MARC WARD/SHUTTERSTOCK

March 2, 2019

Earth’s Inner Core is Relatively Young

March 2, 2019 Earth’s Inner Core is Relatively Young

About this Guide Recent research suggests that Earth’s inner core began solidifying sometime after 565 million years ago, just in time to save the planet’s protective magnetic field from collapse and to kick-start it into its current, powerful phase. Use this Guide to introduce students to the history and current state of Earth’s magnetic field, the structure of Earth’s interior and concepts related to energy transfer, including thermal conduction and convection.

This Guide includes:

Article-based observation, Q&A — Students will answer questions based on the Science News article “Earth’s inner core is relatively young,” Readability: 12.4. Questions ask students to create a timeline for the history of Earth’s magnetic field, consider cause and effect in the creation of the current magnetic field and consider gaps in scientific knowledge. Another version of the article, “Earth’s core may have hardened just in time to save planet’s magnetic field,” Readability: 8.1, appears on Science News for Students.

Article-based observations, questions only — These questions are formatted so it’s easy to print them out as a worksheet.

Cross-curricular connections, Q&A — Use these diagramming prompts to encourage students to think through core concepts including Earth’s inner structure, the creation of a magnetic field and thermal convection. After creating diagrams of the core concepts and sharing those diagrams with the class, students can work together to determine how the core concepts come together to create a diagram of the geodynamo.

Cross-curricular connections, questions only — These questions are formatted so it’s easy to print them out as a worksheet.

March 2, 2019 Earth’s Inner Core is Relatively Young

Standards

Next Generation Science Common Core ELA

Motion and Stability: Forces and Interactions: HS-PS2-5

Reading Informational Text (RI): 1, 2, 4, 5, 7

Energy: HS-PS3-2, HS-PS3-3, HS-PS3-4, HS-PS3-5

Writing (W): 1, 2, 3, 4, 6, 7, 8, 9

Waves and Their Applications in Technologies for Information Transfer: HS-PS4-5

Speaking and Listening (SL): 1, 2, 4, 5, 6

Earth’s Systems: HS-ESS2-4 Reading for Literacy in Science and Technical Subjects (RST): 1, 2, 3, 4, 5, 7, 8, 9

Engineering Design: HS-ETS1-1, HS-ETS1-2, HS-ETS1-3

Writing Literacy in History/Social Studies and Science and Technical Subjects (WHST): 1, 2, 4, 7, 8, 9

March 2, 2019 Earth’s Inner Core is Relatively Young

Article-Based Observation, Q&A Directions: Ask students to answer question No. 1 by looking at only the headline of the article “Earth’s inner core is relatively young.” Then have students read the full article and answer the questions that follow.

1. Based on the headline alone, what terms or concepts do you expect to encounter in this article?

The headline reveals that the article is about the inner structure of the Earth and magnetic fields. Given these topics, I expect to read about the inner and outer core, and perhaps the mantle and crust. I expect to read about different types and temperatures of rock. Concepts I expect to encounter include energy and heat transfer, viscosity and convection, magnetism and magnetic poles.

2. Use the dates and time frames mentioned in the article to construct a timeline covering Earth’s history. Be sure to incorporate and/or note uncertainties.

4.54 billion years ago: Earth formed.

4.2 billion years ago: Clear signs of magnetic field.

2.5 billion to 500 million years ago: Previously proposed ages for the solidification of the inner core.

2 billion to 1 billion years ago: Core and mantle were still molten, assuming the new research is true.

900 million to 600 million years ago: Earth’s magnetic field was weak, according to simulations.

565 million years ago: Earth’s original magnetic field was on the point of collapse, according to the new research.

After 565 million years ago: Inner core solidified and geodynamo began.

3. The article distinguishes between the Earth’s original magnetic field and the magnetic field that exists today. Relate each of the fields to the Earth’s structure. How does what’s happening in the Earth drive the fields?

The original field resulted from heat within the planet driving circulation within the molten core. Today’s field results from the geodynamo, which is driven by the interplay between the solid inner core and molten outer core.

4. Describe what causes the ongoing circulation, called the geodynamo, at the center of the Earth. What phenomenon does the ongoing circulation generate?

Within the Earth, there is a solid inner core and a molten outer core, both composed mainly of iron and nickel, but there is not a hard line between the two. As material cools and crystallizes, it sinks toward the inner core. This crystallization affects the composition of the remaining fluid. More buoyant liquid rises and cooling liquid crystallizes to continue the process. This self-sustaining circulation is called the geodynamo and it generates a strong magnetic field with two opposing poles.

5. How do scientists gain clues to Earth’s past magnetic field? Name and explain the use of two techniques mentioned in the article.

Scientists look for traces of magnetism in ancient rocks and can gain clues to the intensity of the field and times when the magnetic poles switched. These clues come from “magnetic inclusions,” iron-rich grains that line up with the orientation of the magnetic field. Scientists also use computer simulations to gain clues to how circulation would have changed as the planet cooled.

6. Geophysicist Peter Olson says “all planets lose heat.” Name as many instances as you can where heat transfer is mentioned in the article.

In addition to Peter Olson’s mention: As the planet loses heat over time, it cools and its composition changes. The cooling of the inner core leads to crystallization at its center and the geodynamo. Heat-driven circulation within the early Earth’s molten core led to a magnetic field that weakened over time.

7. What gaps in knowledge still exist for scientists studying the history of the Earth’s inner structure and magnetic field?

Scientists don’t know for sure how long the period of a weak magnetic field might have lasted, and they don’t know how recently Earth’s inner core solidified, just that it was after 565 million years ago. Scientists also don’t know how to reconcile new findings with data from the rock record about how fast Earth cooled.

8. What data might help fill in those gaps?

More data from rocks with magnetic inclusions might fill in the time gaps from around a billion to two billions years ago, between 900,000 and 600,000 years ago and since then. Scientists might also look for rocks with magnetic inclusions from other areas of the globe to support or refute the evidence from Canada.

9. Based on the article, why is Earth’s magnetic field important to life on the planet?

Earth’s magnetic field protects it from solar winds, the charged particles constantly ejected by the sun.

March 2, 2019 Earth’s Inner Core is Relatively Young

Article-Based Observation, Q Directions: Answer question No. 1 by looking at only the headline of the article “Earth’s inner core is relatively young.” Then read the article and answer the questions that follow.

1. Based on the headline alone, what terms or concepts do you expect to encounter in this article?

2. Use the dates and time frames mentioned in the article to construct a timeline covering Earth’s history. Be sure to incorporate and/or note uncertainties.

3. The article distinguishes between the Earth’s original magnetic field and the magnetic field that exists today. Relate each of the fields to the Earth’s structure. How does what’s happening in the Earth drive the fields?

4. Describe what causes the ongoing circulation, called the geodynamo, at the center of the Earth. What phenomenon does the ongoing circulation generate?

5. How do scientists gain clues to Earth’s past magnetic field? Name and explain the use of two techniques mentioned in the article.

6. Geophysicist Peter Olson says “all planets lose heat.” Name as many instances as you can where heat transfer is mentioned in the article.

7. What gaps in knowledge still exist for scientists studying the history of the Earth’s inner structure and magnetic field?

8. What data might help fill in those gaps?

9. Based on the article, why is Earth’s magnetic field important to life on the planet?

March 2, 2019 Earth’s Inner Core is Relatively Young

Cross-Curricular Connections, Q&A

Directions for teachers: After students read “Earth’s inner core is relatively young,” have them create diagrams to explain core concepts including Earth’s inner structure, the creation of a magnetic field and thermal convection. After sharing those diagrams with the class, students can work together to create a class diagram of the geodynamo and answer the discussion questions provided.

Suggestion for structuring diagramming and discussion: Divide the class into five groups and review the five diagramming prompts listed below. Assign each group one prompt and allow students to do additional research as needed. You might want to assign specific roles to group members: a drawer, a writer, a presenter and so on. For a 60-minute class period, consider allowing about 20 minutes for each group to diagram the core concept and then 10 minutes for all of the group presentations. Then you can allow 20 minutes to create a class diagram of the geodynamo, with another 10 minutes to discuss the follow-up questions.

Notes to the teacher: Introduction to Geomagnetism by the U.S. Geological Survey is a useful background resource for information on the geodynamo.

Directions for students: The Science News article “Earth’s inner core is relatively young” explores how a change in the Earth’s inner structure created the relatively strong magnetic field that exists today. The concepts below all relate to the geodynamo, which sustains this magnetic field. Follow your teacher’s instructions to draw a diagram that explains one of the concepts. Be as detailed as possible and label your diagram appropriately.

Group prompts:

1. Creation of a magnetic field

Magnetic fields are generated by moving charged particles, or an electric current. As an electric current flows through a wire, magnetic field lines are formed in concentric circles perpendicular to the wire. In their diagram, students should indicate the direction of the magnetic field around the current flow. If the current is flowing in an upward direction through a wire perpendicular to a piece of paper, the magnetic field lines are drawn as concentric circles in the counterclockwise direction on the piece of paper.

2. Thermal convection (include the concept of density)

In thermal convection, heat is transferred through movement of materials in the liquid or gaseous state. As a material heats up from some outside heat source, its molecules get farther apart, which gives the material a lower density. Its lower density causes it to rise and move farther from the heat source. As it rises, cooler materials take its place near the heat source. Those cooler materials heat and rise. This movement creates a circular system of heat transfer known as a convection current. In their diagram, students should include a heat source and a visual representation of this circular system. Students should also show the changes in molecular spacing throughout the circular process.

3. Heat conduction (include the concept of thermal equilibrium)

In heat conduction, heat is transferred through contact between materials. Temperature is a measurement of the intensity or degree of heat present in a material. Heat energy is the result of molecular movement (vibrations, translations and rotations). When contact occurs between objects with different temperatures, heat energy is transferred between moving molecules until thermal equilibrium is met (both objects have the same temperature). In their diagram, students should indicate the temperature of two different substances before and after they are in contact. The initial temperature of one substance should be higher than the other, and once in contact, the higher temperature would decrease and the lower temperature would increase until the temperatures are the same (thermal equilibrium is met).

4. Crystallization (include the concept of heat transfer and use water as an example)

In crystallization, a liquid substance physically changes state to become a solid. As a liquid substance at its freezing point loses thermal energy, molecular motion slows and intermolecular attraction strengthens, which allows molecules to align themselves into a crystalline structure. In their diagram, students should show unorganized molecules of water in a liquid phase and the transition to an organized alignment of water molecules in the solid phase, as ice. Students should indicate the loss of heat energy during the process and show the increase of molecular attraction in the transition. The freezing point conditions should be noted and will remain the same before and after the phase change (for H2O, 0° C at 1 atm).

5. Earth’s inner structure (include composition and approximate depth ranges)

Earth’s inner structure is made up of the crust, mantle and core. The Earth’s crust can be one of two kinds: thinner crust under oceans and thicker crust under continents. The thinner, oceanic crust is made up of basalt and has a depth of about 8 km. The thicker, continental crust is made up of granite and has a depth of up to about 70 km.

The mantle is divided into the upper and lower mantle, which are primarily made up of silicate rocks. The upper mantle, closer to the surface, is up to about 700 km thick and the lower mantle is found between about 700 km and 2,800 km below the surface.

The Earth’s core is divided into the liquid outer core and the solid inner core, both primarily made up of iron and nickel. The outer core is from about 2,800 km below the surface to approximately 5,000 km deep, and the inner core is a sphere approximately 2,500 km wide.

In their diagrams, students should show a cross section of Earth with the correct placement and relative depths of all the components. Composition and depth information should be labeled.

Class prompts:

1. How do the individual diagrams inform the larger geodynamo process, as it is described in the article? How does Earth’s core generate a magnetic field? Draw a diagram of the geodynamo as a class, using group diagrams to inform the larger diagram. Discuss how energy flows and transforms throughout the geodynamo process.

The inside of the Earth is very, very hot because the planet retains thermal energy left over from the cosmic collisions that formed it and those that followed. The inner core is solidifying through crystallization (fourth

concept). This crystallization releases heat energy and, along with the leftover heat from the planet’s formation, provides an energy source for heat conduction (third concept) and convection (second concept). Thermal convection creates cyclical movement of the molten iron and nickel in the core (Earth’s structure, fifth concept), and the resulting flow of electrons produces the magnetic field (first concept). The magnetic field builds because of the complex flow of fluids, which are not only rising and falling but also being twisted thanks to the Coriolis effect.

2. Explain why the geodynamo is considered to be self-sustaining. Why do you think geophysicist Peter Olson says “all planets lose heat”? How would you represent the general energy flow between Earth and space? Will the geodynamo effect last forever?

The interplay of the inner and outer core makes the dynamo self-sustaining over billions of years. Changes in one layer drive changes in another layer and vice versa. All planets lose heat, as Olson says, because planets are not closed systems. They are connected to the vast, empty and cooler space around them. As Earth cools and the inner core grows and crystallizes, heat is transferred up into the mantle and ultimately away from the planet. Encourage students to think about where on Earth they can witness this heat loss and how heat might be added back into the Earth system. If Earth’s core ever fully solidified, the geodynamo would shut down. But that process would take so long that our sun probably will have engulfed the Earth by then anyway.

3. How does life on Earth benefit from the magnetic field and thus the geodynamo? What technologies depend on the field? What could happen to life and these systems if the field weakens or changes?

The magnetic field protects Earth from the dangerous radiation of the solar wind and solar storms. Encourage students to think about why this is important for life today, but also why it mattered when life was first evolving. Without the magnetic field, the radiation would eat away at our atmosphere, including the ozone layer that protects life from ultraviolet radiation. Many organisms rely on the magnetic field for navigation and orientation, including humans. Cellphone GPS systems and military navigation technologies depend on the field, for example. The field also protects our satellites and power grids from damaging radiation.

If the field weakened or flipped, this protection could be temporarily lost. Your compass might think North is in a different direction. Technologies might be damaged. Rates of cancer might increase. What’s more, other animals that navigate via the field could get lost on their journeys. But remind students that the strength of Earth’s magnetic field is already quite variable and a big weakening or flip would likely occur gradually, perhaps over thousands of years.

March 2, 2019 Earth’s Inner Core is Relatively Young

Cross-Curricular Connections, Q Directions: The Science News article “Earth’s inner core is relatively young” explores how a change in the Earth’s inner structure created the relatively strong magnetic field that exists today. The concepts below all relate to the geodynamo, which sustains this magnetic field. Follow your teacher’s instructions to draw a diagram that explains one of the concepts. Be as detailed as possible and label your diagram appropriately.

Concepts:

Creation of a magnetic field

Thermal convection (include the concept of density)

Heat conduction (include the concept of thermal equilibrium)

Crystallization (include the concept of heat transfer and use water as an example)

Earth’s inner structure (include composition and approximate depth ranges)

Class discussion:

1. How do the individual diagrams inform the larger geodynamo process, as it is described in the article? How does Earth’s core generate a magnetic field? Draw a diagram of the geodynamo as a class, using group diagrams to inform the larger diagram. Discuss how energy flows and transforms throughout the geodynamo process.

2. Explain why the geodynamo is considered to be self-sustaining. Why do you think geophysicist Peter Olson says “all planets lose heat”? How would you represent the general energy flow between Earth and space? Will the geodynamo effect last forever?

3. How does life on Earth benefit from the magnetic field and thus the geodynamo? What technologies depend on the field? What could happen to life and these systems if the field weakens or changes?

March 2, 2019 Earth’s Inner Core is Relatively Young

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