Question

a map showing the basement of north american continent. the basement rocks are not often exposed at the surface because they are covered by younger rocks.
a) describe the age distribution of the basement rocks (oldest to youngest rocks).

Explanation:

From west to east across North America, the basement rocks show a clear age progression. The westernmost (Sierra Madre) is the oldest, followed by the 1.8–1.7 Ga zone, then 1.7–1.6 Ga, next the Greenville zone, and the easternmost Appalachians are the youngest.

Answer:

Starting from the oldest basement rocks and moving to the youngest:

1. The oldest basement rocks are located in the western part of the continent (labeled "Sierra Madre").
2. Next are rocks aged 1.8–1.7 Ga, situated east of the westernmost zone.
3. Then come rocks aged 1.7–1.6 Ga, east of the 1.8–1.7 Ga zone.
4. After that are the rocks of the Greenville zone, east of the 1.7–1.6 Ga zone.
5. The youngest basement rocks are in the easternmost Appalachians region.

In short, the basement rocks generally become progressively younger from the western edge of North America toward the eastern edge.