20 Million Year Old Earthcache EarthCache
20 Million Year Old Earthcache
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Difficulty:
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Terrain:
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Size: 
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500m (aprox) walk on a rocky beach. Slippery in places.
The Muir Creek Fossil Beds
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The Muir Creek Fossil Beds Fossils are man’s window into the ancient past. They are the remnants of plants and animals from millions of years ago and they tell us what life was like on earth long before man was around to keep records. By examining fossils from various time periods, scientists have been able to puzzle together the evolution process for many species; discover strange and wonderful creatures; and get a glimpse of what the earth looked like long ago. When a plant or animal dies, it may be preserved in a number of ways. Usually, this happens because it is covered in sand or silt fairly soon after it dies. This has the effect of protecting the dead plant or animal. Over many years the sand or silt continues to be deposited until it turns to stone under its own weight. Fine sand turns to sandstone, silt turns to shale, and a mixture of sand and rocks will turn to a rocky sandstone called a conglomerate. The buried plant or animal may be preserved leaving a 'body fossil'.It may dissolve away leaving only an imprint of its shape in the rock (a 'mold fossil'). If exposed to fresh water, the minerals in the water may replace the cells in the organism and a body fossil, made up of the new minerals, will be the result. Plants are often preserved as a black carbon imprint of the leaves or branches (all the minerals except for the carbon are gone). At Muir creek we are going to be looking at body fossils of shellfish which are mostly preserved with their original shells (made of a mineral called calcite) in layers of sandstone and conglomerate. There are also carbon imprints of leaves and branches.
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Carbon imprints of leaves in sandstone |
A stick in the mud? Not any more... in the stone now. |
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| At Muir Creek, you will be looking at fossils that are 20 to 25 million years old. It is almost impossible to comprehend such a time period, but there are clues to help you understand how long 25 million years is. The main clue lies in the cliffs behind the beach. The only reason you see the fossils at all is because the rock has been exposed by the pounding ocean surf. Now if you look at the cliffs, examine the shells embedded in the sandstone at the bottom of the cliff. Once you have got over the quantity of shells, slowly look up towards the top of the cliffs. All of that rock has been deposited on top of the shellfish since they died. That’s a lot of rock! That’s a lot of time! This is in fact how geologists can tell the age of a fossil, by examining the type and quantity of rock deposited on top of the fossils. The Muir creek fossils beds are in a layer of rock that is called the Sooke Formation. This is a mixture of sandstone and conglomerate. If one were to look at a geological time scale (geologists have given names to periods of time), the Sooke Formation was deposited in a time period called the Oligocene epoch. The Sooke formation is home to a number of fossil types including: bivalves (clams and mussels), gastropods (snails), barnacles, teeth of at least three extinct marine mammals and fish and some inshore plants and trees as well. |
Body fossils of mussels in sandstone |
The gastropods (snails) make particularly nice patterns in the conglomerate (rocky sandstone). |
Check out the 20 million year old snail! |
Shells, shells and more shells in the sandstone. |
Look for the layers in the rock. Each layer is represents deposits from a different time period. In this rock, the lower sandstone has no sea life in it, the upper conglomerate was deposited while the ocean covered the area. |
Be sure to look at the layers in the cliff. Look up... look waaaaay up and I'll call Rusty (ooops). 20 million years of deposits are layered above the shells! |
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If you’re interested, you should do an internet search for 'Oligocene'. You will find all kinds of cool things were going on. India was colliding with Asia to form the Himalayas, modern looking mammals were beginning to evolve, and sea level was falling as ice sheets were forming at the poles.
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To log this cache, you must take (and post) at least three photographs...
1 - a photo of your GPS with some of the fossils to prove you were there.
2 - a photo of a gastropod fossil to show that you learned what a gastropod is.
3 - a photo of a bivalve fossil to show that you learned what a bivalve fossil is.
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Congratulations... M in 3D was First-to-Find this Cache on September 15 2005
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Additional Hints
(Decrypt)
[A couple of notes about the cache:
- The posted coordinates will bring you to a large rock full of fossils on the beach. The fossil beds will be all around you.
- It is best to plan a trip to the site about an hour prior to low tide. You will see more and access will be easier.
- This is a rocky beach area. Access is fairly easy, but it is slippery in places. Be careful.
- Don’t go if the tide is high and strong winds are blowing off the straight of Juan de Fuca. This condition can cause large waves that can be a danger to your health.
- Access is from the west side of Muir creek. There is a small parking lot there. There is a sign that says “No Trespassing, Private Property” placed there by Timberwest. They used to have a forestry campsite here and there was a problem with drinking and litter (don’t forget to CITO). Timberwest is just trying to discourage people from being here, camping here, leaving litter etc. This is Crown Land, there is no timber harvesting here… it is safe and access is allowed. As with all Canadian intertidal zones, the beach is public, crown land]