1. Outline
• Origin & Evolution
o Earth's Place in the Solar
System
o Our Universe
o Beginning and Evolution of
the Universe
 The Big Bang
 Cosmic
Origin, Background
Radiation
 Inhomogeneity
Evolution  Birth of Stars
 Origin of Planets
o How did the Earth Form?
&  Origin of the Solar
System
 Origin of the planets
Composition o How did the Earth Grow &
Differentiate?
 Bombardment
of the Earth  Insulation
 Gravitational
Compression
 Radioactive Decay
GS117 Lecture 2 o Present-Day Earth
January 10, 2000 • Structure of the Earth
o Chemical Layering
C. Lithgow-Bertelloni  Crust
 Continental
 Oceanic
Excellent Lecture Notes on Solar
 Mantle
System Evolution
 Core
o Mechanical
 Lithosphere
 Mantle
 Outer Core
 Inner Core
• Plate Tectonics Primer
o Definition
o Plate Boundaries
Next Slide

2. Our Earth
Earth in the Solar System
Density of terrestrial planets: 4.0-5.5 g/cm3
Density of outer planets: 0.6-1.7 g/cm3
Mass Distribution:
• Sun 99.86% (1)
• Planets 0.135 % (9)
Satellites 0.004 % (32)
Next Slide
Our Universe

3. From the Hubble Deep Field Experiment
Next Slide
Beginning & Evolution
of the Universe

4. Thompson & Turk, 1999
Next Slide
The Big Bang
Introduction to Cosmology
Cosmic Bacgkround Radiation

5. Uniform
Learn about the Big Bang & Cosmic Background Radiation
COBE Educational Resources
The Big Bang
Cosmic Bacgkround Radiation
Inhomogeneity
From NASA's DMR Experiment

6. Next Slide
Birth of Stars
Dense Molecular Clouds
Birth and Death of Stars
Next Slide
The Origin of Planets

7. Circumstellar Disks
Next Slide

8. How did the Earth Form
Formation of the Solar System
Condensation from rotating cloud of dust (nebula)
Next Slide
How did the Earth Grow

9. & Differentiate?
Planetary Formation
• I. Bombardment
• II. Insulation = HOT
START
• III. Gravitational Compression
• (IV. Radioactive Decay)
Next Slide
Present-Day Earth
• I. Hot Start-Melting
• II. Migration of dense material to center
• III. Differentiated Earth
• IV. Present-Day Earth is Still Hot: Why?
o Heat from bombardment and accretion still
needs to be released-this is called
PRIMORDIAL HEAT and is one of the two
main sources of heat in the Earth's interior

10. Radioactive Elements are still decaying and
o
releasing energy, this is the second main
source of heat in the Earth's interior-
RADIOACTIVE DECAY of Th, U, K
• V.Will it stay hot forever? NO!- It's been cooling
down since its origin (4.5-4.6 billion years ago)
• VI. How does it lose its heat?-Through Plate
Tectonics
Next Slide

11. Structure of the Earth
Interior of the Earth is layered (i.e. DIFFERENTIATED)-total
radius 6371 km
• Chemical Differentiation [Layers of different Chemical
Composition]
o crust - two types:
 continental (0-70 km thick; ave 35 km),
 oceanic (0-20 km thick; ave 6-8 km)
o mantle- from (6-35 km depth to 2891 km depth)
o core-Made of iron (from 2891 km depth to the center
6371 km)
 outer part liquid (2891 km to 5120 km)
 inner part solid (5120 km to 6371 km)
• Mechanical Differentiation [Layers that react differently when you
try to deform them]
o Lithosphere [Crust (oceanic or continental) + 70-100 km of
coldest Mantle]-
 COLD
 BRITTLE
 (BREAKS INTO BIG PIECES [TECTONIC PLATES]-and
gives rise to EARTHQUAKE & VOLCANIC ACTIVITY)
o Rest of Mantle-

12.  WARM
 PLASTIC
 Flows and this flow drives plate tectonics
o Core-
 HOT
 LIQUID
 Moves as fast as ocean currents. Generates the Earth's
magnetic field
Next Slide
Plate Tectonics Primer
This is how the geosphere loses its heat and how it
expresses its dynamic nature
Plate Tectonics : the upper mechanical layer of the
Earth (lithosphere) is broken into several rigid pieces,
which we call plates, that move with respect to one
another throughout the course of earth’s history. All

13. deformation occurs at the boundaries between plates.
Explains distribution of earthquakes, volcanoes,
mountains, rock types, etc. There are
three types of plate boundaries.
Three boundaries (all deformation occurs)
• Divergent (material is created)-plates move away
from each other
• Convergent (material is consumed)- plates move
towards each other
Transform (no creation, no consumption; plates
slide past each other)- plates slide past each other