GeoE/EnvE 153: Earth Engineering Spring 2025 Lecture 6: The Earth and It’s Systems

Flashcards covering key vocabulary and concepts from the lecture notes on Earth systems, plate tectonics, the rock and hydrologic cycles, geologic time, and climate change.

Earth Systems

Civil, geological, and environmental engineers deal with ALL aspects of the earth's systems: 1. Lithosphere, 2. Hydrosphere, 3. Atmosphere, 4. Ecosphere, 5. Climate Change

Earth's Age

The universe is approximately 14 billion years old. The Earth accreted about 4.6 billion years ago. The oldest rock exposure is about 3.5 - 4.0 billion years old.

Earth's Composition Layers

Continental crust is granitic, oceanic crust is basalt, mantle is iron-rich silicates, and the core is iron and nickel.

Earth's Heat Engine

The dominant mechanism to redistribute thermal energy is convection. Thermal convection causes rock/mineral mass to rise from the outer core. Conservation of mass implies rock at the Earth's surface must be subducted into the interior.

Major Features of Earth's Surface

Low-density, older rocks (Na, K, and Ca silicates) concentrated through differentiation and recycling of the lithosphere. Denser, younger rocks (Fe and Mg silicates) formed by mantle plumes that generate new oceanic lithosphere.

Isostasy

The state of gravitational equilibrium between the Earth's lithosphere and asthenosphere, where tectonic plates 'float' at an elevation dependent on their thickness and density.

Glaciation & Isostasy

Continental glaciers in Canada were up to 3 km thick, providing up to 30 MPa of stress on the lithosphere. Uplift of continents and subsidence in ocean basins occur as ice melts and sea levels rise.

Plate Tectonics

The lithosphere is broken into about 13 major plates that float on the molten asthenosphere. Rifting occurs at divergent boundaries where rising magma plumes create new crust. Subduction occurs at convergent boundaries as crust is pushed down into the asthenosphere.

Divergent Plate Boundaries

Move apart from one another.

Transform Plate Boundaries

Move horizontally in opposite directions.

Convergent Plate Boundaries

Two plates come together.

Driving Mechanisms of Plate Tectonics

Convective currents in the asthenosphere rise where heat production is greatest and sink where material is cooler. Originating at divergent plates. Relatively cool and dense oceanic crust sinks into the asthenosphere and pulls the trailing lithosphere with it via gravity.

Pangea

A supercontinent that existed about 200 million years ago, showing Paleozoic glaciation.

Oceanic Divergent Plate Boundaries

A constructive plate margin where seafloor is elevated to form oceanic ridges, with the point of divergence at the crest of the ridge.

Continental Divergent Plate Boundaries

A constructive plate margin forming a continental rift where a landmass splits into two or more smaller segments along rift valleys.

Convergent Plate Boundaries

Destructive plate margin at subduction zones. Ocean-continent. Ocean-ocean. Continent-continent: both plates are too light to subduct, creating a collision.

Transform Boundaries

Lithospheric plates slide past each other along vertical fractures called transform faults.

Hydrologic Cycle

The continuous circulation of water between the oceans, atmosphere, and land.

Urbanization Impact on Runoff

Paving of streets/parking lots decreases areas of infiltration. Capturing rainfall on roofs and roads transmit precipitation directly to the main streams by drainage systems can increase rapid surface runoff drastically

Atmospheric Circulation

The Sun provides energy to the Earth's surface via radiative transfer. Unequal heating causes atmospheric circulation to redistribute thermal energy via convection.

Factors Influencing Precipitation Distribution

Circulation cells, orographic effects, and ocean currents.

Hydrosphere & Oceanic Circulation

Shallow currents driven by atmospheric circulation redistribute thermal energy, while deep currents arise when water freezes, becomes saline, sinks, and completes circulation pattern.

Transformation Sediments to Sedimentary Rock

Deposition, cementation, and compaction (lithification)

Igneous Rock Formation

Melting and cooling and solidification (crystallization).

Metamorphic Rock Formation

Heat and pressure (metamorphism).

Principles of Relative Dating (Law of Superposition and Original Horizontality)

In an undeformed sequence of sedimentary rocks, each bed is older than the one above and younger than the one below. Layers of sediments are generally deposited in a horizontal position.

Relative Dating

Placing geological events into sequential order as determined from their position in the geologic record.

Absolute Dating

Results in specific dates for rock units or events expressed in terms of years before the present (years BP).

Principle of Cross-Cutting Relationships

Any geological feature (magma intrusion or fault) is younger than the rock it penetrates.

Dating with Radioactivity

Dating based on the decay rate of unstable (radioactive) isotopes.

Half-life

The time it takes for one-half of the atoms of the original unstable parent element to decay to atoms of a daughter element.

Global Climate Change

Describes trends and variations in Earth’s climate, like temperature, precipitation, and storm frequency.

Global Warming

An increase in Earth’s average temperature, largely due to human activities such as fossil fuel combustion and deforestation.

Factors Affecting Climate Change

Sun's output, Earth's orbit, drifting continents, volcanic eruptions, and greenhouse gases.

Greenhouse Gases

Atmospheric gases that absorb outgoing LW infrared radiation (water vapor, ozone, carbon dioxide, nitrous oxide, methane, CFCs).

Milankovitch Cycles

Periodic changes in Earth’s rotation and orbit around the Sun.

Ocean's Role in Climate

The ocean holds 50 times more carbon than the atmosphere and absorbs it. Ocean water exchanges tremendous amounts of heat with the atmosphere, and currents move energy around the planet.