Why do geologists conclude that the Earth's landforms have changed numerous times throughout its history?

Geologists conclude that the Earth's landforms have changed numerous times throughout its history by using evidence from various geological processes and records.

Here are the steps and logical explanations for this conclusion:

1. Rock Strata and Fossil Records: The layers of sedimentary rock (strata) provide a historical record of Earth’s past. Different strata contain different types of sediment and fossils which show that conditions, such as climate and biology, have changed over time. For example, fossils found in one layer may be of marine creatures while another layer, positioned miles away from any sea, might consist of land plants, indicating that the area was once underwater and later became land.

2. Tectonic Activity: The theory of plate tectonics shows that the Earth’s crust is divided into several plates that float on the semi-fluid asthenosphere beneath them. The movement of these plates has formed mountains, ocean basins, and caused the continents to drift apart or collide (continental drift), reshaping the landforms over millions of years.

3. Erosion and Weathering: Erosion is the process by which rock and soil are worn away, typically by water, wind, or ice. Over long periods of time, erosion can significantly alter landscapes, turning mountains into hills and even into flat plains. Weathering is the breakdown of rocks and minerals at the Earth's surface due to environmental factors like temperature changes, water, and biological activity. These processes continually change the Earth's surface.

4. Glacial Evidence: Glaciers, as they move, erode vast amounts of material and create distinctive landforms like U-shaped valleys and fjords. The advance and retreat of ice ages have left behind glacial deposits and landforms that indicate different climate conditions during Earth's history.

5. Volcanism: Volcanic activity contributes to landscape changes by depositing lava and ash over large areas. This can build up new landforms like volcanic islands, and when volcanoes erode over time, it can lead to the formation of calderas and other structures.

6. Dating Techniques: Advances in dating methods, such as radiometric dating, allow geologists to determine the age of rocks and fossils accurately. This helps construct a timeline of when certain landform changes occurred.

These geological clues and others help construct a picture of a dynamic and ever-changing Earth.