Magnetic Reversals and Variations Name:____________________________

The following table gives the strength of Earth's main field in units such that the Earth's current strength has a value of 11.5 on this intensity scale.

The data are based on the accumulated measurements by geologists from a variety of geological deposits, strata, and ocean sediment samples.

The 'Time' columns indicate how many thousands of years before the present time the field was at the indicated strength. The first table entry says that at 20,000 years ago, the strength was 7.0.

 

Time

Strength

Time

Strength

Time

Strength

Time

Strength

20

 7.0

220

 5.7

420

 8.4

620

 5.5

40

 3.2

240

 6.5

440

 6.3

640

 8.5

60

 5.0

260

 4.5

460

 7.0

660

 7.0

80

 6.6

280

 5.0

480

 6.0

680

 3.5

100

 3.8

300

 6.0

500

 5.7

700

 5.0

120

 4.3

320

 5.8

520

 4.6

720

 5.5

140

 6.5

340

 6.4

540

 3.8

740

 8.2

160

 6.3

360

 8.5

560

 4.2

760

 6.5

180

 2.2

380

 5.0

580

 4.7

780

 0.5

200

 6.0

400

 7.5

600

 6.0

800

 3.4

 

 From the tabulated entries above, answer the following questions:

1...What is the minimum and maximum range of the intensity range?

2...What is the average value of the intensity range?

3...What is the median of the intensity values?

4...What is the mode of the intensity values?

 

 Now plot the data and answer these questions:

5...How many times has the field intensity dipped below 1/2 of its current value?

6...When was the last time that the field intensity reached 1/5th of its current level?

7...When was the last time the field intensity was close to zero?

8...When did the fastest change in the field strength occur in the last 800,000 years? (steepest slope)

9...The current field is decreasing at about 5% per century, in how many years will it reach zero using a straight-line extrapolation?

10...Do you think the field strength will actually reach zero? Explain your reasoning below.