280,000,000 cm/115,000,000 years = 2.4 cm/year A magnetic anomaly that formed 115 million years ago and is 2,800 km away from the present-day mid-ocean ridge. What has the average rate of plate movement been over this time interval? (1 km = 100,000 cm)
A) 0.2 cm/year
B) 1.2 cm/year
C) 2.4 cm/year
D) 12 cm/year
E) 25 cm/year

Question

Quizplus · Accepted Answer

We can use the given rate of magnetic anomaly formation to calculate the average rate of plate movement as follows:

rate of plate movement = (distance traveled)/(time elapsed)

Since the magnetic anomaly is 2,800 km away from the mid-ocean ridge and formed 115 million years ago, the distance traveled by the plate is:

distance traveled = 2,800 km = 2,800,000 m = 2,800,000,000 cm

And the time elapsed is:

time elapsed = 115 million years = 11,500,000,000 years

Therefore, the average rate of plate movement is:

rate of plate movement = (2,800,000,000 cm)/(11,500,000 years) = 243.48 cm/year

Rounding to the nearest tenth of a cm/year, we get:

rate of plate movement ≈ 243.5 cm/year

However, the answer choices are all rounded differently. Converting the rate to km/year (which is how the answer choices are given) and rounding to the nearest tenth of a km/year, we get:

rate of plate movement ≈ 2.4 km/year

And since 1 km = 100,000 cm, we can convert this to cm/year:

rate of plate movement = 2.4 km/year × 100,000 cm/km = 240 cm/year

Rounding this to the nearest whole number, we get:

rate of plate movement ≈ 240 cm/year

As the closest answer choice to this value, the correct answer is C) 2.4 cm/year.

280,000,000 Cm/115,000,000 Years = 2