Welcome to my Earthcache! An Earthcache is a special type of geocache where there is no container to find - instead you are looking for a unique geological feature of the area and need to answer questions, as well as posting a picture, in order to claim the find. This EarthCache takes you to the Swissair Flight 111 Memorial near Peggy's Cove, Nova Scotia. These granite rocks you are standing on are part of a process from approximately 470 million years ago, and they have been shaped by a variety of processes into what you see today. This particular earthcache looks to examine how long the rocks have been in their current position using the study of lichenometry - the study of lichen and how their growth can be used to determine the age of rocks.
ARTHCACHE REQUIREMENTS
As with all of my ECs, I am not looking for PhD thesis level responses, but I am hoping that you take some time to enjoy the area and learn something new. Please include a list of all cachers with your answer, if answering for more than one caching name. There is no need to send individual answers.
To claim a 'find' for this Earthcache you must answer the following questions and send your answers in a message or email to the owner using the link at the top of the page. You can log your find with a photo at GZ. Send your answers to the tasks. I will be in contact if there is a problem, no need to wait for a response as long as the required photo is included in your log.
Observational Task
At GZ, you should be standing on the granite rocks along the trail, just to the west of the Swissair Flight 111 Memorial, between several large bolders covered in various forms of lichen. You will need a ruler or tape measure to be able to answer the required questions.
Questions to Answer:
1. Find a granite surface with visible lichen growth. What colours and patterns do you observe? Try to identify at least one species from the list above.
2. Choose a large, isolated lichen patch and measure its diameter in millimeters. Record your measurement.Using a conservative average growth rate of 0.5 mm/year, estimate how long ago the lichen began growing on this rock.
3. Which of the techniques listed in the description would you suggest using at this location? Why?
4. Based on your findings, what does this suggest about how recently this piece of granite was exposed? Could it be from natural weathering or something more recent like human impact or glacial movement? Explain your reasoning.
5. Photo: Include a photograph of yourself, your GPS, a signature item, thumbs up, etc with the Peggy's Cove lighthouse in the background. You do not need to show your face in the photo, but your photo must be unique to you. In the event of group photos, please have each member of your group upload the photo (each log should have at least one photo uploaded).
Earth Science Lesson: Lichen as Natural Timers
At first glance, Peggy’s Cove is a windswept landscape of smooth granite bedrock and crashing waves — but look closer, and you’ll see small, hardy organisms clinging to the rocks: lichens. These slow-growing, long-living organisms do more than add colour to the stone — they can actually tell us how long the rock has been exposed.
This method of study is called lichenometry, and it’s used by geologists, archaeologists, and climatologists to estimate the age of exposed rock surfaces.
What Is Lichen?
Lichens are not plants — they’re a symbiotic relationship between a fungus and an alga or cyanobacterium. The fungus provides structure and protection, while the algae photosynthesize and produce food. Lichens can survive in extreme environments and often colonize bare rock, including the granite at Peggy’s Cove. Lichens grow in a wide range of forms and colors and are often mistaken for moss. But unlike mosses, lichens are not plants—they don't have leaves, stems, or roots.
How Lichenometry Works
When a rock surface is newly exposed (due to glacier movement, rockfall, landslide, or human activity), lichens begin to colonize it. Because certain species of lichen grow at predictable rates, researchers can measure the diameter of the largest lichen in an area and estimate the minimum time that rock has been exposed.
This technique is especially useful in areas where:
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Rock is hard and stable (like granite),
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Climate is cold or temperate, and
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Dating methods like radiocarbon aren't applicable.
Lichenometry uses the size of lichen thalli (body) to estimate the minimum time a rock surface has been exposed. It assumes that lichen began growing shortly after the rock became exposed and has grown at a steady rate. While the technique is most accurate for surfaces less than 1,000 years old, it can offer valuable insights for older exposures when used carefully.
Common Lichenometry Methods:
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LL (Largest Lichen): Measures the biggest visible lichen to estimate the maximum age.
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5LL (Five Largest Lichens): Averages the largest five for better reliability.
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FALL (Fixed Area Largest Lichen): Focuses on the biggest lichen in a defined space (~1 m⊃2;).
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SF (Size-Frequency): Uses lichen population data across size classes.
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LC (Lichen Cover): Estimates age by measuring how much surface area is covered.
Lichens Found at Peggy’s Cove
Common species of lichen you may observe here include:
Rhizocarpon geographicum ("Map Lichen"):
A greenish-gray crustose lichen with black borders, commonly used in lichenometry. It often grows in circular patches.
Xanthoria elegans ("Elegant Sunburst Lichen"):
Bright orange to red and often found on more nutrient-rich rock faces or near bird perches.
Lecidea spp.:
Small black or gray lichens forming thin crusts — also used in dating studies.
Dragon Horn (Cladonia squamosa)
Usually grows in small patches and extens 0.5-3sm from the face of the rock
Coccocarpia palmicola (coccocarpia lichen)
It's leaf like appearance can be grey, green, brown or tan colours.
These lichens grow extremely slowly — for example, Rhizocarpon geographicum grows at a rate of 0.5 to 1.0 mm per year, depending on local conditions.
Using Lichenometry at Peggy’s Cove
Although this area was last glaciated about 12,000 years ago, many surfaces have been scraped or split by more recent events — such as frost action or wave erosion — creating newly exposed surfaces.
By measuring the largest lichen thalli on such surfaces and comparing them to known growth rates, researchers can estimate when the rock was last exposed — often within a few decades to a few hundred years.
Scientific Notes
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Lichenometry is not precise to the year but gives useful minimum ages.
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Environmental factors like sun, moisture, and rock chemistry can affect lichen growth rates.
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This method is used in Nova Scotia to study glacial history, storm deposits, and even archaeological sites.
Credits & References