Exploring Oceans and Continents: A Hands-On Lab Guide

1 Laboratory Exercise 7: Oceans and Continents The surface of Earth has changed repeatedly across geologic time. In this course, we discussed the present continental configuration and how it is constantly changing as plate tectonics moves lithospheric plates. With modern satellites, we can measure the rate of continent movement and predict how the surface of Earth will appear in 100,000 years or 10 million years. In this laboratory exercise we will explore the present continental configuration, visit important surface features related to plate interaction including mid-oceanic ridges, deep sea trenches, and rifts. Additionally, we will also visit continental configurations in the geologic past and see how these formed prominent geologic features on Earth’s surface. Learning Objectives After you have completed this laboratory exercise, you should be able to: 1. Identify the oceans on Earth and understand when and how they formed. 2. Recognize features on the ocean floor and continents and infer the plate tectonic processes that formed them. 3. Name supercontinents in the geologic past and relate how the formation and breakup of these land masses formed features we see today on Earth’s surface. 4. Understand that Earth’s surface is dynamic and that future continental configurations and oceans could be quite different than they are today. Exercise A: As We Are: Features of Present Oceans and Seas The surface of Earth is fascinating. If we removed water from the oceans, we would see mountains, broad flat abyssal plains, deep valleys or trenches that mark zones of subduction and tall volcanic mountains. These features all result from plate tectonics. The largest mountains on Earth in height above the surrounding plains, are the shield volcanoes that make up the island Hawaii. These shield volcanoes formed where the Pacific Plate is moving over a hot spot. If the Pacific Plate were not moving, these mountains might have reached a size closer to that of Olympus Mons on Mars. If we use Google Earth to view our planet from an eye altitude of 5000 miles, we can see the Hawaiian Islands, the range of undersea mountains (seamounts) extending northward from the Hawaiian Islands and far to the north, trenches where the Pacific Plate is subducting (Figure 1). In this laboratory assignment, we will use Google Earth and accompanying images from our textbook to visit and identify features beneath oceans and seas. Remember to use the zoom bar on the Google Earth image to zoom out to an eye altitude that allows the feature or interest to be viewed in context of its surroundings. Figures 2a and 2b are from the text and show these features labeled.

2 Figure 1. Google Earth image of portion of the northern Pacific Ocean showing the Hawaiian Islands, Emperor Seamounts and Kuril and Aleutian trenches. Eye altitude is approximately 5000 miles . Topographic features are vertically exaggerated to make them more conspicuous.

3 Figure 2a. Prominent features for the seafloor and adjoining landmasses, Pacific Rim. Note that these features are vertically exaggerated, making them appear steeper and more obvious to the viewer. Part of Figure 13.7 from Tarbuck et al., 15 th ed.

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4 Figure 2b. Prominent features of the seafloor and adjacent landmasses, Atlantic and Indian oceans. Note that these features are vertically exaggerated, making them appear steeper and more obvious to the viewer. Part of Figure 13.7 from Tarbuck et al., 15 th ed. Using Google Earth, visit the following modern oceans and seas and identify geologic features on the present ocean floor. These may include mid-oceanic ridges, rift zones, seamounts, trenches, continental shelves and transform faults. Zoom out to an eye altitude of >3000 miles and use Figure 2 to help identify specific features. 1. Latitude: -9.853147 Longitude: 66.798911. Feature Mid-Ocean Ridge 2. Latitude: 35.31 Longitude: 142.04. Feature Trench

5 3. Latitude: -10.996406 Longitude: -79.597464. Feature Trench 4. Latitude: 17.864369 Longitude: 40.1587. Feature Rift Zone 5. Latitude: -22.56 Longitude: -174.79. Feature Trench 6. Latitude: -50.46 Longitude: 170.79. Feature Continental Shelf 7. Latitude: -7.05 Longitude: -102.74. Feature Seamounts 8. Latitude: 52.793786 Longitude: -164.328653. Feature Trench 9. Latitude: 24.891911 Longitude: -167.970694. Feature Seamounts 10. Latitude: 44.723681 Longitude: -28.233742. Feature Transform Fault Exercise B: Supercontinents of the Past Supercontinents form when continental plates collect in the same approximate location on Earth’s surface. Supercontinents occurred deep in Earth’s history, but in this laboratory exercise only three are considered. The oldest supercontinent we are concerned with formed approximately 1.8 billion years ago and is called Columbia or Nuna (Figure 3). Columbia lasted until around 1.35 billion years ago, when it broke apart. The second supercontinent we will consider is Rodinia that existed from 1,130 to 750 million years ago (Figure 3). Starting around 500 million years ago, a large landmass called Gondwana (Figure 4) contained most of the continen tal tectonic plates that were to become Earth’s present southern hemisphere continents. Gondwana and the remaining continents slowly assembled (Figure 4) to form Pangaea that existed from approximately 336 to 173 million years ago.

6 A B Figure 3. Supercontinents before the formation of Pangaea. A. Supercontinent Rodinia as it is believed to have looked approximately 900 million years ago. B. Supercontinent Columbia or Nuna as it is hypothesized to have looked some 1.45 billion years ago. (A. Ohio University; B. Meet and Santosh, 2017)

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7 Figure 4. Migration of continents and assembly of the supercontinent Pangaea during the Late Paleozoic. Figure 12.16 from Tarbuck et al., 15 th ed. B.1. Configuration of Continents Effect on Diversity of Life in Oceans The highest diversity of lifeforms in present and past oceans is/was found in shallow, warm seas of continental shelves. Modern shallow seas are known for coral reefs, lagoons, estuaries and other well- oxygenated water settings that teem with life. Life has adapted to live in all oceanic environments, including adjacent to hot smokers along mid-oceanic ridges where sunlight never penetrates, but by far, the greatest biodiversity is found at or near the ocean surface and in shallow water. With this in mind, when we search for fossils in rocks, we look for rocks that formed from sediment deposited in shallow water. Two examples of rocks from Oklahoma are shown in figures 5 and 6.

8 Figure 5 is a photograph of limestone formed in shallow water. Note the abundance of shells that make up this rock. In contrast, examine the rock shown in Figure 6. This rock is composed almost entirely of small fragments of quartz and clay minerals that accumulated in deeper water. The first thing you will notice is the absence of large fossils in Figure 6. This rock contains microscopic fossils of planktonic organisms that lived near the surface of the ocean. When these organisms died, their shells settled in the mud on the ocean floor and preserved. Because of the depth of the water and a lack of oxygen, there were essentially no bottom dwelling animals living on the ocean floor. As a result, there are no sea shells observed in Figure 6. Figure 5. Lamp shells also known as the brachiopod, were bottom dwelling organisms that lived in shallow water of a well-oxygenated sea. Brachiopods attached themselves to objects on the seafloor or hard, partially lithified sediment.

9 Figure 6. Darker mud-rich rock called shale that formed in deeper ocean water. This rock contains only microfossils of planktonic organisms that lived in shallow water. When these organisms died, their shells accumulated in mud on the ocean floor. Bottom water lacked oxygen so no bottom dwelling organisms could thrive on the seafloor. The arrangement of the continents across geologic time (Figures 7-12) profoundly affected the diversity of life. When continents are spread apart as they presently are, there are more shallow water settings and a greater diversity of life. Furthermore, when continents are closer to the equator, water is warmer, life forms proliferate and tend to evolve quicker than when continents are close to the poles and seas are cooler. The impact of increasing diversity and the availability of settings that favor life forms resulted in geologic processes and the formation of rock types that impacted modern society. As an example, the 48 conterminous states of the United States, are underlain by thick limestone strata of Late Cambrian and Ordovician age. These rocks outcrop prominently in the Appalachian, Ozark, Arbuckle and Guadeloupian mountains as well other areas in North America. To understand why we have these extensive shallow-water limestone beds, all we need to do is look at Figures 7 and 8. The continent of Laurentia, which contains what we now know as North America was located on the equator during the Late Cambrian and Ordovician. In geologic circles the shallow water shelf of Laurentia, which is shown as light blue color in Figures 7 and 8 , is called the “Great North American Carbonate Bank.” Similarly, at different times in the geologic past including the Carboniferous (Figure 9) and the Cretaceous (Figure 11), vast coal deposits formed when continental configuration favored formation of swamps and bogs. Today in North America large swamps occur where the water table is high just landward of the coasts of Florida and Georgia. We know these huge swamps as the Everglades and

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10 Okefenokee. Smaller swamps occur across the southern United States in Louisiana, Alabama, Arkansas and Mississippi. Effects on Climate Most of the moisture that falls on continents comes from the oceans. When prevailing winds bring moisture ashore, precipitation typically increases. Likewise, the interior of continents can be dry if they are beyond reach of moisture-laden air. Often the center of a continent is dry because moisture is removed from the air before the air reaches the interior. This can be the result of mountains that force the air to rise and cool, causing precipitation, and generating rain shadows, or the location of a continent in an area dominated by subtropical high pressure. When individual continents collect to form supercontinents (Figure 10), the interiors of these supercontinents tend to be drier. This is evident in North America where the Carboniferous was apparently much wetter than the Permian and Triassic. By the Cretaceous, North America was wet again. Effect on Sea Level When continents collect to form supercontinents, sea level drops. More of the Earth’s surface is covered by deep ocean basins and the percentage of continental shelves and other shallow water setting decreases. Since all of the Earth’s spheres a re interrelated, it is apparent that the formation of supercontinents could have detrimental effects on the diversity of life and could contribute to mass extinctions. Figure 7. Configuration of continents during the Late Cambrian, 514 million years ago. Dark brown areas are mountains, lighter brown represents land, light blue represents shallow marine water and darker blue deep ocean. At this time, Laurentia (including modern N. America) is located on the equator where warm conditions favored proliferation of marine invertebrates and subsequent formation of shallow marine limestone.

11 Figure 8. Configuration of continents during the Middle Ordovician, 458 million years ago. Dark brown areas are mountains, lighter brown represents land, light blue represents shallow marine water and darker blue deep ocean. Laurentia (including modern N. America) remains on the equator and shallow marine limestone continued to form resulting in thick layers of limestone across much of North America. Figure 9. Configuration of continents during the Late Carboniferous or Pennsylvanian, 306 million years ago. Dark brown areas are mountains, lighter brown represents land, light blue represents shallow marine water and darker blue deep ocean. Light blue areas in Pangea and glaciation in Gondwana contributed to conditions suitable for the formation of swamps and peat bogs that formed the famous coal deposits in the United Kingdom and the United States.

12 Figure 10. Supercontinent Pangaea during the Late Permian, 265 million years ago. Dark brown areas are mountains, lighter brown represents land, light blue represents shallow marine water and darker blue deep ocean. Laurentia (including modern N. America) is now part of northern Pangaea and separated from Gondwana by the Central Pangaean Mountains. Arid conditions dominated North America with red beds and salt deposits in Oklahoma, Kansas and New Mexico. Shallow marine conditions in southern New Mexico and West Texas are now the reservoirs in the famous Permian Basin. Figure 11. Configuration of continents during the Late Cretaceous, 94 million years ago. Dark brown areas are mountains, lighter brown-land, light blue-shallow marine water and darker blue-deep ocean. North America is located in a more temperate climate north of the equator. Shallow seas in Mexico and southern USA are the teeming with life and thick limestones were formed. The Cretaceous interior seaway stretches from the arctic to the Atlantic Ocean. Besides limestone, peat bogs and swamps adjacent to the Cretaceous Interior Seaway form some of the largest coal deposits in the world. Extensive limestones formed across northern Africa.

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13 Figure 12. Breakup of Pangaea and migration of continents to their present positions. This slide summarizes the past 250 million years of Earth’s tectonic history and shows the transition from Pang aea to Gondwana and Laurasia to the 7 major continents today: North America, South America, Antarctica, Africa, Europe, Asia and Australia. Image courtesy of United States Geological Survey. B.1. What will happen in the future? Earth’s continents continue to move. We have followed the changing arrangements of the continents for the past 500 million years. What will happen in the future? The following video by Professor Scotese on future tectonic plate movement and continental configuration provides a science-based expectation of how the future surface of the Earth will look. To view the video, select the following link. http://youtu.be/cW6rMzSOmvU This video shows how computer modeling predicts the future arrangement of continents on the surface of the Earth. This model uses past continental configurations, present directions and rates of plate movement and our understanding of tectonic processes to predict future plate movement. In this case, the application of

14 uniformitarianism is not limited to interpreting the past, but is also integrated with geologic history to predict future plate movement. With the video active, answer the following questions about the future of Earth. 1. The Alps in Europe formed when Africa collided with Europe some 30 million years ago. When is the Mediterranean Sea expected to close again and Africa collide with Europe? a. 10 million years b. 25 million years c. 50 million years d. 100 million years 2. In approximately 100 million years from now, this model predicts that most of North America will be Stretched to the left. 3. The new supercontinent that is modeled to form some 250 million years from now is called Pangea Proxima 4. When is Australia expected to collide with Southeast Asia? a. 20 million years b. 50 million years c. 75 million years d. 100 million years 5. For the next 100 million years, do you expect the Himalaya Mountains to erode away or to keep growing? Please describe the evidence from the video that you used to make your prediction. Prediction: Keep Growing. Evidence: The plates around the Himalayas are still converging which will continue mountain growth 6. During the assembly of Pangea, the continent we know as Africa collided with what is now North America to form the Appalachian Mountains. Based on the model, when is Africa expected to again collide with North America? a. 120 million years b. 150 million years c. 175 million years d. 225 million years B.2. Mass Extinctions in Geologic History Mass extinctions have drastically impacted biodiversity across geologic time. The mass extinction most familiar to the general public is the K-T extinction (Figure 13) around 66 million years ago (Figure 14, #5) that caused the demise of the land-bound dinosaurs. This extinction is attributed to the collision of an asteroid and Earth that altered the atmosphere, caused extreme climate change and according to some hypotheses, generated fires that burned the dinosaurs. Other mass extinctions are attributed to extremely voluminous volcanic eruptions that changed the atmosphere sufficiently to extinguish many life forms.

15 Figure 13. Outcrop of the K-T boundary at Trinidad State Park near Trinidad, Colorado. Coin in image is a U.S. 25 cent piece (quarter) for scale. The most devastating mass extinction in terms of the percentages of both terrestrial and marine life forms affected occurred at the end of the Permian time period around 251 million years ago (Figure 14, #3). Some scientists hypothesize that this extinction event was exceptionally extreme because it occurred after the supercontinent Pangea was formed. Other prominent mass extinctions occurred at the end of the Ordovician Period about 440 million years ago (Figure 14, #1), the Late Devonian about 375 million years ago (Figure 14, #2), and end of the Triassic Period 200 million years ago (Figure 14, #4).

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16 Figure 14. Mass extinctions in the geologic past. C-Cambrian, O-Ordovician, S-Silurian, D-Devonian, M- Mississippian (Lower Carboniferous), P-Pennsylvanian (Upper Carboniferous), P-Permian, Tr-Triassic, J-Jurassic, C-Cretaceous, P-Paleogene, N-Neogene, and Q-Quaternary. Figure is from Tarbuck et al., 15 th ed. Using internet sources such as Encyclopedia Britannica ( www.britannica.com ), query extinction events and collect the information requested below. Review the 5 major mass extinctions shown in Figure 14 and the extinction that started approximately 11,000 years ago and continues today. 1. Mass extinction #1 occurred 444 million years ago. It is proposed to have been caused by the fall of sea level and carbon dioxide levels which triggered a global cooling and affected 85 percent of marine life forms. 2. Mass extinction #2 occurred 419.2- 359 million years ago. It is proposed to have been caused by Possible combination of excessive sedimentation, rapid global warming or cooling, a meteorite or comet, or massive runoff from continents. and affected 22 percent of marine life forms. 3. Mass extinction #3 occurred 299- 252 million years ago. It is proposed to have been caused by Disrupted nutrient cycles. and affected 95 percent of marine life forms and 70 percent of terrestrial. life forms.

17 4. Mass extinction #4 occurred 252-201 million years ago. It proposed to have been caused by Climate change and rising sea levels producing large amounts of CO2. and affected 76 percent of marine life forms and 20 percent of terrestrial life forms. 5. Mass extinction #5 occurred 66 million years ago. It proposed to have been caused by Possible disease, heat waves, freezing cold spells, egg eating mammals, or x-rays from a supernova. Also, possibly an asteroid. and affected 80 percent of life forms. 6. The current extinction started approximately 11 thousand years ago. It is believed to be caused by Climate change, disease, loss of habitat, and competition for resources. After completing this laboratory assignment, please submit it to Canvas or place a hard copy in Dr. Puckette’s mailbox in NRC 105. References Encyclopedia Britannica, 2018, www.britannica.com Meet, J.G., and M. Santosh, The Columbia Supercontinent revisited: Gondwana Research, v. 50, p. 67-83. Ohio University, 2018, www.ohio.edu/cas/geology/about/supercontinents.cfm

18 Scotese, C.R., 2014. Animation: Future Plate Motions & Proxima Pangea, PALEOMAP Project, Evanston, IL. http://youtu.be/cW6rMzSOmvU Tarbuck, Lutgens and Tasa, Earth Science, 15 th ed.

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Laboratory Exercise 7 Oceans and Continents

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