1. Scientific revolutions
Science does not grow by accretion
Science is a discontinuous process, directed along certain paths by ruling paradigms
Paradigm: how a community uses common assumptions or guiding principles to organize knowledge
Communities abandon paradigms when they no longer organize knowledge effectively
New ruling paradigms must ‘gain the consent of the relevant community’
Science moves ahead by these paradigm shifts

2. Special earth sciences perspectives
Many earth scientists use an observation-inference methodology rather than one of several experimental methodologies
Observe and describe objectively features or processes
Interpret features in light of the processes inferred to operate (or have operated) to generate them (draw upon principles from biology, chemistry, or physics)
‘Test’ inferences by making ‘predictions’
Compare ‘predictions’ with observations

3. Methodology leads to the tenet ‘the present is the key to the past’
Observe geologic processes that occur on earth today, and determine how those processes affect rocks at the present time
Assume that analogous processes operated at different times in the past, i.e. throughout geologic time
Infer, by comparing modern and ancient rocks, which processes were responsible for forming ancient rocks

4. Marine geology and the earth system

5. Global topography Highest elevation - Mount Everest
~29,000 ft above sea level
~5.5 miles above sea level
~8.85 km above sea level
Greatest depth - Marianas/Philippine trench
~38,000 ft below sea level
~7.5 miles below sea level
~11 km below sea level
Total range = ~13 miles or ~20 km

6. Radius of earth = 6371 km (3982 mi)
20 km (13 mi) is a large distance to us. Relative to earth’s radius, however, 20 km is small.
Radius of earth = 6371 km (3982 mi)
Diameter of earth ≈ 12,700 km
20 km /6400 km ≈ 0.003
20 km ≈ 0.3% Earth’s radius

7. What is the distribution of elevations on earth
What is the distribution of elevations on earth? Is land area distributed ‘normally’ between the two extreme elevations?
No - elevation is distribution is bimodal
One common elevation corresponds to the elevation of continents
Mean elevation of continents is 840 m above sea level
Second common elevation corresponds to the elevation of sea floors
Mean depth of ocean floors 3-4 km below sea level

8. Greatest changes in average elevation occur between 1 and 3 km below sea level
The best place to locate the transition from continent to ocean is, then, somewhere between 1 and 3 km below sea level
We place the ends of continents at 1 to 3 km below sea level

9. Continents Six continents at present time
Continents possess a wide variety of rock types
Sedimentary rocks
Igneous rocks, either extrusive or intrusive
Metamorphic rocks

10. Continents Six continents at present time
North America, South America, Eurasia, Africa, Australia, & Antarctica
Continents possess a wide variety of rock types
Some rocks originated as rock debris (detritus) or sediment; geologists call these rocks sedimentary rocks
Some rocks originated by freezing molten silicate liquids; geologists call these rocks either extrusive or intrusive igneous rocks
Some rocks originated as sedimentary or igneous rocks, but were changed when the ambient temperatures or pressures changed; geologists call these rocks metamorphic rocks

11. Continents have rocks of all ages, ranging from those formed yesterday to those formed about 4 Ga ago
1 Ma = 1 million years
1000 Ma = 1 billion years = 1 Ga
It is on the continents that we find the most extensive record of earth history

12. Rocks of different origins and ages occur in three fundamentally different geological provinces
Mountain belts
Linear belts of high elevation
Arcuate in plan view
Contain thick accumulations of sedimentary rocks; strata are faulted and folded
Contain extrusive or intrusive igneous rocks
Rocks often metamorphosed in characteristic ways

13. Rocks of different origins and ages occur in three fundamentally different geological provinces
Mountain belts
Long, linear, and smoothly arcuate provinces characterized by generally high elevation
Have thick accumulations of sedimentary rocks of marine origin
Have extensive suites of intrusive igneous rocks and volcanic activity; volcanoes are often explosive
Sedimentary rocks are deformed by faults and folds which accomplish crustal shortening
Sedimentary and igneous rocks are often metamorphosed as well as deformed
Cratons or shield areas
Rift systems

14. Rocks of different origins and ages occur in three fundamentally different geological provinces
Mountain belts
Cratons or shield areas
Broad regions of low elevation & low relief near centers of continents
Core of cratons usually deformed & metamorphosed rocks older than 1 Ga old
Often have a veneer of younger sedimentary rocks, called platform deposits

15. Rocks of different origins and ages occur in three fundamentally different geological provinces
Mountain belts
Cratons or shield areas
Are broad regions of generally low elevation and low relief, generally found near the centers of continents
Surface topography resembles a shield; thus the name
Rocks in cratons are usually deformed metamorphic rocks older than 1 billion years old = eroded roots of ancient mountain belts
Cratons sometimes covered by veneers of younger sedimentary rocks, called platform deposits (many platform sequences contain rocks younger than 600 Ma)
Rift systems