Which geological evidence in currently temperate areas indicates that Earth's climate has varied over time?

• A. Landforms carved by glaciers
• B. Coral reefs
• C. Sand dunes
• D. River terraces

Answer: (A)

Past climate variability leaves clear marks on the landscape, and in temperate regions the strongest evidence comes from landforms carved by glaciers. When Earth was cooler, expansive ice sheets advanced and ground the bedrock, creating characteristic features such as U-shaped valleys, cirques, horns, and polished surfaces with striations. They also left behind deposits like moraines and till, which record the extent and retreat of ice at different times. When the climate warmed, the ice retreated, reshaping the landscape and leaving signals of past ice margins. This combination of sculpted terrain and gla cial deposits provides a direct, long-lasting record that climate has varied over time in temperate zones.

Coral reefs indicate warm water conditions, but they’re typically tied to tropical or subtropical climates and don’t by themselves demonstrate long-term climate variation in temperate areas. Sand dunes reflect wind and aridity and can form under various conditions, not specifically tied to glacial cycles. River terraces tell us about changes in river dynamics, which can result from climate shifts but also tectonics and base-level changes, making them a less direct indicator of past climate variation.