As a result of these observations he has spent many years attempting to reconstruct the effects of volcanic eruptions and extra-terrestrial impacts.
Recent studies of tree rings in Europe and the United States have given scientists astonishingly precise new gauges for reconstructing the history of volcanoes, climate and human endeavor in the last 8,500 years. Hughes, director of the dendrochronology laboratory at the University of Arizona, explained in an interview that large volcanic eruptions leave widespread permanent traces in at least two ways.
Tree rings, as distinctively patterned by fluctuations in the environment as bullets are by gun barrels, were recognized half a century ago as potentially useful historical markers. Andrew Ellicott Douglas of the University of Arizona established the science of tree-ring dating, dendrochronology, when he used the rings discernible in ancient wooden artifacts to determine the age of a prehistoric Indian site. Hammer and his colleagues in Denmark analyzed the Greenland ice. First, volcanoes eject large amounts of sulfur dioxide which, when dissolved in water, is precipitated as sulfuric acid in rain or snow.
But only recently have scientists accumulated enough wood samples and other evidence from bogs, ice layers, medieval ruins, ancient campfires and many other sources to extend dendrochronology to objects almost as old as the last Ice Age. Baillie of Queen's University, Belfast, and his colleagues expect to determine the exact date of a neolithic roadway in Somerset, England. 541 - almost perfectly match the years for which eruptions were also detected in the rings of North American bristlecone pines and in thin layers of acidic ice within the Greenland ice cap. On an ice cap, it is embedded in an ice layer that is gradually covered by successive layers of non-acidic ice.
As such, it is required to make certain information available under the UK Freedom of Information Act.These scot's pine woodlands were open in character and had an understorey of birch.In the ground layer ericaceous shrubs or heather species were important including ling heather and crowberry.His interest in high resolution chronology prompted an interest in catastrophic environmental events that showed up in tree-ring chronologies.He was one of the first to recognise the existence of global environmental downturns as shown by synchronous growth reductions in tree-ring chronologies around the world.The lack of oxygen in waterlogged peat prevents the natural process of decay and ensures the tree trunks and stumps are preserved for years in the accumulating peat.