What has led to these landforms? How do we know?
This is North America right now. You can pick out a lot of features that we've been studying. You can even pick out evidence of different processes. Continental rifting? See where Baja California is separating from the rest of Mexico. Mountain building? You can see the Sierra Nevada, Cascades, and Rocky Mountains, among others. Weathering is seen in the red dirt in the Four Corners area. The Great Lakes are remnants of the giant glaciers that covered the northern region. Shallow limestone shelves are seen surrounding Florida. How we know what we know and what we know about Earth history is touched on very briefly in this Concept.
Fossils are remnants of living creatures. Fossils give clues about what conditions were like when the organism lived. Fossils help geologists understand the geological history of an area. Clues from rocks can help scientists decipher the history of a region too. Relative dating allows geologists to figure out the order of events. Correlation allows them to understand the geological history of a region. Absolute age dating gives real dates for geological events. Radiometric dating uses the ratios of parent and daughter isotopes to indicate age. The solar system began as a cloud of dust and gas. That cloud spun and contracted by gravity. The center became so dense it ignited to form a star. Clumps of matter came together to form the planets. Shortly after Earth formed, a giant asteroid struck the planet. Both Earth and the asteroid melted. Material was flung out into Earth's orbit. That material came together to make the Moon. Earth had to cool before it could support an atmosphere. Once it had an atmosphere, rain fell into basins to create the oceans. Gases in the early atmosphere came from volcanic eruptions. Comets and asteroids also brought in gases. There was almost no oxygen. It was not until the evolution of photosynthesis that oxygen collected in the atmosphere. With oxygen animals could evolve. Also, oxygen was needed to form the ozone layer. The early Earth was extremely hot. Convection and plate tectonics were faster than today. During Earth history, supercontinents formed and broke apart. Seas transgressed and regressed. Ice ages came and went.