Download Cycles of the Lithosphere

Cycles of the Lithosphere
Pgs 54 - 60
Catastrophism Theory –
Uniformity Theory –
James Hutton –
Charles Lyell –
What Modern Geologists Understand –
Geologic Cycle [ Rock Cycle] –
Igneous rocks –
Sedimentary Rocks -
Metamorphic Rocks –
Continental Drift Theory – Alfred Wegener
Continental Drift Theory – J. Tuzo Wilson
Plate Tectonics – explanations
Cycles of the Lithosphere
Pgs 54 - 60
Catastrophism Theory – implies that geological change happens because of sudden catastrophic events like
immense floods and landslides.
Uniformity Theory – implies that geological change primarily occurs through slow, gradual processe.
James Hutton – published Theory of the Earth with Proofs and Illustrations in 1785. He claimed the Earth’s
surface changed by gradual processes like erosion or accumulation of silt at a river mouth. Therefore, the
Earth had to be older than most people thought at the time.
Charles Lyell – published Principles of Geology in 1830. He agreed with Hutton and the theory became
known as the Uniformity Theory.
Modern Geologists Understand –
- Earth is about 4.6 billion yrs old
- Surface has been changed repeatedly by simple processes that take hundreds of years
- Recognize that Earth is dynamic and can change suddenly [i.e. volcanoes, earthquakes, and
floods]
Geologic Cycle [ Rock Cycle] – The interrelated and connected processes that result in the formation of the
three classes of rock.
Igneous rocks – class of rocks formed by the cooling and crystallization of molten rock masses called
magma, or lava.
Magma – molten rock beneath the Earth’s surface – when it cools – Intrusive Igneous Rock
Lava – molten rock that reaches the Earth’s surface – when it cools – Extrusive igneous Rock
- Igneous rocks form 95% of the Earth’s crust.
Sedimentary Rocks – formed by chemical precipitation or the compaction and cementation of particles
weathered and eroded from other rocks.
- Extrusive Igneous rocks form on Earth’s surface – erosion begins immediately [weathering action
of wind, water, and heat]
- Rock is broken down into tiny particles and carried off by wind or rain, they are deposited in
riverbeds or lake bottoms and accumulate over long periods
- Pressure is applied as more and more material is deposited
- Upper layer presses down on lower layers, compacting and squeezing out water and air, and
cementing the particles into layers [strata] in a horizontal pattern.
- Geologic Time Scale – scientists examined successive layers of sedimentary rock and the fossils
found in them to measure the Earth’s age
Metamorphic Rocks – form from other rocks through intense heat and pressure.
1. Heat given off by formation of intrusive igneous rocks is so intense that it changes the formation of
nearby rocks
2. Pressure within the Earth’s crust can become so great at times that a soft rock like limestone can
transform into a hard rock like marble.
Continental Drift Theory – Alfred Wegener
- 1910 – German geologist theorized the continents once fit together as one giant super continent
called PANGAEA
- 200 million years ago it broke into 2 pieces GONDWANALAND and LAURASIA
- They split again
- Over millions of years they drifted apart “Continental drift.’
- Based this on outlines of continent, similar rock types, fossils, and various living species on the
different continents that are separated by Oceans.
- Unable to explain how.
Continental Drift Theory – J. Tuzo Wilson
- Canadian scientist [1960’s] noted that earthquake and volcanic activity took place in similar
regions.
- Often on the Ocean floor
- Ocean volcanoes deposited crustal material on the ocean floor which pushed apart the continents
on either side – SEA FLOOR SPREADING
Plate Tectonics
Plates – rigid sections of Earth’s crust floating on a semi-plastic zone in the Earth’s upper Mantle
- The Upper Mantle is subject to heat currents which cause the them to move from high
temperatures to cooler areas. It drags the plates along.
- Sometimes plates move away from each other, sometimes towards each other
- Mid Ocean Ridges – formed by volcanic activity that marks the boundary between two
separating crustal plates.
- Sunduction zone [Deep Sea Trench] - area where crustal material collide and are dragged down
into the mantle below forming a trench.
Plate Tectonic Explanations
- how continents move
- why mountain chains occur on edges of continents
- how deep sea trenches are formed
- why earthquake and volcanic activity is concentrated in mountainous regions – where plates meet
- why closely related species developed on separate continents [South American Llama is related to
African camel – distant relative roamed PANGAEA – continents drifted apart and two species
evolved to meet the environment.