There were talks on two very different areas of Geology in our September meeting.
In the first half Bob Tuddenham gave a talk on the basics of Radiometric Dating; this topic embraces physics and chemistry as well as geology.
A hundred years ago geologists had no idea of the absolute age of rocks but the discovery of radioactivity with exponential decay in the early 20th Century opened up the possibility of an accurate geological clock. Arthur Holmes, the first Professor of Geology at Durham University, was a leading scientist in the very early development of radiometric dating while many of his colleagues at that time were not convinced this could be achieved.
It was the discovery of isotopes and the development of the modern mass spectrometer in the 1950s that enabled geological ages to be accurately measured. These revealed the vast expanse of time since the Earth was formed 4.6 billion years ago and confirmed absolute ages in the geological stratigraphic column, Radiometric dating was also essential in the discovery of the mechanism for plate tectonics in the 1960s showing that the ocean floor moves out each side of a mid ocean ridge.
In the second half of the meeting, David Saville continued his excellent series of talks on ‘Introduction to Geology’. This talk was first of two on the Jurassic Period. David explained that there had been a mass extinction at the end of the Triassic because of a massive outpouring of lava with the release of extensive carbon dioxide and acidic sulphur dioxide. At the start of the Jurassic, the supercontinent Pangaea was starting to break up and shallow seas were flooding in across NW Europe. The climate was more benign and humid than during the previous Triassic period. There was rich flora and early dinosaurs began to dominate with no obvious predators.
Our next meeting will be at The Witham on Monday *October 26th at 10 am. All are welcome to join us. Please contact the convenor for details.
*or November 23rd