Unit 2-Solid Earth
Introduction to Planet “Earth”
Formation of the Universe-Big Bang
Theory
Big Bang
Formation of Solar System and
Earth

Nebular hypothesis
Nebula=cloud of gases and space dust
 Mainly hydrogen and helium
 Gravity concentrates material at center
of cloud (Sun)
 Protoplanets from smaller
concentrations of matter (eddies)

Protoearth
Larger than Earth today
 Homogeneous composition
 Bombarded by meteorites
 Moon formed from collision with
large asteroid
 Heat from solar radiation
 Initial atmosphere boiled away
 Ionized particles (solar wind) swept
away nebular gases

Protoearth
Radioactive heat
 Spontaneous disintegration of
atoms
 Heat from contraction (protoplanet
shrinks due to gravity)
 Protoearth partially melts
 Density stratification (layered Earth)

Earth’s internal structure
Highest density material at center
(core)
 Lowest density material at surface
(crust)
 Earth layered
 Chemical composition
 Physical properties

Chemical composition
Crust
 Low-density, mainly silicate
minerals
 Mantle
 Mainly Fe and Mg silicate minerals
 Core
 High-density, mainly Fe and Ni

Layered
Earth
Fig. 1.14
Physical properties
 Lithosphere
 Asthenosphere
 Mesosphere
 Outer
core
 Inner core
Physical properties

Lithosphere
Cool, rigid, brittle
 Surface to about 100 km (62 miles)


Asthenosphere
Warm, plastic, able to flow
 From 100 km to 700 km (430 miles)

Fig. 1.15
Lithosphere
 Oceanic
crust
Underlies ocean basins
 Igneous rock basalt
 Average thickness 8 km (5 miles)
 Relatively high density
 3.0 g/cm3

Lithosphere- Crust and Uppermost
mantle fused together.
 Continental crust
 Underlies
continents
 Igneous rock granite
 Average thickness 35 km (22 miles)
 Lower density
2.7 g/cm3
Asthenosphere
 Upper
mantle
 Plastic—deforms by flowing
 High viscosity—flows slowly
Isostatic adjustment

Buoyancy



Less dense “floats” higher than more dense
Continental crust “floats” higher than
oceanic crust on plastic asthenosphere
Questions:


Based on Isostatic adjustment, what is the impact of removing a
large percentage of groundwater from California?
Based on geologic response, what is the impact of removing a
large percentage of groundwater from California?
Fig. 1.16
Origin of Earth’s atmosphere

Partial melting resulted in outgassing
about 4 billion years ago
Similar to gases emitted from volcanoes
 Mainly water vapor
 Carbon dioxide, hydrogen
 Other gases such as methane and
ammonia

Evolution of Earth’s Atmosphere
Some scientists describe three stages in the evolution of Earth’s atmosphere as it
is today
Just formed Earth: Like Earth, the hydrogen (H2) and
helium (He) were very warm. These molecules of gas
moved so fast they escaped Earth's gravity and eventually
all drifted off into space.
1. Earth’s original atmosphere was probably just hydrogen and
helium, because these were the main gases in the dusty,
gassy disk around the Sun from which the planets formed.
The Earth and its atmosphere were very hot. Molecules of
hydrogen and helium move really fast, especially when
warm. Actually, they moved so fast they eventually all
escaped Earth's gravity and drifted off into space.
Young Earth: Volcanoes released gases H2O (water) as steam, carbon
dioxide (CO2), and ammonia (NH3). Carbon dioxide dissolved in
seawater. Simple bacteria thrived on sunlight and CO2. By-product is
oxygen (O2).
Earth’s “second atmosphere” came from Earth itself. There were lots of
volcanoes, many more than today, because Earth’s crust was still forming. The
volcanoes released steam (H2O, with two hydrogen atoms and one oxygen
atom), carbon dioxide (CO2, with one carbon atoms and two oxygen atoms),
ammonia (NH3, with one nitrogen atom and three hydrogen atoms).
Current Earth: Plants and animals thrive in balance. Plants take in
carbon dioxide (CO2) and give off oxygen (O2). Animals take in
oxygen (O2) and give off CO2. Burning stuff also gives off CO2.
Much of the CO2 dissolved into the oceans. Eventually, a simple form of
bacteria developed that could live on energy from the Sun and carbon
dioxide in the water, producing oxygen as a waste product. Thus, oxygen
began to build up in the atmosphere, while the carbon dioxide levels
continued to drop. Meanwhile, the ammonia molecules in the atmosphere
were broken apart by sunlight, leaving nitrogen and hydrogen. The
hydrogen, being the lightest element, rose to the top of the atmosphere and
much of it eventually drifted off into space.
Now we have Earth’s “third
atmosphere,” the one we all know and
love—an atmosphere containing
enough oxygen for animals, including
ourselves, to evolve.
So plants and some bacteria use
carbon dioxide and give off oxygen,
and animals use oxygen and give off
carbon-dioxide—how convenient! The
atmosphere upon which life depends
was created by life itself.
Origin of Earth’s oceans
Water vapor released by outgassing
 Condensed as rain
 Accumulated in ocean basins
 About 4 billion years ago


Ice Comets were also important to
adding water to the Earth system
Fig. 1.17
Volcanic outgassing of
Kilauea volcano on Hawai’i
Ocean salinity
 Rain
dissolves rocks
 Dissolved compounds (ions)
accumulate in ocean basins
 Ocean salinity based on balance
between input and output of ions
 Ocean salinity nearly constant
over past 4 billion years
Life in oceans
 Earliest
life forms fossilized
bacteria in rocks about 3.5 billion
years old
 Marine rocks
 Life originated in oceans?
Stanley Miller’s experiment

Organic molecules formed by ultraviolet
light, electrical spark (lightning), and
mixture of water, carbon dioxide,
hydrogen, methane, and ammonia
Fig. 1.18a
Evolution and natural selection
Organisms adapt and change through
time
 Advantageous traits are naturally
selected
 Traits inherited
 Organisms adapt to environments
 Organisms change environments

Types of life forms
 Heterotrophs
(most bacteria
and animals)
 Autotrophs (algae and plants)
 Anaerobic
bacteria
(chemosynthesis)
 Photosynthetic autotrophs
Chlorophyll captures solar
energy
Photosynthesis and respiration
Fig. 1.19
Oxygen crisis
Photosynthetic bacteria release
oxygen (O2) to atmosphere
 About 2 billion years ago, sufficient
O2 in atmosphere to oxidize (rust)
rocks
 Ozone (O3) builds up in atmosphere


Protects Earth’s surface from ultraviolet
solar radiation
Oxygen crisis
About 1.8 billion years ago, most
anaerobic bacteria killed off by O2rich atmosphere
 Photosynthetic organisms created
today’s O2-rich atmosphere

O2 makes up about 21% of gases in
modern atmosphere
 Animals thrive

Age of Earth

Radiometric age dating
Spontaneous change/decay
 Half-life


Earth is about 4.6 billion years old
Fig. 1.22
Geologic time
scale
Fig. 1.H
End of
CHAPTER 1
Introduction
to Planet
“Earth”