Understanding Erratics
Erratics are large rocks that have been transported a significant distance from their original source by glaciers. They often sit on bedrock of a different type, indicating their foreign origin.
Possible Evidence Statements:
Here are some statements that could be evidence, ranked from strongest to weakest:
1. "The boulder is composed of granite, while the surrounding bedrock is limestone." This is the strongest evidence because it indicates a clear difference in rock type, suggesting the boulder came from elsewhere.
2. "The boulder rests on a hilltop far from any similar rock formations." This suggests the boulder was likely transported, but doesn't give specifics about the origin.
3. "The boulder has a smooth, rounded shape, unlike the angular rocks in the surrounding area." This is suggestive but not conclusive. Glaciers can round rocks, but other forces can too.
4. "The boulder is unusually large for the area." This could be due to various factors, including glacial transport, but isn't definitive.
The Best Evidence
The statement "The boulder is composed of granite, while the surrounding bedrock is limestone" is the strongest evidence for a boulder-sized rock being an erratic. It establishes the clear difference in rock type that is the hallmark of an erratic.
