by Kari Hetcher and Scott Hughes

Reading:  Chapter 9 in The New Solar System, 4th edition, review chapters 12 and 13

This is a pretty extensive module because it represents a review of material covered in an introductory geology course. Use this module to refresh your knowledge of how the Earth works. A lot of information was left out here, but most of it will come up again in other modules.


Module 4 Assignments:

First, answer the study questions identified in Tasks 1 through 4 below.

Then, for Task 5, write a short paragraph that outlines the basic concepts of global warming.

NOTE: While working through this module, you can view much larger, better quality images if you click on the smaller images. If you are using a dial-up browser, some may be slow to load, but worth the wait.

Introduction: A Planetary Perspective

Imagine an interstellar space traveler finding her way to our solar system. She approaches a medium sized, mid-life star, and counts eight planets (or is that nine?) rotating around it, plus a large number of moons rotating around the larger planets. The planetary bodies are of varying colors and sizes, but one strikes her as different in some way. It is a rather small rocky planet, the third one out from that star. It looks blue, green, and white from space, is continually changing, and its dark side twinkles with thousands of faint pinpoints of light. How unique and beautiful that planet is! The traveler has found the original home of Earthlings.

This incredible scenario of a space traveler conjures mental images of our own fascination with far-away mystical places. Indeed, the story may be fiction, yet we envision that it could be true someday -- to have our home planet rediscovered as a land of beauty, a unique dynamic world where internal and surficial processes are diverse, like so many other planetary bodies in the universe!

View two images of our home, planet Earth: (NOTE: One image is a photograph from space provided by NASA; the other one is a computer image modeled from global topography provided by NOAA.)

What geologic features can you immediately recognize from these images?

Check out more images at the JSC Digital Image Collection website.
For updated information on NASA programs and activities, visit NASA News and Features.

Internal and External (Surficial) Planetary Processes

The two pictures below illustrate internal AND external Earth processes. On the left is South Sister volcano in Oregon, which may erupt again someday in the not-too-distant future. The right picture is Mount St. Helens volcano in Washington viewed south into the well-known amphitheater crater created during an explosive eruption in 1980.  Both volcanoes are composite cones in the Cascade Range, a roughly north-south string of volcanoes parallel to the west coast of North America.  These volcanoes belong to a continental magmatic arc, which is the surface manifestation of a subduction zone caused by converging oceanic and continental lithospheric plates.

A lot can be learned about planetary geology from images such as these. Learn to recognize processes, and relate them to mechanisms that are responsible.  What is different about the evolutionary stages of these two volcanoes?  What can be inferred by their morphologic features?  What can be inferred about their relative surface ages?  Even the clouds tell you something about how these mountains evolve through time.

Much of what we know about the Earth as part of a planetary system has been discovered only in the past few centuries. We've come a long way from imagining the Earth as the center of the universe to understanding its meager position in the solar system. The pictures above of two Cascades volcanoes reminds us that we live on a dynamic planet. It is very much alive with internal and external activity. These mountains are composite volcanoes that rise above a platform of older volcanic rocks. They are part of a magmatic arc that is the surface manifestation of internal processes occurring many kilometers deep where crust and mantle interact with each other and higher temperatures and pressures prevail.

Click on the image to the right to see or download a rather large image of the Pacific Ocean topography from the NOAA National Geophysical Data Center.

There is no way that everything we know about the workings of our planet can be covered in this course, but think about the following topics and how they fit into our understanding of the formation of the Earth:

We will use examples from Earth in subsequent modules to evaluate these processes on other planetary bodies.


Birth Of The Earth

Most of what we know about the Earth's interior is derived from studies of rocks at the surface. Internal variations in compositional and physical properties are inferred from studies of other planets, seismic waves, and meteorites.

Composition refers to mineralogy, i.e. the types and abundances of minerals (which are used to classify rock types) and rock chemistry, i.e. the abundances of major-, minor-, and trace-elements, as well as certain compounds, such as H2O and CO2). Mineral and chemical compositions change from one region in the Earth to another.

Physical Properties = density, rheology (response to stresses), and states of matter (solid, liquid, gas). Physical properties also change from one region to another, although the changes do not always coincide with compositional changes.

Most geologists and geochemists believe that the bulk composition of the Earth is approximately chondritic. Planetary bodies in the Solar System accreted from, and are composed of, primordial Solar Nebula material represented by carbonaceous chondrites, which are meteorites comprised of early condensed solar grains and dust. Using isotopic dating (radiometric) techniques, geoscientists have determined the time since meteorites formed in the cooling solar nebula. These techniques yield an age of the Earth around 4.6 billion years old (4.6 x 109 years). In geochronological terms, this would be 4.6 Ga.

During the formation of the Solar System, the inner terrestrial planets formed in the hotter region close to the Sun, while giant gaseous Jovian planets formed in a cooler part of the solar nebula. Refer to Module Two for details. Earth’s average distance from the Sun (1 AU) is about 150 million kilometers (93 million miles), a distance favorable for terrestrial planet formation as well as for condensation of water-bearing minerals.

Accretion of chondritic material into the early planet Earth was followed by internal heating which caused differentiation. Light silicate minerals, such as feldspars and quartz, separated from the heavier metallic minerals and rose to the surface of the planet, eventually forming the continental crust and mantle. The denser materials sank to the center of the planet to form the iron-rich core. This scenario is much like that of the other inner planets which we believe are similarly differentiated.


Plate Tectonics

Answer the questions at the end of this section after visiting several Earth websites and reading about the interior of the Earth in these sites, your textbook and other available resources. You may want to locate an introductory geology textbook if you are not familiar with some of the terms and concepts in this module.

Many of the older geology professors today did not study plate tectonics in their college years because the idea was not yet accepted widely. By the same token, some of the processes we use to explain planetary features may be obsolete in a few years. However, this does not prevent us from exploring all possibilities, keeping our minds open, and learning what comprises our planetary system. To this end we use our home planet as a means of understanding planetary processes, albeit many are not easily recognized on other planetary bodies.

Our knowledge has grown considerably in the past three decades, and it is continually growing and changing. Much of what we know about Earth came from our travels to Earth orbit, and to the Moon during the Apollo missions. The photo of the Tibetan Plateau on Earth, taken from space, illustrates how geology as a planetary science suddenly emerged with space travel.

In 1915, Alfred Wegner, a German meteorologist and geophysicist published the book "Origin of Continents and Oceans" in which he proposed the idea of Continental Drift. His evidence included (1) the puzzle-like fit of South America and Africa, (2) evidence of former glaciers in the hot land of Australia, (3) similar fossils found on different continents, and, (4) similar rock structures and mountain ranges on different parts of the world.

Wegner proposed that a supercontinent called Pangaea (all land) once contained all the continents we now know, and that they began to split apart about 200 million years ago.

This idea was not well received. Who could imagine the continents floating along the planet? What could possibly cause this drift? In the past, people had wondered why there were mountains and huge oceans. Some folks thought that the Earth was once molten, so when it cooled it contracted and shrank leaving continents separated by gigantic chasms. The outer skin of the Earth responded like a piece of dried fruit, folding up and down to accommodate this shrinking. When you think about it, this was a pretty imaginative idea! Wegner also had to contend with strong opposition from religious leaders and the belief that the world was created in 4004 B.C., a date derived by Charles Usher from Biblical accounts of family trees.

Not until the 1950's and 60's did the theory of Plate Tectonics start to become widely believed and accepted. Detailed mapping of the ocean floor showed raised relief ridges that we know to be where oceanic crust is undergoing seafloor spreading. Work by Hess and Vine on magnetic 'stripes' of the ocean floor added credence to this idea by illustrating how magnetic polar reversals are recorded in basalts. Many concepts in geology now fit within the paradigm of plate tectonics. Thus, we have much evidence to show that continents moved around the planet, slowly but surely, slipping along three main types of plate boundaries.

 

Plate Boundaries – Review Figures 8 and 9, p. 118 in the textbook.

 

This figure, from the NASA Goddard Space Flight Center, shows plate boundaries in light blue, measured earthquakes in yellow dots, and recently active volcanoes in red triangles. Study it well in order to make associations of various tectonic regions with the features present in them.

TASK 1: Answer the Study Questions

HELPFUL LINKS

This Dynamic Earth: The Story of Plate Tectonics from the United States Geological Survey,an online book by Jacquelyne Kious and Robert I. Tilling

An Introduction to The ABC's of Plate Tectonic by Donald L. Blanchard

Plate Tectonics: Chemical and physical layers of the Earth, historical development of the theory, and descriptions of the location and types of plate boundaries from Volcano World at the University of North Dakota.


Volcanism

There are two main types of igneous rocks on the Earth: intrusive and extrusive (see Module 3, Planetary Evolution and Processes). Intrusive rocks are those that form as magma slowly cools inside the crust, producing large visible mineral crystals of quartz, feldspars, micas, or amphiboles, among others. Examples of igneous intrusive rocks are granites, diorites, and gabbros, named depending on their chemical and, especially, mineralogical compositions. Extrusive rocks are produced by volcanism; either the relatively quiet eruption of fluid magma forming lava flows, or by explosive volcanism that produces ash and cinder. Volcanic eruptions have played a significant part in the shaping of the Earth and have produced many dramatic features both here and on other planets.  Visit University of North Dakota's Volcano World site for everything you ever wanted to know about volcanoes, and what they tell us about earth processes.

Large igneous provinces on Earth are made of thick sequences of flood basalts such as the Columbia River Basalt of Washington, Idaho, and Oregon. Another example is the Deccan Traps of India.  They represent voluminous fissure eruptions of non-explosive fluid basaltic magma. Both resulted from heating and stretching of the lithosphere related to mantle plumes. These are similar to basaltic lava plains that make up the ancients surfaces of Mercury and the Moon. The closest Earth analog for lava plains-style volcanism is the Snake River Plain of Idaho.

Convergent plate boundaries tend to produce a very different type of volcanism. The magma is slightly more silicic than basalt magma, and more viscous, which causes more explosive volcanism. Generally, their compositions are andesitic or dacitic, which is intermediate between basaltic and rhyolitic. Composite or strato volcanoes, such as Mt. St. Helens in the Cascade Range result from this type of volcanism. They are usually found in magmatic arcs that run parallel to subduction zones.

Other features related to subduction zone volcanism include cinder cones, pyroclastic flows, collapsed calderas, and lahars.

TASK 2:  Volcano study questions

  • Name at least three important types of volcanic features found on other planets.
  • Why are there volcanoes on Mars that are so much larger than those on the Earth?
  • What are Large Igneous Provinces?  Name two of them.  Why are Large Igneous Provinces important?
  • Name the major types of volcanoes and give examples and locations of each type.
  • HELPFUL LINKS

  • Volcano World - Everything you want to know about all kinds of volcanoes, and the structures they create.  From the University of North Dakota.
  • Mount St. Helens: K-8 stories - http://volcano.und.nodak.edu/vwdocs/kids/stories/MtStHelens.html
  • K-12 activities- http://volcano.und.nodak.edu/vwdocs/vwlessons/rocks_activities.html
  • Pinatubo- http://volcano.und.nodak.edu/vwdocs/volc_images/img_pinatubo.html
  • Deadly Eruptions- http://volcano.und.nodak.edu/vwdocs/vw.hyperexchange/deadly_volcs.html
  • Cinder Cone Activities- http://volcano.und.nodak.edu/vwdocs/vwlessons/landforms/land_activities.html
  • Volcano Observatories and Organizations

  • How Volcanoes Work (Vic Camp, UCSD)
  • Hawaii Volcano Observatory
  • Alaska Volcano Observatory
  • Cascades Volcano Observatory
  • Long Valley Caldera Observatory
  • Yellowstone Volcano Observatory
  • Vesuvius Volcano Observatory
  • World Organization of Volcano Observatories (WOVO) (UND site)
  • New Millennium Observatory (NeMO -- off the coast of Oregon)
  • U.S. Geological Survey Volcanoes Hazards Program
  • International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI)
  • American Geophysical Union -- Volcanology, Geochemistry and Petrology Section
  • Nordic Volcanological Institute, Iceland
  • Smithsonian Global Volcanism Network
  • University of Washington - Volcano Systems Center
  • Michigan Technological University Volcano Page

  • Fluvial Systems

    Fluvial features are those created by running water, including rivers, streams, and floods. The water either acts to erode the rocks and soil of the surface, or it deposits its load of sediment. Fluvial erosion forms various landforms on the Earth, as well as on Mars, including river channels and intricate valley systems. Stream erosion may act by the removal of soil, downcutting of stream channels, or by headward erosion of the valley, the shape of which depends on the gradient of the stream channel, the amount of discharge, and the stream load. Visit the Web Links on Rivers and Other Fluvial Processes to get an overview of these systems.

    Go to the Earth from Space website and investigate some famous rivers, such as the Nile, the Mississippi, and the Amazon.  This NASA site has views from space of cities, rivers, deserts, mountains, and many other features.

    We will not spend very much time on fluvial processes. A good understanding of them would require an entire course in geomorphology that focuses on rivers and streams. Althought they are very important on Earth, theya are not so important on other planets, except Mars.


    Eolian Systems

    Any planet that has an atmosphere will experience ongoing eolian activity, caused by the movement of gases (air) across the surface and the concomitant transport of fine-grained dust, silt and sand.

    Between 10 and 30 North and South of the Equator lie some of the most spectacular deserts on Earth. The Moenkopi Plateau is being extensively studied by the USGS. The process of wind transport and deposition of sand have produced unique and interesting landforms, some of which can also be seen on Mars.  Go to Wind Processes and Landforms for discussion, video and more about eolian systems.

    Read about all these landforms and understand them: Chapter 8 from Geomorphology from Space should help in visualizing eolian landforms:

    TASK 3: Eolian Questions

      Mars Exploration from Jet Propulsion Laboratories might be helpful.


    Glaciation

    Continental ice sheets have advanced and retreated over the planet several times. Several factors influence the cyles of ice ages, such as the tilt and precession of Earth’s rotational axis. The most recent large advance of the glaciers was approximately 20,000 years ago, which left behind many glacial landforms across the United States and Canada. An example of a current continental glacial system is the Antarctic ice sheet. Visit the National Snow and Ice Data Center to learn more about Antarctica and other snow and ice environments.  Alpine glaciation can be seen at Grand Plateau, Mt. Cook, New Zealand, from the Glacial Geology at the University of Cincinnati homepage.

    TASK 4: Glaciation study questions

    Look up and define the glacial features listed below. Start at the Glacier Question Page from NSIDC, then visit the Illustrated Glossary of Alpine Glacial Landforms from the University of Wisconsin-Stevens Point.

    For more glacial geology, take some virtual field trips or visit these websites:

    Glacial dams have been known to block large amounts of water behind them. When the ice finally begins to melt, or the excess water builds up behind the dam, causing a catastrophic glacial flood. Evidence of flooding of this magnitude can be seen in the Channeled Scabland.topography of eastern Washington. Steep walls, giant ripple marks, dry waterfalls, cataracts, and huge boulders can be seen along the flood path.  Another type of glacial flood is called a jokulhaup, which often occurs in Iceland during volcanic eruptive periods.


    The Atmosphere

    Photos courtesy of Los Alamos National Laboratory

    osei_logo.jpg (19423 bytes)

    Visit the National Oceanic and Atmospheric Administration for links to many atmosphere resources. Copy of NLOG.jpg (2937 bytes)

    Visit NOAA/OSEI"s Image of the Day to see fascinating photos of significant atmospheric events and find links to many weather, oceanic, and atmospheric research sites. Visit the OSEI homepage from NOAA/Operational Significant Events Imagery to see various images of significant weather and atmospheric events.


    Remember that Earth is a dynamic, living planet.

    Historical geology is the branch of geology that researches how the Earth and all of its systems have changed through time. Early Earth was not much like our home today. The atmosphere was dominantly hydrogen (H) and helium (He) and the planet was being bombarded with asteroids and meteorites. Hydrogen and helium are the most abundant gases in the universe, but probably escaped from the atmosphere into space because they are also the lightest elements.

    As the first couple of million years passed after the birth of the Earth, a second, more dense atmosphere began to develop. This atmosphere was formed by the constant outpouring of gases from the Earth's interior through volcanic eruptions, known as outgassing.

    Volcanism released water vapor, CO2, and some Nitrogen (N2), which led to the formation of the rivers and lakes, and oceans of the world. Note how strikingly different the presence of water has made our planet compared to others. Eventually, through chemical and biological processes, much of the CO2 in the atmosphere became locked up in the carbonate rocks of the planet, and our atmosphere became rich in N2.

    The oxygen upon which we live became the second most abundant gas in our atmosphere through a slow process of photodissociation. This happens when the energetic rays from the sun split apart H2O molecules into Hydrogen and Oxygen. Since the Hydrogen is so light, it probably escaped out into space, leaving the Oxygen to accumulate in the juvenile atmosphere. After oxygen began to accumulate, primitive plants could have evolved. Once plant life appeared on the Earth, photosynthesis could occur which combines CO2 with H2O and sunlight to produce oxygen. This would have dramatically increased the oxygen content in the atmosphere and allowed life to flourish on our planet.

    Earth History websites for you to view:

    More Terms to Look Up and Understand - Many of these terms you will already know from introductory geology courses.

    core

    crust

    lithosphere

    oceanic crust

    biosphere

    stable platform

    subduction zone

    plate tectonics

    igneous

    silicic volcanism

    fluvial processes

    eolian systems

    loess

    ice shelves

     

    mantle

    hydrosphere

    magnetosphere

    mountain belts

    divergent

    island arc

    metamorphic

    composite volcano

    alluvial fan

    deflation basins

    glacial systems

    ice age

    sea ice

    Paleozoic

    shield

    batholith

    convergent

    isostacy

    sedimentary

    ice age

    karst

    blowouts

    continental glaciers

    ground ice

    Archean

    Mesozoic

    continental crust

    atmosphere

    basalt

    continental rift

    transform (strike-slip)

    mass extinction

    flood basalts|

    weathering

    sinkholes

    lag deposits

    thermokarst

    alpine glaciers

    continental glaciers

    permafrost

    Proterozoic

    Cenozoic

    Phanerozoic

     


    TASK 5. Global warming

    Recently, global warming has been a hot topic in the news. Your final task for this module is to examine this controversy using web sites, books, journals, papers on your own. Write one paragraph that briefly outlines (1) evidence both supporting and refuting the global warming hypothesis, and (2) why global warming is a major concern for scientists. If you can, list a couple of real Earth examples of why we should (or should not!) think about this problem.

    There is much evidence for and against global warming that is related to fluvial, eolian, glacial, and climatic processes.

    Here are some global warming websites for you to visit.


    This Is The End Of The Module

    Take a deep breath!  This is the biggest module, because Earth (our home sweet home) is the planet we know best.  When you have finished the work and e-mailed it in, pat yourself on the back for a job well done.

    Glossary

    Did you email your assignments???

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