Welcome to Geology 104

Earth Science

• 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.

• 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 structureThe 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

– 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