Ideas about Evolution of Earth (static to dynamic)

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Ideas about Evolution of Earth(static to dynamic)

• Pre-Renaissance (Static Earth).
• Renaissance to 20th Century (Geophysics
  Continental Drift).
• 20th Century (Sea Floor Spreading).
• Present-Day Perspective (Plate Tectonics
  Paradigm).

Important
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Nature of Earth from the Greeks through the Dark
Ages.

• Pre-1600 Myth and Religious view of Earth
• Catastrophism catastrophic events due to angry
  gods.
• Poseidon (Neptune) god of earthquakes
• Typhon many-headed monster, source of storms
• Zeus sky and weather god
• Hades (Pluto) - god of the underworld
• Vulcan god of fire, volcanoes
• Center of Earth Hades

Important
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Dantes Map of Hell
Geologists
Geophysicists?
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Greek Science
Important

• Knew the Earth was round.
• Assumed that continents were fixed.
• No information about ocean floor or earths
  interior.
• Natural processes (not gods) formed geologic
  features.
• Herodotus (484-426 B.C.), Empedocles (?), Pliny
  (23-79 A.D.) all studied geology, the latter two
  died while observing volcanoes.

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The Development of Geophysics(internal structure
earth)

• Renaissance to 20th century

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Changing Views of Earth Earths Magnetic Field.

• 1600 William Gilbert, Physician to Queen
  Elizabeth I, Published De Magnete. Earths
  magnetic field two-pole bar magnet.

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Changing Views of Earth Earth Structure.

• 1596-1650 Descartes proposed earth had
  metallic interior, middle shell of heavy rock and
  thin surface of sands and clays.

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Changing Views of Earth Beginning of
Geophysics.
Important

• 1687 Newtons laws of motion gravity.
• 1650-1750 Start of Geologic mapping.
• Combine into Start of Geophysics.

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Changing Views of Earth
Important

• Late 1700s Average density of earth 5.5
  g/cm3.
• Since surface rocks 2.7 g/cm3 inner earth must
  be more dense.
• 1785-1795 James Hutton Founder of modern
  geology
• Dynamic view of earth as internal heat engine
  rather than static.
• Magmatism melted rocks coming from depth.
• Uniformitarianism steady state evolution of
  earth.

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Changing Views of Earth
Important

• 1873 J.D. Dana meteorites inner core of
  planets
• Chondritic core (iron and nickle).
• Stony outer parts (Fe,Mg silicates).

• 1900s By turn of century recognized three-fold
  division of earth into core, mantle, and
  lithosphere.

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How Do We Determine Internal Structure and
Composition Today?

• Look at rocks exposed at surface (0-30 km and
  rarely100 km, China).
• Drill holes (15 km, Khola Peninsular, Russia).
• Magmatism (0-200 km deepest diamond bearing
  kimberlites).
• Meteorites
• Chondritic core
• Stony outer parts.
• Geophysics
• Gravity
• Magnetics
• Heat Flow
• Seismic Waves
• Earth precession

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Modern ViewInternal structure of Earth
Core
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Internal structure of Earth
Asthenosphere
Mantle
Mesosphere
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Internal structure of Earth
Important
Lithosphere
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Changing Views of Earth 1800-1940
Important
1934 W.M. Elsasser flow in outer core causes
magnetic field.
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Changing Views About the Continents The
Beginnings of Continental Drift
Important
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Maps of Floating Continents

• 1596 Abraham Ortelius (Dutch Cartographer)
  first suggested that continents joined together
  then separated.
• 1620 Sir Francis Bacon Often thought to be the
  first to suggest continental drift, but really
  only noted similarity in shapes of continents.
• 1846 Dana (geologist) continents and oceans
  stable and never change place.
• 1846 Forbes (biologist) plant and animal
  evolution required continents to be connected at
  some time in the past.
• 1858 Antonio Snider (Frenchman) noticed similar
  plant fossils in the coal seams of North America
  Europe. Made map of floating continents.
• 1872 Reclus proposed that continental drift
  might be the cause of mountain building.
• 1885 Suess (Swiss) plant fossils and glaciation
  in South America Africa similar (Gondwana).

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1858 Antonio Sniders map of floating continents.
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Scientists also recognized series of mountain
belts on edges of continents
Important
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The cores of these mountain belts have been
strongly deformed Called Orogenic Belts.
Early reconstruction of European Alps
Big Folds
Big Faults
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Fit of Continents?Why did mountains form?

• EARLY IDEAS
• A cooling ( shrinking) Earth...
• Continental Drift Theory

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LORD KELVIN AND THE SHRINKING EARTH
As cooled, it shrank!
Didnt know about all heat sources
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1908-1910 F. B. Taylor (American)
Important

• 1908 Published private pamphlet arguing for
  continental drift. Trying to explain formation
  and distribution of orogenic belts. Recently
  discovered mid-atlantic ridge as breaking point?
• 1910 Publication proposed that continents moved
  like huge landslides from the poles towards the
  equators.

• Suggested that
• Moon captured in Cretaceous.
• Initially closer to earth.
• That gravitational forces would move continents.
• Quickly disregarded because
• Only needed 40 km displacement to explain
  mountain belts, not 1000s.
• Tidal effect should stop rotation and/or rip
  apart earth within one year.

Continents Sliding off south pole
Continents Sliding off north pole
Collisions
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1910 Alfred Wegener German meteorologist largely
working in southern hemisphere.
Important

• Evidence of Africa and South America and other
  southern continents being together.
• Shapes of continents fit back together.
• Shared glacial and other geologic features.
• Shared animal and plant fossils.
• Shared climatic zones.

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Fit of Africa and South America
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Fit of old mountain belts in Africa and South
America
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Distribution of glacial deposits
Match of Glacial/Stratigraphic data known by 1937
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Fossil data by 1937 (almost)
Glossopteris leaves
Mesosaurus
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Wegeners continental drift
Important
Wegeners reconstruction of Pangea (Greek all
land) Laurentia (northern landmass). Gondwana
(southern landmass). Only moderately different
from Sniders 1858 maps.
Laurentia
Gondwana
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Important
Wegeners continental drift

• Shapes of continents dont change with time.
• Continents move through ocean basins.
• Continental drift young (Pleistocene) to explain
  young orogeny.
• NS movement due to gravitational attraction of
  equatorial bulge.
• E-W motion due to tidal forces of sun and moon.
• Front edges continents crumpled, forming orogenic
  belts.
• Oceanic islands parts of continents left behind.

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Wegeners continental drift

• Above idea not generally accepted because
• No accepted mechanism for moving continents
  through oceans.
• Arguments about timing of orogenies, thus
  continental movements.
• He was a meteorologist working in southern
  hemisphere.

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What is the Solution?

• Our Next Topics
• Sea Floor Spreading
• Plate Tectonics