The 366 daily episodes in 2014 were chronological snapshots of earth history, beginning with the Precambrian in January and on to the Cenozoic in December. You can find them all in the index in the right sidebar. In 2015, the daily episodes for each month were assembled into monthly packages, and a few new episodes were posted. Now, the blog/podcast is on an occasional schedule with diverse topics, and the Facebook Page showcases photos on Mineral Monday and Fossil Friday. Thanks for your interest!

Ask a Question


Do you have a question about Earth's history or geology in general? Send them to Dick Gibson at rigibson@earthlink.net and we'll try to answer them in a future podcast.You can also post your question as a comment at the bottom of this page, and questions that don't demand a longer discussion may be addressed here.

All submissions will be considered but we can't guarantee that they will become podcasts and we also can't provide a definite schedule for the episodes. Podcasts addressing questions will be tagged with "Questions" in the sidebar index.

Thanks for your interest!

15 comments:

  1. In Louisville, Kentucky, Limestone blocks were used for construction in the 19th century. I frequently see on the surface of an old cut block that there is a rusting chunk about the size of a grain of corn. Is that iron? How did it get in the rock?

    ReplyDelete
    Replies
    1. Thanks for your question. I’m not very familiar with the iron concretions in Kentucky limestone, so this is a general reply.

      Iron in tiny amounts is really quite common in rocks, and because limestone is so soluble, water percolating through the rock can easily pick up the traces of iron, which can then be deposited in a small round concretion. Often such things would form where there’s something in the rock to serve as a nucleus – it might be a fossil fragment, or it might be an open space (tiny, even microscopic) in which the stuff can start to crystallize.

      Rusty-looking iron in sedimentary rocks like limestone could be any of several different minerals, including brownish siderite, iron carbonate, or iron oxide in various forms (limonite, goethite – hydrated types, with water in the mineral structure). It might be in the form of hematite or even magnetite, both iron oxides – hematite is basically rust such as you see on rusting steel.

      It’s possible, but I think quite a bit less likely, that the blobs of iron you see in the rock were originally deposited in the rock as iron-rich fragments. It’s much more likely that the traces of iron scattered through the rock were concentrated by water percolating through the rock.

      I hope this helps! Below are some links to more information. You could also contact the Kentucky Geological Survey, http://www.uky.edu/KGS/ - they might have specific information about the particular rocks you are talking about.

      Many thanks for your question.

      http://geology.about.com/od/more_sedrocks/ig/concretionpics/

      http://www.uky.edu/KGS/rocksmn/other.htm

      http://en.wikipedia.org/wiki/Concretion

      Delete
  2. Mr Gibson

    I just listened to the 365 episodes of your podcast, more or less as they were released, and I am writing to tell you how impressed I am with them! I considered myself a pretty broadly informed geologist, but I learned something substantial from almost every single episode. So, thank you, and well done!

    As you know, in iTunes, only the latest couple dozen episodes are available, and I wasn't clever enough to save the earlier episodes. Is there a place to download the whole year's worth? I would put them back into circulation in my iPod, randomly shuffling them in with the Science, Nature, Palaeocast, Cheap Astronomy, and Decoder Ring Theatre podcasts. (What!? You don't listen to Decoder Ring Theatre?!?)

    I will stay tuned to your channel for upcoming episodes. I know they'll be good.

    Thanks again.


    ReplyDelete
    Replies
    1. Thanks for the nice words - I'm very happy that you enjoyed the series. I plan to assemble the 2014 podcasts into monthly packages - I have started on that but it will be a while (the January / Precambrian were pretty sloppy! So some re-recording to do there.). Many thanks! - Dick Gibson

      Delete
  3. I came across your podcast by accident last January and it quickly became an audio dessert each evening. Thank you so much for all your hard work and for all that you have done to educate and entertain others. Your website is a wonderful place to roam and learn. I have recommended it to my high school students, especially the podcast episodes that covered Northern New Jersey and the Watchung Mountains. They have a wonderful new appreciation for the land they live on, its history and structure. I have given you five stars on iTunes and encourage others to do the same and spread the word. Thanks again, great job!

    ReplyDelete
  4. I'm trying to understand how there can still be 1500' to even 3000' ridges in Pennsylvania when there has been no tectonic activity there in a couple hundred million years? What is keeping parts of Pennsylvania so high considering that it is part of a passive margin? Thanks
    Scott B.

    ReplyDelete
    Replies
    1. My take on it would be this - and recognize that I'm not an expert on the Appalachians.

      There was at least a degree of jiggling, rejuvenation, when the Atlantic opened in Triassic - Jurassic time, with the eastern grabens (and adjacent uplifts) forming. When an ocean opens, there tends to be a regional uplift along the incipient rift - as along the East African Rift system today, so both sides of the pre-Atlantic would have been broadly raised before being broken down the middle by the Atlantic Rift. The "shoulders" of the rift, the Appalachians and their equivalents in Europe-Africa, would have been somewhat high-standing for quite some time (tens of millions of years or more) after rifting began.

      This does beg the question, hasn't enough time gone by to allow enough erosion to flatten it all? My cop-out answer would be, "apparently not." - Since we still have decent hilly mountains there, there must have been either 1) insufficient erosion or 2) some ongoing gentle uplift or 3) both, to account for the presence of mountains today. This is not a satisfying answer; one would like to point to evidence that SHOULD exist for the uplift, or inadequate erosion. I've never looked at typical erosion rates to try to see what 100 million years ought to do.

      Sorry I don't have a good, clear cut answer for your good question.

      Delete
  5. Thank you so much for creating this blog! As a studying geologist I can't not begin to explain how helpful, fun, and interesting your blog has been for me. I visit the Wichita Mountains in Oklahoma often and was pleased to find that you had covered their geologic history here. Thank you once again for taking the time to do this!

    ReplyDelete
  6. Many thanks, Dick, for sharing your wisdom and enthusiasm! I've especially enjoyed the combined episodes from 2015.

    As someone who uses radiometric dating in my work, I really should know the answer to this(!), but how are the half-lives of radioactive isotopes determined? I understand the theory and principles behind the age determination techniques once half-lives are known, but its that initial step that represents a shameful hole in my knowledge. Thanks!

    ReplyDelete
    Replies
    1. Thanks for the nice words. One way to determine half-life is to measure a starting volume of the material, then see how much has decayed into something else in some period of time. You'd use the proportion to calculate the amount of time half the material would decay, the half-life. This would only be practical for stuff with a short (human scale) half life. The other way is to use the count rate, measured by a geiger counter or similar device - the count rate is essentially the rate at which the original material is decaying. The decrease in the count rate is proportional to the amount of the original material, which is also decreasing as it decays, and charting the decrease in the decay rate over time allows the determination of when half the original material would be gone - even if that is millions of years. The observed decrease in count rate might be just a tiny part of the entire decay curve on a graph, but because the radioactive decay is consistent, that short part of the curve can be extrapolated to the entire curve - so, we don't have to wait thousands or millions of years for half the stuff to decay to see what the half-life is. Hope this help! Cheers - Dick

      Delete
  7. I very much enjoy your podcast. Thank you for making such excellent and informative content available. Would you be conducting any geologic field trips in the Montana area in the coming year? I would be very interested.

    ReplyDelete
    Replies
    1. Thanks! I don't really do geology field trips myself (nowadays, mostly Butte history walking tours and such). Various orgs sometimes do - the Tobacco Root Geol Soc (http://trgs.org) is meeting in Idaho this summer, but is often in MT. The Mineral Museum at Montana Tech used to have summer outings - not sure if they still do that. Smithsonian Journeys, including those focusing on National Parks, often have a geological component (I've been a study leader for those, but not since 2006). Thanks for listening and for the nice words.

      Delete
    2. Also, more mining probably than geology - but some geology, certainly - http://granitecountyhistory.blogspot.com/2016/05/granite-county-historical-society.html

      Delete