100 years of dating rocks and minerals, and counting….... Part1 by Dan Condon

Time was born 100 years ago. Geological time, or “isotope geochronology”, to be exact. This may sound like an odd statement but 1913 was a year of two very important scientific events that gave us the tools by which we could date the age of our planet.

Our Dr Daniel Condon explains more about these exciting events and the birth of isotope geochronology…. 
In 1913, Frederick Soddy’s research on the fundamentals of radioactivity led to the discovery of “isotopes.” Later that same year, Arthur Holmes published his now famous book The Age of the Earth, in which he applied this new science of radioactivity to the quantification of geologic time. Combined, these two landmark events did much to establish the field of “isotope geochronology” – the science that underpins our knowledge of the absolute age of most Earth (and extraterrestrial) materials. In celebrating the centenary, this series of blog posts (tagged #geochron100) will highlight a discipline that reflects and responds to the demands of studies ranging from the early evolution of the Solar System to our understanding of Quaternary climate change, and the 4.5 billion years in between.
To paraphrase Monty Python, what’s geochronology ever done for us? Quite a lot it turns out. The quantification of time is fundamental to our understanding of planetary evolu­tion and the geologic processes that shape our own planet Earth. The origin and evolution of life on Earth is recorded within stratigraphic successions that we sequence and order using radioisotopic dates. Geochronology informs our understanding of plate tectonic processes, their influence on the development of topography, and in turn the climate system.  The integration of disparate geologic records via absolute dating illuminates the connec­tions and feedbacks among the biological, climatic and tectonic components of the coupled Earth system, such as those exemplified during the Neoproterozoic era when snowball Earths were followed by the rise of animals. Their causal links to phenomena like biological mass extinctions and changes in atmospheric composition are also tested and revealed by radioisotopic dating. Geochronology has become a key tool of geological mapping and exploration for the mineral and energy resources upon which our society is built. And equally relevant is the role of chronology in under­standing environments during the last tens to hundreds of thousands of years, an understanding that provides the context for anthropogenic climate change. Indeed, geochro­nology has done quite a lot for us.


Arthur Holmes (left) ca. 1910 published ‘The Age of the Earth’ in 1913.  Frederick Soddy (right) in 1922 published a paper on the concept of ‘radio elements chemically non-separable’ which at the suggestion of Dr Margaret Todd, her termed ‘isotopes’.
As I’ve mentioned the year 2013 marks the centenary of two landmark publica­tions that laid the foundations of modern geochronology. Soddy (above right) received the 1921 Nobel Prize in Chemistry for this work, which contributed to the burgeoning field of nuclear physics. At the same time Arthur Holmes (above left) carried out pioneering studies on the application of radioactivity to dating rocks and his prescient realization of the impor­tance of a quantified geologic time­scale instigated the quantitative study of the stratigraphic record, which continues to this day (Gradstein et al. 2012). 

This conver­gence in 1913 of physics and geology marks the birth of isotope geochronology and while these centenaries deserve an auspi­cious marking, the current state of isotope geochronology also merits celebration. This month we are holding a science meeting at The Geological Society entitled ‘The first century of Isotope Geochronology: the legacy of Frederick Soddy and Arthur Holmes’, where speakers (but not including Prof Iain Stewart! ☺) from across the globe will be talking about a wide range of applications, from Mars rover exploration through to mass extinctions 200 million years ago, and recent climate change that gives us some insight into what magnitude of change we could be expecting in the coming years.  Geochronology has never been more relevant.  So please stop by GeoBlogy in the coming weeks/months for a look at the exciting work we’re doing and how it attempts to answers some really important questions. We’ll also try and answer why “ABSOLUTE AGES AREN’T ALWAYS EXACTLY?”, what Donald Rumsfeld has to do with dating rocks, and what we’re doing to make them better dates…


Follow Dan on Twitter @DanJCondon to hear more about his work and the upcoming meeting #wsmith13
Gradstein, F., Ogg, J., Schmitz, M.S., and Ogg, G., 2012, The Geologic Time Scale 2012 2-Volume Set, 1st Edition.  ISBN: 9780444594259


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