At http://phys.org/print357194318.html … in the deserts of Utah, Nevada, and southern Oregon ancient shorelines can b e found on hillsides above dry valley floors, left behind like bathtub rings. These are the mark of former lakes that once existed in what is now a hot and dry region in the shadow of the mountains.This whole region was much wetter long after the end of the Ice Age, with springs and marshes and water in abundance (in comparison with today). When did the desert form – or dry out? Well, dampness still existed until 8200 years ago – isn't that surprising? Or is it. This date corresponds in calendar years to 6200BC – a time when ocean sea levels last fluctuated to any great measure, but exactly why that occurred at that time is something of a mystery.
The researchers came to this conclusion after analysing stalagmites from a cave in the Great Basin National Park and found moisture levels dropped dramatically 8200 years ago. On a geological time scale the moisture content dropped so suddenly – like falling off a cliff. Archaeologists should find evidence out there, the spokesperson added, for some pretty big changes in how people were living at that time, just before and just after 6000BC. Did they move to Montana – or elsewhere?
This is a pretty dramatic finding and it is difficult to see how it can be contributed solely to climate change – as it occurred so quickly (virtually instantaneously). Catastrophism might explain what happened – and we might note that there was a cool period of weather between 6200-6000BC which could be described as a mini Dryas event. What was going on? If a cosmic event occurred at the Younger Dryas boundary we might think in terms of a cosmic event 8200 years ago – but not as extensive as 12800 years ago.
We may also note that the desert belts (one in the northern and another in the southern hemispheres) are like bands circling the Earth, sandwiched between the subtropics and the temperate zones (also bands that circle the Earth). The desert belt would therefore appear to have a connection with the Earth's rotation.
There is another thing to bear in mind, the post 6000BC period is known as the Mid Holocene Climatic Optimum – lasting for several thousand years. It was not universally a climatic optimum of course, as the Great Basin dried out – at the same time as the Sahara and the Arabian deserts. It is known as an optimum because the tree line reached its highest altitude at that time, and its largest extent in a northerly direction – almost encroaching on the Arctic. The situation in the southern hemisphere is not clear cut as continental land masses to not impinge to any great extent on the Antarctic zone. Patagonia may have been warmer – and wetter.
Here is the rub – wetter weather (and warmer weather) moved northwards (and probably southwards) which allowed farming to prosper in marginal areas such as Scandinavia and Highland Scotland – even in the northern isles. Was the Earth in a more upright position during the Optimum? Did the jet stream shift – from the desert belt to higher latitudes? In NW Europe this era is defined as the Atlantic Period (of weather, or climate) a generally warmer and wetter phase suggesting changes in the Atlantic ocean currents (and cloud carrying winds) – but was it universal and continuous?