Time defined by Geology, Rocks and Minerals

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Time defined by Geology, Rocks and Minerals
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Why rocks?

• Geology allows us to use rocks to see what the
  past was like on Earth
• -environment
• -life forms
• -tectonic events
• -catastrophes

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Geologic Time Scale

• Art by Ray Troll

Periods are defined by their MASS extinctions
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Eras and New Mexico

• Precambrian- 9/10ths of Earths History
• 4600- 542 MYA
• Where we are now started underwater, at the very
  end of this time period New Mexico surfaced.
• Granite and other metamorphic rocks formed during
  this time (Sandia Mt. and Sangre de Cristo) but
  because so long ago, much lost due to erosion.

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Paleozoic 542- 251 MYA

• Fossils of trilobites come from, aquatic
  lifeforms, fish
• New Mexico was flooded with small seas, deposits
  of limestone and sandstone from those beaches and
  reefs that formed- Guadalupe Mts.
• End of this era PANGEA forms, land becomes swampy
• CARBONIFEROUS epoch- zooplankton and algae
  decompose to create modern petrol, coal

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Mesozoic- 251- 66 MYA

• NM dries out again- leaves layered rock you see
  today- mesa and buttes
• Environment a mix of swamps and deserts depending
  on where you are in state, on and off flooding of
  areas- shale, limestone, sandstone
• Era of dinosaurs- NM State Fossil- Coelophysis
  (Triassic)
• KT/ KPg Event- band in the rocks- SOMETHING
  caused a mass extinction which denotes the end of
  Mesozoic Era (asteroid(s)?)

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Cenozoic 66 MYA to NOW!

• In NM, lots of volcanic activity- like the Valle
  Caldera- Redondo Peak- Lava Dome
• Volcanoes also formed Mogollan Mts, Datil Mts,
  Black Range, Sierra Blanca and Ship Rock- lots of
  igneous rocks
• Albuquerque Volcano Field also formed during this
  time- Cinder cones
• Anthropocene- possible rename for our epoch/
  period

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How do we know the age of rocks?

• Look at the layers!
• LAW OF SUPERPOSITION- the oldest rocks are at the
  bottom, the youngest are at the top
• Nicholas Steno- Relative Stratigraphy 1669
• Evidence came in 1890- 1940
• Rock dating using Radiometric Decay, looking at
  isotopes (ex U-235 decays to Pb- 207)
• - Date Igneous and Metamorphic only

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Additional Evidence

• Carbon Dating viable organic remnants of life
  forms
• Cosmic Radiation- He-3
• U-238, Zircon apatite has U- 238 as part of its
  crystalline structure
• Paleomagnetism- Earths Magnetic field switches
  naturally

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Properties of Rock and Minerals
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What is a mineral?

• Naturally occurring
• Inorganic
• Distinctive physical properties
• Crystalline structure, consistent elemental
  composition/ atomic structure

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Mineral properties

• Color
• Luster
• Habit (Shape)
• Cleavage Fracture
• Streak
• Hardness
• Other

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Color

• Not mineral specific

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Luster

• How minerals reflect light

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Mineral Habit (Shape)

• Shape a mineral takes if grown unimpeded
• Mineral Java Applet

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Cleavage Fracture

• Cleavage planes of weakness along which minerals
  can break, weak areas of bonding- categorized by
  quality and difficulty
• Fracture surfaces along which minerals can
  break, curved surface, irregular

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Streak

• The powdered form of a mineral

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Hardness

• Based on Mohs scale of hardness

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Other Properties

• Specific gravity
• Reaction to acid
• Striations
• Magnetism
• Florescence

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• Ore- metal or mineral in its pure form that is
  economically useful
• Alloy- solid mixture of 2 or more metals, created
  by smelting
• Stainless steel- Fe, Cr, Ni

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Classifying Rocks

• Rocks are classified by how they formed, what
  theyre made of, grains (texture)
• Rocks are made up of minerals- aggregate
• There are 3 general classes of rocks- Igneous,
  Sedimentary, Metamorphic

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• Igneous Rocksare formed when lava and magma
  crystallize to form solid rock-
• Extrusive/ Volcanic- formed on surface, shiny and
  glassy
• Intrusive/ Plutonic- formed beneath
  surfaceporphyritic- cools in 2 stages and forms
  in different sized crystals

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Igneous Rocks
Plutonic- gabbro, granite, monzonite,
granodiorite Volcanic- basalt, pumice, obsidian,
rhyolite (what the Valle is made of)
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• Metamorphic Rocksare formed when an existing
  rock is partially melted, squeezed, or both-
  changes on a mineral, chemical or structural
  level
• Foliation- forms in layers/bands
• Gneiss- metamorphosed GRANITE
• Marble- metamorphosed LIMESTONE
• Quartzite- metamorphosed SANDSTONE

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Metamorphic Rocks
Schist
Gneiss
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• Sedimentary Rocksare formed when sediments
  (sand, clay, and silt) are compressed and become
  solid rock
• Erosion- surface broken and worn away (rain)
• Deposition- sediment settles by water or wind
• Compaction- process which pressure squeezes
  layers together
• Cementation-during compaction, minerals dissolve
  in water and glue the layers together

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Clastic, Organic, Chemical

• Clastic- rock fragments are squeezed together
  (shale, sandstone, conglomerate)
• Organic- remains of plants and animals deposited
  into layers (coal, limestone- coral reefs)
• Chemical- chemicals precipitate out of water and
  form a rock layer by layer (limestone, travertine)

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Sedimentary Rocks


Shale
Conglomerate

Sandstone

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Plate Tectonics

• Plate Movements and convection currents drive the
  Rock Cycle by pushing rocks back into the mantle,
  where they melt and become magma again.