Slabbing

1 Oct 2017

An article in Scientific American covers the same ground as a press release reported here a week or so ago - see www.scientificamerican.com/article/scientists-closing-in-on-the-dawn-of-... ... which tells us geologists have been comparing early Earth with Iceland - where black lava fields stretch as far as the eye can see and beaches with black sand can be found. Black rocks and black sand can be seen elsewhere of course, with an origin in volcanic lava eruptions. The new theory is that over the course of time the world became less black and more grey, blueish, and in general lighter coloured rocks predominated. The black rocks disappeared - but where. Well, the theory is that they were swallowed up in the Mantle and later re-emerged as lighter coloured rocks -such as the granites. This implies that Plate Tectonics on Earth has been in progress for billions of years - an estimate of 3.5 billion years ago or even earlier is being suggested. This flies in the face of some former geological thinking - and evidence of subduction and regurgitation is of course produced in the models rather than in field research. However, field research involving a trip to Iceland appears to be central to the theory. The black lava fields and black sand gave rise to the theory on the basis that Iceland sits on the Mid Atlantic Ridge and represents newly formed volcanic material (emerging out of the innards of the Earth). In other words we now have black rocks with an origin in volcanic eruptions and lighter coloured rocks emerging out of the earth at subduction zones. Iceland is not on a subduction zone - it is thought to be where ocean spreading is taking place, a continuous process of lava erupting and causing the ocean floor on both sides to push the Americas away from Europe and Africa. Hence, white coloured rocks are being formed a long way away from Iceland, and the theory is that they are reconstituted and reformed black rock. This, they speculate, must imply Plate Tectonics was taking place in very early periods of earth history.

It is quite a convenient theory in some ways as it allows a vast timescale to allow rocks to emerge at plate boundaries and ocean basins to be sculpted, mountains to rise up, even altering the composition of the atmosphere and oceans by gradual geological change. In a catastrophist model the changes would have been more rapid - but not necessarily reducing the timescale radically. It does however allow a shorter timescale - if evidence emerges to suggest this. Why one would want to reduce earth history, on the other hand, is the big question. If it is only to repudiate the uniformitarian model that is fine, by itself, but if it involves belief systems, that is less convincing. As it stands now the uniformitarians have an enormous period of time in which to play and fiddle around with the data. They hold all the cards. Yet, there is also a lot of evidence to show that some big geological events took place very quickly - particularly boundary events at geological ages. At the same time surviving life forms required enough time to evolve in order to fill in all the niche places in the geological record as seen in the fossil record (at the next boundary event).