The Geoguide

The Geoguide On The Geoguide, you will learn about the different types of geology, types of rocks, gemstones, and lots of other stuff-- a true geologists dream! Physical Geology Physical geology is a branch of geology that studies the physical things of Earth, such as rocks, minerals, the very soil your house is sitting on right now, and internal and external events, such as tectonic plate movements, weathering, and volcanism. It also focuses on how Earth works, like how mountains are formed and erosion. The study of igneous, metamorphic, sedimentary rocks, and their formation. Understand the Earth’s interior structure, such as moving lithospheric plates, volcanoes, and earthquakes. Examine erosion, weathering, glaciation, and water action that change the very landscape as you read this. Be able to identify the stone and minerals you walk on every single day. Igneous alt=An image of granite.|thumb|A piece of the intrusive igneous rocks, granite. Igneous rocks are rocks formed when molten rock, magma or lava, cools and solidifies. Intrusive igneous rocks are slow-cooled inside Earth and coarse-grained. Ten examples of intrusive igneous rocks include: GraniteA common heavy, dense, and highly durable white-to-pink feldspar and dark flakes of biotite or amphibole coarse-grained rock GabbroA underground equivelent of basalt, dense, coarse-grained identifiable by its dark color, heavy feel, and crystalline texture Diorite Peridotite Pegmatite Syenite Granodiorite Diabase Aplite Anorthosite alt=An image of basalt.|thumb|A piece of the extrusive igneous rocks, basalt. Extrusive igneous rocks are rapidly-cooled outside the Earth and are generally smooth and shiny, but they can be porous or "bubbly". Ten examples of extrusive igneous rocks include: Basalt Andesite Rhyolite Obsidian Pumice Scoria Tuff Dacite Pitchstone Phonolite Metamorphic alt=An image of slate.|thumb|A piece of the metamorphic rocks, slate. Metamorphic rocks are pre-existing rocks (igneous, sedimentary, or other metamorphic rocks) transformed by intense heat, pressure, and chemically active fluids deep within the Earth's crust. These rocks are characterized by recrystallization without melting, leading to changes in mineralogy and texture, often producing foliated (layered) or non-foliated structures. Ten examples of metamorphic rocks are: Slate Phyllite Schist Gneiss Marble Quartzite Amphibolite Hornfels Migmatite Eclogite alt=An image of sandstone.|thumb|A piece of the sedimentary rocks, sandstone. Sedimentary Sedimentary rocks are formed at the Earth's surface by the accumulation, compaction, and cementation of sediments, like mineral particles or organic matter. They often form in layers and are identified by their banded appearance, presence of fossils, and softer, porous nature. Ten examples of sedimentary rocks include: Sandstone Limestone Shale Conglomerate Breccia Siltstone Dolostone Chert Coal Gypsum Understanding Earth's Insides Now that you have learned the three different categories of rock identification, let's learn about the stuff right under you! Lithospheric Plates Lithospheric plates, or tectonic plates, are large, rigid, moving segments of Earth's outermost layer, comprising the crust and upper mantle. Ranging from 40–280 km thick, they essentially "float" on the pliable asthenosphere, fitting together like a giant puzzle. The main three events that happen with lithospheric plates include: Convergent (Colliding): Plates collide, causing subduction or mountain building. Divergent (Spreading): Plates move apart, creating new crust. Transform (Sliding): Plates slide past one another, often causing earthquakes. Volcanoes Volcanoes begin as magma deep within the Earth, created by heat and pressure at tectonic plate boundaries or hotspots. This buoyant magma rises through cracks in the crust, collecting in chambers before erupting as lava, ash, and gases. Solidifying layers build mountains over time. Some types include: Magma vs. Lava: Magma is molten rock below the surface; once it erupts, it is called lava. Composite Volcanoes (Stratovolcanoes): Tall, steep cones built by layers of ash and thick lava. Shield Volcanoes: Broad, gentle slopes formed by fluid, runny lava. Cinder Cones: Small, simple, cone-shaped volcanoes built from blobs of congealed lava And the three states include: Active: Currently erupting or showing signs of, or expected to, erupt soon. Dormant: Not currently active, but has erupted recently and may erupt again. Extinct: Not expected to erupt again. How They Happen Volcanic eruptions are driven by pressure from dissolved gases in the magma, which expand as the magma rises. Eruptions can be explosive (releasing ash and rock) or effusive (releasing lava flows). Earthquakes An earthquake is the intense shaking of Earth's surface caused by the sudden release of energy in the crust, typically when tectonic plates shift and slip along faults. These events occur due to built-up stress, creating seismic waves that shake the ground. How Earthquakes Occur Tectonic Plate Movement: The Earth's crust is divided into massive plates that constantly move and slide past one another. Fault Lines: When these plates get stuck but continue pushing, stress builds up until the rock fractures and breaks along faults. Energy Release: This sudden release of stress produces seismic waves, which travel through the ground, causing shaking at the surface. Key Terminology and Locations Hypocenter (Focus): The location below the Earth's surface where the earthquake starts. Epicenter: The point on the Earth's surface directly above the hypocenter, often experiencing the most intense shaking. Mainshock & Aftershocks: The main earthquake is the mainshock, while smaller, subsequent shakes in the same area are aftershocks. Fault Types: Includes strike-slip (sliding past), normal (pulling apart), and thrust (pushing over) faults. While most earthquakes are tectonic, they can also be triggered by volcanic activity, landslides, or human activities like mining and hydraulic fracturing. Events That Change The Land Since you have now learned about Earth's internal components, let's focus on the things that change the very land! Erosion Erosion is the natural process of wearing away and transporting soil, rock, and sediment by agents like water, wind, and ice, often leading to landscape changes like mountains shrinking or riverbanks eroding. It decreases agricultural productivity, causes ecological damage, and is distinct from weathering because it includes transportation of material, whereas weathering only breaks it down. The three main types include: Water Erosion: Includes splash, sheet, rill, and gully erosion. Wind Erosion: Occurs through deflation, removing loose soil and sand. Ice Erosion: Glacial movement that carves valleys and moves debris. Examples: Rain washing soil from hills, ocean waves reshaping coastlines, and rivers carving canyons. Effects: Land degradation, loss of nutrient-rich topsoil, destruction of habitats, and potential desertification. Erosion vs. Weathering: Weathering is the immediate breakdown of rocks (disintegration), while erosion is the removal and transport of that material to a new location. Erosion can act as a natural "cleaning" process but, when accelerated by human activity (e.g., deforestation, construction), it causes massive on-site and off-site damage. Weathering Weathering is the breakdown of rocks, soils, and minerals at/or near the Earth's surface through physical, chemical, and biological processes. Driven by water, ice, temperature changes, and organisms, it transforms bedrock into sediment, creating landscapes like the Grand Canyon. It differs from erosion, which transports these materials. The three main types of weathering are: Physical/Mechanical Weathering: Breaks rocks into smaller pieces without changing their composition, often through ice wedging, thermal expansion, or salt crystallization. Chemical Weathering: Alters the molecular structure of minerals, causing them to dissolve or break down, often via water, oxygen, or acids. Biological Weathering: Occurs when living organisms (roots, burrowing animals, bacteria) break down rocks. Primary Causes and Processes Physical Processes: Frost Wedging (Cryofracturing): Water seeps into cracks, freezes, and expands, splitting the rock. Thermal Expansion: Constant heating and cooling in desert environments cause rocks to weaken and peel (exfoliation). Pressure Release: As overlying rock is removed, underlying rock expands and cracks. Chemical Processes: Oxidation: Oxygen reacts with iron-containing minerals, creating iron oxide (rust). Carbonation/Dissolution: Rainwater mixed with CO2 creates weak carbonic acid that dissolves rocks like limestone. Hydrolysis: Water reacts with minerals to break them down, often forming clay. Biological Processes: Tree roots grow into crevices and pry rocks apart, while burrowing animals expose new surfaces to air and water. Weathering constantly changes the landscape, wearing away surfaces to form landforms such as arches, pedestals, and sea caves. It is essential for soil formation and prepares rock material to be moved by erosion. Human activity, such as burning fossil fuels, accelerates chemical weathering through acid rain. Deposition Deposition is the process where transported sediments, such as rock fragments, soil, debris, or organic matter, settle and are laid down in new locations as transporting agents (water, wind, ice) lose energy. It builds up landforms like deltas, beaches, and sand dunes, acting as the final step in the erosion-transport-deposition cycle. Process: As water or wind velocity decreases, the transporting medium can no longer carry sediment load, causing particles to sink and settle. Larger particles typically settle first. Forms of Deposition: Fluvial (Rivers): Creates floodplains, deltas, and alluvial fans. Aeolian (Wind): Forms sand dunes and loess deposits. Glacial (Ice): Deposits moraines, drumlins, and erratic boulders. Marine (Ocean): Creates beaches, spits, and deep-sea sediment layers. A function of deposition is that it forms new land, creates sedimentary rock layers (through compaction/cementation over time), and contributes to, or degrades, habitats. A method of managing deposition is by controlling water velocity and reducing erosion sources, such as by managing agricultural runoff or stabilizing shorelines to reduce coastal erosion. Historical Geology While physical geology studies the current things about earth, historical geology studies the things that happened to earth in the past, like how Theia crashed into Earth and made the moon or how the first ever cyanobacteria developed oxygen out of methane and carbon dioxide during the Proterozoic Eon. In Historical Geology, you will learn about: the Paleozoic Era (The Age of Ancient Life): 252-541M years ago. the Mesozoic Era (The Age of Reptiles): 66-252M years ago. the Cenozoic Era (The Age of Mammals): current era. and the Precambrian Eons; explained later on and how creatures of their times affected our modern world. The Precambrian Eons There isn't a Precambrian Era, but it consists of 3 eons, the Precambrian Eons. It also includes a period. These include: the Hadean Eon: 4.6-4.0B years ago (Earth was molten and bombarded by asteroids). the Archean Eon: 4.0-2.5B years ago (Earth's crust cooled, forming oceans and single-celled life): Neoarchean: 2.8-2.5B years ago (stabilized Earth's crust into the first continents, oxygen-producing cyanobacteria rose, initiating photosynthesis). the Proterozoic Eon: 2.5B-541M years ago (cyanobacteria filled Earth with oxygen, setting up complex life); Cryogenian: 720-635M (Earth dramatically cools, glaciers stretch to the equator, Earth is almost completely encased in ice) the Ediacaran Period: 635-538M years ago (massive global ice ages melt, soft multicellular organisms evolve, tube and disc-shaped dominate the sea floor). Periods Of The Paleozoic Era Cambrian: 541-485M years ago (major animals are aquatic, trilobites and brachiopods rule, jawless fish emerge, super-continent Gondwana forms near the South Pole, the rest is bare rock) Ordovician: 485-443M years ago (coral reefs begin to form, moss-like plants and fungi emerge on land, ice age starts, freezing oceans with glaciers, causing a mass extinction). Silurian: 443-419M years ago (Earth's climate stabilizes, glaciers melt, sea levels rise, vascular plants with stems evolve, early spiders, centipedes, and insects move onto land). Devonian: 419-359M years ago (fish develop armored scales and sharp jaws, trees and deep-rooted forests appear, tetrapods evolve from lobe-finned fish and crawl onto mudflats, rapid cooling and oxygen drops in the ocean causes another mass extinction). Carboniferous: 359-299M years ago (tropical swamp forests cover the continents and die, forming coal beds, oxygen levels rise to 35% letting massive insects to evolve, animals lay amniotic eggs, allowing them to breed away from water). Permian: 299-252M years ago (every continent collided, forming Pangea, Pangea's size creates vast, dry deserts in the interior, synapsids and reptiles spread across the dry land, massive volcanic eruptions in modern-day Siberia wipe out 95% of marine life). Periods Of The Mesozoic Era Triassic: 252-201M (Pangea starts to crack apart, Earth is hot and dry, dinosaurs and mammals first evolve). Jurassic: 201-145M (oceans flood continental rifts, giant plant-eating dinosaurs dominate, first birds take flight). Cretaceous: 145-66M (flowering plants appear, Tyrannosaurus rex rules the land, asteroid impact wipes out dinosaurs). Periods Of The Cenozoic Era Paleogene: 66-23M (climate is warm and tropical, mammals grow much larger, birds diversify rapidly). Neogene: 23-2.6M (global temperatures cool down, vast grasslands spread, early human ancestors evolve). Quaternary: 2.6M-present (giant ice ages over continents, modern humans spread globally, large mammals go extinct). How The Mountains Were Made Taconic Orogeny: 450M years ago (an island arc collides with eastern North America, creating volcanic roots of the early Appalachian mountains). Alleghenian Orogeny: 325-260M (Africa collides with North America during the assembly of Pangea, lifting the Appalachian Mountains to the height of the modern Himalayas). Theia, The Moon, And Earth alt=An image of the Moon.|thumb|The Moon About 4.5 billion years ago, the early Earth was molten and hot. Theia: a rogue planet roughly the size of Mars, flying through space at 25,000 miles per hour (40,000 km/h). Then, Theia delivered an off-center, blow to Earth. If it had been a head-on collision, both planets would have been pulverized into space dust. The Ultimate Splatter Zone The impact was so violent that it completely vaporized Theia and blasted a massive chunk of Earth’s outer crust into orbit. For a brief period, Earth looked a bit like Saturn, surrounded by a glowing, ring of molten rock and debris. You might think it took billions of years for that debris to form our Moon, but gravity does not like to wait around. Scientists estimate that the ring clumped together to form the Moon incredibly fast—potentially in less than a century, or even just a few months. The Proof Is In The Moon Rocks When Apollo astronauts brought rocks back from the Moon, scientists checked their "chemical DNA" (oxygen isotopes). Usually, planets from different parts of the solar system have completely unique chemical signatures. But the Moon's rocks perfectly matched the Earth's crust. How Theia Changed Earth Forever Without this catastrophic cosmic car crash, life as we know it wouldn't exist. Theia left behind three permanent parting gifts: Our Seasons: The impact hit Earth so hard it knocked our planet onto a permanent 23.5-degree tilt. Without Theia, we wouldn't have Summer, Fall, Winter, or Spring. A Supercharged Core: Theia’s heavy iron core sank straight into the molten Earth and merged with our own. This gave Earth a massive magnetic field, acting like a giant shield that blocks deadly solar radiation. Longer Days: Right after the crash, an Earth day lasted only 5 hours because the planet was spinning at breakneck speed. The Moon's gravity has spent the last 4.5 billion years acting like a brake pad, slowing our spin down to a comfortable 24 hours. Largest Creatures Of Each Period There are thousands of millions of different creatures that spawn from each period, but these are the largest of each: Cambrian: Anomalocaris (a small three-foot-long marine predator with giant armored eyes and grasping claws that ruled the shallow seas). Ordovician: Cameroceras (a massive twenty-foot-long straight-shelled squid that dominated the deep ocean). Silurian: Pterygotus (a huge seven-foot-long sea scorpion with large flattening swimming paddles and sharp crushing claws that prowled the shallow coastal waters). Devonian: Dunkleosteus (a terrifying thirty-foot-long armored predator fish with bone-shearing jaw plates instead of teeth that terrorized the deep seas). Carboniferous: Arthropleura (a monstrous eight-foot-long land-dwelling millipede with a heavily armored, multi-segmented body that patrolled the lush forests). Permian: Moschops (a heavy-set fifteen-foot-long mammal-like reptile with a barrel shaped body and a thick barrel-vaulted skull that roamed the ground). Triassic: Shastasaurus (a gigantic seventy-foot-long marine reptile with a highly elongated toothless snout and slender flippers that commanded the open oceans). Jurassic: Maraapunisaurus (a colossal 115-foot-long long-necked sauropod dinosaur with whip-like tails and massive column-like legs that stomped across the land). Cretaceous: Patagotitan (a titanic ninety-foot-long sauropod dinosaur with a small head, immensely long neck, and heavy pillar legs that reigned over the continents). Paleogene: Basilosaurus (a predatory sixty-foot-long early whale with an extremely elongated eel-like body and small vestigial hind legs that haunted the ancient seas). Neogene: Megalodon (a ferocious fifty-foot-long apex predator shark with robust, triangular serrated teeth the size of a human hand that controlled the global oceans). Quaternary: Blue whale (an immense one hundred-foot-long marine mammal with a streamlined, mottled blue-gray body and expansive baleen plates that inhabits the modern oceans). Fossils Fossils are the preserved remains, impressions, or traces of ancient life trapped inside Earth's crust. They act as nature's time capsules, allowing historical geologists to reconstruct vanished ecosystems, track evolution over millions of years, and pinpoint the exact ages of rock layers. Types Of Fossilization Animals and plants turn into fossils in several distinct ways, depending on how they were buried and what minerals were nearby: Petrification: Mineral-rich water seeps into organic cavities and turns the original bone or wood entirely into solid rock (like petrified wood). Molds and Casts: An organism dissolves inside a rock layer, leaving an empty hollow space (a mold) that later fills with sediment to create a perfect replica copy (a cast). Carbonization: Intense underground heat and pressure squeeze out all liquids and gases, leaving a flat, thin, black film of carbon on the rock (common for leaves and fish). Preservation: The rarest form where an entire organism is kept perfectly intact by being frozen in ice, dried out in caves, or trapped inside sticky tree sap (amber). Trace Fossils: Rather than saving the body itself, these capture the active behavior of ancient life, including fossilized footprints, feeding burrows, and coprolites (fossilized poop). How Geologists Use Fossils Fossils are not just museum display pieces; they are essential field tools used by geologists to solve mysteries about Earth's past: Index Fossils: Certain creatures (like Trilobites) lived everywhere on Earth but only for a very short geological timeframe. Finding one instantly reveals the exact age of that rock layer. Ancient Climates (Paleoclimate): Finding a fossilized tropical palm tree or crocodile in modern-day Antarctica proves the freezing continent was once a warm, swampy jungle. Continental Drift Evidence: Discovering the exact same freshwater reptile fossils in both South America and Africa helped prove the continents were once physically joined together. Mass Extinctions Earth's history has been completely rewritten five different times by catastrophic events known as the "Big Five" mass extinctions. These events wiped out the dominant species of their time, clearing the way for entirely new creatures to evolve. Ordovician-Silurian Extinction: Intense global cooling and freezing ice ages locked up Earth's water, causing sea levels to drop drastically and destroying the shallow ocean habitats. Late Devonian Extinction: A massive drop in ocean oxygen levels suffocated marine life, hitting reef-building creatures and armored predator fish the hardest. Permian-Triassic Extinction ("The Great Dying"): The most devastating extinction in Earth's history, caused by massive volcanic eruptions in Siberia. It released toxic gases, triggered severe global warming, and wiped out 96% of all marine species. Triassic-Jurassic Extinction: Huge underwater volcanic rifts opened up as Pangea began to split apart, raising carbon dioxide levels and triggering rapid climate changes that eliminated early reptiles. Cretaceous-Paleogene Extinction: A massive six-mile-wide asteroid smashed into modern-day Mexico, triggering global wildfires, a nuclear winter, and blocking out the sun, which famously wiped out all non-avian dinosaurs. Supercontinents A supercontinent is a single, massive landmass made up of most or all of Earth's continental crust smashed together. Driven by tectonic plate movements, Earth goes through a "supercontinent cycle" roughly every 300 to 500 million years, where landmasses continually crash together, break apart, and scatter. The Timeline Of Earth's Major Supercontinents Vaalbara (3.6 to 2.8 Billion Years Ago): Earth's earliest known hypothetical supercontinent, forming when the planet was mostly ocean and small volcanic island chains collided. Kenorland (2.7 to 2.1 Billion Years Ago): Formed near the equator during the Neoarchean era, its breakup eventually triggered a massive global ice age due to rapid climate shifts. Columbia / Nuna (1.8 to 1.3 Billion Years Ago): A giant landmass stretching across the globe that marked the first time large, modern continental blocks fully assembled. Rodinia (1.1 Billion to 750 Million Years Ago): A massive supercontinent surrounded entirely by the Mirovia ocean, centered around modern-day North America before fracturing apart into a freezing, ice-covered Earth. Pannotia (633 to 550 Million Years Ago): A short-lived landmass clustered near the South Pole that formed just before the Cambrian explosion of complex marine life. Gondwana (550 to 175 Million Years Ago): An ancient southern supercontinent composed of modern-day South America, Africa, Antarctica, India, and Australia. It existed as its own massive entity for millions of years before merging into Pangea, and then splitting back apart later. Pangea (335 to 175 Million Years Ago): The most famous C-shaped supercontinent that united almost all of Earth's dry land, including the northern landmass of Laurasia and the southern landmass of Gondwana, creating a single home for early dinosaurs. How Supercontinents Altered Earth's Climate And Crust The formation of a supercontinent completely breaks the planet's normal systems, creating extreme environments found nowhere on modern Earth: Hyperarid Interior Deserts: Because the landmass is so incredibly wide, rain clouds from the surrounding oceans dry up completely before they can ever reach the center. This creates massive, lifeless "super-deserts" in the heart of the continent. Mega-Monsoons: The vast temperature difference between the roasting-hot interior landmass and the cold surrounding super-ocean creates violent, seasonal shifting winds, resulting in catastrophic monsoon downpours along the coastlines. The "Snowball Earth" Effect: When supercontinents split apart, they create brand new coastlines that rapidly absorb carbon dioxide from the atmosphere. This can drop global temperatures so fiercely that ice sheets completely cover the planet from poles to equator. Mantle Superplumes and Volcanic Traps: When a supercontinent sits over one spot on Earth's crust for millions of years, it acts like an insulating blanket. Heat builds up directly underneath it, eventually triggering colossal volcanic eruptions (large igneous provinces) that rip the continent apart and spew toxic gases into the atmosphere. How Geologists Prove They Existed Matching Coastlines: The continental shelves of separate continents (like South America and Africa) fit together perfectly like giant jigsaw puzzle pieces. Fossil Belts: Identical ancient plant and animal fossils are found in narrow strips across oceans where the continents used to touch. Matching Mountain Ranges: Rock layers and mountain chains (like the Appalachians in North America and the Scottish Highlands) share the exact same age, type, and composition. Paleomagnetism (Magnetic Alignment): When volcanic rocks cool, iron minerals inside them align perfectly with Earth's magnetic north pole like tiny compass needles. Geologists measure this locked-in magnetic angle to calculate exactly where a continent was located on the globe millions of years ago. Orogenic (Mountain Building) Belts: When tectonic plates crash together to form a supercontinent, the immense pressure crumples the crust upwards, leaving behind massive global scars of matching metamorphic rock layers across modern state and country borders. Global Mineral Belts: Highly specific copper, gold, and uranium deposits match up perfectly in straight lines when you stitch the continents back together, showing they were formed by the exact same underground magma chambers. How Supercontinents Drive Evolution The locking together and breaking apart of landmasses acts as the ultimate evolutionary accelerator for life on Earth: The Isolation Engine: When a supercontinent fractures into smaller islands and separate continents, animal populations become completely isolated from one another. This forces rapid, localized evolution to fill unique environmental niches (similar to how Madagascar or Australia evolved highly unique wildlife). The Competition Arena: Conversely, when continents crash together into a single landmass, previously isolated species are forced to compete for the same food sources and habitats. This triggers massive evolutionary "arms races" where only the fittest, most adaptable creatures survive. Future Supercontinents (The Next 250 Million Years) Because tectonic plates never stop moving at a rate of a few centimeters per year, scientists have calculated four potential layouts for Earth's next ultimate supercontinent: Pangea Ultima: A configuration where the Atlantic Ocean slows down, reverses direction, and closes completely—bringing the Americas crashing back into Africa and Europe. Novopangea: A layout where the Pacific Ocean closes entirely instead of the Atlantic, causing the Americas to slam straight into Asia and Australia. Aurica: A scenario where both the Atlantic and Pacific oceans close down completely, forcing a brand new ocean basin to rip open right through the center of modern Asia. Amasia: A unique collision where all continents drift northward, clustering together directly over the North Pole, leaving Antarctica isolated at the bottom of the world. Category:Shelf:Geology