Introduction to Geology and Rock Types

• Geology is the study of the Earth, its structure, composition, processes, and history
• It encompasses the study of rocks, minerals, landforms, and the forces that shape our planet

Rock Types

• Igneous rocks form from the cooling and solidification of magma or lava
  • Intrusive igneous rocks cool slowly beneath the Earth's surface, resulting in large crystals
  • Extrusive igneous rocks cool quickly on the Earth's surface, resulting in small crystals or a glassy texture
• Sedimentary rocks form from the accumulation and cementation of sediments such as mineral grains, rock fragments, and organic matter
  • Clastic sedimentary rocks form from the accumulation of broken pieces of rocks and minerals
  • Chemical sedimentary rocks form from the precipitation of minerals from water
  • Organic sedimentary rocks form from the accumulation of organic matter
• Metamorphic rocks form when existing rocks are changed by heat, pressure, or chemical reactions
  • Foliated metamorphic rocks have a layered or banded appearance due to the alignment of minerals
  • Non-foliated metamorphic rocks do not have a layered appearance

Plate Tectonics

• The Earth's lithosphere divides into several large and small plates that move and interact with each other
• Plate boundaries are the regions where these plates interact
  • Divergent boundaries are where plates move apart, resulting in the creation of new crust
  • Convergent boundaries are where plates collide, resulting in subduction, mountain building, or volcanic activity
  • Transform boundaries are where plates slide past each other horizontally, resulting in earthquakes
• Plate movement is driven by convection currents in the Earth's mantle
• Hot spots are areas of volcanic activity that are not associated with plate boundaries

Geological Time Scale

• The geological time scale is a system of chronological dating that relates geological strata to time
• It divides into eons, eras, periods, epochs, and ages, based on significant geological and biological events
• The Precambrian Eon represents the earliest part of Earth's history, comprising about 88% of geological time
• The Phanerozoic Eon is the current eon, characterized by the proliferation of complex life forms
  • The Paleozoic Era is marked by the appearance of diverse marine invertebrates, fish, and the colonization of land by plants and animals
  • The Mesozoic Era is known as the age of reptiles, with the dominance of dinosaurs and the evolution of early mammals and birds
  • The Cenozoic Era is the current era, characterized by the rise of mammals, birds, and flowering plants, as well as the evolution of humans

Fossil Formation

• Fossils are the preserved remains or traces of ancient organisms
• Fossil formation typically happens when an organism is buried rapidly by sediment, protecting it from decay and destruction
• There are several types of fossilization:
  • Permineralization occurs when minerals fill the pore spaces of an organism's remains
  • Replacement occurs when the original material of an organism is replaced by minerals
  • Casts and molds are formed when an organism decays, leaving a void in the surrounding sediment (mold), which can then be filled by minerals (cast)
  • Compression fossils form when an organism is flattened between layers of sediment
  • Trace fossils are indirect evidence of past life, such as footprints, burrows, and coprolites (fossilized feces)
• Fossils provide valuable information about the history of life on Earth, evolution, past environments, and climate change

Minerals and Crystals

• A mineral is a naturally occurring, inorganic solid with a definite chemical composition and crystalline structure
• Minerals are the building blocks of rocks
• Crystal structure refers to the orderly arrangement of atoms, ions, or molecules in a crystalline solid
• Minerals can be identified based on their physical properties, such as:
  • Color is the visual appearance of a mineral
  • Streak is the color of a mineral's powder
  • Luster is the way a mineral reflects light (e.g., metallic, glassy, dull)
  • Hardness is the resistance of a mineral to scratching
  • Cleavage is the tendency of a mineral to break along specific planes of weakness
  • Fracture is the way a mineral breaks irregularly
  • Density is the mass per unit volume of a mineral
• Silicate minerals are the most abundant minerals in the Earth's crust and contain silicon and oxygen
• Other important mineral groups include carbonates, oxides, sulfides, and sulfates