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Welcome to Geology 104
Earth Science
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Geology
Oceanography
Meteorology
Climate change
The Scientific Method
Steps of the Scientific Method
• Observe some aspect of the universe and collect
facts about the observations
• Develop a tentative explanation, or hypothesis,
about the observations
• Construct experiments to test the hypothesis
• Accept, modify or reject the hypothesis on the
basis of extensive testing
• Repeat steps 3 and 4 until there are no
discrepancies between hypothesis and
experiment and/or observation.
When consistency is obtained the
hypothesis becomes a theory:
• provides a coherent set of data which
explain a class of phenomena.
• a framework within which
observations are explained and
predictions are made.
1. Observe and Gather Data
2. Formulate One or More Hypotheses
Test the Hypothesis or Hypotheses
Accept, reject or modify the hypothesis, based on
whether testing supports the observation
Attributes of the Scientific Method
• It is unprejudiced; one does not have to
believe a given researcher, one can redo
the experiment and determine whether the
results are valid
• It is repeatable: most experiments and
observations are repeated many times
• The theory must be falsifiable; there must
be some experiment or possible discovery
that could prove the theory untrue.
The Nebular Theory
• The solar system began as dust
and gas (from an exploding
supernova?) which then
collapsed due to gravity.
• The nebula contracted into a
rotating disk.
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Repeated collisions of rocky
and metallic material coalesced
into asteroid, then planet-sized
bodies.
• Age of the earth and solar
system about 4.6 billion years
(4600 million years).
• Heating and subsequent cooling
of Earth caused heavy metals to
sink to the interior and lighter
elements to rise to the surface.
Earth in Space
Earth’s internal structure
The separation of heavy
and light elements
caused a layered Earth
consisting of:
– Crust: silica (SiO2)rich composition
– Mantle: silica and
iron composition
– Core: iron and nickel
composition
The crust and mantle are further divided into
“spheres” depending on density and physical
state (e.g. solid or molten).
Earth’s “spheres” by physical state
• Lithosphere – rigid
solid which make up
the tectonic plates,
includes both crust
and the uppermost
part of the mantle.
• Asthenosphere –
partially molten
“weak” layer directly
beneath the
lithosphere
• Mesosphere – lower
mantle, mostly solid
• Core
– outer core (molten)
– inner core (solid)
Crust (part of the lithosphere)
Continental and Ocean Crust
• Continental crust
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thicker (average 35-40 km)
older (up to 4 billion years old)
less dense than ocean crust.
varied composition (generally
granitic).
• Ocean crust
– thinner (averages 5-7 km )
– younger (200 million years old
or less)
– more dense and iron-rich
– composed of dark volcanic
basalt.
Example of the Scientific Method: From
Continental Drift Hypothesis to Plate
Tectonic Theory
• Observation: Some of the boundaries of the continents
look as though they had once fit together
• Initial hypothesis: In the geologic past, all the continents
were together and are now moving apart (continental
drift)
Prediction: You should find fossils of the
same type at these now-separated
continental boundaries
Prediction: You should find evidence of
similar climates at the now-separated areas
Prediction: You should find matching rock
types and orientation of mountain ranges at
the now-separated areas
Continental Drift Hypothesis
Rejected!
How did the continents move through the
oceans?
• Tidal influence of the moon? Experiments
proved this to be false
• Continental crust plows through or slides
over ocean crust? Experiments proved this
to be false
Advancements in technology cause the
rejected hypothesis to be modified.
Sea Floor Spreading Hypothesis
and Plate Tectonic Theory