The different hues are produced by different minerals. For example, some petrified logs have a red or pink tint to them. Internal hematite is responsible for this hue. Now if there's a greenish color in your favorite hunk of wood, that means a mineral called "native iron" is inside the fossil. And shades of black are associated with "fool's gold" — also known as pyrite. Caches of petrified wood can be found all over the world , from New Zealand to Greece to Argentina.
Within the United States, there's an especially-famous motherload in eastern Arizona. Petrified Forest National Park is about an hour's drive away from Winslow.
Two hundred and twenty-five million years ago, it was the site of a dense forest loaded with conifers and about a dozen other tree species. Log jams were often created when deceased trees fell into the prehistoric rivers that ran across the landscape. Scores of these plants were then buried rapidly in sediment and silica-rich volcanic ash. Up in the Pacific Northwest, there's a much younger petrified forest with a more dramatic origin story. Around 15 million years ago, volcanic eruptions sent molten lava flowing across central Washington.
Near the present-day city of Vantage, elms, sycamores, conifers, and ginkgoes would periodically die and then sink to the bottom of local lakes.
Once that lava touched the lake water, it hardened into pillow basalt an igneous rock, which is formed by the cooling of molten magma or lava. This encased the logs, shielding them from oxygen and allowing the petrification process to occur. It's illegal to harvest petrified wood in Petrified Forest National Park. Nevertheless, light-fingered park visitors steal around one ton's 0.
Yet, the kidnapped wood tends to find its way home. People often feel remorse after swiping the fossils and mail them back to the park. The on-site Rainbow Forest Museum has in fact dedicated an entire room — aptly named "the guilt room" — to specimens that were returned with letters of apology.
Sign up for our Newsletter! Mobile Newsletter banner close. Iron-rich solutions require sulfur to form fossils, so iron-petrified fossils most commonly occur in marine environments, with some rarer examples found in clay. The best known petrified fossils may be petrified forests. Many of these fossils retain so much of the appearance of the trees that the original species and growth habits can be identified. Trees, however, are not the only petrified life.
Examples of siliceous fossils include deep-sea marine fossils made of opal, an amorphous silica, and terrestrial fossils, especially plant fossils, made of chert, jasper and other siliceous minerals. Whale bones petrified by calcite, sand dollars petrified by iron pyrite crystals, dinosaur eggs and even ancient dung preserved as stone have been found around the world.
Karen earned her Bachelor of Science in geology. She worked as a geologist for ten years before returning to school to earn her multiple subject teaching credential. Karen taught middle school science for over two decades, earning her Master of Arts in Science Education emphasis in geosciences along the way.
Related Articles Kinds of Fossil Rocks. The 5 Types of Fossils. What Is a Body Fossil? Fossil Facts for Children. Steps of Fossil Formation. Why Is the Rock Cycle Important? Three heaping teaspoons to two teaspoons of water should be enough. Since Plaster of Paris sets quickly, you should mix it as needed, not in advance. Setting the Scene Ask students to reflect on the first investigation when they studied fossil specimens.
Have students think about the following question: Is a fossil the actual remains of a living thing or something else? If it is something else, what is it? Presenting the Investigation Question After the scene is set, introduce your students to the investigation question: How does a living thing become a fossil? Have your students brainstorm ideas about how this investigation question could be investigated. How would you design an experiment that could be used to test the investigation question?
What materials would be needed? What would you have to do? What would be measured? How long would the experiment take? Assessing What Your Students Already Know In the last investigation, students found out that they could slow down decay after an organism is covered by sediment.
Here are some initial questions that your students can discuss, in pairs, then in groups: What happens to a living thing after it is completely buried by mud or sand? Can the decay of a living thing be completely stopped? How might water that flows through a rock affect a living thing buried in the rock? What happens to living things buried in sediment as the sediment becomes rock?
How do fossils become rock? Have your students share their ideas with the class and record them as a list on a flipchart. Ask students the following: What would you like to learn about how a living thing becomes a fossil? Exploring the Concept Activity 1: Fossil Molds and Fossil Casts Expected Time: Two half- hour sessions on separate days Explain to students that they will be modeling several processes by which fossils are formed.
First, they will model what happens when a shell in the bottom of the ocean or a bone that ended up on the bottom of the ocean becomes fossilized. Ask students to place some clay on the bottom of a small container. Tell them that this clay represents the clay at the bottom of the ocean. Have students press a shell or bone into the clay. Tell them that this is a living thing that was buried in the clay. They should then remove the shell or bone, making a mold.
Tell them that over time the mud was compacted and cemented into sedimentary rock. As the rock formed, water entered the rock and dissolved or decayed the shell or bone inside the rock.
This left an imprint, or mold. In a second container, prepare some Plaster of Paris by adding water and mixing until it is creamy and barely flowing. Instruct students to pour the Plaster of Paris into the mold.
Tell them that the space left behind by the shell was later filled with minerals from water that flowed through the spaces in the rock.
Students should let the Plaster of Paris harden overnight. The next day, students put on goggles to gently tap and remove the fossil cast. Ask students the following questions: Are molds and casts the original unchanged remains of a living thing?
What features of a living thing are preserved by a mold or cast? Instruct them to identify the fossils as molds, casts, or other. Explain to students that they will now model a process whereby the remains of a buried organism or part of an organism are replaced by minerals.
Have students cut two pieces of sponge into bone shapes. One piece will be used to simulate fossil formation and the other will be used for comparison. Have students fill a cup with hot water and stir in Epsom salts until no more will dissolve.
Instruct students to add a few drops of food coloring. Instruct students to pour the salt water mixture into a pan. Have students put one sponge bone into the pan. Instruct them to observe the movement of water through the holes of the sponge. Tell students they will be letting the pan sit for several days until the sponge is dry.
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