This activity models how sedimentary rock layers are formed, and then uplifted.
Optionally, paper fossils can be added to the sedimentary layers, to model how fossils are exposed as uplifting and erosion occurs.
Making the sedimentary layers:
Layer the sand and sugar alternately in the container. It seems to work best if the lighter sugar layers are about 1cm deep and the dark sand layers are 1-2mm deep. Make at least three layers of each, depending on the container size.
This step models how sediment is carried by water and wind, to build up in layers in oceans, lakes and deserts.
As layers add on the top, the lower layers are compressed, eventually forming sedimentary rock as they get deep enough.
Modelling fossil formation:
If adding fossils to the model, add the most recent fossil in the layer below the top layer. Older fossils can be in about the 3rd layer. (See last two photos.)
Sometimes when an animal or plant dies it falls into the sediment. Hard animal body parts such as bones and shells are preserved and are slowly turned into rock. Hard plant parts can be preserved, or plants make impressions (prints) between rock layers.
Hold the cardboard paddle upright and push it to the bottom of the container of sedimentary layers, at one end. Slowly slide the cardboard along the container, making sure that it stays touching the bottom as it moves. Try and move it as smoothly as possible.
Sand and sugar may spill out of the top of the container. Watch through the side as the layers buckle and fold.
Stop the uplifting when the folds are clear before they start getting muddled up - when the cardboard paddle is about half way along the container. Then add lightly crumpled sheets of tissue to hold the paddle upright in place.
The sand and sugar spilling from the top of the container mimics erosion - the top of a mountain is worn away by wind and water - exposing lower layers of rock.
Modelling fossil discovery:
If fossils have been added, the more recent fossils in the higher sedimentary layers are exposed as the top layers erode away (fall off the top of the model). The lower layers with their older fossils will likely remain hidden.
Older fossils in real rock are harder to find as they are more rarely exposed, while the newer fossils are more frequently revealed as sedimentary uplifting occurs. A fossil is dated by the age of the sedimentary rock layer in which it is found.
Note that real fossils do not just fall out of the rock. Once a part of a fossil is exposed by erosion, geologists carefully chip and brush around it before lifting the fossil out of the rock.
Using fossils, scientists can construct a map of what life forms existed at what times. Fossils show a gradual change of how living things look through time, over millions of years.
Fossils have shown how life moved onto land (Tetrapods), how whales evolved from land mammals, and reveal missing links (Archaeopteryx is the missing link between dinosaurs and birds).
Study the folding patterns:
Allow students to visit all of the models, to see the different patterns of folding.
Students can optionally use the attached worksheet to draw the shapes of the folds in models of their choice.
Pick out a couple of examples to bring to group discussion.
Show images of real sedimentary folds. Try https://www.geologyin.com/2016/09/10-amazing-geological-folds-you-shoul… or https://www.easternct.edu/cunninghamw/ees-356-teaching-resources/struct…
Ask students to find the same folding patterns in their models as in the images.
Just as in their models, real sedimentary rock layers are folded and buckled upwards as tectonic plates converge, move under and over each other. When plates collide and slide past each other, earthquakes happen.
The Alps and Himalayas were formed over 10s of millions of years - the Alps from the African and Eurasian tectonic plates colliding and the Himalayan Mountains from the convergence of the Indian and Eurasian plates. At the summit of Mount Everest there is marine limestone.
The Canadian Rockies were formed when the tectonic plate of the Pacific Ocean pushed under (subduction) the continent, causing it to wrinkle upwards.
Different model of tectonic plates colliding, using a rug bunching up on a smooth floor:
The mountain-building is analogous to a rug being pushed together on a hardwood floor. The rug bunches up and forms wrinkles (mountains). In Canada, the subduction of the Kula plate and the terranes smashing into the continent are the feet pushing the rug, the ancestral rocks are the rug, and the Canadian Shield in the middle of the continent is the hardwood floor.