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Chapter 8: Problem 10

Scientists know the history of Earth's magnetic field because a. the magnetic field hasn't changed since the formation of Earth. b. they see how it's changing today, and project backward in time. c. the magnetic field becomes frozen into rocks, and plate tectonics spreads those rocks out. d. they compare the magnetic fields on other planets to Earth's. e. there are written documents of magnetic field measurements since the beginning of Earth.

Short Answer

Expert verified
Option (c): The magnetic field becomes frozen into rocks, and plate tectonics spreads those rocks out.

Step by step solution

01

Analyze each option

Examine each given option to determine its validity in the context of Earth's magnetic field history.
02

Consider option (a)

Option (a) suggests that the magnetic field hasn't changed since Earth's formation. This cannot be true as scientific evidence shows the magnetic field has reversed and fluctuated over time.
03

Evaluate option (b)

Option (b) states that scientists project backward from current magnetic field changes. While current changes are studied, projecting backward doesn't alone explain the entire history of the magnetic field.
04

Assess option (c)

Option (c) proposes that the magnetic field becomes frozen into rocks and plate tectonics spreads these rocks out. This is supported by evidence where magnetic minerals in rocks record the direction and intensity of the magnetic field during rock formation.
05

Review option (d)

Option (d) claims comparison with other planets' magnetic fields. Each planet has a unique magnetic history and this wouldn't offer a complete understanding of Earth's magnetic field history.
06

Inspect option (e)

Option (e) suggests written documents since Earth's beginning. This is incorrect as written records do not span back to Earth's formation.
07

Determine the best answer

Based on the evaluation, option (c) is the most accurate. The magnetic field is recorded in rocks, and the movement of these rocks through plate tectonics helps scientists trace changes.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

magnetic field changes
Earth's magnetic field hasn't always been the same. It has gone through many changes over millions of years. These changes include reversals of the magnetic poles. A reversal means that the magnetic north and south poles swap places. Scientists know this because they can see the patterns in rocks and sediments.
By studying these patterns, we understand that the magnetic field's strength and direction can fluctuate. These fluctuations are known as geomagnetic secular variation. Knowing about these changes helps scientists predict future changes.
plate tectonics
Plate tectonics is a scientific theory explaining the movement of Earth's lithospheric plates. These plates float on the semi-fluid mantle beneath them.
When these plates move, they can carry rocks that have recorded the magnetic field with them.
This movement helps spread the records of magnetic field changes across the Earth. Scientists study the magnetization of rocks to understand past plate movements and reconstruct the history of the magnetic field.
This method gives a more precise timeline of how the continents have shifted and how the magnetic field has evolved.
rock magnetization
Rocks can contain tiny minerals that act like little magnets. When these rocks form, especially volcanic rocks, they can capture a snapshot of Earth's magnetic field. This process is known as rock magnetization.
The minerals align with the magnetic field at that time. Once the rock hardens, the magnetic information is locked in place.
Over millions of years, as tectonic plates move, these rocks are carried to new locations. By studying these rocks in different locations, scientists can reconstruct the magnetic history.
scientific evidence
Understanding Earth's magnetic field history relies on several pieces of scientific evidence:
  • Magnetized Rocks: By examining the magnetic minerals in rocks, scientists find clues about past magnetic fields.
  • Seafloor Spreading: Patterns of magnetic stripes on the ocean floor show how the magnetic field has flipped over time.
  • Radiometric Dating: This method helps date rocks precisely, linking magnetic records to specific time periods.
  • Computer Models: Advanced models simulate magnetic field changes and offer insights into past behaviors.
All these pieces work together to give a comprehensive picture of Earth's magnetic history.

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Most popular questions from this chapter

Compare the kinetic energy of a 1-gram piece of ice (about half the mass of a dime) entering Earth's atmosphere at a speed of \(50 \mathrm{km} / \mathrm{s}\) to that of a 2 -metric-ton SUV \(\left(\text { mass }=2 \times 10^{3} \mathrm{kg}\right)\) speeding down the highway at \(90 \mathrm{km} / \mathrm{h}\)

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