the scientific method. goal: explain how universe works scientific method: the process where ideas...
TRANSCRIPT
The Scientific Method
Goal: Explain How Universe Works
• Scientific method: the process where ideas are formed, tested, and refined
• Step 1:– Questions sparked by observation or
experiments
• Alfred Wegener• 1910Pangaea
Strange Observations
But what does it all mean?
• Step 2:– Formulate hypothesis: tentative explanation built
on strong supporting evidence
• Continental drift?– Continents were once part of giant
supercontinent, Pangaea (“all earth”) and have since drifted apart to their current locations
Wegener’s Hypothetical Earth
• Late Carboniferous– 300 Ma
• Middle Tertiary– 50 Ma
• Early Quaternary– 10 ka
But… (the hardest part)
• Step 3:• All hypotheses must be tested
– Counter-evidence you’re wrong, back to beginning
– Support confidence, becomes scientific theory basis for future tests
Wegener couldn’t test it…
• Mechanism for continental migration?!• His idea: continents floated like boats on
ocean basin crust pulled by tides of Sun and Moon– Unfortunately, forces are much too weak
• Open and shut?– Wegener was apparently wrong
The Building Blocks of Earth Science
Eratosthenes (~250 B.C)
• Experiment– If the Sun is far enough
away, its rays are parallel
– A well in Syene, a pole in Alexandria 800 km apart at same time, same day
– No shadow in Syene but shadow in Alexandria
Disproving the Flat Earth Theory
• Earth must be curved
• Calculated that earth was a sphere, 250,000 stadia in circumference at the equator– Not sure how big a stadion
• Attic stadion (~185 m): 46,620 km (over by 16.3%)• Egyptian stadion (~157.5 m): 39,690 km (<1%!)
– Actual circumference 40,075.16 km
Isaac Newton
• Discovered how to measure the Earth’s mass by the strength of gravity
– Density (D) = Mass (M) / Volume (V)
– With Eratosthenes’ circumference…
– Could estimate average Earth (D) = 5.5 g/cm3
What Was the Earth Made Of?
• Major problem:
– Surface rocks mostly low density = 2.7 g/cm3
– Some iron-rich rocks had density = 3.5 g/cm3
• So where was the dense material?– Something REALLY DENSE had to account for the
high average density
The Dense Nougat Center
• Emil Wiechert, German Physicist Pressure increases with depth, makes sense that deep rocks, more compact, higher density Iron-nickel meteorites densest material identified
• Wiechert’s hypothesis: Earth must be layered and iron/nickel settled to core under gravity Si-rich low-density “mantle” – sandstones, etc Iron-rich “core”
How to Go from This to This?
Earthquakes Provide Answers
• What are earthquakes or seismic waves?– Waves that travel through rock
• What is a wave?– Movement of energy
with little permanentmovement of mass
– Frequency = peaks/s– Velocity = frequency * wavelength
• P-wave = – compressional
• S-wave – shear (secondary)
Body Waves(Waves that pass through the Earth)
Surface Waves(Waves that occur at the Earth’s surface)
• Love = side to side
• Rayleigh = up and down
Notes About Earthquakes
• All earthquakes involve all wave types
• Body waves travel fastest– P-wave (5-6 km/s in crust), S-wave (3.5 km/s)
• Seismic waves travel faster through denser, more rigid rocks– P-waves can travel through liquids, solids, gas– S-waves cannot travel through liquids, gases
How Do We Know?
The Seismograph
• Recording earthquakes
What is an Epicenter?
• Epicenter –location on earth’s surface• Focus – place where fault first moved• Recall P and S-wave times