind of chemical processes likely to have created the first living cells.