Geophysics/Tectonics Brief Review of the Universe

GLY 325

Anthropic Principle

The Multiverse

Geologic Time

(1) Beginning of our Universe with the “Big Bang” 12 billion years ago (12 Ba).

(2) 12 Ba to 7 Ba -- Galaxies, Stars, Planets form and are destroyed.

(3) ~7 Ba -- A particular Red Giant star catastrophically exploded (supernova).

(4) 4.6 Ba -- The remnants of the particular supernova in (3) forms into our solar system including EARTH.

History of the Earth (the short version):History of the Earth (the short version):

Geologic Time

Open Universe

Closed Universe

Compositionof the Universe

Geologic Time

Geologic Time

Step 1: Accretion of cm sized particles

Step 2: Physical Collision on km scale

Step 3: Gravitational accretion on 10-100 km scale

Step 4: Molten protoplanet from the heat of accretion

History of the Earth (the short version):History of the Earth (the short version):

Final step is differentiation of the earth:

==> Light objects float; heavy objects sink. Thus, Iron-Nickel Core and oxygen-silicon Crust

Segregation of the Earth by composition.

History of the Earth (the short version):History of the Earth (the short version):

EarthComposition

Mantle(Fe, Mg)

Core(Ni, Fe)

Crust(Si, O, Al)

6400 km

2900 km

0 km

40 (6) km

To reiterate:(1) Original Protoearth was molten (2) Dense material (molten nickel and iron)

flowed to the center (3) Lighter material (molten silicon) flows to

the top (4) Earth cools and solidifies into basic core,

mantle and crust structure ==> During cooling, the earth has a lot of

trapped gasses in its interior….

History of the Earth (the short version):History of the Earth (the short version):

Outgassing --> Early Formation of the Earth's Atmosphere

Present day composition of volcano effluents: Water Vapor --> 60%

Carbon Dioxide --> 24%

Sulfur --> 13%

Nitrogen --> 5.7%

Argon --> 0.3%

Chlorine --> 0.1%

History of the Earth (the short version):History of the Earth (the short version):

It is likely that there was NOT enough water released via outgassing to account for the present day oceans

Most of the water was likely delivered to the earth after it formed via collisions with left over planetisimals and cometisimals.

History of the Earth (the short version):History of the Earth (the short version):

On Mars it was too cold and water vapor condensed (i.e, came out of the atmosphere). Hence the atmosphere is all Carbon Dioxide

On Venus it was too hot for water vapor to condense (no liquid water). So weathering could not progress and CO2 could not disolve in liquid water. Hence the atmosphere remained rich in Carbon Dioxide

On Earth it was just right. The carbon dioxide content of the earth's atmosphere is now all locked up in rocks and oceans.

History of the Earth (the short version):History of the Earth (the short version):

There are two keys to the evolution of planetary atmospheres:

Fate of the water vapor (gaseous, liquid, solid)

Fate of the Carbon Dioxide (stays in atmosphere vs. dissolves in liquid water or locked in rocks)

History of the Earth (the short version):History of the Earth (the short version):

After condensation of water vapor, the earth's oceans were produced, thus sweeping out the carbon dioxide and locking it up into rocks.

Currently, our atmosphere is 72% nitrogen and 28% oxygen (everything else like H2 and CO2 exists only in trace amounts).

So where did the oxygen come from...?

History of the Earth (the short version):History of the Earth (the short version):

Introduction to Whole Earth Geophysics and Tectonics

Geology 325

Geophysics

The application of physical principles to the study of the earth. Includes branches of seismology, geothermometry, hydrology, physical oceanography, meteorology, gravity and geodesy, terrestrial magnetometry, tectonophysics, engineering and exploration geophysics, geochronology, and geocosmogony.

The study of the earth by quantitative physical methods, especially by seismic reflection and refraction, gravity, magnetic, electromagnetic, and radioactivity methods.

Geophysics

Based on measuring five Earth properties:1. Density (measured as the local force of gravity).

2. Magnetization (measured as the local magnetic force).

3. Acoustical response (measured in terms of voltages derived from geophones or hydrophones).

4. Electrochemical (measured by various electrodes, Geiger counters, etc).

5. Heat flow (crustal thickness)

Potential Field Methods

The measured strength and direction depends on your position of observation within the field.

The measured strength of the field generally decreases with increased distance.

Gravity and magnetics are potential field methods.

Gravity Methods

Measures localized changes in the acceleration of gravity as a result of changes in density.

Affected by the thickening or thinning of the crust.

Affected by the presence or absence of mass (mountains or deep valleys).

Gravity Methods (for our purposes) Used to measure crustal thickness, obtain

information on deep crustal structure, and obtain information on transitional crustal zones (continental margins).

Magnetic Methods

Measures localized changes in the direction and strength of the magnetic field as a result of changes in magnetic susceptibility (χ) and remnant magnetism (Jrem).

Magnetic Methods (for our purposes) Identification of magnetic reversal stripes on the

sea floor was one of the key components of recognizing plate tectonics.

Paleomagnetism and polar wander curves were critical in determining the locations of continental plates during geologic time.

Paleomagnetism were critical in determining the presence of exotic terranes.

Used to map the transition zone between continental and oceanic crust.

Used to map deep crustal structure.

Seismic Methods

Measures the rigidity or elastic properties by examining the velocity of seismic waves through the Earth.

Natural sources of seismic waves are earthquakes.

An example of man made or induced sources are explosions or striking a surface with a hammer.

Seismic Methods

Essential for determining the composition, phase, and depth boundaries of the Earth’s interior.

Essential data for developing the plate tectonic paradigm.

Heat Flow Methods

Measures the thermal conductivity (k) of the rocks and their geothermal gradient to calculate heat flow (q).

Heat Flow Methods

Essential for understanding plate motion, rifting, and hot spots.