Journeys of Dr. G at Tyler Arboretum

The sabbatical project continues, exploring all that Tyler Arboretum has to offer

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The geologic journey of Tyler Arboretum, Part 2

In my first post on Tyler’s geologic journey, I discussed how the planet is viewed by geologists, how the surface of the Earth is broken into tectonic plates that are either pulling apart (divergent boundaries), coming together (convergent boundaries), or sliding past one another (transform boundaries) – see this map and view this animation for a quick review.  These plates have been shifting and moving throughout all of Earth’s history, which means Tyler Arboretum has also traveled through geologic time.

Something else to keep in mind – our global sea level has risen and fallen throughout geologic time.  There are various causes for why ocean level fluctuates, but the main causes of this fluctuation are the changing size of the ocean basins, and the change in the volume of glacial ice over time.  The more water we have locked up in ice sheets, the less water we have in our ocean basins, and vice versa.  So when you look at a map of our modern-day continent and the position of its shoreline, note that our shoreline has changed through time, depending upon how high or low the water levels are in the ocean basins.

Comparison of two sea level reconstructions during the last 500 million years. Note that sea level has changed over a scale of hundreds of meters. It is estimated that if all of the current glacial ice sheets melt, global sea level will rise an additional 80 meters.

OK, so to review… we know there are tectonic plates that are in constant motion across the surface of our planet, and our ocean levels have gone up and down.  So what does this mean for the geologic journey of Tyler Arboretum?  Time to investigate through paleogeographic maps (thanks to the efforts of C. R. Scotese, PALEOMAP Project (!  The maps below were constructed from evidence found in the rock record.  Dark blue represents deep water, light blue represents shallow water, and the lightest blue/white color represents ice sheets.  Brown is for the land exposed above sea level, and the curved lines show the position of plate boundaries (those divergent/convergent/transform motions).  The white outlines are just for reference – although you will see the familiar shape of North America on most of these maps, please note that North America did not exist through most of Earth’s history – certainly not as we know it today!

Late Precambrian Supercontinent and Ice House World

This is the best reconstruction that we can make from the data and technology we have available for what our planet might have looked like 650 million years ago (the age is in the upper left corner, during a time period we call the Late Proterozoic Era).  Notice the Southern Hemisphere is covered with much ice, as well as portions of the Northern Hemisphere.  Can you find Pennsylvania?  We were part of a landmass called Laurentia in the Southern Hemisphere and rotated 90 degrees to the right.  You can see the outline of the modern-day west coast under water and the east coast – well, under ice!

Cambrian: the beginning of the Paleozoic Era

At 514 million years ago, the oceans are becoming filled with hard-shelled organisms for the first time, which is not surprising given the extensive shallow seas covering the continents.  Note that Laurentia has moved up to the Equator, but we know that pieces of New England and Florida were still at the South Pole.

The Late Carboniferous a Time of Great Coal Swamps

Zipping ahead to the period of time also known as the Pennsylvania Period, you can see that we are still south and not that far from the Equator.  These were the perfect conditions for the famous Pennsylvania coal deposits to form in the Equatorial Zone, while extensive ice sheets were covering the Southern Hemisphere.

At the end of the Permian was Greatest Extinction of All Time

And here we are, with Pennsylvania north of the Equator, and at one of the most significant times of geologic history (certainly for the biologic record).  When the Pangea formed ~245 million years ago, pulling together all of the landmasses into one giant supercontinent, it is estimated that anywhere from 95-99% of the file that existed on the planet at that time went extinct.  This is the largest mass extinction event in Earth’s history (not the most popular, of course).  Note that the dinosaurs still had not yet appeared on the planet!

Pangea Begins to Rift Apart

The “Jurassic” Period of geologic time really did exist – and there were dinosaurs around at the time.  It also marks the time of the formation of the Northern Atlantic Ocean and the splitting of the supercontinent Pangea, when we finally become North America!

The End of the Dinosaurs

And just for those curious, here is what our planet looked like 65 million years ago when the dinosaurs went extinct, showing the site of an asteroid impact that contributed to the demise of the dinosaurs.  Notice how high the water levels are and the absence of ice.

We are still drifting apart from Europe and Africa, as the Atlantic Ocean continues to widen at the divergent plate boundary that runs under the middle of the ocean basin.

So there you have it!  Tyler Arboretum has been under water, under ice, south of the Equator, and neighbors with fellow continents during Pangea’s formation.  Where will Tyler be in the future?  There have been maps constructed for where geoscientists believe the plates are heading – look at the maps for the future world 50 million years in to the future, 150 million years, and 250 million years!

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The geologic journey of Tyler Arboretum, Part 1

I’ve been blogging about my journeys around Tyler Arboretum, making sure I include pieces of the fascinating history of this property that has passed through the hands of the Minshalls, Painters, and Tylers.  But the history of the Arboretum actually begins well before 1681, when Thomas Minshall purchased the property from William Penn.  There is an entire GEOLOGIC history that extends much further back in time!  As a geologist and an educator, I can’t resist the opportunity to share some of the physical and environmental changes this location has gone through during Earth’s history.  I hope you find this as interesting as I do!

First, I have to start with how geologists view the planet today.  When you visit any classroom, past and present, the walls are decorated with various posters and maps.  The maps we grew up with are political geography maps, where each country on the map is a different color.  But as we know, rivers and mountain ranges and even the ocean do not stop at political boundaries.  Geologists have a different type of map we use to look at the planet – yes, we use colors as well, but the colors define tectonic plates (see map from the U.S. Geological Survey below).

The layers of the Earth (from USGS)

On this map, you will see the familiar outline of our modern-day continents, but the boundaries on this map are defined by areas of movement and motion taking place in a zone we call the lithosphere (remember learning about the layers of the Earth – the core, mantle, and crust?  The crust and uppermost part of the mantle make up the lithosphere).  The lithosphere is broken in to several rigid “plates” (each shown in a different color on the map above), where there is minimal tectonic activity in the center of the lithospheric plates, but much more tectonic activity (volcanoes, earthquakes, etc.) at the boundaries between plates.

From the map above, can you see why Tyler Arboretum does not have any volcanoes and does not experience earthquakes, but the west coast of the USA does?  We are in the middle of a lithospheric plate – close to the coast of our continent, yes, but the edge of our continent is not in the same location as the edge of our North American plate!  Earthquake-filled California has one of the most famous transform plate boundaries running almost parallel to the coast, the San Andreas Fault.  (If you are thinking back to that 2011 earthquake that occurred in Virginia, hold on – I’ll get to that in a future post!)

Earth’s history starts 4.6 billion years ago, with the formation of our solar system (view this short NOVA video for more on the solar system, and this video from National Geographic on the early formation of Earth).  Fortunately, the outer surface of our planet has cooled enough to where we formed the solid crust, and the trapped heat inside the Earth escapes through volcanoes – which just happen to occur at plate boundaries (with some exceptions, such as the Hawaiian islands and Yellowstone).  New lithospheric material is created at some plate boundaries through volcanic activity (the cooling of lava once it erupts) at divergent margins, while old lithospheric material is destroyed and recycled back down in to the Earth as molten material at other plate boundaries called convergent margins (this Smithsonian video does a great job showing the connections between plate boundaries, volcanoes, and even earthquakes).  This constant cycle of creating new material and destroying old material, as well as boundaries where plates just slide past one another, is what has caused the plates to move and change their shapes over time.

Wait… the plates are moving???  Yes, even today, all of the plates are moving across our planet, including our own North America!  Do you feel “the Earth move under your feet?”  Don’t feel bad if you do not – the plates move on average about a few centimeters a year, the same rate that your fingernails grow.

So now that I have set the stage with a very quick overview of the structure of our planet and the constant movement occurring, we are about ready to jump in to looking at where Tyler Arboretum has journeyed over geologic time!  We can’t go back to the very beginning, as the oldest rocks on the planet only date back to about 4 billion years old (remember, plate tectonics causes the constant creation and destruction of the lithosphere, so there is a good chance that really old rocks are going to meet up with a convergent plate boundary and be destroyed).  It is through the study of unaltered rocks (meaning, rocks that have not been super-heated or crushed by colliding plates) and the history of changes in Earth’s magnetic field that geologists and geophysicists have traced the positions and pathways of the plates – and that will kick off “Part 2” of my Geologic Journey of Tyler Arboretum series!  Stay tuned to learn how our current location was once under water and even located south of the Equator!

I will not be focusing on specific rock types or the history of Appalachian Mountain building in Part 2, although I will discuss the serpentine of Tyler’s Pink Hill in a future post.  For anyone interested in this part of Pennsylvania’s geologic history, I encourage you to read the Pennsylvania Geological Survey’s The Geological Story of Pennsylvania (written for a general audience).  And if you have any Pennsylvania geology questions, please feel free to leave them in the comments section under this post, and I will be more than happy to answer them!  (One question I’ll answer right away – no, we have never found dinosaur bones in Pennsylvania, but the world’s first mounted dinosaur skeleton was put on display at the Academy of Natural Sciences – the Hadrosaurus foulkii, discovered in Haddonfield, New Jersey!)


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What Lies Beneath?

If you take a stroll along the Native Woodland Walk in the Arboretum, you may come across a “magical path” with “villages, hamlets, and castles, created for gnomes, fairies, wizards, goblins, and other magical folk.”  And as you continue on, you will come across this interesting structure, visible from the pathway:

What lies beneath?

Magically appearing in 2010 (with a little help from Pine Street Carpenters, Inc.), this unexplained door leading underground plays an important role in The Tyler Arboretum Writing Project.  Visitors of all ages are encouraged to use their imaginations to create a story or poem inspired by this exhibit, titled with the simple question, What Lies Beneath? Submissions (5,000 words or less) to this community writing project are collectively housed on the website:  Feel free to read through the almost 100 submissions that have already been posted.

And then, put on your own creative writing cap and submit your answer the question… What Lies Beneath?

What lies beneath?

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November’s Trail Ramble

November 2013 Trail RambleI had such a great time during the September Trail Ramble (see my blog post about the hike!), that I was excited to participate again in November’s Trail Ramble, led again by our fearless leader Lois Brooks.  The description for this month’s walk follows:

November 3 – The 3.1 mile Painter trail provides a quality hike with two stream crossings and lovely hilltop views of the Arboretum.

At first, I’ll admit I was a little hesitant to participate in this hike, especially when the Summer 2013 issue of Tyler Topics listed the following in the Take A Hike! column:

Painter Trail (most challenging, stream crossings, great views) – This trail is named for the Painter Brothers, who farmed this land.  A favorite of serious hikers and trail runners, this is also a good challenge for intermediate hikers.  This trail affords hilltop views of the Arboretum and Rocky Run, two stream crossings, plentiful wildflowers, and a chance to discover mushroom patches in the woodlands.

But Lois put the minds of myself and the rest of the trekkers to rest.  She explained the layout of the route and told us there were several places where the other trails of Tyler cross the Painter Trail in case we wanted to turn back or explore trails that were not as steep.  She said we weren’t in a race, and we could take as much time as we wanted/needed as we moved along.  This “pep talk” was extremely helpful and started us all off with a positive “can do” attitude!

November 2013 Trail Ramble

Starting out on the Painter Trail

The weather could not have been more perfect for a walk outdoors.  The crisp, fall air and sunny skies made for an enjoyable walk through the colorful leaves on the trees and on the leaves that had fallen to the ground.

November 2013 Trail Ramble

One of the many beautiful sites along the Painter Trail

Lois provided us a valuable warning, that we should be careful hiking this trail in the fall right after a heavy rain, as the water in the streams is higher and the leaves become very slippery.

November 2013 Trail Ramble

One of the two stream crossings we completed during the “ramble”

November 2013 Trail Ramble

Sunlight was able to shine through the spots where the leaves had already fallen off the trees

We did not stay on the Painter (Red) Trail the entire time.  We zigzagged between the Blue, White, and Orange Trails as well – all of which led us back to the gated part of the Arboretum to finish our hike on the Scenic Loop.

November 2013 Trail Ramble

We walked a total of 3.5 miles on this afternoon – and every step was worth the beautiful sites and sounds of fall at Tyler!

I sure hope there is a Trail Ramble for December or January – it would be great to keep walking on Tyler’s trails and to see the Arboretum in the winter season as well!  I guess I’ll just have to see what the next issue of Tyler Topics lists for the winter activities (can’t wait!).


PA Chapter of The American Chestnut Foundation Fall Meeting

The Pennsylvania Chapter of The American Chestnut Foundation (PA-TACF) held their annual fall meeting at Tyler Arboretum on Saturday, November 2.  If you have been following this blog, then you have seen my previous posts on the Chestnut Nursery program that Tyler participates in with The American Chestnut Foundation – all managed by the amazing volunteers that donate their time to Tyler!

The meeting began with some announcements by the chapter president, and then the morning continued with two talks on “A Sense of Place – Northern Research Station of the USDA Forest Service” and “Are Deer Facilitating Plant Invasions?”  After some general membership announcements and lunch, the talks continued with “USDA-ARS Research Update on Renewable Fuels from Agricultural Feedstocks and Forestry Feedstocks…” and the final talk by… yours truly!  I was asked to give a talk that served as an overview of Tyler Arboretum (what I titled “The Tyler Experience”).  After my talk, the meeting adjourned to going over and visiting Tyler Chestnut Nursery and/or going on an exploration of Tyler’s sites and trails.  The full agenda can be viewed online.

The meeting was held in The Barn and had over 50 people in attendance.  I sat in the back row and saw an audience very engaged and passionate about not only their work restoring the American chestnut, but also very interested in learning about the related topics shared by the speakers.

2013 PA Chapter Meeting, The American Chestnut Foundation

Kristine Averill (PhD candidate from Penn State University) speaking on her research, examining whether deer demonstrate a preference for native or invasive exotics

As my academic training is mostly in the physical sciences and not as deep in the natural sciences, I learned quite a bit at this meeting!  I’ve had an introduction to the chestnut work through my own reading and volunteering with Tyler, but this conference was very helpful in framing the “big picture” of the ecosystem and related fields.  I was also interested to see the PA Chapter was selling Biltmore Sticks, a measurement tool I had read about but had never seen before (learn more online and in this video about this field tool).


Photo of a Biltmore Stick

There was also a mention during the General Membership Announcements section about the need to do even more outreach, and the chapter had this very nice display set up that was geared to teach younger kids about the American chestnut.  I agree that each one of us has the opportunity to “get the word out,” whether it be through public talks or using social media (you can “like” the PA-TACF Facebook page) – or, by blogging (like I do!).

2013 PA Chapter Meeting, The American Chestnut Foundation

Display created by the PA Chapter of The American Chestnut Foundation, used for outreach and education purposes

Overall, I was honored to be able to share the mission of Tyler with this group, as well as provide a peak in to the history, nature, and education mission of the Arboretum.  And I even learned some new items along the way – the USDA Forest Service is doing science to keep “forests in forestry,” deer population management will help in managing plant invasions, and there is much research being done (and that continues to be worked on) relating to biofuels.

This is one of many, many events I know where Tyler serves as a host for outside organizations to have meetings, receptions, etc.  For the PA Chapter of The American Chestnut Foundation, I can’t think of a more perfect setting they could have selected for their meeting!