The Geologic Time Scale defines eras in terms of
A)major worldwide extinctions of life on Earth.
B)reversals in Earth's magnetic field.
C)the beginning of the radioactive decay of elements in minerals.
D)major plate tectonic events.

Question

Quizplus · Accepted Answer

The Geologic Time Scale is primarily defined by the major worldwide extinctions of life on Earth, which mark the end of one era and the beginning of another. Other events, such as changes in Earth's magnetic field or plate tectonic events, can also be used to define boundaries within eras, but they are not the primary basis for dividing the geologic time scale into eras. Radioactive decay of elements in minerals is used to determine the absolute ages of rocks and minerals, but not to define the boundaries between eras.

The Geologic Time Scale Defines Eras in Terms of