Knowt
EARTHSCI
Synopsis:
Stratified Rocks
Stratified rocks, also known as sedimentary rocks, are formed by the accumulation of sediments that get compacted and cemented over time. These sediments can include minerals, small rock fragments, and organic material. The layers, or strata, in these rocks are often visible and can tell us a lot about the Earth's history. For example, each layer may represent a different period of deposition, and the characteristics of the layer can give clues about the environment at that time.
Relative and Absolute Dating
Relative Dating: Relative dating is a method used to determine the sequence of events in relation to one another without knowing their exact age. This is often done by studying the layers of rock (strata) and using principles such as the Law of Superposition, which states that in undisturbed layers of rock, the oldest layer is at the bottom and the layers become progressively younger towards the top. Other methods include looking at fossil succession and cross-cutting relationships.
Absolute Dating: Absolute dating, on the other hand, provides a more precise age for a rock or fossil. This method often involves measuring the decay of radioactive isotopes in the sample. For example, radiocarbon dating measures the amount of carbon-14 left in an organic material to determine its age, while other methods like potassium-argon dating are used for dating older geological materials.
Understanding both relative and absolute dating techniques is essential for reconstructing the history of our planet and the life it supports.
Indroduction:
Index Fossils: Index fossils, or guide fossils, are the remains of organisms that lived during a specific, relatively short time period but were widespread geographically. These fossils are incredibly valuable to geologists because they help date and correlate the age of rock layers. By comparing the presence of index fossils within different rock formations, geologists can determine the relative ages of those rocks.
Formation of Fossils: Fossil formation is a process that takes millions of years. Here's a simplified version of how it happens:
Organism's Death: When an organism dies, it may be quickly buried by sediment such as mud, sand, or volcanic ash.
Preservation: Over time, more sediment accumulates over the remains, and the conditions (such as lack of oxygen) slow down the decay process.
Mineralization: Minerals from the surrounding sediment seep into the organism's remains, replacing the organic material and turning it into rock-like structures. This process is known as permineralization.
Exposure: Over millions of years, geological processes such as erosion and tectonic activity can expose these fossils at the Earth's surface, where they can be discovered.
Geologic Time Scale: The geologic time scale is a system used by geologists to divide Earth's history into various segments based on significant geological and paleontological events. The scale is organized into several hierarchical units:
Eons: The largest time units, which include the Hadean, Archean, Proterozoic, and Phanerozoic eons.
Eras: Subdivisions of eons, such as the Paleozoic, Mesozoic, and Cenozoic eras within the Phanerozoic eon.
Periods: Subdivisions of eras, such as the Cambrian, Ordovician, and Jurassic periods.
Epochs: Subdivisions of periods, such as the Paleocene and Holocene epochs.
By using index fossils and the geologic time scale, geologists can piece together Earth's history, understand the timing and relationships between different geological events, and make sense of the complex history of life on our planet.
EXOGENIC AND ENDOGENIC PROCESSES
Weathering + the process of
Exogenic Processes
Weathering and Erosion
Mechanical Weathering +
Chemical Weathering + new substance
Physical / Mechanical Weathering
Abrasion + occurs when rocks are broken down by being hit or impacted by other rocks, sand, or sediment
Root Wedging + roots growing into the cracks of a rock.
Frost Wedging + when water expands as it freezes
Thermal Stress + heat, causes rocks to expand
Chemical Weathering + process that breaks down rocks and minerals through chemical reactions
Oxidation + oxygen reacts with iron in the rock, iron oxide, creating rust
Hydrolysis + hydrogen breaks down the chemical bonds of minerals in rocks
Carbonation + Water and carbon dioxide, making carbonic acid, which weakens rocks
Weathering Process
Disintegrated and decomposed
Broken into pieces
Caused by
