Transcript Class Notes - LSU Geology & Geophysics

CHAPTER 1
GROTZINGER, JORDAN,
PRESS & SIEVER,
Earth Scientists study:
rocks
the earth
the moon
the physical evidence for the solar system
chemistry of the solar system
physics of earthquakes
past biology
The main difference between Earth Science and the
rest of the sciences (except for astrophysics) is the
use of “DEEP TIME”. For us a million years passes like
a 15-minute smoke-break.
Geological processes can take place more slowly than
people can notice. But because they run for extremely
long periods of time their effects are great.
Water recharge in Baton Rouge takes 1000 years
Climate change has been accelerated by CO2 emissions
over the past 100 years.
The Scientific
Method
Fig. 1.1
The Scientific Method
•A philosophical approach
•A deductive reasoning approach
•Starts with numbers… trends….
Patterns…. i.e. OBSERVATIONS
•Explains observations using one or several
reasons, i.e. HYPOTHESES
•Verification that the explanation works by
many experts
The Scientific Method
•If you know the answer already that is not
science
•Science is a process
•Barriers to science are human e.g., greed,
dishonesty, fear of change, hunger for
power, cultural conditioning...
Uniformitariansim
“The present is the key to the
past”
— James Hutton
Natural laws do not change but
rates and intensity of processes
may vary.
Some Geologic Events are Slow
The Grand Canyon
It took more than 250
million years to deposit
this sequence of rocks.
The rocks at the bottom
of the canyon are about 2
billion years
old.
Fig. 1.2
Some Geologic Events are Rapid
Meteor Crater
This feature (~2
km across)
formed in less
than one minute
about 50,000
years ago
“The chances that a bolide 1-2 km in diameter will
hit the earth by 2880 is 1:300”
Martian ventifact (NASA)
Rivers on Titan
NASA
Some Geologic Investigations
are Microscopic
1 mm
Features less than 0.1 mm can give important information
about the history of many rocks.
Some Geologic Investigations
are Microscopic
NASA
Big Bang Hypothesis
13-14 billion years ago, all matter and energy was
concentrated into a single, inconceivabley small
(and very dense) point. This hypothesis stems from
a mathematical solution to the problem
This hypothesis was tested through the Doppler
shift in stellar spectrum, which implied that matter
was flying apart in all directions throughout the
universe
The Hubble Telescope
Can detect faint light that has
travelled for billions of years, ….
from the start of the current
universe
Nebular Hypothesis and the origin of
our Solar system
•Older than 4.56 billion years ago
•Gravity is the cause of “condensation” of
the cloud
•Cloud contracted WHILE spinning ever
faster
•H and He are the most common elements
•H and He collected to form fusion
reactions
Nebular Hypothesis and the origin of
our Solar system
•Fusion is more energetic and atomic fission
but requires greater pressures
•Hydrogen “fuel” burns to create He
Fig. 1.3
Fig. 1.3
Nebular Hypothesis and the origin of
our Solar system
•Planetesimals (early-stage, immature, small
planets) on the periphery of this
contracting, spinning dust cloud began to
clump together locally.
•Denser materials fell closer to the sun
•Less dense materials (gases) could escape
to greater distances from the sun e,.g.,
Jupiter floats in water
Fig. 1.3
Nebular Hypothesis and the origin of
our Solar system
•Mercury, Venus, Earth, Mars are called the
terrestrial planets
Size of the Planets
Fig. 1.4
Size and Relief of
Venus, Earth, Mars
Fig. 1.9
Pre-scientific medicine
Humours: yellow bile, black bile, phlegm, blood
Methods of treatment like blood letting, forced
vomiting and purges were aimed at expelling a
harmful surplus of a humour. They were still in the
mainstream of American medicine after the Civil
War. Other methods used herbs and foods
associated with a particular humour to counter
symptoms of disease, for instance: people who had a
fever and were sweating were considered hot and wet
and therefore given substances associated with cold
and dry. (Wikipedia, the free encyclopedia, 2006)
Origin if the Moon- Science at work
OBSERVATION: The Pacific is large? Why so
large?
Charles Darwin’s great grandson hypothesized
that the Moon came from the Pacific Ocean
(HYPOTHESIS)
Origin if the Moon- Science at work
HYPOTHESIS TESTING:
Pacific Ocean is 70-200 my old
Such an impact would have melted the earth
and reset all radioactive clocks to 0 years old
about 100 my after the melting.
Nebular Hypothesis and the origin of
our Moon
•Oldest rocks on the moon are 4.47 by
•A Mars-shaped bolide hit the earth about
4.5 by
Formation of the Moon
(about 4.5 billion years ago)
Composition of the Earth (70%)
•Key earth elements in the crust: Si, O
•Key earth elements in the earth: Fe, Si, O
Chemical Composition of
Earth
Whole Earth:
Crust:
Fe+O+Si+Mg = 93%
Si+O+Al = 82%
Fig. 1.7
Composition of the Earth
•What is responsible for the distribution of
light and dense elements by depth?
•How did they get there if the Earth was
solid?
How old is the Earth?
How old is the Earth?
Younger than the planetesimals
4.56 by
How old is the Earth?
Older than the moon
How old is the Earth?
Older than the moon
are 4.47
…...but
to form
by
……… oldest rocks
the moon could have started
earlier … 4.5 by
What was happening between
4.56 and 4.5 by ?
•(1) Accretion to create the first
earth… a “magma” earth (100 millionyear-period
What happened to the Earth
at 4.5 by ?
•Earth was hit by a giant bolide (before 4.47
by) that remelted it and led to the
formation of the moon
What was happening between
4.5 and 4.4 by ?
•(1)Mainly cooling and differentiation:
Gravity pulled the denser materials toward
the core when the Earth was still molten
Global Chemical
Differentiation
Fig. 1.6
Earth as a Group of Interacting
Systems
•Atmosphere, Hydrosphere, Lithosphere,
Asthenosphere, Deep Mantle, Inner Core
interact
•e.g. Volcanic degassing creates warm
periods in Earth’s history
•The oceans buffer greenhouse gases
•The Core’s magnetic field allows migration
of fish and birds
Major Components of the
Earth System
Fig. 1.10
END OF CHAPTER 1