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The Accretionary Wedge #60 – Momentous Discoveries in Geology Summary Post

I have to admit I have been a bit lax with the summary post for AW60.  I blame turkeys. It was the Canadian Thanksgiving weekend recently and what with school, the holiday and other things blogging slipped a little lower on my list of priorities that I would like. I also had to submit a paper recently so most of my October writing mojo went into getting that out. My apologies to the submitters to this blog carnival. However, hopefully this post can remedy that.

For the 60th Wedge I asked people to post about momentous discoveries in geology. We all work in or hobby in? a field that is rife with discoveries and more are being made every day. Past me explains it nicely below:

For this wedge the topic will be momentous discoveries in geology or its sub-disciplines that you feel have altered or shaped our understanding of how the Earth works, or opened new doors into research that had never been considered before. The discovery you choose does not have to be universally recognized as momentous but should be in your opinion. It could be something that we take for granted every day, but is in actuality part of the underpinnings of our science.

This topic got a great response within the geoblogger community and I am grateful to all those who wrote such fantastic posts.  Here they are in no particular order:

Hollis of In the Company of Plants and Rocks wrote a great post about Nicholas Steno, a true father of geoscience, and someone who made some of the first observations that have since become basic tenets of geology.

My fellow EGU blogger Simon Redfern wrote an inspiring piece commemorating the 50th anniversary of a very special paper by Vine and Matthews that describes the birth of plate tectonics by observing the magnetic anomalies that occur over mid-ocean ridges. In this seminal paper they postulated that crust was being created at these ridges and preserving the signature of the Earth’s magnetic field as it cooled. This observation has to be one of the most paradigm shifting in geology within the last century.

Photo stolen from Simon.


Sara Mynott, and EGU official blogger, wrote a wonderful post about an interesting tool that goes by the innocuous initials CTD and how this tool has revolutionized the field of oceanography. The CTD is used to detect the conductivity, temperature and depth of the water column once it is deployed from a ship and some can even take samples for further analysis.

This is a CTD (left). Often deployed off research ships with a large bundle of sampling bottles known as a rosette (right), CTDs record the conductivity (and hence, salinity), temperature and depth of water in the ocean, allowing physical oceanographers to get a good look at it’s structure and work out which water masses are moving where. (Both the CTD and rosette images are credited to NOAA)


Next up is a post by Holly Ferrie of Cambriangirl about something that I had never heard of before: GBinSAR technology, “a piece of space tech that fell to Earth” as she puts it. Ground-Based Interferometric Synthetic Aperture Radar is used to monitor any sort of ground movement from space. It can even detect glacial flow! Holly points out that this marvellous piece of technology can even be used to save lives.

Next up is EGU blogger Flo Bullough’s post at Four Degrees about the discovery of the magical world of nano. Flo describes the early history of nanoparticles, which extends much earlier into human history than I every considered. Flo then describes the official discovery of nanoparticles and the technological advancements that have made their study possible and opened the microscopic world to science.

The Lycurgus Cup – a 4th-century Roman glass cage cup , which shows a different colour depending on whether or not light is passing through it; red when lit from behind and green when lit from in front due to the incorporation of nanoparticles – You can go and see it in the British Museum! Source – Johnbod, Wikimedia Commons.


Fellow EGU blogger, Will Morgan of Polluting the Internet also made a wonderful contribution about the discovery Aitken nuclei by a fellow named John Aitken…surprise! These Aitken nuclei of which will writes are particles that promote the formation of clouds, also known as condensation nuclei, and their discovery has had wide reaching effects in understanding how clouds form, the chemistry of these partcles and how they all come together to affect climate on Earth. The condensation nuclei under 100 nanometres are called Aitken nuclei.

Next up is Mary Beth from The Rocks Know who is discussing the contribution of a guy name Gene Shoemaker. Dr. Shoemaker studied impact craters and the strange high-pressure minerals that can form in them. He was also the first person to observe the collision of a comet with another planet, which opened the door to the entire field of study for near-Earth objects.

Fellow EGU blogger Marion Ferrat, also of Four Degrees, wrote a great post about the discovery of the Earth’s inner core by Danish seismologist Inge Lehmann. Lehmann discovered the solid inner core of the Earth by observing the behaviour of seismic waves following an earthquake and carefully studying the locations they were recorded. Her observations led her to postulate the existence of an inner core that refracts and reflects seismic waves in a ways that had not been considered. The seismic boundary between the inner and outer core is now known as the Lehmann discontinuity.

Seismic waves travelling through a layer of the Earth - Source: Julia Schäfer, Wikimedia Commons.

Seismic waves travelling through a layer of the Earth – Source: Julia Schäfer, Wikimedia Commons.


Last, but not least, is my own contribution. I wrote about one of my favourite topics in the geosciences and certainly one of the most useful: radioactivity. In my post I tried to highlight the incredibly wide range of uses that radioactivity has as tool within geology. The first to come to mind is radioactive dating, but I also discussed using radioactviy as a tracer, and some of the different isotopes and elements that can be used in this way by environmental geologists.

Cherrenekoff radiation is a pretty way to demonstrate radiation. (Photo: Matt Herod)

Cherenkov radiation is a pretty way to demonstrate radioactivity. (Photo: Matt Herod)


To conclude, I’d like to thank all of the contributors to this edition of the wedge. I apologize again for my tardiness in getting this summary post out, but I think after looking at all of the wonderful posts listed here it is hard not to be amazed a the scope of geology and the incredible magnitude of the discoveries over the past century and before!

Thanks for reading and contributing!



Matt Herod is a Ph.D Candidate in the Department of Earth Sciences at the University of Ottawa in Ontario, Canada. His research focuses on the geochemistry of iodine and the radioactive isotope iodine-129. His work involves characterizing the cycle and sources of 129I in the Canadian Arctic and applying this to long term radioactive waste disposal and the effect of Fukushima fallout. His project includes field work and lab work at the André E. Lalonde 3MV AMS Laboratory. Matt blogs about any topic in geology that interests him, and attempts to make these topics understandable to everyone. Tweets as @GeoHerod.


  1. Great post again Matt! I was also happy to read the link to the CTD article. As a limnologist, the CTD is the one of the most important components of my research!

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