1. Earth Structure

2. obvious from space that Earth has two fundamentally different
crust
obvious from space that Earth has two fundamentally different
physiographic features: oceans (71%) and continents (29%)
from:
global topography

3. Earth’s Plates

4. MORB Genesis

5. Submarine Pillow Basalt Formation

6. Volumes of Igneous Rocks on Earth

7. Convergent Margin Magma Genesis

8. Forms of Energy work = Force x distance
Energy: commonly defined as the capacity to do work (i.e. by system on its surroundings); comes in many forms
Work: defined as the product of a force (F) times times a displacement acting over a distance (d) in the direction parallel to the force
work = Force x distance
Example: Pressure-Volume work in volcanic systems.
Pressure = Force/Area; Volume=Area x distance;
PV =( F/A)(A*d) = F*d = w

9. Forms of Energy E (k) = 1/2 mass * velocity2 E (p) = mass * g * Z
Kinetic energy: associated with the motion of a body; a body with mass (m) moving with velocity (v) has kinetic energy
E (k) = 1/2 mass * velocity2
Potential energy: energy of position; is considered potential in the sense that it can be converted or transformed into kinetic energy. Can be equated with the amount of work required to move a body from one position to another within a potential field (e.g. Earth’s gravitational field).
E (p) = mass * g * Z
where g = acceleration of gravity at the surface (9.8 m/s2) and Z is the elevation measured from some reference datum

10. Forms of Energy (con’t.)
Chemical energy: energy bound up within chemical bonds; can be released through chemical reactions
Thermal energy: related to the kinetic energy of the atomic particles within a body (solid, liquid, or gas). Motion of particles increases with higher temperature.
Heat is transferred thermal energy that results because of a difference in temperature between bodies. Heat flows from higher T to lower T and will always result in the temperatures becoming equal at equilibrium.

11. Heat Flow on Earth Dq = Cp * DT
An increment of heat, Dq, transferred into a body produces a
Proportional incremental rise in temperature, DT, given by
Dq = Cp * DT
where Cp is called the molar heat capacity of J/mol-degree
at constant pressure; similar to specific heat, which is based
on mass (J/g-degree).
1 calorie = J and is equivalent to the energy necessary
to raise 1 gram of of water 1 degree centigrade. Specific heat
of water is 1 cal/g°C, where rocks are ~0.3 cal/g°C.

12. Heat Transfer Mechanisms
Radiation: involves emission of EM energy from the surface of hot body into the transparent cooler surroundings. Not important in cool rocks, but increasingly important at T’s >1200°C
Advection: involves flow of a liquid through openings in a rock whose T is different from the fluid (mass flux). Important near Earth’s surface due to fractured nature of crust.
Conduction: transfer of kinetic energy by atomic vibration. Cannot occur in a vacuum. For a given volume, heat is conducted away faster if the enclosing surface area is larger.
Convection: movement of material having contrasting T’s from one place to another. T differences give rise to density differences. In a gravitational field, higher density (generally colder) materials sink.

13. Magmatic Examples of Heat Transfer
Thermal Gradient = DT between
adjacent hotter and cooler masses
Heat Flux = rate at which heat is
conducted over time from a unit
surface area
Thermal Conductivity = K; rocks
have very low values and thus
deep heat has been retained!
Heat Flux = Thermal Conductivity * DT

14. Convection Examples

16. Rayleigh-Bernard Convection

17. Convection in the Mantle

18. convection in the mantle
models
from:
convection in the mantle
observed heat flow
warmer: near ridges
colder: over cratons
from:

19. From: "Dynamic models of Tectonic Plates and Convection" (1994) by S
From: "Dynamic models of Tectonic Plates and Convection" (1994) by S. Zhong and M. Gurnis

20. examples from western Pacific
blue is high velocity (fast)
…interpreted as slab
note continuity of blue slab
to depths on order of 670 km
from:

21. example from western US
all from:

22. Earth’s Geothermal Gradient
Average Heat Flux is
0.09 watt/meter2
Geothermal gradient = DT/ Dz
20-30°C/km in orogenic belts;
Cannot remain constant w/depth
At 200 km would be 4000°C
~7°C/km in trenches
Viscosity, which measures
resistance to flow, of mantle
rocks is 1018 times tar at 24°C !
Approximate Pressure (GPa=10 kbar)

23. Earth’s Energy Budget
Solar radiation: 50,000 times greater than all other energy sources; primarily affects the atmosphere and oceans, but can cause changes in the solid earth through momentum transfer from the outer fluid envelope to the interior
Radioactive decay: 238U, 235U, 232Th, 40K, and 87Rb all have t1/2 that >109 years and thus continue to produce significant heat in the interior; this may equal 50 to 100% of the total heat production for the Earth. Extinct short-lived radioactive elements such as 26Al were important during the very early Earth.
Tidal Heating: Earth-Sun-Moon interaction; much smaller than radioactive decay
Primordial Heat: Also known as accretionary heat; conversion of kinetic energy of accumulating planetismals to heat.
Core Formation: Initial heating from short-lived radioisotopes and accretionary heat caused widespread interior melting (Magma Ocean) and additional heat was released when Fe sank toward the center and formed the core

24. Rates of Heat Production and Half-lives

25. Heat Production through Earth History

26. Gravity, Pressure, and the Geobaric Gradient
Geobaric gradient defined similarly to geothermal gradient: DP/Dz; in the interior this is related to the overburden of the overlying rocks and is referred to as lithostatic pressure gradient.
SI unit of pressure is the pascal, Pa and 1 bar (~1 atmosphere) = 105 Pa
Pressure = Force / Area and Force = mass * acceleration
P = F/A = (m*g)/A and r (density) = mass/volume

27. Earth Interior Pressures
P = rVg/A = rgz, if we integrate from the surface to some
depth z and take positive downward we get
DP/Dz = rg
Rock densities range from 2.7 (crust) to 3.3 g/cm3 (mantle)
270 bar/km for the crust and 330 bar/km for the mantle
At the base of the crust, say at 30 km depth, the lithostatic pressure
would be 8100 bars = 8.1 kbar = 0.81 GPa

28. Changing States of Geologic Systems
System: a part of the universe set aside for study or discussion
Surroundings: the remainder of the universe
State: particular conditions defining the energy state of the system

29. Definitions of Equilibrium