Probing A Common History

Everyone has heard speculation about the lost continent of Atlantis, but names of the very real landmasses of Laurentia and Avalonia are familiar to only a few. Warren Huff and Carlton Brett, professors of geology, know more than most about the two, and they’re about to discover even more. NSF has awarded Huff and Brett $195,000 for three years to study “High Resolution Sequence and Event Stratigraphy of Mid Silurian Strata in Eastern Laurentia and Avalonia.”

Most people probably do not realize that “Laurentia” was the name for ancestral North America or that Avalonia was a landmass that included parts of Great Britain. Huff and Brett dispute the generally held theory that the Silurian Period of geologic time, ranging from 417- 440 million years ago, was relatively quiescent. They contend that, on the contrary, Avalonia was in the process of colliding with ancestral North America, and they conclude that the two regions shared what they call “a common history.”

Their approach rests on what they describe as new geologic discoveries about the areas: rapid changes in climate and sea level in the aftermath of a major glacial episode, mountain-building in North America’s eastern ledge, re-diversification of marine life from one of the largest extinctions in earth history, and development of the first terrestrial ecosystem on land. To prove that major sea oscillations and large-scale mountain building affected eastern North America and the micro-continent of Avalonia, Huff and Brett will examine ash layers from explosive volcanoes, shifting types and locations of sediments from mountainous areas, and ancient earthquake deposits.

Huff observes, “Our ability to produce precise correlations, in part by using newly discovered volcanic ash layers, will permit evaluation of ancient lands and seas through a series of perfectly resolved time-slices. These correlations will allow recognition of widespread or global events, as well as local patterns. In this way, we will construct the history of sea level and climatic fluctuations and development of paleogeography (sea basins, local arches, and mountainous terrains). Finally, we will investigate the interaction of these physical events and the evolution of the rapidly changing biosphere during the Silurian time.”

Brett adds, “The Silurian turns out to have been a very dynamic time: recent research shows that during this period the Earth fluctuated between ‘icehouse’ (cool and with icecaps/glaciers) and ‘greenhouse’ (warm with little ice) climatic states, rather like the present Earth, and there appear to have been several linked major crises in marine life during this time. The rocks provide a detailed record of sea level and climatic fluctuations, as well as changes in the biosphere. By studying a time slice of several million years like the Silurian, we may begin to understand the dynamics of global change: how rapidly the Earth can shift from one climatic state or sea level to another, and what the connections are to evolution and extinction events in life history. In working toward long term environmental models, we may better understand the changes of our present dynamic Earth.”