PART I: Our Island in Space |
| 1.1 | Wandering Planet |
| Earth, Mars, and Jupiter are shown in orbit around the Sun. Seen from an alternate geocentric perspective, Mars and Jupiter show retrograde motion as Earth overtakes them in orbit. A telescopic view shows moons in orbit around Jupiter, evidence used by Galileo to challenge the Ptolemaic belief that all heavenly bodies revolve around the Earth. [by Declan DePaor] |
| 1.2 | Pole Star |
| This animation shows how the stars move across the night sky as seen from various observation points on Earth. The "Trace View" presents a time-lapse image that tracks a representative sample of stars as they move around the North Star. [by Declan DePaor] |
| 1.3 | Doppler Effect |
| The everyday phenomenon examined here is an essential principle underlying the Hubble's Expanding Universe theory; one could say its application shed light on fundamental questions about changes to the size of the Universe over time. [by Declan DePaor] |
| 1.4 | Red Shift |
| This animation demonstrates the Doppler effect as applied to light by simulating the effect of a star's velocity upon the starlight as viewed from Earth. Use the horizontal scrollbar to change the star's velocity. Notice the red shift as the star recedes from you, and the blue shift as it moves toward you. The greater the star's speed, the greater the spectral shift. [by Declan DePaor] |
| 1.5 | Solar System Formation |
| This animation shows the collapse of a rotating dust cloud to form a solar system with a central star and orbiting planets. The angular velocity vector is yellow. Escape of light elements to the outer regions occurs immediately after the collapse phase.
[by Declan DePaor] |
| 2.1 | Mass of Earth Experiment |
| Sir Isaac Newton predicted that the gravitational attraction of a nearby mountain would deflect a plumb bob from its vertical position. In 1772 Nevil Maskelyne proposed to calculate the mass of the Earth by measuring this deflection. His experiment, which provided a first reasonable estimate of Earth's mass, is shown here.
[by Declan DePaor] |
| 3.1 | Wegener–Continental Drift |
| This animation presents a view of the continents at the level of map precision available to Alfred Wegener, who proposed that the continents once existed as a vast supercontinent, Pangea, that later fragmented. Test the fit of the continents for yourself by clicking and dragging a continent to a new location; then, using the arrow keys on your keyboard, rotate the continent into position.
[by Declan DePaor] |
| 3.2 | Bullard Fit of Continents |
| The Bullard fit animation of Continental Drift includes the continental shelves and shows how Africa, South America, Europe and North America may have once fit together.
[by Declan DePaor] |
| 3.3 | Magnetic Reversals |
| The polarity of Earth's magnetic field reverses with time. The main figure demonstrates how sea-floor anomalies, also known as magnetic stripes, develop during sea-floor spreading. The inset image records the reversal of Earth's dipole.
[by Declan DePaor] |
| 3.4 | Wandering Poles or Drifting Continents? |
| This animation compares true versus apparent change in the orientation of Earth's magnetic field, and explains how the apparent globe-wandering path of the magnetic poles can be explained as a product of continental drift.
[by Declan DePaor] |
| 3.5 | Sea Floor Spreading |
| This animation shows progressive stages in the opening of the Atlantic Ocean. The youngest rocks (in red) clearly outline the mid-ocean ridge system, complete with transform faults. The oldest ocean crust (in blue), is confined to offshore regions adjacent to the United States, Canada and western Africa. This distribution demonstrates that the North Atlantic began to open before the South Atlantic.
[by Declan DePaor] |
| 4.1 | Basic Plate Boundaries |
| Geologists define three types of plate boundary, based simply on the relative motions of the plates on either side of the boundary. These basic types-divergent, convergent, and transform plate boundaries–are shown in the following three-part animation.
[by Stephen Marshak] |
| 4.2 | Formation of Ocean Crust |
| Formation of Ocean Crust Oceanic crust forms around and above a steady-state magma chamber. As the animation progresses, gabbro forms on the sides, dikes form above, and pillows form at the Earth's surface. Note that although the ridge maintains a consistent size and shape, the sea-floor grows wider.
[by Stephen Marshak] |
| 4.3 | Transform Faulting |
| This animation shows the development of a transform fault along a divergent plate boundary. Plates slide past one another along a transform fault without the formation of new plate or the consumption of old plate. As this process occurs, new sea floor forms along the mid ocean ridge.
[by Stephen Marshak] |
| 4.4 | The Process of Subduction |
| At convergent plate boundaries or convergent margins, two plates, at least one of which is oceanic, move toward each other. But rather than butting each other like angry rams, one oceanic plate bends and begins to sink down into the asthenosphere beneath the other plate. This sinking process, termed subduction, is shown in the following animation.
[by Stephen Marshak] |
| 4.5 | Hot Spot Volcanoes |
| This animation shows how hot spot volcanoes arise. A mantle plume beneath an oceanic plate creates a hot spot at the base of the lithosphere, and a volcano forms. Because the hot spot remains fixed as the plate moves over it, this volcano eventually becomes extinct and a new one forms. In time, a chain of extinct volcanoes develops, with a live volcano over the hot spot as the last link in the chain.
[by Stephen Marshak] |
| 4.6 | The Process of Rifting |
| Rifting is the process by which a continent splits and separates to form a new divergent boundary. This animation shows the progressive formation and evolution of a continental rift, and the formation of a mid-ocean ridge.
[by Stephen Marshak] |
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| PART II: Earth Materials |
| 5.1 | Mineral Growth |
| Minerals grow outward from a central seed to fill the available space; their shape is controlled by the shape of their surroundings. After the animation is complete, click and drag each crystal to reveal its individual shape.
[by Stephen Marshak] |
| 5.2 | Crystallization |
| This animation shows the progressive growth and interlocking of mineral crystals as they cool from a melt. It illustrates how some minerals interfere with the growth of other crystals.
[by Declan DePaor] |
| 6.1 | Formation of Igneous rocks at Mid-Ocean Ridges |
| Igneous magmas form at mid-ocean ridges because of decompression melting of the rising asthenosphere. As you saw in Chapter 2, magma rises into the crust and pools in a magma chamber during sea-floor spreading. Some cools slowly along the margins of the magma chamber to form massive gabbro, while some intrudes upward to fill vertical cracks that appear as the newly formed crust splits apart. Magma that cools in the cracks creates basalt dikes, and magma that makes it to the sea floor extrudes as pillow basalt.
[by Stephen Marshak] |
| 7.1 | Formation of Cross Beds |
| When blowing sand builds into sand dunes in a desert, the sand tumbles up the windward side of the dune, and settles in quieter air on the leeward side. This animation shows how cross beds develop during the deposition of sediment.
[by Stephen Marshak] |
| 7.2 | Transgression and Regression |
| As sea level rises the coast migrates inland (transgression) and retreats seaward (regression), and a record of this movement is preserved in the strata of the sedimentary basin. View 1 shows how this sedimentary sequence is formed; View 2 examines a segment of the landscape millions of years later, after the land has been uplifted and erosion has occurred.
[by Stephen Marshak] |
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| PART III: Tectonic Activity of a Dynamic Planet |
| 10.1 | Types of Faults |
| This animation shows the differences between the three types of faults and illustrates how they are formed. View 1 shows a normal fault, View 2 shows a reverse fault, and View 3 shows a strike-slip fault.
[by Stephen Marshak] |
| 10.2 | Seismic Wave Motion |
| Seismologists distinguish between different types of seismic waves based on how they move, and whether they travel along the Earth's surface (surface waves) or pass through its interior (body waves). This animation shows two types of body wave motion: View 1 shows shear body waves (also called S-waves) and View 2 shows compressional body waves (P-waves).
[by Stephen Marshak] |
| 10.3 | How a Seismograph Works |
| Seismologists use two basic configurations of seismographs, one for measuring horizontal ground motion, like the one shown in this animation, and the other for measuring vertical ground motion. Both work on the principle of inertia as described by Newton's law, which states that an object at rest tends to remain at rest unless acted on by an outside force. Thus, during an earthquake, vibrations cause the frame of the seismograph to move. The pendulum apparatus remains fixed as the paper cylinder moves back and forth beneath it.
[by Stephen Marshak] |
| 11.1 | Process of Folding |
| Layers of rock can wrinkle or contort into a series of wave-like curves that geologists call folds. Not all folds look the same—some look like an arch, some like a tough, and some have other shapes. This animation examines how two types of folds are formed. View 1 illustrates the formation of a flexural-slip fold, and View 2 shows the formation of a passive-flow fold.
[by Stephen Marshak] |
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| PART IV: History Before History |
| 12.1 | Geologic History |
| A cross-section through the earth reveals the variety of geologic features. View 1 of this animation identifies a variety of geologic features; View 2 animates the sequence of events that produced these features, and demonstrates how geologists apply established principles to deduce geologic history.
[by Stephen Marshak] |
| 12.2 | Types of Unconformity |
| This animation shows the stages in the development of three main types of unconformity in cross-section, and explains how an incomplete succession of strata provides a record of Earth history. View 1 shows a disconformity, View 2 shows a nonconformity and View 3 shows an angular unconformity.
[by Stephen Marshak] |
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| PART V: Earth Resources |
| 14.1 | Oil Formation and Trapping |
| This animation shows the successive stages in the formation of an oil reserve. In View 1, organic material settles, is buried, and is transformed by heat and pressure into oil. In View 2 an oil trap is formed: the area folds into an anticline, and oil migrates and accumulates in the anticline crest.
[by Stephen Marshak] |
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| PART VI: Processes and Problems at Earth's Surface |
| 17.1 | Evolution of a Mean dering Stream |
| People building communities along a riverbank mistakenly assume that the shape of a meandering stream will remain fixed for a long time. In fact, in a natural meandering river system, the river channel migrates back and forth across the floodplain. View 1 illustrates the processes of erosion and deposition, and View 2 shows the evolution, in map view, of a meandering stream.
[by Stephen Marshak] |
| 18.1 | Tides |
| Ocean tides vary during the Lunar month according to the combined influences of the Sun and Moon. In this animation the viewpoint is fixed relative to the Earth, and so the Sun and Moon appear to orbit clockwise. The Sun is much more massive than the Moon, but is also much further away. Thus, its gravitational pull (yellow arrow) is only about half that of the Moon (gray arrow). Note the new moon (top, right) and spring tide (left) at the start of the month. As the month proceeds, the Sun's apparent motion is faster than the Moon's. Thus the Moon's gravitational pull lags behind that of the Sun, leading to a neap tide after 7 days. On day 14, the Moon is opposite the Sun, resulting in a full moon.
[by Declan DePaor] |
| 22.1 | Glacial Advance and Retreat |
| Glacial advance and retreat is determined by the balance between the accumulation of snow and the removal of ice by sublimation, melting, and calving (ablation). When the rate of ablation below the snowline equals the rate of accumulation above it, the glacier is stationary, as in View 1. During glacial retreat, View 2, the rate of ablation exceeds the rate of accumulation, and the position of the toe retreats toward the origin of the glacier. Glacial advance, View 3, occurs when the rate of accumulation exceeds the rate of ablation. For all views, pay attention to the motion of the stones. Note that in all cases, ice flows downhill.
[by Stephen Marshak] |
| 22.2 | Milankovitch Cycles |
| Why do glaciers advance and retreat periodically during an ice age? In 1920, Mulutin Milankovitch showed that regular variations in the shape of Earth's orbit and the orientation of its axis create variations of solar intensity at high latitudes: warm summers in which glaciers retreat, and cool summers when they advance. These climate cycles, called Milankovitch Cycles, are determined by three factors: orbital eccentricity, shown in View 1, changes in the tilt of Earth's axis, View 2, and the precession of Earth's axis, View 3.
[by Stephen Marshak] |
| 23.1 | Snowball Earth |
| The Snowball Earth Hypothesis proposes that during an ice age 900 mya, the entire land and oceanic surface the Earth was covered by ice. This animation shows four proposed stages to the formation and destruction of Snowball Earth conditions:
•During "normal" climate periods there are ice caps at the poles; sea level rises and falls.
•During "metastable" climate times ice sheets expand and contract dramatically.
"Runaway snowball" conditions develop and ice nearly envelopes the Earth; atmospheric carbon dioxide is not absorbed by the frozen ocean.
The rising concentration of unabsorbed carbon dioxide gas leads to a "runaway greenhouse effect"; Earth warms and the ice shell rapidly vanishes.
[by Declan DePaor] |
