Major Ideas
Weathering is a process by which, mechanically or chemically, rocks are broken down into smaller pieces. Erosion is the process that carries, or transports, the smaller pieces of rock (called sediment) to another place by wind, water, ice, and gravity. Deposition is when the sediment is “dropped off” and settles down to form a new layer of rock. These three processes are key to the formation of the Grand Canyon. Over billions of years, sediment from different environment types have deposited, leaving a geological record of the Colorado Plateau.
By looking at the sedimentary rock layers of Sandstone, Limestone, and Shale in the Grand Canyon, we can infer the environments that once existed there. Sandstone is a sandy textured rock that was formed by sand and clay compacting under either a desert or a beach. Shale is a smooth layered rock that as formed by silt and clay (cannot see individual particles without magnification) from a swampy environment and often has fern fossil imprints. Limestone fizzes when hydrochloric acid is dropped on it due to the calcite in its mixture. Calcite is commonly found in shells. Limestone is a sandy textured rock that often has imprints of shells and marine life and was formed in an ocean.
Scientists can date the rocks relative to other layers based on how they are deposited. If a rock layer is at the bottom, it settled first and therefore, is older than any other layers above. On the other hand, if a rock layer is found near the top of a landform, it must mean it was deposited later and is younger than the preceding layers. Scientists call this method of relative dating the Law of Superposition. Another clue to finding the age of rock layers is fossils. Fossils are any remains, traces, or imprints of a plant or animal that has been preserved in the Earth's crust (evidence of past life). If we know when an organism was alive and we find its fossil in a rock layer, we can infer the age of the rock. On the flip side, if we know the age of the rock layer, we can also find the age of unknown fossils. Fossils are important evidence used to piece together Earth's Geologic History.
Earth's history is organized into a Geological Timeline. This timeline is broken down into Eons, Eras, and Periods. Looking at events in Earth's history, we learned that humans have only been around a "blink of an eye" compared to everything else. Included in the events is Pangaea, a supercontinent that once existed when the dinosaurs roamed the Earth. Before their extinction, however, Pangaea had broken up and the continents drifted apart. The three pieces of evidence that supported the theory that Pangaea once existed include: the continents fit together like puzzle pieces, fossils of the same plants and animals were found on different continents, and the rock layers were the same at different continents. From these observations came the Theory of Continental Drift which was published by Alfred Wegener, a German scientist who claimed that the conintents are in constant motion over time. We now know a lot more about Tectonic Plates and how they are indeed moving the continents 1-10 cm per year on top of the Earth's mantle (a layer of hot magma). Energy is needed to move all things, from charges in an electrical circuit to the tectonic plates on the Earth's crust. The energy for the plates movement comes from the center of the Earth where is it very hot!
"The present is the key to the past" means that geologists know about Earth's past by studying rocks and fossils from millions of years ago. Fossils and rocks tell us about the plants, animals, and environments that existsed during that time period.
By looking at the sedimentary rock layers of Sandstone, Limestone, and Shale in the Grand Canyon, we can infer the environments that once existed there. Sandstone is a sandy textured rock that was formed by sand and clay compacting under either a desert or a beach. Shale is a smooth layered rock that as formed by silt and clay (cannot see individual particles without magnification) from a swampy environment and often has fern fossil imprints. Limestone fizzes when hydrochloric acid is dropped on it due to the calcite in its mixture. Calcite is commonly found in shells. Limestone is a sandy textured rock that often has imprints of shells and marine life and was formed in an ocean.
Scientists can date the rocks relative to other layers based on how they are deposited. If a rock layer is at the bottom, it settled first and therefore, is older than any other layers above. On the other hand, if a rock layer is found near the top of a landform, it must mean it was deposited later and is younger than the preceding layers. Scientists call this method of relative dating the Law of Superposition. Another clue to finding the age of rock layers is fossils. Fossils are any remains, traces, or imprints of a plant or animal that has been preserved in the Earth's crust (evidence of past life). If we know when an organism was alive and we find its fossil in a rock layer, we can infer the age of the rock. On the flip side, if we know the age of the rock layer, we can also find the age of unknown fossils. Fossils are important evidence used to piece together Earth's Geologic History.
Earth's history is organized into a Geological Timeline. This timeline is broken down into Eons, Eras, and Periods. Looking at events in Earth's history, we learned that humans have only been around a "blink of an eye" compared to everything else. Included in the events is Pangaea, a supercontinent that once existed when the dinosaurs roamed the Earth. Before their extinction, however, Pangaea had broken up and the continents drifted apart. The three pieces of evidence that supported the theory that Pangaea once existed include: the continents fit together like puzzle pieces, fossils of the same plants and animals were found on different continents, and the rock layers were the same at different continents. From these observations came the Theory of Continental Drift which was published by Alfred Wegener, a German scientist who claimed that the conintents are in constant motion over time. We now know a lot more about Tectonic Plates and how they are indeed moving the continents 1-10 cm per year on top of the Earth's mantle (a layer of hot magma). Energy is needed to move all things, from charges in an electrical circuit to the tectonic plates on the Earth's crust. The energy for the plates movement comes from the center of the Earth where is it very hot!
"The present is the key to the past" means that geologists know about Earth's past by studying rocks and fossils from millions of years ago. Fossils and rocks tell us about the plants, animals, and environments that existsed during that time period.