The Accretionary Wedge

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.

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.

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

I am lucky enough to play host to the 60th edition of the Accretionary Wedge. First, I’d just like to highlight the fact that there have been 60 previous and excellent wedges and ! WOW.  This has to be one of the best blog carnivals out there, and here is to another 60 great AW’s in the future.

There are lots of sayings out there about how science is a journey with many steps and paths or a giant building made of many small blocks that contribute to the enormity of an entire field. All of these cliches are pretty much pointing out the same thing. Namely, that the knowledge base in each field is composed of the work of thousands of people all contributing a little bit and slowly building an understanding of the natural world. This is very true, however, some of these contributions are bigger than others, and geology is no exception. Over the history of geology there have been many major discoveries that advanced the science, from the original work of Hutton, Lyell, Steno and Darwin, to more modern revelations. Each discovery has in some way altered our perception of how the Earth works and either opened new avenues of research or provided previously unknown constraints and laws. Therefore, 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.

A tool that changed the world. The telescope of Galileo. I just saw it in Florence along with his middle finger!

The due date for this wedge will be on September 30 and, as usual, add a link to your post in the comments below. I’ll then compile them into a summary post.

Happy discovering,

Matt

For this AW I had originally drawn a blank. I don’t have that many pictures of signs in my photo collection and most of them really aren’t that interesting anyways. However, I was struck by a flash of inspiration on a hike in Gatineau Park last night. My girlfriend and I were doing the beautiful King Mountain trail plus a nice add on loop that took us off the beaten path as well. While doing to the King loop though, we came across an interesting sign that I thought would be worth sharing and make a nice contribution to July’s Accretionary Wedge at Georneys.

Canada’s very first geodetic reference point! It is a now a national historic site. (Photo: Matt Herod)

The sign/cairn pictured here shows the location of the very first point in the Geodetic Survey of Canada in 1905. The site is now a national historic site as well as one of practical value. Geodesy today is much more complex than it was in the past, but the basic aims remain the same. The purpose of geodesy is to measure and describe the shape of the Earth, called the geoid, and understand the factors that affect its shape such as glaciations, tides, and gravity. In order to do this most countries have developed a geodetic network that defines the precise position and elevation of a variety of reference points. These points can then be used to characterize the shape of the earth very precisely as well as observe any changes that could result due to changes in the Earth’s gravity field or isostatic uplift.

Geologists rely very heavily on geodesy in order to make maps, plot samples, investigate climate change, do geophysical work, hydrogeology, etc. The list goes on and on for why geologists depend on geodesy and why these two disciplines are extremely interrelated. It is not only for applied geology that geodesy is relevant though. Most of us use geodesy and benefit from its contributions daily. The big one that I am sure everyone is familiar with are global positioning systems aka. GPS, which use the coordinate systems and geoid provided by geodesy to navigate.

A close up of the information plaque. In both official languages, of course. (Photo: Matt Herod)

There was a pretty nice view from the cairn. (Photo: Matt Herod)

One great example of geodesy in action is how by using the control network of points around Canada the geodetic survey of Canada has been able to plot how much certain parts of the country are rising or falling due to isostatic rebound.

Source

Next time you are reading a map or listening to instructions from your GPS, think about the field of geodesy that made the whole thing possible.

Cheers,

Matt