Outline of Earth Science - Part I

Atoms are the building blocks of matter.

• Elements
  • There are about 90 natural elements. The eight most abundant elements in Earth's crust are Oxygen, Silicon, Aluminum, Iron, Calcium, Sodium, Potassium and Magnesium.
  • The name of an element is defined by its Atomic Number, the number of protons in its nucleus.
  • Each element has a standard symbol (ex. H for Hydrogen, C for Carbon and O for Oxygen).
  • All elements have mass (add up all the particles).
  Up to nineteen more elements are accepted by some authors, many only exist under laboratory conditions or are unstable at Earth-normal temperatures and pressures.
  
  
• Subatomic particles
  1. Protons have a mass of one and a positive charge. [ + ]
  2. Neutrons have a mass of one and no charge. [ * ]
  3. Electrons have a mass of .0079 and a negative charge. [ - ]
  Protons and neutrons form the nucleus and electrons whiz around them in shells. The number of electrons in the shells starts 2:8:8. For more, consult a college physics text.
  
  
• An atom with an unbalanced charge is called an ion. Some ions are more common than others.
  • Cations are elements which have lost an electron and have a positive charge. The # of protons is greater than the # of electrons.
  • Anions are elements which have gained an electron and have a negative charge. The # of electrons is greater than the # of protons.
  
  
• An atom with more neutrons than protons in its nucleus is called an "isotope" of that element. Isotopes are unstable and decay at known rates, known as "half-lives."

Atoms are joined by chemical bonds including:

• Ionic bonds-- "static cling" -- usually 1:1 -- ex. salt NaCl and galena PbS
• Covalent bonds -- share electron(s) -- usually not 1:1 -- ex. water H₂O, silica SiO₂, diamond C
• Metallic bonds-- nuclei share a cloud of electrons -- ex. copper Cu, silver Ag, gold Au and pyrite FeS₂
• van der Waals forces -- weak bonding -- ex. graphite C, talc, plane cleavage of mica

Compounds form when two or more atoms bond together in a known proportion. Examples include

• water H₂O
• carbon dioxide CO₂
• salt NaCl
• sugar C₆H₁₂O₆.

Chemical changes can decompose compounds. Chemical reactions are described by chemical equations. In chemical equations, the reactants are on the left side and the products on the right side. The direction of the arrow (like traffic arrows) shows either

1. single arrow process cannot be reversed
2. double arrow the process can be reversed.

Photosynthesis is an oxidation-reduction reaction.

Consult the periodic table in your book. Be sure you find the names of the atoms and are able to use them correctly.

Minerals are:

• natural -- not man-made
• inorganic -- although they may have formed from organic remains
• solid -- not liquids like oil or natural gas
• crystalline -- arranged in a particular order
• have a definite chemical composition (ex: Salt, NaCl and so on)
• and regular physical properties

Minerals have physical properties:

• crystal habit - shape when it formed
• cleavage (clasts of same shape as parent)
• fracture (clasts not same shape as parent)
• specific gravity (density in metric units)
• color (reflected light from mineral)
• luster (appearance of reflected light)
• streak (color of powdered mineral)
• hardness on Moh's scale related to standard minerals or items 1--Talc, 2--Gypsum, 2.5--Fingernail, 3--Calcite, 3.5--Copper Penny,
  4--Fluorite, 5--Apatite, 5.5--Glass Plate,
  6--Orthoclase - Potassium Feldspar, 7--Quartz, 8--Topaz,
  9--Corundum, 10--Diamond
• Some of the other properties of minerals are magnetism, birefringence, acid fizz, melting point/freezing point, color given off when burned and fluorescence under ultraviolet light.
• Not every mineral has every property. Gold, for example, does not form crystals and a mineral which has cleavage, may or may have fracture.

Minerals are divided in two groups based on their anions:

I.) Silicate Minerals have SiO₂ as anions,

II.) Non-silicate Minerals (anions are "3-ates, 4-ides and an -ive")

Consult the relevent chapters in your book. Construct tetrahedral models (see my Math Links page) and study mineral specimens where available. Read labels on household items. Where do you use these items in daily life?

Rocks

Igneous rocks ("born from fire") form from fully melted minerals. Most igneous rocks are silicates. When native metals and other minerals occur in igneous rocks, they are exploited as ore bodies. Igneous rocks are based on their mineral composition and their crystal texture. The source of the magma controls composition while texture is a function of cooling time and water concentration.

Extrusive rocks are called fine-grained because they have small crystals. They cooled quickly and didn't have much time for the crystals to form. Volcanic ash forms as molten rock with dissolved water in it arrives at the surface. The loss of confining pressure on the magma changes the water to steam which explodes outward in all directions.

Glassy igneous rocks such as scoria and pumice have holes which record water bubbles and are sometimes filled with primary or secondary mineralizations. Another glassy igneous rock, obsidian or volcanic glass, needs some time to cool down.

Intrusive rocks have plenty of time to form and sometimes grow crystals of amazing sizes. The granite group known as pegmatite granites often include larger than normal crystal growth attributed to the presence of water in the melt which must, therefore have been at relatively low temperatures.

Sedimentary Rocks

• Physical weathering produces pieces called "clasts" which may be transported, deposited and lithified into physical sedimentary rocks. The three agents of physical weathering are
  1. gravity (9.8 meters/second squared or 32 feet/second squared) moves the largest to smallest clast sizes.
  2. steam, water, ice - whether flowing or changing phase, the "universal solvent" is also a prime mover of clasts and ions.
  3. wind can only carry smaller clasts.
  
  
  
• Chemical weathering produces minerals and ions which may be transported, deposited and lithified into chemical sedimentary rocks. Chemical weathering is facilitated by all natural rain being slightly acid. As water falls through the atmosphere, some reacts with carbon dioxide to form carbonic acid. H₂0 + CO₂ ---> H₂CO₃

  In areas with high sulfates such as around cars and trucks, some factories and active volcanos, sulfuric acid rain is produced. H₂0 + SO₃ ---> H₂SO₄

  Increasing acidity results in more erosion by dissolution as well as reducing deposition because clays stay in suspension in even slightly acid waters.

I. Silicate Weathering

II. Non-silicate Weathering

Sedimentary Rocks are classified by size of particle or their chemical nature.

The sorting of the clasts reveals the environment of formation.

Milling and rounding by erosion against other clasts produces wedgies, rounds, cylinders, angulars and flats. Each shape is diagnostic of the energy level of the agent of transport. Each clast may be worked and reworked by several agents of transport.

Immature sediments are freshly broken with angular edges. They are usually found within a short distance of the parent material. The rock types Arkose and Breccia are composed of angular clasts. On the other hand, mature sediments are rounded from milling and tumbling and are found from near the parent or even a considerable distance away from it. The rock types Conglomerate and Sandstone are composed of rounded clasts.

Sedimentary rocks are cemented together with either carbonate or silicate. If carbonate, the matrix will fizz when mild acid is applied. If the cementing matrix is pure silicate, it will not fizz even under strong acids. Either form of cement may be strong or weak.

Sedimentary structures assist in defining environments of formation. These structures include:

• stratification or bedding
• cross-bedding may show current direction
• ripple marks show direction and intensity of flow
• mud cracks show changing hydrology
• fossils reveal specific environmental conditions
• changes in sediment show different seasons or different sources

Metamorphic rocks change shape or texture, not chemical composition.

• The three "agents of metamorphism" are
  1. heat,
  2. pressure and
  3. chemically active fluids.
  
  
  
• Metamorphic rocks are divided into two main types.
  • Foliated metamorphic rocks include: slate, gneiss and schist. All three are silicates and can form from either an igneous or sedimentary parent material.
  • Non-foliated metamorphic rocks such as marble, talc, graphite or jade. Marble and graphite most commonly form from sedimentary deposits, while talc and jade are usually formed from igneous parent materials.
  
  
  
• Metamorphic grades are rated low, medium or high depending on duration and intensity of force. Rock can be heated hardly at all, or to temperatures immediately below its melting point. Different minerals become volatile at different temperatures and pressures and will migrate. Some, like garnets, tend to concentrate and recrystalize as temperatures drop. There are three ways to change rock temperature:
  1. Add or remove heat.
  2. Add or remove water or other volatiles.
  3. Increase or decrease the pressure.
  
  
  
• Three kinds of metamorphism all leave characteristic signatures.
  • Regional metamorphism refers to metamorphism over large areas
  • Contact metamorphism occurs adjacent to heat or pressure zones
  • Hydrothermal metamorphism occurs when fluids escape or are altered by metamorphism.

Geologic Time

1. Original horizontality - sedimentary beds are deposited relatively flat.
2. Superposition - in undisturbed beds, younger is on top of older.
3. Cross-cutting relationships - the material being cut is older than the cutting material.
4. Lateral continuity - you can see the same age formation in different places (William Smith's breakthrough).
5. Faunal succession - Certain plants and animals were only alive at certain times. For example, people never coexisted with dinosaurs; therefore any bed containing dinosaurs is older than the time of man.
6. Inclusions -- bits of older geomaterials included in younger deposits. Also true for xenoliths in granite.

Unconformities show where rock is missing, in one of three ways:

• Disconformity can be hard to see. It occurs where sedimentary layers were deposited on top of sedimentary layers following some interval of erosion. Disconformity is common in Illinois, Wyoming and North Coast, CA shorelines.
• Nonconformity occurs when two different kinds of rocks occur one on top of the other; for example, igneous overlain by sedimentary rocks.
• Angular unconformity occurs when one group is tilted but the next rock layer is not. Examples of this include the famous Sikkar Point in Scotland, and the less dramatic but easier to get to, Split Rock in Illinois.

Fossils -- plants, animals and traces

• Index fossils record things which lived only in certain times (ex: trilobites in Paleozoic or Glossopteris in the Mesozoic)
• Banded iron formations (BIFs) record the actions of ancient microbes and provide much modern iron ore. BIFs are found on continental cratons including near Lake Superior on North America and in Western Australia.
• Understandably, the fossil record is incomplete. There are some places on Earth today, both rare and uncommon, where fossilization does not occur now. In some places, no fossils are possible such as along active beaches; while in others, fossilization is more common but the event is more rare, like a lavaflow or a mudslide. In addition, fossils laid down are constantly being eroded, so that the fossil record disappears all the time, but not at a constant rate.
• Charismatic megafauna are the most familiar creatures from any particular time, but they are not the only plants/animals alive. Fascinating things are learned from exposures composed of only the smallest things such as the determination of the line between freshwater and saltwater at Mazon Creek, IL (Carboniferous age).

Absolute dating is done by means of radioactive decay ages correlated to tree-ring analysis. The correlation is necessary because the ratio of two carbon isotopes, C¹² and C¹⁴, are not fixed, but change slowly over time. However, the ratio of the two is fixed in an organism upon death and the unstable C¹⁴ parent material will decay into C¹² daughter material at a known rate, called its half-life which is about 5700 years. Eventually all the parent material decays into daughter material, and so this form of dating only works for about the last 40,000 years. For almost all other rocks, therefore Potassium/Argon or Zircon dating must be used because those materials have longer half-lives than C¹⁴.

Accurate dating is a combination of absolute dating techniques, additional evidence from flora and fauna, and good common sense.

What do all these names mean?

Most of Earth's history occurs in the the PreCambrian which is divided into three eons: the Hadean, the Archaen and the Proterozoic. Hadean is a reference to the Greek underworld "Hades." Archaen comes from the word for ancient and Proterozoic means "at the beginning of life. The fourth Eon is named "Phanerozoic" which means "apparent or obvious life." The division between the Precambrian and the Phanerozoic occured about 600 million years ago (mya).

The Phanerozoic Eon is divided into three Eras: the Paleozoic ("Ancient Life), the Mesozoic ("Middle Life") and the Cenozoic ("Recent Life").

• The Paleozoic Era is divided into six periods: the Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian and Permian. The periods are divided on characteristic trilobite fauna.
  1. The Cambrian is named from the Latin word for Wales because rocks of this age outcrop and were studied by early geologists in Wales. During the Cambrian, we know most about its desert land areas, warm seas and rapid diversification of life. Almost all the modern animal phyla arose in the Cambrian. Most of the continents form a large landmass, occasionally refered to as the Old Red Sandstone Continent. (ORSC)
  2. The Ordovician is based on a Celtic word. The Ordovices were a tribe living in Wales during Roman times. Primitive fishes mark this period. The ORSC continued to break up.
  3. The Silurian is based on a Celtic word. The Silures were another tribe living in Wales during Roman times. During the Silurian jawed fishes roamed the oceans while invertebrate animals and plants colonized the land.
  4. The Devonian is named for Devon, England, where rocks of this age were first studied. Lobe-finned fishes, amphibians and land insects colonized shore habitats and the first forests.
  5. The Carboniferous refers to the coal bearing rocks of its two periods the Mississippian, named for the bluffs along that river, and Pennsylvanian which refers to the state and Both reference where the outcrops were first known. The southern Continents are joined into Gondwana at this time. The northern ocean is closing as North America and Laurasia approach. Warm, swampy margins laid down over millions of years became the coals mined out in Russia, Europe and North American in the past 200 years.
  6. The Permian is named for an area in Russia where outcrops of this age were defined and named. The Permian-Triassic boundary is noted as a time of ecological change with most continents ground together, massive mountain building and subduction.
  
  
• The Mesozoic Era is divided into three periods: the Triassic, Jurassic and Cretaceous.
  1. The Triassic refers to the subdivision of this period into three parts. Mammals, dinosaurs and other land life diversified.
  2. The Jurassic is named for the Jura Mountains in Europe where the outcrops were first studied and named. Dinosaurs continued to be dominant on land. The earliest bird fossils are Jurassic.
  3. The Cretaceous refers to the great chalk deposits laid down in this final dinosaur era. The great Chalk Cliffs and downs of England are of this period. Flowering plants arose in the Cretaceous. T rex. lived at the end of the period. The Cretaceous-Tertiary boundary (referred to as the K-T boundary in many books) is noted for an apparently global iridium anomaly and an apparent mass extinction event which took out the dinosaurs but was survived by insects, spiders, frogs, crocodiles, turtles, birds, mammals and most fish groups. The border may therefore be arbitrarily placed on human interest in the loss of a charismatic megafaunal group.
  
  
• The Cenozoic Era is divided into the Tertiary and Quaternary Periods.
  1. The Tertiary Period was named when there were only four divisions of Earth History. It and Quaternary are the only two that stuck. The Epochs in the Tertiary are named the Paleocene, Eocene, Oligocene and Miocene.
     1. The Paleocene ("Ancient time") is actually the first epoch of the Tertiary. Placental mammals appeared and collisions which produced the Rocky Mountains and the Himalayan orogenies began.
     2. The Eocene ("Dawn time") is the second epoch of the Tertiary. It had warm climates. Most modern mammal familes arose in the Eocene.
     3. The Oligocene is the third epoch of the Tertiary, when true carnivores arose and gradually replaced creodonts.
     4. The Miocene is the fourth epoch of the Tertiary. Grasses and grazing mammals arose in the Miocene.
     
     
  2. The Quaternary Period was named when Earth history was divided into only four parts. It and Tertiary stuck, Primary and Secondary became Paleozoic and Mesozoic respectively. The two Epochs of the Quaternary are the Pleistocene and the Holocene.
     1. The Pleistocene is the older of the two epochs of the Quaternary. Glaciers ebbed and flowed in the northern hemisphere. Hominids arose and spread worldwide. Numerous other species declined or disappeared including mammoths, mastodons, and saber-toothed tigers.
     2. The Holocene is the younger of the two epochs of the Quaternary. It began at the end of the last Ice Age about 11,000 years ago and has been the time of human civilization.

Additional resources

• Visit rock and mineral links for "pictures and information about every kind of mineral known to man." [per a comment I received via email] Print out tetrahedral models and follow links to crystal patterning and sacred geometry derived from the study of natural minerals.
• Visit a few fossil links and see animations of ancient sea life, or read more about dinosaurs and other extinct creatures.
• Outline of sedimentary rocks. Follow this link to an outline of sedimentary rocks developed for a 300-level ESCI class.
• Outline of Historical Geology developed for ESCI 211 and updated in 2005. Includes a more detailed rock cycle review as well as taphonomy, phylogeny, and classification of fossils and living animals as well as discussions of plate tectonics and the formation of North America.