PROJECT EXPLORE INSTRUCTIONAL MODULE #5 FOCUS QUESTION: ANTARCTICA GEOLOGY: WHAT IS UNDER ALL THAT ICE? ............................................................................ Gerry Hill Rosemount Senior High School Rosemount, Minnesota BACKGROUND INFORMATION The continent of Antarctica is divided into two large geologic areas -- East and West Antarctica. East Antarctica is the large bean-shaped land mass centered on 90 degrees east longitude. West Antarctica is the area centered on 90 degrees west longitude and includes the Antarctic Peninsula, Marie Byrd Lane, and the area east and north of the Transantarctic Mountains. Because of the thick ice sheet, geologic details are not possible to obtain for all of Antarctica, an area the size of the United States and Mexico combined. For the purposes of this module an overview will suffice. East Antarctica is a large Precambrian shield, a stable portion of a continent composed of old rocks that have changed very little over a long time. It is similar to shield areas in Brazil, Africa, India, and Australia. The oldest rocks found in this area are over 3 billion years old. These rocks are metamorphic rocks overlaid by younger, flat-lying ocean-deposited sediment. The rocks were recrystallized during an orogeny, a mountain building episode caused by plate collisions, in the early Paleozoic Era (about 500 million years ago). Typical samples would probably include gneiss, schist, granitics, shale, sandstone, and limestone. The land of East Antarctica is low in elevation with large bays indenting the coastline. The weight of the thick ice sheet has pushed the land down so far that if it were removed, the land would rebound nearly 2,000 feet. East Antarctica was part of Gondwana, the large, single, land mass made up of the present continents of South America, Africa, India, Australia, and Antarctica. Gondwana existed as far back as 1 billion years ago and moved and rotated in the southern hemisphere as a unit until about 200 million years ago when it began to break up and finally broke apart from present land masses about 40 million years ago. Gondwana was part of Pangaea, the supercontinent made up of all the major continents in the Paleozoic Era. West Antarctica is a more recent addition to the continent. It was built up over the last 500 million years by the addition of small continental fragments (called microplates), four of which have been identified. They include the Ellsworth Mountains block, the Antarctic Peninsula, an unnamed block of igneous rocks and metamorphosed sediments, and the Marie Byrd Land block. The collisions that added these microplates to Antarctica have built up the mountains of West Antarctica. Unlike East Antarctica, if the ice were removed in the west, the land would have considerable relief. The area would probably appear as a series of island chains and mountain ranges. The Transantarctic Mountains (nearly 15,000 feet at their highest) were formed by the Ross Orogeny in the early Paleozoic (about 500 million years ago). They consist of flat-lying sedimentary rocks. Typical rocks would include sandstone, shale, limestone and some coal. The Ellsworth Mountains were formed in the early Mesozoic (about 190 million years ago). They are as high as 16,000 feet and are steeper than the Tetons with twice the relief above the surrounding land. The Antarctica Peninsula and the rest of West Antarctica were the most recent additions. The Andean Orogeny of late Mesozoic and early Cenozoic (about 60 to 80 million years ago) formed the peninsula. This activity coincided with the final breakup of Gondwana as South America, Australia, and Antarctica split apart. The peninsula is an extension of the Andes of South America and like these mountains, is made of igneous intrusive rocks, volcanics, and metamorphosed sediments. Marie Byrd Land has recent volcanic rocks and one of the only active volcanoes is found on the peninsula. Another active volcano, Mt. Erebus, is found on Ross Island, just west of the Transantarctic Mountains. Typical rocks would include andesite, basalt, granitics, dolerite (a course-grained basalt), slate, marble, and quartzite. Antarctica is currently tectonically stable in that it experiences little or no volcanism, earthquakes, and is not in motion. The mountainous regions of Antarctica contain mineralized areas that were mostly formed by the intrusive activity during the Ellsworth and Andean Orogenies. The extent and nature of these resources, and whether they might be economic, is covered in another module. The mountains have also played a part in making Antarctica the best meteorite hunting ground on Earth. The ice sheet acts like a storehouse for the meteorites, incorporating them within the ice and keeping them safe from weathering and erosive forces and eventually dumping them into the sea as the ice flows off the continent. Some of the mountains, however, act as a barrier to this seaward ice movement. The ice is prevented from flowing over or around these mountains and sublimates (changes directly to vapor from the ice phase) at the inland base of the mountains. This process leaves the meteorites on the surface as more and more old ice moves to the surface and melts. The result is that more meteorites have been recovered in Antarctica in the last 15 years than in all other places on Earth combined. There are also fossils in the rocks of Antarctica. The Paleozoic rocks of the Transantarctic Mountains have plant fossils of Permian age in the coal beds, the younger rocks of these mountains have fossils of Triassic reptiles and amphibians. Fossils of a 40 billion year old mammal (a marsupial) have been found in the Antarctic Peninsula, suggesting a connection between Antarctica and South America at that time. OBJECTIVES: PROCESS OBJECTIVES The students will be able to describe the general geology of the land under the Antarctic ice and to explain from where the rocks may have come. CONTENT OBJECTIVES The student will know that Antarctica is made of two major geologic areas, East and West Antarctica. The students will know that East Antarctica is a very old continental shield. The students will know that West Antarctica is a younger area built by microplate collisions in the last 500 million years. The students will know that the rocks of East Antarctica are metamorphic rocks like gneiss and schist, granites, and sediments from oceans. The students will know that the rocks of West Antarctica are of all types: igneous, metamorphic, and sedimentary. The students will know that the Trans-Antarctica Expedition crossed the mountains in the first part of their journey. The students will know that Antarctica was part of Gondwana. The students will know that Gondwana was a name for the single land mass made up of the continents of South America, Africa, India, Australia, and Antarctica joined together from about 1 billion years ago until it slowly broke up from 200 to 40 million years ago. The students will know that Antarctica is not now experiencing any tectonic events like the growth of mountains, major earthquakes, and extensive volcanism, but does have a few active volcanoes. EQUIPMENT AND MATERIALS Necessary materials include rock samples of all three types, a map of Antarctica with the Expedition route and major geologic features on it, and a map of Gondwana available in the supplementary package. EXPLORATION/ ASSESSMENT OF PRIOR KNOWLEDGE This is a two part activity designed to stimulate student interest in the topic and provide an indication of the students' prior knowledge of the topic. The information is important for determining the starting point and level of difficulty for the instruction. Begin this module by asking of the class if any students knows anything about the geology of Antarctica. Oral responses most likely will be few, if any. Then, have the students observe an igneous rock, a sedimentary rock, and a metamorphic rock and speculate regarding how they were formed. The students will need to have some knowledge of basic rocks and rock types in order to understand these lessons. They should also be familiar with the basics of Plate Tectonics Theory (like mountain building, rifting, continental movement). CONCEPT INVENTION ACTIVITY There are two parts to the concept invention activity. The first will help the students understand the basic geologic regions of Antarctica. The second activity will introduce students to the basic rock types found in these regions. Part A: Hand out copies of the map of Gondwana with the blank Antarctica among the other continents. Instruct the students to fill in the general geologic features they would find in Antarctica if there was no ice covering the land. They should be instructed to include at least the shield area of East Antarctica, the Transantarctic Mountain Range, and the more mountainous areas of West Antarctica. Part B: This activity works with the rocks found in the different areas of Antarctica. Divide the room into an east area and a west area. In the east area place on perhaps four desks or tables the rocks typical of East Antarctica. These would include gneiss, schist, granitics, and sedimentary rocks. Inform the students that this area is now relatively flat. In the center, place four sets of rocks representing the Transantarctic Mountain Range: sedimentary rocks like sandstone, shale, and limestone. On the west, part put rocks for the newer additions to the continent: quartzite, marble, andesite, basalt, slate, and granite. Inform the students that these rocks also represent a land with mountains in it. Label the three groups for age. The east is Precambian, the mountain range is early Paleozoic, and the west is late Mesozoic and early Cenozoic. Assign small groups of two or three students to one of the sets of rocks in the three regions. The students at each location are then to: 1-Identify the rocks by type, if possible, by name. 2-Interpret how each area was formed in terms of geologic processes like sedimentation or tectonic events such a volcanism or metamorphism. 3-Write a brief geologic story of how their part of Antarctica was formed. Then have one small group from each region meet together to develop a "complete" story of how the entire continent formed. The story should end up including the formation of the East Antarctic shield 1 to 3 billion years ago, the formation of the Transantarctic Mountains from plate collisions about 500 million years ago, and the growth of West Antarctica by microplate collisions from 200 to 40 million years ago. APPLICATION ACTIVITIES Select one or more of these activities to provide students practice applying their new knowledge. I-Using a map of the Expedition's route, put out rock samples that represent the land under the ice along the route. (This activity can also be done without rock samples if none are available. Simply use the names of the rocks in place of actual samples.) Have the students identify the rocks and interpret the geologic story of the land under the route. This can be done all at once or place by place as the Expedition progresses. Location 1 - Antarctic Peninsula Rocks: new basalt and 60 to 80 million year old slate and andesite. Location 2 - Ellsworth and Transantarctic Mountains Rocks: 190 million year old quartzite and granite and 500 million year old sandstone, shale, and limestone Location 3 - South Pole and eastward to the coast Rocks: 1 to 3.5 billion year old gneiss, granites, and sandstone. Then have the students: 1-Identify the rocks at the 3 locations. 2-Write a short description of how the rocks probably formed. 3-Given the ages and rock types, write a short geologic story of the land under the Trans-Antarctica Expedition's route. II-Hand out a classroom "map" with the relatively flat east, mountain range center, and mountainous west areas marked. The students should then follow these instructions: 1-Fill in the rock names in the areas shown on the "map." 2-Write a short description for each area telling how the rocks probably formed. 3-Taking the rock/area ages into account, write a geologic story of this area (Antarctica). Be sure to include all geologic events and rock-forming processes. EVALUATION MULTIPLE CHOICE: 1-The geology of East Antarctica is best described as: a. A young sedimentary basin b. An old mountainous region c. An elevated plateau, relatively young d. An old continental shield 2-The geology of West Antarctica is best described as: a. A mountainous area made of small additions to the continent b. An old continental shield c. A young sedimentary basin d. An area built from nothing but volcanoes 3-Limestones and shales in the Transantarctic Mountains indicate that the rocks of these mountains: a. Were once part of an ocean floor b. Came from volcanoes c. Were changed due to heat and pressure d. Were once part of a great desert 4-Basalt rocks found on the Antarctic Peninsula tell us: a. That oceans once covered this area b. Volcanoes erupted here c. Deserts used to exist here d. That at one time rivers flowed in this area 5-Very old gneiss and schist in East Antarctica tell us: a. That this area experienced metamorphism long ago b. That volcanoes were once here c. That glaciers have been here long ago also d. That oceans covered this area in the past SHORT ESSAYS 1-What does the fact that West Antarctica has mountain ranges built up over the last 500 million years mean? 2-How do the geology and geologic history of East and West Antarctica differ?