Researchers are comparing the intelligence levels of incoming freshmen and graduating seniors. Assuming that there is not a systematic difference in intelligence levels between the two groups and researchers reject the null hypothesis, they have committed:

Type 1 error

Explanation:

In statistics and research, a type 1 error results when a researcher rejects a true null hypothesis and accepts the alternate hypothesis instead.

From this question let's say the null hypothesis is there is no systematic difference between two groups

And the alternate says there is systematic difference between two groups.

We commit a type 1 error when we reject the null hypothesis which is correct and accept the alternate hypothesis which is false.

permafrost layer, it exists beneath a layer of soil, rock or sediment.