Scientific Method, Igneous Rocks, Sedimentary

• Science describes the material universe through repeatable observations and hypothesis testing.
• Repeatable observations involve re-sampling from the physical universe.
• A common misconception is that subjects not replicated in a lab are "unscientific" because they can’t be repeated.

Hypothesis Testing

• Hypotheses must be testable and falsifiable.
• Falsifiable hypotheses can be disproven.
• Non-falsifiable statements are speculation.
• A null hypothesis states "no effect," and a hypothesis states "an effect."
• Science supports or rejects hypotheses rather than proving them.

Theories vs. Laws

• Theories are statements of process comprising many hypotheses.
• Laws and theories can be considered facts but may be overturned.
• Something is unscientific if it doesn’t adhere to the scientific method.
• Unscientific doesn’t necessarily mean wrong, just not testable.

Earth’s Beginnings

• Density differences separate the Earth’s layers, like the crust and core.
• The solar system is just one of over 100 galaxies.
• Uniformitarianism suggests that processes happening today likely occurred in the past.
• Newton’s law of motion states that objects in motion stay in motion, and objects at rest stay at rest.

Big Bang Theory

• The universe expanded ~14 billion years ago.
• Evidence for the expanding universe includes wavelengths and the Doppler effect.
• Wavelengths moving away appear redder (redshift), and those moving closer appear bluer (blueshift).
• The majority of galaxies have a reddish tint, indicating they're moving away.
• Vesto Slipher determined the speed at which celestial objects were moving away.
• Hubble discovered more than one galaxy.
• Background cosmic radiation is considered an echo of the Big Bang.

Nucleosynthesis and Star Formation

• Nucleosynthesis is the creation of atoms.
• Stellar nucleosynthesis involves the creation of atoms in stars reaching a tipping point at iron.
• Elements heavier than iron are created in supernovas.
• Nebulae are clouds of debris in space where stars form, either through gravitational collapse or supernova.
• Hydrogen and helium are the most abundant elements in the universe.
• Cold temperatures lead to contraction and increase density.
• Accretion is the process of growth or obtaining mass at high speeds.
• The formation of the Sun led to further nucleosynthesis.
• Gravity forces celestial bodies to become round.
• Earth formed 4.6 billion years ago; the oldest rocks are dated to 3.8 billion years ago, and grains within rocks to 4.4 billion years ago.
• Early Earth was partially molten.
• Meteorites, especially from Mars, help determine the age of the Earth.
• Radiometric dating helps understand Earth's earliest moments.
• The Earth's core is primarily iron and nickel due to their density aka the iron catastrophe.
• The magnetic field's shape changes over time and allows for the formation of the ozone layer.
• The moon's origin was initially uncertain.

Plate Tectonics and Continental Drift

• Plate tectonics is a unifying theory of geology.
• Alfred Wegener, a German geophysicist and meteorologist, proposed continental drift in 1915.
• Continental drift suggests that continents have slowly moved across the Earth’s surface.
• Pangaea is the name given to the collection of continents.
• Evidence for continental drift includes matching fossils and geographical landmarks on different continents.
• Other corroborating evidence includes the continuity of ancient mountain belts, major faults, and ancient climate evidence.
• Wegener's evidence for continental drift was initially ridiculed because he could not provide a mechanism for the movement and the Earth was thought to be solid.

Paleomagnetism and Seafloor Spreading

• Paleomagnetism eventually supported Wegener's hypothesis.
• The Earth’s magnetic field is generated by the iron-rich core.
• Latitude can be determined by Paleomagnetism and the magnetic angle.
• Rocks preserve magnetization when they form.
• The Curie temperature is the boundary temperature above which materials lose magnetic properties.
• Magnetic reversals occur where north and south magnetic poles change places.
• Magnetic stripes on the ocean floor provided evidence for magnetic reversals.
• Sonar technology development in the 1950s aided this discovery.
• Stripes are explained by magma generation as plates move apart.
• Symmetric movements of the seafloor occur away from major ridges.
• Marie Tharp and Bruce Heezen produced the first map of the seafloor.
• Tharp's ideas were confirmed by drilling on the ocean floor.

Subduction and Plate Boundaries

• Subduction is the process by which the ocean floor sinks back into the Earth's interior at subduction zones, leading to volcanoes and earthquakes.
• Oceanic crust is denser than continental crust, causing it to be subducted.
• Identified the mechanism to keeps things the same size - subduction
• Continents drifting are moving, supporting Wegener's idea.
• Plates move at about the speed that nails grow.
• Oceanic crust is denser due to iron and magnesium.
• Basalt is a common rock in oceanic crust, while granite is found in continental crust, which is not as dense.

Types of Plate Boundaries

• Divergent boundaries involve plates moving apart, often starting as continental rifting where continents expand and split.
• Convergent boundaries involve plates moving together: oceanic-oceanic, oceanic-continental (oceanic subducts), and continental-continental (mountain building).
• In oceanic-oceanic convergence, older plates subduct because they are colder and denser.
• Convergent boundaries lead to volcanoes and earthquakes.
• The Wilson cycle describes the opening and closing of ocean basins;. The Pacific is in the older stage, and the Atlantic is younger.
• Transform plate boundaries involve plates sliding past each other, causing medium-damaging earthquakes.
• Plates move at 15-100 mm/year, with the fastest movement at 170 mm/year.

Plate Tectonics and Hotspots

• Plate tectonics are driven by internal heat.
• Hawaii's volcanoes are due to a hotspot, rather than a plate boundary.

Igneous Rocks and the Rock Cycle

• The three types of rocks are igneous, sedimentary, and metamorphic (formed by heat and pressure).
• Rocks are aggregates of minerals.
• Igneous rocks form from the cooling and crystallization of molten rock (magma)
• Lava is molten rock that reaches the surface while magma stays below

Magma Formation and Transport

• Igneous rocks tie into the rock cycle as products of materials that melt inside the earth at convergent plate boundaries.
• What's needed to melt rock and form magma is heat and pressure
• Rocks are composites of minerals that melt at different temperatures which results in partial melting melting only part of the rock materials.
• Magma forms and transports because Water is a volatile and is the main reason for erosion.
• The mantle melts at a higher temperature.
• Magma reaches the surface by rising from density differences, or melting/breaking weak points in the crust.
• Not all magma reaches the surface; some cools below the surface.

Textures of Igneous Rocks

• Texture describes a rock's overall appearance based on the size, shape, and arrangement of mineral grains, which is affected by the composition of the melt and rate of cooling.
• Fast cooling leads to small grains.
• Slow cooling leads to large grains.
• Aphanitic textures lack visible crystals, while phaneritic textures have visible crystals.
• Volcanic glass (obsidian) forms from cooling molten material very quickly.

Extrusive vs. Intrusive

• Cooling rate depends on where igneous materials cool:. Extrusive rocks cool faster on the surface, while intrusive rocks cool slower beneath the surface.
• Plutons are crystallized remnants of magma chambers.
• Intruding magma heats the existing rock it touches.
• Can classify rocks based on texture and composition, using silica content: felsic (more than 66% SiO2), intermediate (52-66% SiO2), mafic (45-52% SiO2), and ultramafic (less than 45% SiO2).
• Viscosity is a material's resistance to flow (stickiness).
• Felsic compositions are high in silica, low in iron and magnesium.

Evolution of Igneous Rocks

• As magma cools, it becomes more felsic.
• Materials that are least dense cool/crystallize last.
• Assimilation is the melting of intruded existing rock into magma, altering the composition.
• Fractionation and assimilation act in unison.
• A xenolith is rock left intact from assimilation, providing insight into the lower mantle.
• Magma composition affects volcanic eruptions.
• A volcano is a structure formed when magma becomes lava and erupts onto the surface, either on land or underwater.
• Most volcanoes are located at the Ring of Fire, a convergent plate boundary.
• At divergent plate boundaries melting will occur faster when pressure is removed.
• Mafic is rich in iron and magnesium, felsic means feldspar and silica.
• Bowen's reaction series describes the temperature at which rocks cooled.

Sedimentation and Sedimentary Rocks

• Weathering breaks down rocks and minerals, and it's called eroding when materials start to move
• Sediment is naturally occurring unconsolidated material like fragments of bedrock, minerals, shells, and/or crystals.
• Weathering forces include water and air.
• Two types of weathering are physical and chemical.
• Chemical erosion involves water, acidic fluids, etc.

Erosion and Lithification

• Water is the strongest eroding force.
• Sediments can be transported thousands of kilometers before being deposited.
• Lithification is when sediments become rocks, this includes: Compaction to compress together and Cementation when water starts to act like glue and hold things together.
• Lithification leads to two types of sedimentary rocks, clastic (sediments, single grain) and chemical/biochemical sedimentary rock (created by something).
• Clastic sedimentary rocks are the end product of sediments transported primarily form mechanical weathering.
• What you can find:
  • Clast composition helps determine the source area,Grain size indicates proximity to the source.
  • Sorting measures the variation in grain sizes; well sorted sediments are of similar size, while poorly sorted sediments have various sizes.
  • Grain shape, whether blocky or round, and if the clasts are angular or rounded depend on how long something has been reworked/moved.
• Sediment maturity indicates the degree to which the sediment evolved from initial weathering; mature sediments are well sorted and well rounded while immature are angled.

Chemical and Biochemical Sedimentary Rocks

• Chemical/biochemical sedimentary rocks Formed from the inorganic precipitation of minerals from solution.
• Chemical sedimentary rocks have a non-clastic texture, composed of interlocking crystals rather than broken fragments.
• Examples of sedimentary rocks include:
  • Evaporites made by precipitation of salts left by seawater evaporation.
  • Travertine composed of calcite created from hot springs or caves; calcite is tested with acid.
  • Oolitic limestone formed from cementation of ooids.
  • Biochemical limestone made of fragments of fossil shells and CaCO3.
• Rocks are classified on mineral composition.
• Chalk is a white, soft, porous biochemical sedimentary rock made of skeletal remains from microorganisms.
• Coal is highly compressed plant remains from oxygen-deficient environments, older than 250 million years.
• Examples of things to look at: Beds, Cross Beds, Graded Beds, Mudcracks, and Ripple Marks.

Sedimentary Structures and Sea Level

• Beds are layers of sediment or sedimentary rock with distinctive characteristics.
• Cross beds are inclined layers caused by wind and water.
• Graded beds are sedimentary layers with coarse grains at the bottom and fine grains at the top.
• Mudcracks are surface cracks that form when sediment is exposed to air and dries out.
• Ripple marks are small curving ridges formed from water and wind currents.
• Sediment deposition is strongly linked to sea level in transgression and regressions.
• Transgression is flooding due to sea level rise and Regression is exposure due to sea level fall.
• Rock type helps us know what the sea level was as it will predict what the rock is.
• Sedimentary rocks are of economic value.
• There are examples that say that the larger the grain, the more energy.
• Weathering breaks down rocks and erodes and then sediments compact and cement.
• Carbonates are either biochemically precipitated by corals, chemical/ formed through evaporation aka evaporites.
• Asymmetrical ripple marks move in one direction, symmetrical mean more than one.

Metamorphism and Metamorphic Rocks

• Protolith is the parent rock before metamorphism where mudstone/shale is the most common.
• Changes to metamorphic rock: recrystallization, phase change.
• Example diamond and graphite.
• Directed pressure is pressure from specific directions, coming from every single direction.
• There are also fluid Interations: Hydrothermal fluids are the very hot water solutions.
• Speed up metamorphic reactions.
• Metasomatism consists of compositional changes during metamorphism.

Relative Dating and Stratigraphy

• William Smith introduced the principle of faunal succession.
• Faunal succession states that fossils in successive rock layers occur in predictable orders
• Relative dating figures out the order layers were formed. It also figures out the rate at which rock layers were formed, flooded, etc.
• Lithostratigraphy uses features of rock layers to perform geologic correlations
• Superposition states the layers over top are younger therefore faults go either down = normal or faults go up = reverse.
• Unconformities represent missing time due to erosion and weathering.

Walther's Law and Biostratigraphy

• Walther’s law of facies states preserved environments stack vertically and it means you should be able to read the rock record like a book, from start of deposition to end
• Biostratigraphy uses fossils to perform geologic correlation defining biostratigraphic units and uses index fossils.
• Index fossils need to be abundant, easily identifiable, geographically widespread and preserved in many types of rocks/ Independent of environment, narrow stratigraphic and temporal range.

Explore the scientific method, hypothesis testing, characteristics of igneous and sedimentary rocks. Understand the roles of falsifiability, uniformitarianism, and Bowen's reaction series.