What do crop marks in archaeology indicate?

The correct answer highlights how crop marks are an important archaeological indicator of sub-surface features. Specifically, they occur when crops are planted over buried structures or variations in soil. When there are differences in soil quality due to buried archaeological features, such as walls or ditches, crops can exhibit varied growth patterns. For example, plants might thrive over areas where ancient structures have enriched the soil, leading to a visual contrast in the growth of the crops. This method allows archaeologists to infer the presence of underlying historical features without excavating the site, making it a vital non-invasive technique for studying past human activity and settling patterns.

The other choices do not effectively capture the specific role that crop marks play in archaeology. While changes in weather patterns may influence how crops grow, they do not account for the archaeological significance of crop marks. The presence of buried artifacts might influence the state of the soil, but crop marks do not directly signal where artifacts are located. Lastly, while ancient settlement patterns can be suggested by crop marks, they are mainly a result of the different growth of crops over culturally significant soil features rather than indicating the locations themselves.