It will come as no surprise to regular readers of Skeptophilia that I have a fascination for considering how the terrain of the Earth has changed over its history. It's a topic I've come back to again and again as scientists piece together the shifting topography of the continents, molded by plate tectonics and glaciations and even the occasional meteorite impact.
It's tempting to think that you have to go back hundreds of millions of years to see a significant difference from what we have now, as we did in yesterday's post about the peculiar geology of Scotland. In some cases, though, things have changed on a far shorter time scale, so recently that the remnants of the past lie right beneath the surface of the modern landscape.
The Fens are a region in eastern England, lying in Lincolnshire, Cambridgeshire, and Norfolk. It's virtually all dead-flat and only a meter or two above sea level, so the whole area is prone to flooding -- water is controlled by a network of levees and drainage channels that crisscross the entire nearly four thousand square kilometer region. You'd think this would discourage people from living there, but the opposite is true; it's been settled since Mesolithic times, mostly because of the excellent quality of the soil for agriculture. The largest communities in the Fens are understandably concentrated on the highest ground, which are nicknamed "islands" (and in rainy periods, they sometimes are islands in actual fact). The largest of these is Ely, a beautiful cathedral city that is now home to twenty thousand people.
It's a strange and surreal landscape, prone to long periods of fog and swirling mist, largely devoid of trees, dominated by wide grassy marshes that are home to a great variety of birds and other wildlife. The region so impressed composer Ralph Vaughan Williams that he wrote his melancholy and evocative piece In the Fen Country to try to capture the otherworldly beauty of the place.
What brings up this topic today is a study by researchers at the University of Cambridge that appeared in the journal Quaternary Science Reviews last week, which showed that only five thousand years ago, the Fens looked very different -- and traces of that vanished landscape still lurk right below the surface.
Farmers plowing the rich soil to plant crops such as grains, vegetables, potatoes, canola, and mustard frequently find their plows getting snagged on heavy logs that then have to be dug up and dragged out. "A common annoyance for Fenland farmers is getting their equipment caught on big pieces of wood buried in the soil, which can often happen when planting potatoes, since they are planted a little deeper than other crops," said study lead author Tatiana Bebchuk. "This wood is often pulled up and piled at the edge of fields: it's a pretty common sight to see these huge piles of logs when driving through the area."
Upon analysis, Bebchuk and her team found that nearly all of the wood came from yew trees -- many of them absolutely enormous, on the order of twenty meters tall. Only five millennia ago, what is now the marshland of the Fens was a huge forest of yew trees.
Then, about 4,200 years ago, all of them suddenly died.
The reason, Bebchuk found, was a sudden influx of salt water as the world warmed following a cold period, and sea levels rose. Within a generation the yew forests were nothing more than a vast expanse of bleached trunks, which ultimately fell and were buried in the marshy soil. Replacing them was an ecosystem of salt-tolerant marshland grasses that still dominate the region today.
What's curious is that this coincided with significant events in other parts of the world -- a serious drought in China, and the collapse of the Egyptian Old Kingdom and the Mesopotamian Akkadian Empire. Whether these are all directly related is, of course, impossible to say; it's rare that complex historical events have only a single cause. Climate change may, however, been a significant contributor -- otherwise this is quite the coincidence."We want to know if there is any link between these climatic events," said Bebchuk. "Are the megadroughts in Asia and the Middle East possibly related to the rapid sea level rise in northern Europe? Was this a global climate event, or was it a series of unrelated regional changes? We don't yet know what could have caused these climate events, but these trees could be an important part of solving this detective story."