This post is by Jessica Fries-Gaither, a 2024-2025 Albert Einstein Distinguished Educator Fellow at the Library of Congress.
Analyzing one primary source is good, but using multiple sources can be even better. The Paleontology, Past and Present primary source set includes two items that, when analyzed alongside this photograph of petrified wood, allow students to consider both the process of fossilization as well as the ways in which scientists studied fossils and discovered how ancient plants and animals were preserved in this way.
This photograph shows several pieces of petrified wood, or wood that has been turned to stone through a process called mineralization. For this to happen, the wood was buried under sediment and saturated with mineral-rich groundwater. Over time, the minerals formed crystals that gradually replaced the wood until the entire piece was made of rock.
Show students this photograph (without the title or caption) and invite them to look closely. What do they notice? What ideas do they have about what they see? What do they wonder? Students will likely recognize the objects as pieces of a tree but may not know that they are stone and not, in fact, wood.
Once students have shared their initial observations, reflections, and questions, share the photograph’s title, Fossilized tree specimens in the Petrified Forest. Ask students to reflect on the title. Do they have new ideas about the objects in the photograph? What new questions do they have? Students may wonder about the meaning of the word, “petrified,” or wonder how wood could become a fossil.
Next, invite students to repeat the observe, reflect, question protocol with the photograph of Arthur Kochler holding a piece of petrified wood (shown below). What do they notice? What do they wonder? Can they make any connections between the first photograph and this one?
Students may not immediately identify the object that Kochler is holding as wood, in which case sharing the title of the photograph may be helpful. Guide students to notice the scientific tools in the photograph. How might Kochler use those tools to study the piece of wood? How might he have known the age of the wood?
Arthur Kochler, wood identification specialist of the Department of Agriculture, says the piece of wood he is holding is 12,000,000 years old.
Finally, direct students examine Robert Hooke’s drawing of petrified wood as viewed under a microscope. Once again ask them: what do they notice? What do they think they are viewing in this drawing? What questions do they have?
Drawing of Petrified Wood as Viewed Under a Microscope. Robert Hooke, Micrographia, 1665.
Students may comment on the orderly rows of dark ovals without understanding that these represent the crystalline structure of the fossilized wood. Comparing the drawing with microscope pictures of petrified wood may help them better interpret Hooke’s drawing.
This instructional sequence of stacking three related primary sources prompts student curiosity about a type of fossil with which they are less familiar. It can serve as a launching pad for further investigation into the processes of fossilization and the ways in which scientists study fossils.
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