Rocks and Rock Layers

Fossil Tell a Story Let’s look at all of the interesting (and helpful) things they can tell us about the past … because they have a lot to tell!

Clues to Past Climates If you have gone bike riding on Slickrock trail in Moab, you have ridden on ancient sand dunes. What type of climate do sand dunes suggest?

Clues to Past Weather Conditions Sedimentary rocks have clues to past climates and ecosystems. These rocks were ancient sand dunes, with layers that formed at different times, at different angles, depending on which direction the wind was blowing. This is called cross-bedding and can be found all over Southern Utah.

Clues to Past Waterways Ripple marks found near a river bed that is still running with water. Ancient ripple marks, now fossilized, show where a river used to run.

Clues to Past Animal Life What might have made these marks? Most likely … worms moving along soft sand or mud.

Clues to Past Animal Behavior Dinosaur footprints can indicate areas of gathering … either for food or mating. These prints that have been preserved have taught us a lot about the eating, hunting and possible migrating habits of these animals.

Rock Formations Also Offer Clues to the Past Fossils are usually buried in old rock layers. These layers occurred at different times in the Earth’s history. Each layer has a time and a story, and the next few pages show what information we can gather from rock layers.

Layering of Sedimentary Rocks You have probably noticed layers on exposed mountain sides before. These layers tell a great deal about the history of the area and are great tools for scientists.

Rock Layers Sedimentary rocks form from layers of sediment that collect in horizontal layers. Over time, with pressure and chemical cementing, rocks form. Sometimes, the layers are exposed by erosion, like these canyon walls in Dinosaur National Park.

Uplift These layers near Denver, Colorado show how horizontal layers can be altered by uplift. In this case, the Rocky Mountains rose and changed these layers. Can you tell which layer is oldest? Answer: The layer that is on the far left is oldest.

Twisting Sometimes layers of sedimentary rock are twisted by earthquake faults.

Slipping Sometimes layers of sedimentary rock slip past each other because of earthquake faults.

Slipping From a Different Angle This picture shows Becks Spur which is in North Salt Lake City. The cliff is the Wasatch fault it was not made by people. When the Wasatch Fault slips the mountain rises and the valley falls.

A Closer Look The scratches were formed as the rocks slipped past each other.

The Importance of Order Now, it isn’t always an easy job to figure out which layer came first. But if you look at all the clues given, a good guess can be made. The key is to notice the details. Picking out the details helps you to put things in the order of their occurrence. Then you can put together a history for that area, including theories about climate, animal life, seismic activity and much, much more.

Order of Events Read the following list of events carefully. Then determine the correct order for the sentences. I got out bread, peanut butter and jelly. I ate the sandwich. I put the two pieces of bread together. I spread a layer of jelly on another piece of bread. I was hungry. I spread a layer of peanut butter on a piece bread.

Figuring Out the Order of Events How did you determine the order of the sentences? If you did it like many people, you based your sentences on what you know normally happens when you make a lunch. Geologists do the same thing to determine the order of past events. The process of putting things in a "correct order" based on experience is called Relative Dating. Relative Dating is determining whether an object is older or younger than other objects or events. It doesn’t give an exact age but a relative (or comparison) age. This means that you know which events came first, but not the exact time when they happened.

Clues to Help Figure Out Past Events It’s a lot like what happens with the photos someone takes over a lifetime. Instead of putting them into a photo album, they are packed away in a box. Where are the oldest pictures going to be in the stack? At the bottom or the top? What about the newer pictures? Where are they in the stack? Rock layers are a lot like the stack of pictures. The layers at the bottom are the oldest. Each layer will be successively younger or more recent. This is called Superposition. Superposition is the principle that says younger rocks lie above older rocks in an undisturbed sequence.

Fossils Offer Important Clues Scientists use the fossils of animals to help determine relative age. Certain groups of fossil animals and plants occur in the geologic record in a specific order. If a scientist finds one of those fossils they can then assume the age of the rock based on the age of the fossil.

Rock Layers Offer Clues, Too But sometimes something will get in the way. Igneous intrusions -areas where igneous rock cuts across layers of pre- existing rock. -the principle of cross- cutting relationships states that the intrusions are younger than the rock they cut.

Relative Dating Practice With all that background knowledge you now have, it’s time for you to be the geologist. There are five different pictures of one rock sequence throughout time. Number the pictures from one to five with one being the oldest and five being the youngest. Below each picture, choose the process that describes what has taken place and write that term in the space provided.

More Relative Dating Practice Examine the figure to the right, then answer the following questions: Is Rock layer "A" younger or older than the other rocks? What evidence explains your answer? Is the fault (dotted line labeled "L") older or younger than layer D? Explain your answer. List the rock layers in order from oldest to youngest. (include the lines "K" and "L").

The End

Relative Dating Answers Answer to the first question: Answers to the next group of questions: 1. Younger - It represents an intrusion which is younger than the rock it cuts through. 2. Younger - the fault occurred before erosion and the sedimentation of layer D 3. E, F, G, H, I, J, L, K, D, C, B, A

The Element of Earthquakes And sometimes earthquakes can get things a little jumbled up … literally! Go to THIS PAGE for a lesson in how faults can affect the “order” of the Earth’s layers. Do the investigation and answer the analysis questions. Label this assignment, “Move Over, I’m Coming Through” and file it in your Science Journal.

Were You There? What did North America look like 2 million years ago? Were there rivers and lakes? Were there mountains in the same places as modern day? Was North America in the same location as it is today? To answer these questions, geologists construct maps of the lands and seas, as they existed in past ages. This process of reconstructing ancient geography is called paleogeography. Like a private detective, geologists analyze the clues they find preserved in the rocks. The types of fossils contained in the rocks are clues for the geologists. When interpreted, these clues can give direct knowledge about the distribution of the lands and the seas, but also about the natural environment of the area. This helps the geologists to infer where the mountains and basins were located in the geologic past.

Were You There? The distribution of fossils (skeletons, shells, leaf impressions, footprints, and dinosaur eggs) in rocks of a certain age tells something about the ancient distribution of lands and seas on the Earth's surface. The remains of coral found in land- locked Iowa indicate that this region was once covered by a coral reef. Clam shells found in old limestone of Pennsylvania and New York indicate a shallow sea once covered the area. The remains of ancestral horses and camels in rocks of South Dakota show that the area was then dry land or that land was nearby.

Were You There? The distribution of the fossils will help to identify the ancient areas of land and sea and also the approximate shoreline. The distribution of living forms shows that thick- shelled fossil animals once lived in shallow water close to shore, while thin- shelled, delicate fossil animals probably lived in deeper, calmer water offshore.

Were You There? Fossils can also be used to indicate the former temperature of water. In order to survive, certain types of present-day coral must live in warm and shallow tropical salt waters, such as in the seas around Florida and the Bahamas. When similar types of coral are found in the ancient limestone, they provide a good estimate of the marine environment that must have existed when they were alive. All these factors -- depth, temperature and currents -- that are revealed by fossils are important to help clarify the picture of ancient geography

Pretend You Were There You are to be the paleontologist now, and use research to determine what fossil evidence you will see in your geologic column. Choose one of the areas listed below to study. For the area you have chosen to study, you need to learn about its geologic history. Imagine that you are a paleontologist and are trying to determine the evidence of change in your specific location. You might try to find pictures of the area as well as pictures of the fossil record found in that area. Present your fossil findings as a newspaper article. Areas to Choose From: Freshwater aquatic Marine aquatic Hot and dry desert Arctic Tundra Semi arid desert Coastal desert Cold desert Tropical forest Temperate forest Taiga (coniferous) forest Savanna Temperate Alpine Tundra For information on ecosystems you might look in a library or search on the Internet. Your newspaper article should answer the following questions: How do your fossil findings indicate the ecosystem which was once present? How will a change in ecosystems be evident in the fossil record? What specific fossils would you find in each layer of rock? Title this assignment “If You Were There”, and file it in your Science Journal.

New Fossils on the Rock Have you ever wondered about why fossils that are found in more recently deposited rock layers resemble existing species? Read on and see if you can discover the answer to this question.

New Fossils on the Rock The process of fossil formation begins as a living thing dies and is covered by something, so that there is no oxygen to decay, and fossilization begins. With time, nature will replace the bones, or hard parts of the critters body, with minerals, which preserves it within the rock. More recent fossil remains can be found closer to the surface, while older fossils representing animals that died long ago would be found deeper in the earth. For example, more recently evolved animals, like birds, mammals, and modern day lizards, are likely to be closer to the earth's surface than dinosaur or trilobite fossils.

New Fossils on the Rock Therefore scientists may get a general idea as to the age of a fossil by the depth of the fossil in the rock layers of Earth. Also, they can tell the age of the rock by the fossil they find within that rock layer.  Because Earth's species have been constantly changing, more recently deposited rock layers would contain fossils resembling the species of today.

New Fossils on the Rock The following pictures represent an example of this concept: This picture represents the surface of the earth now. The lizard is an example of a living critter that lives on the surface, of which some may become fossilized in time.

New Fossils on the Rock This picture represents the rock layer where many ancient fossils have been found dating 400 million years ago.  This layer use to be the surface layer and the fossil found here use to live on the surface of the land, just like the lizard

New Fossils on the Rock This is a picture of a trilobite.  These critters lived 400 million years ago in a very shallow sea.  Scientist are able to determine the age of layers of rocks, plus the environment in which they lived, by studying fossils and rock layers.  Because trilobites loved so long ago, they are often found in layers of rocks that are much older!

New Fossils on the Rock We started off with this question: Have you ever wondered about why fossils that are found in more recently deposited rock layers resemble existing species? Have you figured out the answer? Write a short paragraph explaining your answer to this initial question. Label it “New Fossils on the Rock” and file it in your Science Journal.