• Human geologic environment (the earth) is made up of geologic materials
•  We must study the materials of the earth

• Rocks, minerals, soil, etc.
•  Rocks constitute the “GROUND” for houses, etc.
•  Rocks are related to environmental processes like earthquakes, landslides, etc.

1. How earth, minerals, rocks formed?
2.  Why several geologic events occur today?
3.  How were these events in the past?
4.  How will they be in the future?

• Geologists answer these questions using certain CONCEPTS as CORNERSTONES
• The concept of UNIFORMITARIANISM (UNIFORMITY)
•  States that the “PRESENT IS A KEY TO THE PAST.”
•  We must know the present in order to study the past

1.  Interpreting the past
2.  Predicting potential future events

• Except for possible differences in rates, chemical and physical processes in the past as same as present.

• A big “Cosmic Ball” exploded and discharged GAS(Hydrogen, Helium + minor other ELEMENTS)
•  A billion years later, cloud of gas SEGREGATED to smaller clouds called GALAXIES
•  MILKY WAY is our galaxy.
•  Under gravity, smaller clouds (NEBULA) formed from the galaxies

• One nebula from MILKY WAY condensed under gravity.
•  It contracted and rotated.
•  Flattened into a disc, with SUN in the middle, and eddies (gathering materials) formed the PLANETS.
•  Solar energy from SUN removed loose gas & dust.
•  Sun burnt off excess hydrogen & PLANETS became fully developed.

• 4.6 billion years ago, some eddies swirled around the SUN to form the earth.
•  Eddies consisted of SILICON, IRON, OXYGEN, MAGNESIUM, ALUMINUM & other minor ELEMENTS.
•  Eddies formed 3 main concentric layers of differing chemistry constituting the EARTH:
•  CORE (Inner Layer)
•  MANTLE (Middle Layer)
•  CRUST (Outer Layer)

• 16% total volumes of earth
•  Density of 10 - 13 g/cm3
•  Consists mainly of IRON & NICKEL
•  Seismic waves indicate tow sublayers in CORE
•  A SMALL SOLID INNER LAYER (INNER CORE)
•  A LARGE LIQUID OUTER LAYER (OUTER CORE)

• Surrounds core
•  83% of earth’s volume
•  Density 3.3 - 5.7 g/cm3
•  Has 3 sub zones:
•  Lower Mantle: Solid & Forms most of earth’s interior
•  Asthenosphere: Surrounded by Lower Mantle
•  ** BEHAVE PLASTICALLY & FLOWS SLOWLY

C. UPPER MANTLE:

•  SOLID and surrounds asthenosphere
•  Together with overlying CRUST forms LITHOSPHERE

• Plates mover over asthenosphere
•  Interaction of plates responsible for phenomenon:
•  Earthquakes, Volcanic Eruptions, Mountain Ranges, formation of oceans, etc. (Plate tectonics)

•  Outermost layer of the earth
•  2 types
•  a. CONTINENTAL CRUST
• 20 - 90 km (thick)
•  Average density 2.7 g/cm3
•  Contains SILICON & ALUMINUM
• b. OCEANIC CRUST
•  5 - 10 km (thin)
•  Density 3.0 g/cm3
•  Mainly Igneous Rocks (Basalts)

MATERIALS OF THE EARTH

 Made up of matter

Matter: Anything with Mass & occupies SPACE, e.g., atmosphere, water, plants, animals, rocks, minerals, etc.

Matter occurs in 3 phases: SOLID, LIQUID, GAS
 
 

Elements and Atoms:

•  Matter is made up of chemical elements
•  Elements consist of SMALLER PARTICLES, (ATOMS)

• Atoms consist of a NUCLEUS
•  A nucleus is composed of (a) one or more PROTONS (b) NEUTRON

The nucleus makes up most of the MASS or WEIGHT of the atom.

•  Negatively charged particles encircle the NUCLEUS and are called ELECTRONS
•  The Number of protons in the nucleus of an atoms determines:
•  The ATOMIC NUMBER of the element
•  What element is, e.g., Hydrogen has 1 protein in nucleus, hence atomic number is 1.

•  This is the number of PROTONS & NEUTRONS
•  Electrons do not contribute to mass of an atom.

• Atoms of the same element may have different numbers of NEUTRONS, and therefore, different ATOMIC MASS NUMBER or ATOMIC WEIGHT

e.g., Carbon (C)has atoms with 3 different ATOMIC MASS NO.: 12C, 13C, 14C
•  All 12C, 13C, 14C have 6 protons
•  Thus they are all carbon, BUT,

12C has 6 neutrons
13C has 7 neutrons
14C has 8 neutrons

ATOMIC STRUCTURE

An atom may loose an electron to become positively charged OR may gain an electron to become negatively charged

A negatively OR positively charged atom is called an ION.

e.g.,

MINERALS:

• Naturally occurring, inorganic, crystalline solid with definite chemical composition and physical properties

Definition excludes: synthetic (man-made) diamonds, rubbies, orgainc animals, plants, deposits like coal, oil, etc.
•  Usually crystalline, i.e., 3-dimensional, regular framework:
• Most minerals are SILICATES, i.e., consist of Silicon and Oxygen +/- other metallic elements
•  Building block of silicates is SILICON TETRAHEDRON
•  Having one Silicon Atom, and 4 Oxygen Atoms

•  Isolated tetrahdra
•  Continuous or single chain of tetrahedra
•  Continuous double chain
•  Continuous sheet (Mica group)
•  3-dimensional Network of tetrahedra (Quartz)

•  Chemical composition
•  Crystal structure
•  Physical properties
•  Most useful properties
•  Color, Luster, Crystal form, Cleavage& Hardness

Rocks:

•  Make up most of earth crust
•  Aggregates of one more minerals & glass and some organic matter
•  3 main classes: Igneous, Sedimentary, Metamorphic

Sedimentary: Fragments of pre-existing rocks & those from chemical and biochemical activities

Metamorphic: Pre- existing rocks that have been transformed (or metamorphosed by changes in Heat and Pressure)

Igneous Rocks:

•  Formed from magma (molten complex of silicates)
•  Once formed, magma moves toward surface, thus losing heat and minerals begins to recrystallize accroding to BOWEN’S REACTION SERIES (Rate at which magma cools to form rock determines SHAPE and SIZE of minerals and rocks.)

TEXTURE & ROCKS

Large grains                                                               Small grains
(Phaneritic texture)                                                    (Aphanitic texture)
- Crystallizing at DEPTH                                          - Crystallizing at SURFACE
(Plutonic Rocks)                                                       (Volcanic Activity)
e.g. Granite                                                                Ryolite
       Gabbro                                                                Basalt

Sedimentary Rock:
-    Derived from physical and chemical weathering of pre-existing rocks.
-    Broken pieces of rocks or sediments
-    When consolidated or cemented, become sedimentary rocks (Clastic Rocks)

CLASSIFICATION USING GRAIN SIZE:

Sediments                                                             Sedimentary Rock
(Consolidated)                                                     (Unconsolidated)
(mm)
<0.004             Clay                                                Shale
0.004 - 0.062   Silt                                                  Siltstone
0.062 - 2.00     Sand                                                Sandstone
>2.00               Gravel                                             Conglomerate

Sedimentary Rock may also be formed from chemical and biochemical processes (Called Non-Clastic Rocks)

Metamorphic Rocks:
-    Formed from pre-existing rocks by change in temperature (Heat), Pressure & chemical processes
-    May form by FOLIATION, with
            - New structures, textures, layering
            - No new minerals are formed
-    Degree of foliation may vary, this is used for their classification
e.g. Slate (shale)     schist     gneiss
-    May also form by RECRYSTALLIZATION
        -    Pre-existing rocks are made larger, more perfect grains, new minerals formed
-    Marble (Limestone)
-    Quartzite (Sandstone)
 

The Rock Cycle:

-    Inter-relationship between the different rock types:
 

**WHY STUDY ROCKS!!!

-    Make up the earth
-    Contain mineral resources
-    Time (Can be obtained from knowledge of rocks)

Read Things                     ROCK DEFECTS

Dip, Strike, Joints & Faults.
 

GEOLOGIC TIME

-    Time is main aspect separating geology from other sciences.
-    People seconds, hours, days & years
-    To the geologist, recent events are those that occurred in the last million years or so
-    Compare history of earth to one calendar year. January 1st December 31st (4.6 billion years)
 

Geologic Time Scale

-    Geologic Time is divided into: Eon, Era, Periods, Epochs

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