How does drilling a hole in the ground help us understand the origin of vertebrate life on land?
The borehole is crucial in understanding how the different fossil locations in the Tweed area relate to each other in time. All the localities where tetrapod fossils have been found are in river beds where only a few tens of metres of Ballagan Formation are exposed. So it is impossible to correlate between the sites using the rocks exposed at the fossil sites.
What is needed is a continuous section of rocks through the sequence containing all the fossil localities to work out the order of evolution. A continuous section exists at Burnmouth, about 10km north of Berwick, but this is in a fault zone and at the coast which means we don’t know for certain how it relates to the fossil sites. By drilling the borehole inland, close to the fossil sites, we now have another continuous section and by comparing it with Burnmouth we can erect a time frame in which the fossil localities can be placed.
Crucially the core from the borehole also provides a continuous record of the climate and environmental change through the time that the tetrapods evolved. This will be created by assembling evidence from the sedimentary rocks in the borehole, along with geochemical information and the occurrence of fossil plant spores (palynology). Unlike the coastal outcrop at Burnmouth the borehole core is unaffected by weathering and erosion which can alter or destroy many of these types of evidence.
So what have you found?
|borehole is 7 inches (102mm) in diameter|
|The carbonado diamond drill bit ; before (left) and after drilling the borehole (right)|
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