GEOL unit1 pt4

Structure of the Geologic Time Scale: Eons 

  • Geological time divided into four eons: 

  1. Hadean (4567 to 4000 Ma)- oldest

  2. Archean (4000 to 2500 Ma) 

  3. Proterozoic (2500 to 538.8 Ma) 

  4. Phanerozoic (538.8 Ma to present)-youngest

Structure of the Geologic Time Scale: Eons 

Proterozoic Eon 

  • “Before Life” 

  • 2500 Ma – 538.8 Ma 

Archean Eon 

  • “Ancient” 

  • 4000 Ma – 2500 Ma 

Hadean Eon (oldest) 

  • 4567 Ma to ~4000 Ma

isotope - same number of protons, different number of neutrons, different atomic mass

Phanerozoic eon

  •  “visible life”

  • 538.8 Ma to present

  • We live in the Phanerozoic eon

Structure of the Geologic Time Scale: Eras 

  • Eons are divided into eras 

  • The Phanerozoic eon is divided into three eras: 

  1.  Paleozoic era (oldest) »538.8 Ma (“early or ancient life”)

  2. Mesozoic era »252 Ma (“middle life”) 

  3. Cenozoic era »66 Ma (“new or recent life”) 

  • We live in the Cenozoic era

Phanerozoic eon— the past 538.8 Ma of Earth’s history —is divided into three eras: 

  1.  Paleozoic (“early or ancient life”) 

  2. Mesozoic (“middle life”) 

  3. Cenozoic (“new or recent life”)

Put time boundaries in areas of mass extinction 

EX: paleozoic era ended with the extinction of dinos

Structure of the Geologic Time Scale: Period 

  • Eras are divided into periods 

  • Cenozoic era, which represents the past 66 Ma, is divided into three periods 

1. Paleogene (oldest) 

2. Neogene 

3. Quaternary (present)

EON ->ERA-> PERIOD ->EPOCH 

-Four eons 

  • Hadean 

  • Archean 

  • Proterozoic 

  • Phanerozoic 

-Phanerozoic eon divided into three eras 

  • Paleozoic 

  • Mesozoic 

  • Cenozoic 

-Eras are further divided into periods 

The cenozoic era is divided into three periods 

  • Paleogene 

  • Neogene 

  • Quaternary

- Periods are divided into epochs

Element 

  • Most fundamental substance into which matter can be separated by chemical means 

  • An element is a pure substance that cannot be separated into other materials

  •  ~92 naturally occurring elements

  • Can also be synthesized (made) in a lab

  • Organized in a periodic table so that those with similar properties line up

Atom 

  • Smallest unit of an element that possesses the properties of the element 

Composed of: 

  • Protons: charge of +1 

  • Nucleus

  • Neutrons: charge of 0 

  • Electrons: charge of –1 

  • Electrons exist as a cloud of negative charges surrounding the nucleus

 Isotopes 

  • Iron has four naturally-occurring stable isotopes, 54Fe, 56Fe, 57Fe and 58Fe

  •  Iron always has atomic number 26, but its mass number can be 54, 56, 57, or 58

  • 54Fe = 26 protons, 28 neutrons 

  • 56Fe = 26 protons, 30 neutrons 

  • 57Fe = 26 protons, 31 neutrons 

  • 58Fe = 26 protons, 32 neutrons

Ions 

  • Atoms that have as many electrons (-1 charge) as protons (+1 charge) are electrically neutral 

  • Atoms can gain or lose electrons in their outermost shells 

  • Atom that loses or gains electron(s) has a net electric charge and is called an ion

  • An ion is atom that is not neutral 

  • Ions form in solution 

  • Ex: saltwater

  • An ion with an excess negative charge (it has more electrons than protons) is an anion 

  • example: Cl– has a single excess electron so has -1 charge 

  • An ion with an excess positive charge (it has more protons than electrons) is a cation 

  • Example: Fe2+ is missing two electrons so has +2 charge 

  • Importance: attraction between cations and anions is the bonding force that often holds matter together 

  • cations are positive- Grumpy Cat always has a positive attitude!

Chemical Bonds 

  • A chemical bond is an attractive force that holds two or more atoms together

  •  There are several types of chemical bonds: 

  1.  ionic bonds form when a cation and an anion (ions with opposite charges) get close together and attract each other 

  2.  covalent bonds form when atoms share electrons 

  3.  In materials with metallic bonds, some of the electrons can move freely

Chemical Bonds: Ionic Bonding (transfer)

  • One atom (metal) transfers an electron to another atom (nonmetal)

  •  Attractive force is set up that creates an ionic bond

Halite (NaCl)—Example of Ionic Bonding

  • The transfer of an electron from a sodium(NA) to (CL) chlorine atom leads to the formation of a Na+ ion and a Cl- ion

Covalent Bonding (share)

  • Electrons from different nonmetal atoms “pair-up” 

  • No electrons are lost/gained 

  • No ions are formed 

  • Each atom shares the electrons in order to fill the outer shell

  • Two hydrogen atoms combine to form a hydrogen molecule, held together by the attraction of oppositely charged particles- positively charged protons in each nuclei and negatively charged electrons that surround these nuclei.

Metallic Bonding (free flow)

  • Positive metal ions attract conducting electrons 

  • Atoms are so tightly packed that electrons can be shared among several atoms 

  • Valence electrons are free to migrate among atoms

  • This mobility accounts for the high electrical conductivity and ductile behavior of metals

Van der Waals Bonding (stick together)

  • Weak attraction between electrically neutral molecules that have asymmetrical charge distribution

Minerals

  • Minerals are all around us!

  •  the graphite in your pencil

  • the salt on your fries

  • the drywall on your walls

  • the trace amounts of gold in your computer 

  • everything made of metal is derived from minerals

  • minerals can be found in a wide variety of consumer products including paper, medicine, processed foods, cosmetics, electronic devices, and many more

  • Minerals are there, even if you can’t see them with your eyes

Definition of a Rock: 

  • Naturally occurring aggregate of minerals

Never, ever confuse rocks and minerals! minerals are to rocks as letters are to words.

Naturally Occurring

  • true minerals grow in nature, not in factories 

  • only naturally occurring inorganic solids are minerals

  • chemists can manufacture materials that have characteristics virtually identical to those of real minerals

  • Such materials can be referred to as synthetic minerals

  • Synthetic products are not minerals!

(generally) Inorganic

  • distinction between inorganic and organic compounds not always clear

  • living (organic) vs nonliving (inorganic) 

  • biogenic CaCO3 becomes problematic…

  • carbon (organic) vs no carbon (inorganic

  • calcite, graphite, diamond, etc. become problematic…

  • define an organic compound as one containing both carbon and hydrogen

  • Coal (not a mineral)

Solid

  • A mineral, like any matter in the solid state, can maintain its shape indefinitely, so it will not conform to the shape of its container

  • Minerals cannot be liquids (such as oil or water) or gases (such as air) 

  • Liquid mercury is not a mineral (because it’s a liquid!)

Crystalline Material: Specific, Orderly Crystalline Structure

  • In a crystalline material, the atoms reside in an orderly, fixed pattern, locked in place by chemical bonds

  • The three-dimensional geometric arrangement of atoms or ions that defines that pattern is called a crystal (crystalline) structure

  • Minerals have a specific, orderly crystalline structure 

  • René-Just Haüy (1743-1822) 

  • Opal is a mineraloid (not a mineral!) because although it has all of the other properties of a mineral, it does not have a specific, orderly crystalline structure

  • crystalline structure of a mineral controls its physical properties 

  • diamond and graphite are minerals

  • diamond and graphite have the same chemical composition [(carbon (C)], but the carbon atoms form different crystalline structures 

Definite Chemical Composition 

  • minerals have a specific (definite) chemical formula or composition

  • Can be expressed by a specific chemical formula

  • Quartz is SiO2 …always 

  • Calcite is CaCO3… always

  • Halite is NaCl… always

How do minerals form? 

  • New mineral crystals can form in several ways: 

  1.  Solidification (freezing) of a melt

  2. Precipitation from aqueous solution (water)

  3. Solid-state diffusion 

  4. Biomineralization 

  5. Chemical Weathering 

  6. Precipitation from gaseous emanations (i.e. precipitation directly from a gas) 

  7. Metamorphism

Solidification (freezing) of a melt 

  • Happens when a liquid (magma/lava) cools and turns into a solid 

  • Similar to water freezing

  • When the magma/lava is hot, atoms are mobile

  • When the magma/lava cools, atoms slow and begin to chemically combine

  • water crystallizes to form ice (a mineral) 

  • magma/lava crystallizes to form minerals

Precipitation from aqueous solution (water) 

  • ions dissolved in an aqueous solution reach saturation and start forming crystalline solids 

  • drop in temperature or water loss through evaporation can cause ions to reach saturation

Solid-state diffusion 

  • results from the movement of atoms or ions through a solid to arrange into a new crystal structure 

  • Garnets, for example, grow by diffusion in solid rock 

  • During this process, they replace pre-existing minerals

Biomineralization 

  • takes place when minerals grow at the interface between the physical and biological components of the Earth System

  • This process can happen because metabolic processes of some living organisms can cause minerals to precipitate either within their bodies, on their bodies, or immediately adjacent to their bodies 

  • Shells (composed of the mineral aragonite or calcite) produced by marine organisms grow when these organisms extract ions from the water they live in

Chemical weathering

  •  minerals unstable at Earth’s surface may be altered to other minerals

Precipitation directly from a gas can occur around volcanic vents or around geysers 

  •  volcanic gases or steam enter the atmosphere and cool, so some gas molecules of some elements are able to bind together 

  • some of the bright yellow sulfur deposits found in volcanic regions form in this way

Metamorphism 

  • formation of new minerals directly from the elements within existing minerals under conditions of elevated temperature and pressure 

  • No melting occurs!

  • EX: blue kyanite

  • Graphite and diamond are both made entirely out of carbon

  • If we put graphite under a huge amount of pressure, the carbon atoms will be squeezed together and will rearrange themselves into the more compact crystal structure of diamonds

Minerals

  •  ~3800 minerals (!) 

  • Rock-Forming Minerals

  • common minerals that make up most of the rocks of Earth’s crust 

  • less than 2 dozen 

  • A much more manageable number!!!

  • composed mainly of the 8 elements that make up most of Earth’s crust

  • Most minerals are made up of a cation (a positively charged ion) or several cations and an anion (a negatively charged ion (e.g., S2–)) or an anion complex (e.g., SO4 2–)

  • For example, in the mineral hematite (Fe2O3 ):

  • the cation is Fe3 + (iron) 

  • the anion is O2– (oxygen) 

8 most common elements in Earth’s crust 

  1. Oxygen

  2. Silicon

  3. Aluminum 

  4. Iron

  5. Calcium

  6. Sodium

  7. Potassium

  8. Magnesium

Mineral Classification

  • We classify minerals according to the anion part of the mineral formula

  • recall, an anion is a negatively charged ion such as Cl- or CO 3 -2

  • mineral formulas are always written with the anion on the right

  • pyrite (FeS2 )

  • Fe 2 + is the cation 

  • S – is the anion

Silicate Structures: Independent (or Isolated) Tetrahedra

  • In this group, the silica tetrahedra do not share any oxygen atoms

  • Silica tetrahedra bond to other elements, not other silica tetrahedra

  • The attraction between silica tetrahedra and positive ions (cations) holds these minerals together

  • Examples: Olivine, Garnet, Zircon, Kyanite

Olivine 

  • Olivine composed of individual (independent) silica tetrahedra 

  • in olivine, the –4 charge of the silica tetrahedron is balanced by two divalent (i.e., +2) iron or magnesium cations

  • Olivine can be either Mg2SiO4  or Fe2SiO4 , or some combination of the two (Mg,Fe)2SiO4

Silicate Structures: Single Chains 

  • In a single-chain silicate, the tetrahedra link to form a chain by sharing two oxygen atoms 

  • strongly bonded so cleavage cuts parallel to the chains 

  • two planes of cleavage at 90 degrees

Single Chain Silicate Minerals: Pyroxenes 

  • The most common of the many different types of single-chain silicates are pyroxenes

  • Pyroxenes important components of dark-colored igneous rocks

  • Augite most common mineral in the pyroxene group

  • Black in color 

  • Two distinctive cleavages at nearly 90 degrees 

  • Dominant mineral in basalt

Silicate Structures: Double Chains

  •  In a double-chain silicate, the tetrahedra link by sharing two or three oxygen atoms

  • minerals cleave parallel to the double chains

  • two planes of cleavage at 60 and 120 degrees

Double Chain Silicate Structures: Amphiboles

  • Amphiboles are the most common type of double chain silicates

  • Hornblende most common mineral in this group

  • Two perfect cleavages exhibiting angles of 120 and 60 degrees

Silicate Structures: 2D Sheet Silicates 

  • All the tetrahedra in this group share three oxygen atoms and therefore link to form two-dimensional sheets

  • Other ions, and in some cases water molecules, fit between the sheets in some sheet silicates

  • Because of their structure, sheet silicates have cleavage in one direction and occur in books of very thin sheets

  • bonds between sheets are weak 

  • This group includes micas and clays (which occur only in extremely tiny flakes)

2D Sheet Silicate Structures: Muscovite 

  • Common member of the mica family 

  • Excellent cleavage in one direction 

  • Clear, thin sheets 

  • Produces the “glimmering” brilliance often seen in beach sand

Silicate Structures: 3D Framework Silicates 

  • In a framework silicate, each tetrahedron shares all four oxygen atoms with its neighbors, so the tetrahedra are configured in a threedimensional structure 

  • Examples:Feldspars, Quartz 

  • All oxygen ions are “shared” between tetrahedra

Feldspars 

  • Most common mineral group

  • Forms under a wide range of temperatures and pressures 

  • Exhibit two directions of perfect cleavage at 90 degrees

Quartz 

  • Only common silicate mineral composed entirely of oxygen and silicon 

  • Hard (7) and resistant to weathering

  • Breaks with conchoidal fracture 

  • Often forms hexagonal crystals 

  • Colored by impurities (various ions)

Nonsilicate Minerals: Halides

  • minerals that make up the halide group include those in which the halogen elements of fluorine, chlorine, bromine, and iodine are combined with one or more metals

  • includes halite, sylvite, fluorite

  • halogen elements are the anion

Nonsilicate Minerals: Oxides

  • Oxide minerals have oxygen (O2–) as their anion 

  • but we exclude those minerals with oxygen complexes such as carbonate (CO3 2–), sulphate (SO4 2–), and silicate (SiO4 4–) from the oxide group 

  • several minerals of great economic importance including the chief ores of iron, chromium, manganese, tin, and aluminum 

  • Hematite (iron oxide Fe2O3 )

  •  Magnetite (Fe3O4 )

  •  Corundum (aluminum oxide Al2O3 )

Nonsilicate Minerals: Sulfates/Sulphates

  •  basic unit of the sulfate minerals is the sulfate anion, SO4 2- 

  • sulfate anion combines with metal cation to form the sulfate minerals

  •  the metal cation has a +2 charge, which balances the –2 charge on the sulfate ion

  • many sulfates form by precipitation out of water at or near the Earth’s surface 

  • Common sulfate minerals: 

  • Barite (BaSO4 )

  • Gypsum(CaSO4 .2H2O)

  • Anhydrite(CaSO4)