A piece of news that has been causing some feelings of grief can be found at http://news.discovery.com/history/archaeology/mysterious-earthen-rings-p… … which is all about human made earth structures, ditches and circular formations, found in the Amazon rainforest of Bolivia, and apparently were there before the jungle – which is the mystery. The same story is also at the Daily Mail (which appears to have developed a strong science column and always has lots of images to illustrate what they are saying) – go to www.dailymail.co.uk/sciencetech/article-2685049/Amazonian-rainforest-jus…
The above links were sent in by Gary Gilligan. He had a post at Thunderbolts a couple of years ago – go to www.thunderbolts.info/wp/2012/10/28/the-amazon-rainforest/ … in which he claimed the rainforest could not have existed when the Sahara desert was green (the first half of the Holocene) as it is seeded by an astonishing amount of dust with an origin in the desert – some 54,000 tons a day crosses the Atlantic and influences the ecosystem in S America. This amounts to 40 million tons of dust a year that is deposited in rainfall over the Amazon basin – see also his web site at www.gks.uk.com/Sahara_Desert_Amazon/.
Environmentalists might not be too impressed with this story as it is supposed the rainforest ecosystem is pristine – going back thousands, if not millions of years. In the grand scheme of things some sort of rainforest must have existed there for such a length of time otherwise the rich evolution in the natural world could not have happened – so has the story been misrepresented by journalists? Well, the slant of the original research is that the ecosystem can come and go in different parts of Amazonia. It is not a static ecosystem covering the whole region – therefore it is affected by climate change. In the specific part of Bolivia under review humans built their earthworks in an area that was free of what we might term jungle – it was, instead, a grassland dominated environment. That doesn't mean the whole of Amazonia was savannah – and it is well known that in the Pleistocene the rainforest was a much more patchy affair.
At http://frontiers-of-anthropology.blogspot.co.uk/2014/07/-pre-rainforest-… … says that human made ring like ditches scattered across Bolivia and Brazil were there before the rainforest – during a period in which grassland dominated the landscape as opposed to strictly tropical rainforest. Presumably the rainfall levels were lower at that time, and this appears to explain the sediment cores used in the research (the cores go back 6000 years). We may note the Sahara formed over a longish period, and caused human migrations in around 4000BC, and again, around 3000BC. The advent of the sand is a different matter – as it depends on when the sand originated. North Africa is thought to have periodically see-sawed between desert and savannah on a number of occasions. It was a green area attractive to humans on a number of occasions – and at other times was a desolate place, much like today. The Sahara is mostly a stony desert – very arid. The sand deposits are what film makers prefer but they represent a quite small proportion of the whole – as far as dunes are concerned. The Sahara dust may therefore not strictly be confined to sand (although when the wind blows our way that seems to be what crosses the Channel).
The actual research article is in the July 7th issue of the PNAS journal (the Proceedings of the National Academy of Sciences) which indicates it is not to be sniffed at. However, on the links above the Daily Mail appears to score over the others, although presumably all are based on an official press release. The area in question was savannah two thousand years ago – which is not too surprising as we know that in the Roman Warm Period the climate was much warmer in NW Europe with less rainfall and the Romans were able to grow Mediterranean crops. This came to an end in the Late Roman period when the climate cooled and became wetter. How this might transfer to Bolivia is something else – and how long the savannah regime dominated the ecosystem is not clear from the press release. What I found more interesting was that the idea that rainforest hunter gatherers may not always have proliferated – and people that farmed were once common to the region (but where did they go?). Well, according to the research the farmers thrived for many years, all the way down to the arrival of the Europeans. The impact of that, depopulation caused by introduced diseases, and cultural collapse as a result of a completely alien belief system and outlook, which all happened just 500 years ago. Were these earthen structures still being being used shortly before Columbus?
Finally, the authors of the article add their obligatory CAGW add-on (otherwise they would not have been published in such a friendly manner) by saying that the growth of the rainforest, post Columbus, led to the Little Ice Age (because the jungle absorbed all the co2 as it mushroomed in such a short space of time). HaHa. Nothing like a bit of comedy.