rocks 2

 What is the difference between relative age and absolute age?

relative age tells you which rocks and fossils are older than others, while absolute age tells you the exact age of a rock or fossil

What are Steno’s principles (original horizontality, superposition, lateral continuity, cross-cutting relationships), and how can they be used to determine the age of a rock?

Steno’s principles are the foundational rules that geologists use to determine the relative age of rocks and establish the order in which events happen. The four principles will explain how to determine the age of a rock on future flashcards.

Original Horizontality

If sedimentary rock layers are found tilted, folded, or steep, a geological disturbance (such as a mountain building or faulting) must have happened after the layers formed.

Superposition

In an undisturbed stack of rocks, the oldest layers are on the bottom of the stack, and the youngest layers are on the top of the stack.

Lateral Continuity

Sedimentary layers extend outwards in all directions across a basin until they thin out, pink or meet a barrier. If a valley or canyon cuts through a layer, the matchin rock types on both sides were originally where part of the same layer.

Cross-cutting

Any geological feature such as a fault, fracture, or igneous intrusion, that cuts through or disrupts an existing rock layer is younger than the rock it intersects.

What are unconformities?

Buried breaks or gaps in the geologic record where rock layers are missing because of erosion or a pause in sediment deposit.

What is an index fossil, and how can it be used to date a rock?

An index fossil is the preserved remains or trace of a plant/animal that lived for a brief period of time, was geographically widespread and existed in large numbers.

Index fossils are used for relative dating because the organism only lived during a specific known time of Earth’s history. Finding an index fossil means that the rock layer must have formed during that exact time span.

What type of information can be reconstructed from sediment cores?

Sediment cores act as natural time capsules that allow scientists to reconstruct millions of years of Earth’s environmental and climate history.

What factors can influence sediment accumulation rate?

Sediment Accumulation Rate is the rate at which sediment is built up in a specific area over a given period of time.

Sediment Supply —> the total volume of material available

Water Flow Velocity —> Fast moving water or wind carries particles easily and keeps them suspended, when it slows down so does sediment deposition.

Particle Size and Shape —> Heavier and coarser particles drop out of suspension quickly, while lighter particles stay suspended for longer,

Water Depth and Basin Size —> shallow or smaller water bodies allow more accumulation, while deeper water bodies have slower accummulation rates.

Climate and Weather —> heavy rainfall and melting ice increase soil erosion, which washes more sediment into water bodies.

Human Activity —> Deforestation, construction, agriculture, and damming rivers alter how much spil erodes and where sediment will get trapped/released

Water Temperature —> Cooler water increases density and slows down the settling speed of particles.

Vegetation and Organisms—> plants, algae, and coral reefs trap floating sediment, while organisms will stir up sediment

Subsidence —> The ground will sink over a long period of time and creates space for more sediment to pile up

How are isotopes used for age dating?

Isotopes are used for age dating through radiometric dating, a method that measures radioactive decay or parent isotopes into daughter isotopes.

What is half-life?

The time required for a quantity of a substance to reduce to half of its initial value.

How does half-life relate to age?

By measuring the ratio of the remaining parent isotope to the accumulated daughter isotope in a sample, scientists can see how many half-lives have passed.

What kind of rocks can be dated using isotopes?

Radiometric dating works best on Igneous and Metamorphic rocks.

If you know the ratio of daughters to parents and half-life (or decay constant), how can the age of the rock be dated?

Convert the Ratio to parent fraction —> fraction remaining = parent / (parent + daughter)

Use Radioactive decay equation —> Parent atoms remaining = original parent atoms e^(- decay constant * age of rock)

Age of rock = ln(original parent atoms / Parent atoms remaining) / decay constant

How does carbon dating work?

Carbon dating measures the decay of radioactive carbon in organic remains to calculate how long ago an organism died.

Can rocks of all ages be dated using carbon dating?

No, rocks cannot be dated using carbon dating. Carbon dating only works in the presence of Carbon-14 which only forms from once-living things.

What are examples of radioactivity we are surrounded by?

We are surrounded by low levels of natural and man-made radioactivity, known as background radiation. Radon gas, Cosmic radiation, medical procedures (x-rays, CT scans), smoke detectors, etc.

 How are radiogenic isotopes related to nuclear power generation?

Radiogenic Isotopes: Isotope that radioactively decays from an
‘unstable’ parent to a ‘stable’ daughter isotope

When they are unstable, they go through nuclear fission which creates nuclear energy.

 What are some pros and cons of nuclear energy?

Pros: reliable, low-carbon power source, a tiny amount of nuclear fuel produces way more energy than fossil fuels.
Cons: High financial costs and long-term waste challenges, terrible accident risks

 What are the physical and chemical differences between the inner core, outer core, mantle, upper mantle, and crust?

Crust: rich in lighter silicate minerals, rigid, and solid

Upper Mantle: Ultramafic rock rich in silicate materials, extends from the crust

Lower Mantle: Composed of dense silicate rocks rich in iron, magnesium, and calcium, makes up 83% of earth’s volume, confining pressure keeps lower mantle in a hot, hard, solid state.

Outer Core: metallic alloy composed primarily of iron and nickel, mixed with lighter elements like sulfur and oxygen. Liquid state.

Inner Core: A dense metallic alloy of mostly iron and nickel. Solid state, remains solid because the freezing point of iron is raised higher than the ambient temperature by intense pressure.

What is a tectonic plate? What parts of the Earth are part of it?

Tectonic Plate: massive irregularly shaped slab of solid rock that makes up Earth’s outer shell.

The Crust and the Upper mantle make up the Tectonic plates.

Are earthquakes found at all plate tectonic boundaries? Which ones?

Yes, earthquakes occur at all three main types of plate tectonic boundaries.

Convergent Boundaries (plates collide): One plate is pushed under another plate or they smash together to form mountains. Most destructive type of earthquake

Divergent Boundaries (plates pull apart): Magma rises to fill the gap as plates drift away from each other. Makes frequent but small/shallow earthquakes

Transform Boundaries (plates slide past each other horizontally): Rough edges of the plates grind sideways past one another, getting stuck until stress snaps. Produces frequent and shallow quakes near the surface.

What is the difference between transform, convergent, and divergent plate boundaries?

Convergent is where plates collide, creates mountains, oceanic trenches and destructive earthquakes. Destroys crust.

Divergent is when two plates pull apart from each other, mild volcanic eruptions and shallow earthquakes are created. Creates Crust

Transform is when two plates grind and slide past each other, fault lines, very small earthquakes, and no volcanic activity. Nothing happens to the crust

Why do plates move?

Tectonic plates move because of intense heat inside the Earth and gravity acting on the planet’s rigid outer shell.

What was Wegener’s hypothesis for continental drift, and why was his hypothesis initially rejected?

Wegner proposed that all of Earth’s continents were once joined together in a single super-continent called Pangaea before breaking apart and slowly drifting to their current positions over millions of years.

This was originally rejected because he could not explain how solid landmasses could plow through crust and because scientists believed that the Earth’s crust was completely solid and immovable.

What evidence eventually led to acceptance of plate tectonic theory?

Ocean-floor mapping and the acceptance of plate tectonic theory.

 What is the elastic rebound theory?

The elastic rebound theory explains how energy is stored and released in the Earth’s crust during an earthquake. Pressure builds up as plates grind past each other, rocks bend and store energy, the rocks snap back when the pressure becomes too much, and then an earthquake happens.

How do GPS stations monitor plate motion?

GPS stations monitor tectonic plate motion by continuously receiving radio signals from orbiting satellites to track their exact 3D position on Earth’s surface over time.

How do you read a GPS station?

You look at the the Time Series Data to see how the station is shifting over time. The top graph in the Time Series Data shows North+South Motion) latitude, the middle graph shows East-West Motion (longitude), and the bottom graph shows elevation of the station.

How is the total rate of GPS station movement calculated?

Total rate is calculated by this formula:

Total Rate = Sqrt( [north-South velocity]² + [East-West Velocity]² )

How do you read GPS vectors?

GPS vectors can be drawn as arrows. The length of the arrows shows the speed (magnitude) and the direction of the arrow shows where the land is drifting.

At transform boundaries, are both plates always moving in opposite directions?

Yes, the plates are moving in opposite directions.

 What type of motion will lead to earthquakes: similar rates or different rates?

Earthquakes happen when plates move at different rates causing the fault to become locked and accumulate elastic stress.

How do GPS station data change during an earthquake?

During an earthquake, there will be a sudden jump in the time-series graph.

How do you calculate total displacement during an earthquake?

You measure the final distance between two points before the fault moved.

Total Displacement = sqrt( x² + y² + z²) where x = east/west, y = north/south, and z = vertical

Using displacement during an earthquake, how is magnitude calculated or estimated?

M = Rigidity x Area x Slip

Rigidity = shear strength or stiffness of the rock along the fault

Area = total surface area of the fault plane that slipped during the earthquake

Slip = average distance of displacement

What does earthquake magnitude tell you about damage?

Magnitude tells you the total amount of energy released at the source or the size of the seismic event.

Under 2.5: Rarely felt by people; recorded only by seismographs.

2.5 to 5.4: Often felt, causing little to no structural damage, though weak buildings can experience minor issues.

5.5 to 6.0: Slight damage to normal buildings and localized risks to vulnerable structures.

6.1 to 6.9: Can cause serious, destructive damage over areas up to roughly 100 kilometers across, especially in populated regions.

7.0 to 7.9 (Major): Causes serious, widespread destruction over large areas.

8.0 or greater (Great): Can totally destroy communities and cause catastrophic damage across hundreds of kilometers

What is mean recurrence interval, and how is it calculated?

The mean recurrence interval is the estimated average time in years between natural events.

Recurrence Interval = (n + 1) / m
n = the total number of years or historical record.

m = the magnitude rank of the specific event (most severe = 1, second largest = 2, etc)

If there are no earthquakes, how can mean recurrence interval be estimated?

The mean recurrence interval can be estimated using geological slip rates. Using GPS and satellite measurements, scientists can measure how fast tectonic plates or fault blocks are creeping or accumulating strain.

How is earthquake probability calculated?

Analyzing historical earthquake rates, fault slip accumulation, and ground motion models.

If we are calculating the probability of an earthquake of a given magnitude happening in the next X years, is the probability of occurring or the probability of NOT occurring used?

Both are used. Mostly because calculating the chance of an event happening over a period of time is much harder to compute rather than computing how likely something won’t happen.

How is seismic risk calculated?

Combining the likelihood of an earthquake shaking the ground with how much damage and loss it can cause to people and property.

What is a hazard?

Something like ground shaking or surface faulting and the potential those have to cause damage or injury.

What is vulnerability?

The susceptibility of people buildings, infrastructure, and communities to suffer damage or injury when an earthquake occurs. This would be something like landslides, liquefaction, or other buildings collapsing on surrounding things.

What is value?

The magnitude and intensity of an earthquake

How does seismic activity vary with different geologic materials?

Seismic activity vary depending on the density, elasticity, and water saturation of the ground.

Hard materials (granite/basalt): high velocity (waves travel fast), ground shakes less, less damage because structures are on solid bases.

Soft sediments: low velocity, ground shakes more, shakes longer, and can cause liquefaction

What is liquefaction?

The process where a solid or gas turns into a liquid, or the condition of being in a liquid state.

How does plate tectonics influence Earth’s climate?

Plate tectonics drive Earth’s climate by controlling carbon dioxide, position of continents, ocean currents, and mountain uplift.

How does weathering remove CO₂ from the atmosphere?

Weathering removes CO2 when a series of chemical reactions that convert CO2 into stable dissolved ions and solid minerals. Acid rain can form and when it falls it can react with rocks. That reaction breaks down minerals and converts the carbon into stable ions. The ions will then wash through soil and go into oceans and rivers.

How can mountain building influence global climate?

Mountain building exposes fresh rock to the atmosphere where rocks go through weathering and can lock carbon away for millions of years.

What type of bedrock is most commonly associated with cave formation in New York?

Limestone

How did Paleozoic shallow seas contribute to cave formation in New York?

Paleozoic seas supplied the materials and building blocks required to form the limestone. The seas deposited sediments and held millions of sea creatures that would die and accumulate on the seafloor.