This is an interesting one as uranium isotopes are used to date rocks and float the geochronological time span. The story is at http://phys.org/print340960522.html … and no doubt some people are inclined to doubt the whole exercise. Never the less it is all part of the Uniformitarian construct and requires understanding by critics and those with just a thirst for general knowledge. Basically, uranium isotopes are used to date the different rocks assigned to the different periods in the geochronology that has been developed over the last couple of hundred years. This has nothing to do with that aspect but is interesting as it shines a light on how scientists work within the consensus theory. There is also a nice little book out there to expand on the dating theme which is available second hand on Amazon – and no doubt other places where used books are for sale. It is 'The Dating Game: One Man's Search for the Age of the Earth' Cherry Lewis, Cambridge University Press:2000
Long lived radioactivity is the name of the game, and therefore a study of the global cycles of the isotopes is important – important enough to be published in the journal Nature (January 15th, 2015). It begins with an image that is derived from modelling. In the image below they illustrate the process of subduction where rock in the crust is forced downwards into the mantle …
… the green worm snaking deep into the mantle, which is assumed to well back up again at the Mid Ocean Ridges where new basalt sea floor is constantly being created. So, we can see the paper begins on the assumption the mainstream theory of Plate Tectonics is correct, and rely on that being a real world occurrence – rather than a hypothesis that is open to some debate. Of course, they have no choice but to take that position as they require a starting point – in order to create an ending point (or viable explanation of what is going on). It also involves other assumptions. One of these is that an oxygen free atmosphere prevailed in the Early history of the Earth, and this meant uranium was immobile within rocks. It is released via weathering and break down over long periods of time of the rocks. The mobile residue is then washed down into rivers and eventually reaches the oceans where there is a continuous process of incorporating mobile uranium isotopes into sea floor rocks. Hence, the sea floor, which eventually subducts, contains mobile uranium isotopes.
Researchers have found a high ratio of uranium 238 to uranium 235 in modern ocean sea floor – which supports the theory. Meteorites used in the research did not have these isotopes – which is all part of the theory too as meteorites are thought to represent the immobile uranium situation as existed in the Early stage of the Earth. Basically, it is thought they are all part of the building blocks of the planet, and the meteorites chosen for the exercise all appear to conform to that pattern. Meteorites live in cold space so they have not weathered as rocks on the Earth – wind, rain, frost etc. Now, the method in the madness, if you like, is the idea that subducted former ocean floor should re-emerge with evidence of mobile uranium (isotopes) as the rocks have been altered. This regurgitated rock should display evidence of the process that had been taking place prior to its journey deep into the mantle (going by the image above). It is very clever stuff – quite brilliant in concept and adaptation (but it appears to depend on a great deal of modelling).
The researchers came up with a surprising discovery, hence the paper in Nature. Rocks being regurgitated at the Mid Ocean Ridges comes out with evidence of mixing, which includes evidence of mobility in uranium isotopes, and this appears to be strong evidence that subduction does actually take place – and is not solely a hypothesis. In contrast, island basalts have a ratio very similar to the meteorites used in the study and therefore suggests a pre-oxygen origin of the rock that is spewed out by volcanoes. Ocean lavas, it goes on to suggest, come from a deep source in the mantle – which is not necessarily what Plate Tectonics has been telling students these 30 odd years. How does that work – and how much of the mobile uranium isotopes exist at Mid Ocean ridges, and why. If subduction does not take place how would that make this research look? Might the Mid Ocean Ridges be regarded as all part and parcel of the sea floor and therefore finding uranium isotopes present would be expected? Volcanic lava, on the other hand, clearly has an origin in the mantle – explaining the absence of mobile uranium isotopes. There are always two ways of looking at research.