Physical Geology Introduction

Fall Semester, 1997
John C. Butler
Room 304 SR I

The Scientific Method


	Attempt To Explain - Hypothesis

	Testing The Hypothesis

	More Observations - Predictions

	Modification of the Hypothesis


Physical Geology

"Geology is the science that studies Earth -- how it 
was born, how it evolved, how it works, and how
we can help preserve it."





What is the extent of the relationship between 
internaland external processes and Earth materials?

Observations play a major role in the geosciences.  

Experimental approach, while sometimes desirable is
difficult - TIME


	The present is the key to  the past:




Earth's History is recorded in the materials it is made
 up of:

	Composition - chemistry

	Texture - size, shape, 	arrangement of constituents

	Structures - features - such as layers

	Geologic Setting

 Origin of Planets

	Universe began ~10 to 15 billion years ago - 
	Big Bang Hypothesis

	Since then the universe has expanded to form the 
	galaxies, stars and planets

	Nebular Hypothesis - dust clouds - consist 
	primarily of hydrogen and helium and "dust"

 particles attract each other under the influence of gravity


 as the dust clouds contract the pressure acting on the 
 hydrogen and helium increases

 at sufficiently high pressures some of the hydrogen
 reactsto form helium - light is emitted

 the chemical elements are formed within the interiors
 of stars


Naturally occurring solids

Inorganic in origin 
	(not part of a life process)

Crystalline arrangement
	(an orderly internal structure)

Fixed composition
	(or variable within fixed limits)

Rocks: Records of Geologic Processes

Rocks are made up of one or more minerals

Three major rock types:




Igneous - Fire Formed	

	Depending upon the composition of the starting material,
	some liquid may be produced.

	In general, a mixture does not have a unique 
	melting point.

	Mixtures exhibit a melting range

	The magma (liquid) migrates upwards (most liquids 
	are less dense than the solids that produce them)
	and cools.

	Crystals grow from the liquid and compete for space - 
	An Interlocking Texture.

	If cooling takes place at depth an Intrusive Igneous
	Rockis formed

­ Plutonic .... relatively coarse grains

	If cooling takes place at the surface an Extrusive 
	Igneous Rock forms

­ Volcanic ... relatively fine grained

Sedimentary Rocks

	Form at or near the Earthıs surface


	The Earth has a reactive atmosphere

		­ Water
	­ Carbon Dioxide
	­ Oxygen 

 Genesis of Sedimentary Rocks

	Physical Weathering- reduction in size

	Chemical Weathering- change in composition


			Solid Particles ... clastics by water, wind, ice

			Ions in Solution ... chemical

	Clastics - particles do not form interlocking texture

	Chemical - grow from solution

	Sedimentary rocks tend to be layered

	The loose grains (sediment) must be converted to 
	sedimentary rock by cementation or compaction

Metamorphic Rocks

	Changed rocks - in response to changes in Temperature
	and Pressure.

	New Minerals may grow

	All rocks can be metamorphosed

The Earth - Compositional Variations ... Heterogeneous	

	0-  40 (miles)  Crust - relatively young
	­ continental crust and oceanic crust

	MOHO separates crust from mantle

	10- 400  Upper mantle

	400-2890 Mantle

	2890-5150  Outer core - Liquid

	5150-6378  Inner core - Solid

The Earth is a Dynamic Planet

	Distribution of Earthquake Epicenters

	Distribution of Volcanoes

	Distribution of Rock Types

Distribution of Rock Types


		­ shallow water marine
	­ near the equator
	­ organic

	­ plant material ... reducing environment ... 

The Earth  Post 1960ıs

	Lithosphere - the crust and the upper mantle
  ­ behaves as a RIGID solid

	Asthenosphere - from the lithosphere down to some 
	400 miles ­ behaves as a PLASTIC substance

Excess Heat	

	Temperature - function of motion of molecules/ions

	Heat - ³that which flows when two bodies at 
	differenttemperatures are brought in contact.

	Heat - Conduction ... heat flows by the 
	increased vibration
	 of ions/molecules

	Convection ... physical movement of a fluid 
	(including air) driven by a temperature gradient

	Radiation ... from hot object ... part of 
	the electromagnetic spectrum

Behavior At Boundaries	

	Extensional - Tension - pull apart

	Compressional - push together

	Transform - slide past one another