GRAND CANYON GEOLOGY PROGRAM PROGRAM PLAN FOR DOCENTS

Transcription

1 GRAND CANYON GEOLOGY PROGRAM PROGRAM PLAN FOR DOCENTS The following is a suggested format for this program. Please feel free to incorporate your own experiences and creativity; however, maintain the Arizona State Academic Standards when you do this program. AGE/GRADE LEVEL DURATION GROUP SIZE DOCENTS LOCATION BACKGROUND ESSENTIAL QUESTIONS This program is appropriate for grades hour 30 students plus one educator/chaperone for every six students 2 docents Geology Gallery, Half class moves into Branigar Chase for activities, while half class remains in Gallery for Scavenger Hunt. This program should help students understand that although much is known about the age of the rock layers exposed at Grand Canyon and the environment at the time they were formed, scientists are still trying to solve how Grand Canyon itself was formed. The Colorado River carved it, but how the river got there and began the process remains a mystery. By the end of the program, students should be able to discuss the following questions: 1. Where did the rocks in the Grand Canyon come from? What was the Earth like when these rocks appeared? How do we know? 2. The layers of rock were in place long before the Grand Canyon formed. What would be strong enough to cut through all that rock to make a canyon? Is Grand Canyon finished growing and changing? 3. Why is the formation of the Grand Canyon such a mystery? What are some of the possible explanations? Scientists must gather evidence to support their theories about how Grand Canyon formed. Why might that be difficult with the Grand Canyon? 4. Why is the Grand Canyon located in Arizona and not Mississippi? KEY WORDS Geology Igneous Erosion Crust Metamorphic Volcanism Mantle Sedimentary Uplift Colorado Plateau Core Deposition Plate tectonics (grade 5 8) Lithosphere (grade 7) MNA s Geology of the Grand Canyon page 1

2 MATERIALS NEEDED One hard boiled egg, Map of Earth and map of Pangaea, Map of Colorado Plateau, map/picture of Grand Canyon, Introduction to Grand Canyon Geology by Greer Price, Carving Grand Canyon by Wayne Ranney, (Spreader) shoe box, two strips of paper, rocks (Milky Way tectonics) small Milky Way bars for each student, paper towels (Speedy erosion) paint roller pan, soil, paper cup, drinking straw, clay, container of water, bucket for used water, small rocks to alter water stream (Jigsaw World) map of Pangaea, world today map and world cut up map for each student, scissors, blank paper, glue, papers with scavenger hunt questions, pencils, paleographic maps INTRODUCTION Greet students and introduce yourself. Begin program in the lobby to show where Colorado Plateau fits into the map of the Four Corners area. Proceed to map of Colorado Plateau in Geology Gallery. Geographic Province named for the Colorado River not so much a plateau, but a region of many plateaus. Show map/pictures of Grand Canyon. Follow course of Colorado River. What makes the Canyon unique? What do you think made the Canyon? Why would it be on the Colorado Plateau in Arizona and not in Mississippi? (page 37 in Carving Grand Canyon describes five unique conditions of the Plateau) Geologists know age and origin of exposed rocks, but mysteries still exist concerning formation of Canyon itself (page 144 Carving Grand Canyon lists some facts geologists do agree on). Teach or reinforce. Take hard-boiled egg and crack shell. What does it remind you of? Could be tiny model of Earth. Thin shell is Earth s crust, divided into plates (Earth s crust is made up of rocks and is 5 30 miles thick in some places). Within the shell is the firm, but slippery mantle (also made of rocks, but doesn t behave like rocks we see. (It moves slowly with consistency of silly putty). Move pieces of shell around. Notice how shell buckles in places and exposes mantle in others. Same thing happens on Earth sometimes resulting in formation of mountains. Earth seems solid, but ground beneath your feet is slowly moving all the time. We humans aren t sensitive enough to notice. What happens when we do feel the Earth move? (earthquake).yoke of egg is like Earth s core (made up of hot mass of metals). Instead of egg, may use Earth Balls, page 16 from Geology Crafts. Grade 7 8 Earth s crust is not quite connected huge pieces or plates, dozens of miles thick, pushing, bumping, scraping and pulling apart. The outer 60 miles (100 km) of the Earth encompassing the crust and uppermost portion of mantle make up solid, brittle lithosphere. First geologist to formulate hypothesis that continents move was Alfred Wegener in Most geologists of his day thought he was crazy and scientists did not accept his theory until the late 1960s! Proposed that about 225 million years ago there was a supercontinent called Pangaea (all land). Look at map of Earth and Pangaea. What gave Wegener his idea? How could he prove his hypothesis? He discovered that same types of rock and fossils of the same creatures could be found in places where continental puzzle pieces fit, even though those places were separated by hundreds of miles of oceans. Would plate movement have MNA s Geology of the Grand Canyon page 2

3 any effect on climate? Why? The migration of continents through geologic time, explains many of the climate changes we observe in the geologic record at Grand Canyon. The three rock types that the Earth is made of are beautifully exposed at Grand Canyon. Review the three rock types (igneous, sedimentary and metamorphic) An Introduction to Grand Canyon Geology by Greer Price pages might be a good review. Most of the rocks are flatlying, undeformed sedimentary layers, laid down over long periods of time by rivers and seas (oceans). Desert winds are responsible for the deposition of a small part of the sedimentary layers. Many of the colors of the rocks are due to the presence of small amounts of iron oxides and other minerals. The oldest rocks in the Canyon (1.8 billion years old), found by the river, consist of ancient igneous and metamorphic (formed by heat and pressure) rocks that formed deep within the Earth when island arcs (like Hawaii today) collided with the continental mass. Grand Canyon is one of few places on Earth where we can see and hike through large part of Earth s history - see layers of rock laid down by volcanoes and oceans, raised up as mountains, eroded by rain and wind, walked on by ancient animals and then to be once again raised up and worn down. Look at pictures (pages in Greer Price book) of the environment at the time that each sedimentary layer was deposited. Compare these pictures of the environment at the time of deposition, with the paleographic maps showing the location of today's continents at the time of deposition. Where was today s Grand Canyon on the Colorado Plateau on the North American plate situated at the time of each deposition? Why is determining the age of rocks important to understanding the history of the Earth? How do0- scientists figure out the age of various rock layers? After the sedimentary rock was deposited, the next geologic event in the making of Grand Canyon was the process that involved the uplift of the Colorado Plateau. Uplift is a rise of part of the Earth s surface and can turn sea (ocean) bottoms into land. How and when this occurred is still a subject of debate. After the uplift or perhaps while uplift was occurring the Colorado River began the process of erosion that formed the Canyon. Compared to the exposed rock layers, Grand Canyon is young and probably occurred within the last six million years. Erosion caused by rain and runoff from snowmelt continues to widen and shape the Canyon. Most erosion happens during flash floods that sometimes make dramatic changes to the Canyon. In addition, softer layers of sedimentary rock (shales) erode more easily than harder layers (limestones and sandstones) resulting in slopes and cliffs. Erosion of softer layers may cause the harder layers to collapse. These processes continue today. ACTIVITIES Possible activity suggestions. Divide class. Half do activities in Branigar Chase and half work on scavenger hunt in Geology Gallery 1. Spreader from Earth Science for Every Kid. Many geologists think the MNA s Geology of the Grand Canyon page 3

4 force driving the Earth s plates is supplied by huge currents circulating in the mantle (grade 7 8 under the lithosphere). These currents force molten rock from mantle to surface where it erupts through long cracks, for the most part, along ocean floors. Cut.5 in x 3.5 slit from center of shoe box bottom and a section in center of one of box s largest sides. Cut two 3 x 11 inch strips of paper, put together and run up through slit in box. Pull strips out about 4 in., fold back on opposite sides and place narrow, light rocks on each side (representing continents (North America and Europe) bordering Atlantic Ocean. Hold papers under the box and slowly push strips up through the slit representing hot, molten rock moving out of crack in the mid-atlantic ridge. New material pushes against old and causes it to spread. Atlantic Ocean may be widening by about 1 inch each year. Greatest mountain chains on Earth are forming under ocean. As ocean widens, continents of Europe and North America are moving apart. How could you change the demonstration to show an ocean plate (Pacific) sinking under a continental plate (North America)? Why does this happen? Ocean crust is heavier. Often creates volcanoes. How could you change demonstration to show two plates sliding past each other? Happens with Pacific plate and North American. Earthquakes occur. 2. Milky Way Plate Tectonics Alternative for Spreader is to give every student small Milky Way or Snickers bar. Use fingernail to make a few breaks in crust (top of bar). See if students can determine the three possible ways for plates to move. Gently pull plates apart exposing magma, which will push its way up through the crust. This happens due to rising heat from Earth s interior. Push plates back together, slide one half of bar forward and half backward creating San Andreas fault. Finally, push plates on both ends and squeeze together. If two continental plates, mountains result. 3. Speedy Erosion, Wander experiments from Earth Science for Every Kid, demonstrate how the speed of running water affects erosion and also how the shape of waterways is altered by obstacles such as rocks and materials that cannot be moved or dissolved easily by running water. Use a slanted container like a paint roller pan. Make a hole in paper cup near bottom rim. Cut a straw in half and insert half in hole (seal with modeling clay). Cover the paint pan with thin layer of dirt. Set cup on high end of pan with straw pointing downhill. Hold your finger over end of straw and fill cup with water. Open straw and observe movement of water. Remove used water. Put a wooden block or book under high end of paint pan to raise it 6 inches. Try experiment again. Observe that as slope increases, water flows more quickly. Energy of flowing water increases with speed. Moving water hits dirt and moves it forward. Remove used water. Try experiment third time, but this time place a rock directly in front of straw. Continue to change direction of stream of water by placing more rocks in path of the water. The stream meanders as water moves in the direction of least resistance. Review process of erosion. Water from Colorado River carved Grand Canyon and water from rain and snowmelt helped make it wider. Do you think the Canyon has stopped growing and changing? 4. Edible Geology Type this into google and you ll find an excellent gelatin, fruit cocktail experiment that illustrates what happens when MNA s Geology of the Grand Canyon page 4

5 sedimentary rocks are formed (some with fossils) and what happens to the layers when they are acted on by forces of nature, including uplifting, faulting, wind and water erosion. The gelatin layers would have to be made in advance by docent, but forces of nature can be done live. 5. Jigsaw World (grade 7 8) Look at world today map (arrows indicate direction of plate movement) and look at map of Pangaea. Cut pieces in world cut up map. Make a prediction of what world will look like in 100 million years (using arrows from world today map). Paste continental pieces into their future configuration. Predict where new mountains will form. 5. Scavenger Hunt. Ask half class to look around Geology Gallery and find answers to as many of following questions as time permits. Grade 4 8: What rock in the geology gallery is like the Earth s core? (Meteorite). Hint: It weighs 400 pounds. Where did it come from? Grade 5 8: Look at How Continents Move. What kind of plate tectonic movement occurs at the San Andreas Fault? How were the Himalayas formed? What tectonic plate are we riding? Grade 5 8: Look at the Changing Face of Earth. The location of today s Grand Canyon on the Colorado Plateau, on the North American plate has changed position through time. What s the connection between this and the different rock layers (Hint: limestones from ocean deposits, sandstones from windy, desert deposits) that have been deposited there? Grade 4 8: Look at the pullout by Layers of Time. The schists and igneous rocks at the bottom of Grand Canyon are remains of a mountain range. How high was it? What could have happened to this mountain range? Hint: Schist is a metamorphic rock formed by intense heat and pressure Grade 4 8: What is the metamorphic rock called that is in the gallery? Why do you think there is only one? Grade 4 8: Find the shark s tooth in the gallery. Was it found in igneous, sedimentary or metamorphic rock? In what type of rock would you most likely find fossils? Why? Why are fossil teeth the only remains we find from ancient sharks? Grade 4 8: Can you find an example of the oldest fossilized life form on Earth? Hint: It s found in the Bass Limestone near the bottom of the canyon. When did this life form live? What was the environment like at the time? Where could you find something similar today? Grade 7 8 Where was the North American plate located at this time? Grade 7 8: More is missing from the rock record at Grand Canyon than remains. What is a missing rock record called? What could have happened? Grade 7 8: What dinosaur bones were found in Grand Canyon? Hint: Trick question! Grade 4 8: Find the glass case with the photograph of Dr. Colbert in Antarctica He found the fossil bones of what land MNA s Geology of the Grand Canyon page 5

6 mammal type reptile? Why was this important? Grade 4 8: Look at future of Grand Canyon. Draw a picture of Grand Canyon hundreds of millions of years from no, if current cycle of erosion continues. POSSIBLE EXTENSION As you travel through the Colorado Plateau, see if you can identify some of the rocks you observe and imagine what depositional environment existed when the rocks were forming. If you get a chance to hike down the Bright Angel Trail in Grand Canyon, each step is like stepping back in time 20,000 years. Handout: Excellent, concise discussion about the Layers of the Grand Canyon How Were They Formed? What Do They Contain? written by Docent Jeri Grandy (see attached). ARIZONA ACADEMIC STANDARDS SCIENCE Strand 1: Inquiry Process Concept 1: Observations, Questions, and Hypotheses Grade 4: Observe, ask questions and make predictions PO 2. Formulate a relevant question through observations that can be tested by an investigation. PO 4. Locate information related to an investigation. Grades 5 8 Formulate predictions, questions, or hypotheses based on observations. Locate appropriate resources. PO 1. Formulate questions based on observations that lead to the development of a hypothesis PO 3. Explain the role of a hypothesis in a scientific inquiry. 1. Where do you predict the Earth s plates will be 100 million years from now? What are you basing your prediction on? 2. Where did all the rocks in Grand Canyon come from? 3. What was the Earth like when these rocks were deposited? 4. How do we know? 5. Why is it important for scientists to gather evidence to support their theories? Why might that be difficult in the case of Grand Canyon? Concept 3: Analysis and Conclusions Grades 5 8: Analyze and interpret data to explain correlations and results; formulate new questions. PO 2. Form a logical argument about a correlation between variables or sequence of events PO 5. Formulate a conclusion based on data analysis 1. What are some of the possible explanations for the formation of the Grand Canyon? 2. How do you think it formed? 3. Is Grand Canyon finished growing and changing? 4. How do you know? Concept 4: Communication Grades 4 8: Communicate results of investigations MNA s Geology of the Grand Canyon page 6

7 PO 1 (grade 4): Communicate verbally or in writing the results of an inquiry. PO 5 (grades 5 8): Communicate the results and conclusion of the investigation Strand 2: History and Nature of Science Concept 1: History of Science as a Human Endeavor Grades 5 8: Identify individual, cultural and technological contributions to scientific knowledge PO 2 (grades 6 & 7): Describe how a major milestone in science or technology has revolutionized the thinking of the time (plate tectonics) Concept 2: Nature of Scientific Knowledge Grades 6 8: Understand how science is a process for generating knowledge. PO 2. Describe how scientific knowledge is subject to change as new information challenges prevailing theories (plate tectonics). Strand 6: Earth and Space Science Concept 1: Structure of the Earth Grades 5 8: Describe the composition and interactions between the structure of the Earth and its atmosphere. PO 2 (grade 7): Describe the properties and the composition of the following major layers of the Earth: Crust Mantle Core PO 3 (grade 7): Explain the following processes involved in the formation of the Earth s structure. Erosion Deposition Plate tectonics Volcanism PO 4 (grade7): Describe how the rock and fossil record show that environmental conditions have changed over geologic and recent time. Concept 2: Earth s Processes and Systems Grades 4 8 Understand the processes acting on the Earth and their interaction with the Earth systems. PO 1 (grade 4): Identify the Earth processes that cause erosion. PO 2 (grade 7): Distinguish the components and characteristics of the rock cycle for the following types of rocks: Igneous Metamorphic Sedimentary PO 3 (grade 4): Describe the role that water plays in the following processes that alter the Earth s surface features: Erosion MNA s Geology of the Grand Canyon page 7

8 Deposition Weathering PO 3 (grade 6): Analyze the effects that bodies of water have on the climate of a region PO 3 (grade 7): Analyze the evidence that lithospheric plate movements occur. PO 4 (grade 4): Compare rapid and slow processes that change the Earth s surface, including: Rapid volcanoes, floods Slow wind, weathering PO 4 (grade 7): Explain lithospheric plate movement as a result of convection. PO 6 (grade 4): Analyze evidence that indicates life and environmental conditions have changed (e.g., fish fossils in desert regions). PO 6 (grade 7): Relate plate boundary movements to their resulting landforms, including: Mountains Faults Volcanoes MNA s Geology of the Grand Canyon page 8

9 GRAND CANYON GEOLOGY PROGRAM OVERVIEW FOR EDUCATORS/PARENTS AGE/GRADE LEVEL This program is appropriate for grades 4 8 DURATION GROUP SIZE LOCATION BACKGROUND ESSENTIAL QUESTIONS KEY WORDS USED IN THE PROGRAM hours 30 students plus one educator/chaperone for every six students Geology Gallery, Half class moves into Branigar Chase for activities, while half class remains in Gallery for Scavenger Hunt. This program should help students understand that although much is known about the age of the rock layers exposed at Grand Canyon and the environment at the time they were formed, scientists are still trying to solve how Grand Canyon itself was formed. The Colorado River carved it, but how the river got there and began the process remains a mystery. By the end of the program, students should be able to discuss the following questions: 1. Where did the rocks in the Grand Canyon come from? What was the Earth like when these rocks appeared? How do we know? 2. The layers of rock were in place long before the Grand Canyon formed. What would be strong enough to cut through all that rock to make a canyon? Is Grand Canyon finished growing and changing? 3. Why is the formation of the Grand Canyon such a mystery? What are some of the possible explanations? Scientists must gather evidence to support their theories about how Grand Canyon formed. Why might that be difficult with the Grand Canyon? 4. Why is the Grand Canyon located in Arizona and not Alaska? Geology Igneous Erosion Crust Metamorphic Volcanism Mantle Sedimentary Uplift Colorado Plateau Core Deposition Plate tectonics (grade 5 8) Lithosphere (grade 7) ARIZONA ACADEMIC STANDARDS ADDRESSED BY THIS PROGRAM SCIENCE Strand 1: Inquiry Process Concept 1: Observations, Questions, and Hypotheses Grade 4: Observe, ask questions and make predictions PO 2. Formulate a relevant question through observations that can be tested by an investigation. PO 4. Locate information related to an investigation. Grades 5 8 Formulate predictions, questions, or hypotheses based on observations. Locate appropriate resources. PO 1. Formulate questions based on observations that lead to the development of a hypothesis PO 3. Explain the role of a hypothesis in a scientific inquiry.

10 Related Questions: 1. Where do you predict the Earth s plates will be 100 million years from now? What are you basing your prediction on? 2. Where did all the rocks in Grand Canyon come from? 3. What was the Earth like when these rocks were deposited? 4. How do we know? 5. Why is it important for scientists to gather evidence to support their theories? Why might that be difficult in the case of Grand Canyon? Concept 3: Analysis and Conclusions Grades 5 8: Analyze and interpret data to explain correlations and results; formulate new questions. PO 2. Form a logical argument about a correlation between variables or sequence of events PO 5. Formulate a conclusion based on data analysis Related Questions 1. What are some of the possible explanations for the formation of the Grand Canyon? 2. How do you think it formed? 3. Is Grand Canyon finished growing and changing? 4. How do you know? Concept 4: Communication Grades 4 8: Communicate results of investigations PO 1 (grade 4): Communicate verbally or in writing the results of an inquiry. PO 5 (grades 5 8): Communicate the results and conclusion of the investigation Strand 2: History and Nature of Science Concept 1: History of Science as a Human Endeavor Grades 5 8: Identify individual, cultural and technological contributions to scientific knowledge PO 2 (grades 6 & 7): Describe how a major milestone in science or technology has revolutionized the thinking of the time (plate tectonics) Concept 2: Nature of Scientific Knowledge Grades 6 8: Understand how science is a process for generating knowledge. PO 2. Describe how scientific knowledge is subject to change as new information challenges prevailing theories (plate tectonics). Strand 6: Earth and Space Science Concept 1: Structure of the Earth Grades 5 8: Describe the composition and interactions between the structure of the Earth and its atmosphere. PO 2 (grade 7): Describe the properties and the composition of the following major layers of the Earth: Crust Mantle

11 Core PO 3 (grade 7): Explain the following processes involved in the formation of the Earth s structure. Erosion Deposition Plate tectonics Volcanism PO 4 (grade7): Describe how the rock and fossil record show that environmental conditions have changed over geologic and recent time. Concept 2: Earth s Processes and Systems Grades 4 8 Understand the processes acting on the Earth and their interaction with the Earth systems. PO 1 (grade 4): Identify the Earth processes that cause erosion. PO 2 (grade 7): Distinguish the components and characteristics of the rock cycle for the following types of rocks: Igneous Metamorphic Sedimentary PO 3 (grade 4): Describe the role that water plays in the following processes that alter the Earth s surface features: Erosion Deposition Weathering PO 3 (grade 6): Analyze the effects that bodies of water have on the climate of a region PO 3 (grade 7): Analyze the evidence that lithospheric plate movements occur. PO 4 (grade 4): Compare rapid and slow processes that change the Earth s surface, including: Rapid volcanoes, floods Slow wind, weathering PO 4 (grade 7): Explain lithospheric plate movement as a result of convection. PO 6 (grade 4): Analyze evidence that indicates life and environmental conditions have changed (e.g., fish fossils in desert regions). PO 6 (grade 7): Relate plate boundary movements to their resulting landforms, including: Mountains Faults Volcanoes LAYERS OF THE GRAND CANYON How Were They Formed? What Do They Contain?

12 Jeri Grandy, Docent Museum of Northern Arizona Anyone who visits the Grand Canyon is overwhelmed by its size, beauty, and grandeur. But would they be so impressed if the Canyon were a solid gray or brown color? Much of its magnificence arises from the bands of color the layers of buff-colored Kaibab Limestone and Coconino Sandstone, the bright reddish-orange layers of the Supai Group and the Redwall Limestone, and the dark Precambrian rocks at the bottom of the Inner Gorge, bordering the Colorado River. Not only are the layers of the Canyon different colors, but the rocks composing the layers vary in hardness, mineral composition, fossils, and other inclusions. Because of the action of freezing, thawing, and rushing water, rocks break down in ways that are determined by their structure, composition, and hardness. Some layers are composed of hard rock, which, has eroded into steep vertical cliff walls. Others are composed of softer rock that crumbles and forms slopes. Together, the hard and soft layers form unique canyon-wall profiles. Under varying lighting conditions, the colors seem to grow richer or softer. Shadows cast by the shapes of the canyon walls change as the sun progresses across the sky. It is the variation and change in shapes and colors that continue to intrigue visitors, photographers, and artists. Why are the rock layers different colors, textures, and shapes? Why does each layer consist of one or more different rock types and fossils? The answers to these questions lie in the processes that formed each layer. PRECAMBRIAN ROCKS The oldest rocks at Grand Canyon are combinations of igneous and metamorphic rocks at the very bottom of the canyon, known as the Inner Gorge. Vishnu Schist is the dark, nearly black, hard rock visible from many Canyon overlooks where we can see the river. About 1,800 million years ago the continents were smaller and configured differently than they are now. The area that is now the Grand Canyon was part of the sea floor with a series of volcanic islands nearby. These volcanoes formed above a subduction zone a place where an oceanic plate plunges below a continental plate in a process that generates heat and molten material. About 1,700 million years ago, these volcanic islands collided with the North American continent. A vast quantity of new continental crust was formed, and high mountains rose. The extreme pressure produced intense heat in the subducted crust. It formed molten rock that thrust through the crust, forming the brilliant pink veins of quartz that we now see in the walls of the Inner Gorge. The rock in these colorful veins is called Zoroaster Granite. For the next 500 million years, erosion wore these mountains down to a nearly level plain. Then an ocean invaded and laid down mud and sand for the next 300 million years, resulting in sedimentary deposits over two miles thick. Together, these layers of sedimentary rocks are called the Grand Canyon Supergroup. One layer of the Supergroup, the Bass Limestone, fascinates us because it contains the earliest known fossilized life forms on earth. You can see a sample in the MNA Geology Gallery. SEDIMENTARY LAYERS

13 All of the layers of the Grand Canyon above the Precambrian rocks are sedimentary (with the exception of later volcanic intrusions). They were laid down during the Paleozoic Era, beginning about 550 million years ago. In many parts of the Grand Canyon, the Supergroup is missing, having eroded away hundreds of millions of years ago. Here, the Paleozoic sediments, which date around 550 million years ago, rest immediately on top of the Vishnu Schist. Because the top of the Vishnu dates to about 1,700 million years ago, there is a time gap of about 1,200 million years. John Wesley Powell named this time gap the Great Unconformity. The time represented by that gap is longer than the time represented by all of the remaining layers of the Canyon. More is missing from the Grand Canyon than remains. The Tapeats Sandstone is the lowest sedimentary layer. It rests on Precambrian rocks immediately above the Great Unconformity. It was formed about 550 million years ago (Cambrian period) on the shore of a large sea (the Cambrian Sea) that was slowly advancing over the land. The types of life forms had multiplied considerably to include algae, other ocean plants, and trilobites. Trilobites would continue to live throughout the Paleozoic Era. Fossil trilobites are found in suitable environments all the way to the top of the Grand Canyon. The Bright Angel Shale rests on the Tapeats Sandstone. It was formed about 540 million years ago (Cambrian period) from muddy near-shore sediments as the ocean slowly advanced further onto land. Today this layer is a greenish shale with fossils of worm burrows, trilobites, and brachiopods. Because it is soft and crumbly, the shale forms slopes in the Canyon. Hikers on the Tonto Trail can parallel the base of the Bright Angel Shale (most of the time) for roughly 70 miles. The Muav Limestone rests on the Bright Angel Shale. It was formed about 530 million years ago (Cambrian period) from limy offshore deposits as the Cambrian Sea advanced still further onto the land. Today, in some parts of the Canyon, this layer forms the base of the large Redwall Limestone cliff. In some parts of the Canyon, especially in the western section, the Temple Butte rests on the Muav Formation. Fossils include algae, sponges, crinoids (sea lilies), and trilobites. The Temple Butte Limestone rests on the Muav Limestone, though in some parts of the Canyon, it has either been eroded away altogether, or it was never deposited. Today we see this layer primarily in the western part of the Grand Canyon. It was formed about 370 million years ago (Devonian period) in the marine waters or estuaries * of the Devonian Sea. If you have been doing your math, you see there is a major unconformity (time gap) between the Muav and the Temple Butte layers. All of the Silurian and Ordovician layers either have been eroded away or were never deposited. Because the Temple Butte was formed in estuaries, it contains the fossils both of marine and fresh-water animals. In the eastern region of the Canyon it contains bony plates that once belonged to freshwater fish. In the western region there are numerous marine fossils. The Redwall Limestone is a prominent wall of the Canyon, averaging 500 feet in thickness. It rests on the Temple Butte Limestone and, where there is no Temple Butte Limestone deposited, it rests on the Muav Limestone. Resting on top of the Redwall Limestone is the Supai Group. The bright red iron oxides of the Supai Group have washed down over the face of the Redwall and stained it red. Where the Redwall is chipped, we can easily see that it is actually a gray color. The Redwall was formed about 335 million years ago (Mississippian period) in the quiet marine waters that covered much of North America. The continent, at that time, lay close to the equator, and the sea was teeming with life. Calcium carbonate precipitated out of the billions of shells on the ocean floor and produced very pure limestone. The Redwall contains numerous marine fossils, including crinoids, corals, bryozoans, brachiopods, and cephalopods, trilobites, and fish. * An estuary is the wide mouth of a river, where the river water mixes with the seawater.

14 The Supai Group rests on the Redwall Limestone. It was formed about 300 million years ago (end of the Mississippian, through the Pennsylvanian, and into the Permian periods). It represents widely changing environments of deposition, probably resembling the Gulf Coast of Texas today. Viewed from the Canyon rim, we see the Supai as combinations of bright red cliffs and slopes. Fossils in the Supai Group are numerous and include ferns and the tracks of reptiles and amphibians. The Hermit Shale rests on the Supai Group. It was formed about 280 million years ago (Permian period) probably from stream deposits on a broad coastal plain, lagoon, or swamp. Today this layer appears as dark red or maroon cliffs and slopes. It is the uppermost red layer of the Canyon, and it contrasts sharply with the light tan layer of the Coconino Sandstone just above it. The Hermit Shale is rich with plant fossils, including ferns and conifers (Araucarian Pines) similar to the trees forming the petrifed wood in Petrified Forest. Hermit Shale also contains fossilized tracks of reptiles and amphibians as well as fossils of giant dragonflies and fin-back reptiles called Dimetridons. The Coconino Sandstone rests on the Hermit Shale. Unlike the other Canyon layers that were formed under the sea or along coastlines, the Coconino Sandstone was formed by windblown sand at a time 270 million years ago (Permian period) when North America had a warm, dry, terrestrial environment probably resembling the Sahara Desert of today. From the rim of the Canyon, or just below the rim on the Bright Angel Trail, we see in the Coconino layer what appears to be a wall of sand dunes evidence that this layer was once a field of dunes. Within this formation are fossilized tracks of reptiles and scorpions, but no fossil bones of any animals have ever been found. Coconino Sandstone splits easily along the layers of the original dunes. These layers are called crossbeds. The buff-colored stone used as facing in many Flagstaff buildings is Coconino Sandstone. The Federal Building at 114 North San Francisco Street was built of brick in 1937 and faced with slabs of Coconino Sandstone. Because it splits in such flat sheets, it is still used extensively as flagstone for walkways around Flagstaff. These stones are not hauled from the Grand Canyon! (That would be illegal as well as unaesthetic.) The Coconino Sandstone, like most other layers of the Grand Canyon, extend over much of the Colorado Plateau. The Coconino Sandstone for the buildings in Flagstaff were quarried near Ash Fork, about 45 miles west of Flagstaff. The Toroweap Formation rests on the Coconino Sandstone. The Coconino desert was eventually submerged under another ocean. The Toroweap was formed about 260 million years ago (Permian period) from shallow water marine sediments along a changing shoreline. The Toroweap Formation is the tree covered layer between the Kaibab Limestone (top layer of the Grand Canyon) and the cliff of Coconino Sandstone below it. The Toroweap consists of thin sandstones that are rich in fossils of sponges, brachiopods, and crinoids. The Kaibab Formation rests at the rim of the Grand Canyon. It covers most of Flagstaff as well. Following the formation of the Toroweap there was a brief period of erosion and the invasion of yet another ocean. The Kaibab Formation, about 250 million years old (Permian period), was formed in a shallow marine environment in warm tropical seas. We find fossils of bryozoa, rugose coral, coiled cephalopods (snails), crinoids, sponges, trilobites, brachiopods, sea urchins, and sharks teeth. You can find some of these fossils in the limestone walls and buildings in downtown Flagstaff. In particular, it is fascinating to examine the Ice House on Birch Avenue at the corner of Verde Street. The Babbitt family built the Ice House in 1946 to store ice for purchase by truckers carrying produce from California. The Babbitts used thousands of chunks of Kaibab Limestone in the construction. If you walk along Birch Avenue, studying the building s wall, you will find fossils of oval-shaped clams, sea snails, scaphopods (tusk-shaped tubular shells), nautiloids, sea urchins, and brachiopods. The Final Chapters

15 Cutting of the Canyon itself is quite another story. It has been occurring in the blink of an eye, geologically speaking. But it is a complex and incomplete story, filled with academic debate. We might say that as the Canyon evolves, so do theories on its formation. We ll leave those stories for another chapter. ADDITIONAL READING Aitchison, Stewart. (1999). Grand Canyon. Sierra Press, Mariposa, CA. Chronic, Halka. (1988). Pages of Stone: Grand Canyon and the Plateau Country. The Mountaineers, Seattle. Jackson, Marie D. (1999). Stone Landmarks: Flagstaff s Geology and Historic Building Stones. Piedra Azul Press, Flagstaff, AZ. Price, L. Greer. (1999). An Introduction to Grand Canyon Geology. The Grand Canyon Association, Grand Canyon, AZ. Sadler, Christa. (1993). Life in stone: Fossils of the Southwest. Plateau. 64(3). Museum of Northern Arizona, Flagstaff, AZ. Tegowski, B.J. (1996). Easy Field Guide to Invertebrate Fossils of Arizona. Primer Publishers, Phoenix. Readers may also be interested in the website of the Grand Canyon Historical Society,