This is an earthcache and you are required to complete these tasks to count this as a find. This brings you a sign along a sidewalk with two pieces of petrified wood, where you'll be able to observe and answer the questions after reading the information below. Please send answers to the cache owner. Once you have sent the answers you may log the cache.
- In your own words, describe how 'petrified wood' is formed.
- Can you see specific structures in the wood in either of these pieces (think bark, rings, knots, cell evidence - looks like wood)?
- What colors do you observe in the petrified wood? What impurities are these from?
- Take a photo of yourself (face not required) or a personal item here! Please avoid showing the answers in your photo.
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What is petrified wood? Why was it so frightened its not able to move any longer? Most likely, millions of years ago, a large, herbivorous dinosaur approached a gathering of trees. At first they were afraid. Then they were petrified. All their rings turned to stone inside. But they survived. Yes, they survived. (Thanks to EJKPBR for this cute song cover!)
Orrrrr....
This petrified wood is from fossilized Metasequioa (Dawn Redwood). This genus of tree is still alive today, and the species is a native of China. Metasequoia is a relative of the West Coast Redwoods we find in California today. Since these trees grew in North Dakota, it shows that this state used to have a milder climate (like coastal Georgia or Mississippi), 60 million years ago (during the Paleocene Epoch, Tertiary Period).
They formed as floods inundated the floodplain environment they lived in, burying the bases of trees. The unburied trunks and branches decayed away. Often the stumps spout from a lignite bed or paleosol horizon which itself marks a former forest or swamp floor.
Permineralization/Petrification
Permineralization is the process by which minerals replace organic material in an organism. Another word commonly used to describe this is petrification. Scientists like to use the word permineralization because it describes the process of how the organism turned to stone, instead of its stony outcome. This is a process, and you have to get off to the right start, or else you decay! First, the wood has to be covered by sediment quickly in order to prevent normal decay (oxygen is needed for fungi to decompose their dead hosts). This can happen when rivers overflow their banks, or when volcanish ash covers a forest. Once buried, water seeps through the wood, carrying minerals with it. The minerals coat cell walls and fill interceullar cavities. It is a complex chemical process involving pressure, heat and pH balance. Logs are often oval in cross-section since they were compressed and flattened by the weight of overlying sediments. This process can take millions of years.
There are different gradations (stages or degrees) of fossilization. The cell structure of the organic cells can be destroyed, and you only find a log of petrified wood. Other times, growth rings, bark, knots, and even the cellular structure itself is preserved by the minerals. Silica and other minerals are much smaller than organic molecules - the minerals don't replace the organic ones 'molecule for molecule' - but can coat and surround the organic molecule with silica.
The petrified wood you see by the sign is from Plummer Ranch, southern Golden County in North Dakota. In North Dakota, there are variations on petrified wood - some are well silicified, while others are quite splintery. Some is even lignite coal (which is are coalified trees). Coal and petrified wood are often found near each other. Even within one specimen, there can be various gradations. Petrified wood can be very brittle and shatter like glass, however, it is also as strong as steel. Petrified wood is between 7 and 8 on Mohs Hardness Scale. It is also very heavy and weighs between 160-200 pounds per cubic foot. Sometimes, people will pick up a piece and realize it's petrified only when they feel how heavy it is!
The colors in the petrified logs come mainly from three minerals; pure quartz (silicone dioxide) which is white or clear, manganese oxides form blue, purple, black, and brown, and iron oxides provide yellow, red, orange, and brown coloring. Here are the hues of impurities that can occur while the wood is being permineralized:
· Carbon – black
· Cobalt – green/blue
· Chromium – green/blue
· Copper – green/blue
· Iron Oxides – red, brown, & yellow
· Manganese – pink/orange
· Manganese oxides – black/yellow
Resources:
https://www.dmr.nd.gov/dmr/ndgs/petrified-wood
https://www.geocaching.com/geocache/GC7X2W8_prehistoric-siding
https://www.nps.gov/articles/000/permineralization-and-replacement.htm