Questions:Modeling of Earth's Interior
Base your answers to questions 1 through 6 on the information below and on your knowledge of Earth and Space Sciences.
Modeling Earth's Interior
While other planets experience tectonic deformation in the form of volcanic activity, Earth is the only planet currently known to exhibit active plate tectonics involving multiple plates. To gain a better understanding of Earth’s interior, scientists have developed models using seismic waves, rock samples, and laboratory experiments. These models assist scientists in the visualization of Earth’s complex interior and crustal dynamics.
Conditions within Earth’s interior cause different substances to be found at different depths. The table below shows regions within Earth’s interior where some substances are found.
| Region (depths) | Substances |
|---|---|
| inner core (6371-5150 km) | solid, stable iron |
| outer core (5150-2891 km) | liquid iron |
| lower mantle (2891-670 km) | magnesium and iron-bearing silicon |
| transition zone (670-410 km) | structures with both SiO4 and SiO6 groups (e.g. majorite garnet) |
| upper mantle (410-40 km) | olivine, pyroxene, garnet, spinel |
| crust (average depth 40 km) | feldspar, quartz |
The graph below shows some information about the velocity of seismic waves as the waves travel through Earth's Interior
1. Which row in the table below correctly describes the substance(s) found in Earth's interior and the characteristic of that interior layer of Earth?
| Row | Substance(s) in Earth's Interior | Characteristics of Earth's Interior |
|---|---|---|
| A | liquid iron | found in a layer where compressional velocity is greatest in Earth's interior |
| B | solid, stable iron | found in a layer where compressional wave velocity is approximately 11.2 km/sec |
| C | pyroxene and quartz | found only at a depth of 500 kilometers |
| D | magniesium silicates | found in a layer where shear wave velocity is greater than compressional wave velocity |
- Row A
- Row B
- Row C
- Row D
2. Seismic wave information was used by scientists to infer the depth of Earth's interior layers and the states of matter found in these layers. For each piece of evidence (A and B) below, place an X into the appropriate box to indicate the characteristic that can be inferred and explain how this evidence changes and is used to determine this characteristic. [1]
| Evidence from Graph | Characteristic's of Earth's Interior Layers | ||
| Change in Density | Change in Magnetism | ||
| A Sudden change in velocity | |||
Explanation 1: ___________________________________________________________________________________ ___________________________________________________________________________________ ___________________________________________________________________________________ |
|||
| Depth | State of Matter | ||
| B Presence of certain types of seismic waves | |||
Explanation 2: ___________________________________________________________________________________ ___________________________________________________________________________________ ___________________________________________________________________________________ |
|||
Techtonic processes are responsible for the formation of many types of rocks and minerals found on Earth. The model below shows some information about different tectonic plate interactions found on and below Earth's surface.
All models of Earth's interior depend on indirect evidence. These models predict the sources of heat in Earth's interior. The substances found in the different layers of Earth's interior determine the possible source of heat in each layer. The core contains elements that "like to be with iron", but the mantle and crust contain "rock-loving" elements. These elements are the source of rock-forming minerals of the Earth's crust. Uranium, thorium, and potassium are unstable isotopes that are examples of these "rock-loving" elements.
3. Which statement correctly describes a source of heat within Earth's interior?
- Radioactive isotopes in Earth's interior decay in the mantle and crust, further driving convection currents that cycle materials.
- Radioactive activity in the mantle and crust helps to cycle materials into Earth's inner core and asthenosphere.
- Radioactive elements in Earth's interior decay, cycling materials in convection currents only within Earth's crust.
- Radioactive isotopes in Earth's interior decay, cycling materials in convection currents formed in the mantle and asthenosphere.
The model below represents processes involved in rock formation. Tectonic processes labeled A and B are missing.
4. Using evidence from the Earth's Surface and Interior Model, complete the Rock Cycle Model by identifying one tectonic plate interaction that is responsible for the formation of each rock type indicated. [1]
Tectonic interaction A: ____________________________________________________________________
Tectonic interaction B: ____________________________________________________________________
Certain magnetic minerals in rocks can record the direction and intensity of Earth's magnetic field at the time they are formed. The direction of Earth's magnetic field has reversed several times during Earth's history. These reversals are recorded in the bedrock of the ocean floor.
The model below shows some information about the age and magnetic polarity of ocean floor bedrock along the Juan de Fuca ridge system.
5. Which statement correctly compares locations on the Juan de Fuca Ridge Model
- The basalt at location A is older than the basalt at location B
- A greater amount of outward flow of energy from Earth's interior occurs at location A than at location B
- The magnetic polarity of basalt at location A is the same as the magnetic polarity at location B
- The motion of the tectonic plate is from location B to location A
6. Describe how the pattern of magnetic field reversal of ocean floor basalt shown in the rocks on either side of the Juan de Fuca Ridge is evidence for convection currents in the mantle. [1]
___________________________________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
Answers
1. 2
2. Allow 1 credit for Change in Density as the characteristic for evidence 1, States of Matter for evidence 2, and appropriate explanations. Acceptable explanations include, but are not limited to:
Explanation 1:
- The velocity of seismic waves change as the waves travel from a less dense layer to a more dense layer
- The transition from one Earth layer to another is associated with an increase in density, and this is where a sudden change in velocity occurs.
Explanation 2:
- Shear waves cannot travel through a liquid, but can travel through a solid. The
presence of sheer waves indicates the state of matter of that layer.
- The outer core is a liquid and shear waves do not travel through a liquid. The state
of matter of an Earth layer affects the presence of the type of seismic wave.
3. 4
4. Allow 1 credit for both tectonic plate interactions. Acceptable responses include, but are not limited to:
Tectonic interaction A:
- continental convergence
- convergence of two tectonic plates
- subduction of one plate under another plate
Tectonic interaction B:
- rifting/divergence along ridge
- sea-floor spreading (at mid-ocean ridge)
- rising magma above a hot spot (creating an island arc)
5. 2
6. Allow 1 credit. Acceptable responses include, but are not limited to:
- Convection currents cause rising magma to reach the surface, solidify into rock with a certain magnetic polarity, and move away from the ridge, forming a mirror image
pattern on either side of the ridge.
- Convection currents cause magma to rise to the surface and form basalt, pushing the
older basalt with a different magnetic polarity away from either side of the ridge.
- Convection currents cycle materials at the ridge, pushing rocks further from both
sides of the ridge. The pattern of the magnetic field on each side of the ridge is a mirror image of the other.