W1-3 Matter

• Chapter 3 discusses matter, its states, and its composition on Earth

Earth Materials

• The 3 common states of matter are solid, liquid, and gas
• Materials in the same state may differ
• Lava and water are both liquids, but lava is non-aqueous and water is aqueous
• Matter can coexist in various states and phases
• For a uniform composition of H2O, matter coexists as liquid and solid, with water and ice as 2 different phases which are separated by physical boundaries
• Different phases can coexist in the same state such as oil and water liquids or types of solid beans
• Gases only have one phase and one state
• Chemical elements are substances into which matter can be separated
• An atom is the smallest particle with properties of a chemical element
• Atoms contain protons and neutrons in the nucleus, with electrons orbiting
• The atomic number measures the number of protons in an atom's nucleus
• Electrons are considered massless
• Atomic mass is the sum of neutrons and protons in the nucleus
• Isotopes are atoms sharing an atomic number but having different mass numbers
• Radioactive isotopes are used in radioactive dating
• An atom is electrically neutral because protons' positive charge balances with electrons' negative charge
• An ion is an atom with excess positive or negative charge
• A positive ion is a cation, and a negative ion is an anion
• Compounds form when anions and cations combine via bonds
• A molecule is the smallest unit retaining properties of a compound

Organic Matter

• A main distinction is whether matter is organic or inorganic
• Organic matter has compounds of carbon atoms bonded covalently
• Organic origin implies the compound is biotic
• Organic compounds tend to occur in long, chain-like polymer structures
• Biopolymers include proteins made of amino acid chains, nucleic acids (e.g., DNA) made of nucleotides, and carbohydrates
• Carbohydrates are based on carbon, hydrogen, and oxygen
• Lipids, like fats, oils, phospholipids, waxes, and steroids, are an important family of organic molecules but not polymers

Composition and Internal Structure of the Earth

• Earth inherited its overall composition from its location in the solar nebula
• Earth has internal layering that originated early in solar system history due to chemical differentiation of the partially molten planet
• Earth's layers are distinguished by composition, rock strength, and state of matter
• The three major compositional layers in the Earth are the core, mantle, and crust
• The core is composed of metallic iron with a solid inner core and a liquid outer core
• The mantle is composed of dense rocky matter
• The crust is thin and composed of less dense rocky matter
• The core and mantle have nearly constant thicknesses
• The crust varies in thickness by a factor of 9
• The average oceanic crust is 8 km thick
• The average continental crust is 45 km thick but ranges from 30-70 km
• The oceanic and continental crusts differ fundamentally in composition
• Scientific reasoning, indirect sampling, and indirect measurement provide information about the core and mantle that otherwise is inaccessible
• In addition to compositional layering, the Earth contains layers with differences in rock strength
• Mesosphere is the "middle sphere" within the mantle
• Asthenosphere is the "weak sphere" in the uppermost mantle
• Lithosphere is the "rocky sphere" of the outermost 100 km
• Of the 92 naturally occurring chemical elements, only 12 occur in Earth’s crust
• The crust is dominated by oxygen and silicon
• With the other ten elements, oxygen and silicon compose all common Earth materials

Minerals

• Minerals are the building blocks of the geosphere
• They are naturally formed
• Minerals are inorganic
• Minerals are solid
• Minerals have a specific chemical composition
• Minerals have a characteristic crystal structure
• The two characteristics that allow the study of minerals are Crystal structure and Composition
• Crystal structure is how the atoms of the elements are packed together
• Composition is the major chemical elements that are present and their proportions
• Oxygen and silicon form the basis for the most common rock-forming minerals, and the most common mineral group: silicates
• Other mineral groups are oxides, sulfides, carbonates, sulfates, and phosphates
• Silicates are built of the silicate anion (tetrahedron)
• The silicate anion joins together by sharing their oxygen atoms to form chains, sheets, and three-dimensional networks
• Silicates are the most abundant minerals in the continental crust
• Feldspars are the predominant variety of silicates
• Feldspars are 60% of minerals in Earth’s crust
• Quartz is 15% of minerals in Earth’s crust
• All silicates are 95% of minerals in the crust
• Non-silicates are 5% of the Earth’s crust
• Minerals are identified by their distinct properties that result from their composition and crystal structure
• Some ways to identify minerals include crystal form and growth habit, cleavage, luster, hardness and specific gravity, and color
• In 1669, Nicolaus Steno discovered that the angle between mineral crystal faces is constant and gives each a distinctive crystal form
• He speculated this was due to ordered particles, but proof by use of x-rays would not arrive until 1912
• Crystals only form when a mineral can grow freely in open space
• Cleavage is a mineral’s tendency to break in preferred directions along weak planar surfaces
• Luster is the quality and intensity of light reflected from a mineral surface
• Color is often not a reliable means of identification because it can be determined by chemical impurities in the composition
• Color in opaque minerals can be a property of grain size but is resolved using the mineral’s streak
• Hardness refers to the relative resistance of a mineral to being scratched
• A mineral's crystal structure and the strength of its chemical bonds govern hardness
• Hardness is classified using Moh’s relative hardness scale, which has 10 hardnesses that are not at equal intervals
• Specific gravity is easier to measure then density and is therefore more commonly used
• Specific gravity is the ratio of the weight of the substance to the weight of an equal volume of pure water
• The densities of some minerals are distinctive, such as gold and galena

Rocks

• A rock is any naturally formed, nonliving, coherent aggregate mass of solid matter that constitutes part of a planet, asteroid, moon, or other planetary object
• Minerals are the most common and abundant building blocks of rocks
• The three families of rocks are igneous rocks, sedimentary rocks, and metamorphic rocks
• Igneous rocks form from the cooling and consolidation of magma or lava
• Sedimentary rocks form from either chemical precipitation of material or deposition of particles transported in suspension
• Metamorphic rocks form from changing a rock as a result of high temperatures, high pressures, or both
• Earth’s crust is mainly igneous and metamorphic rock however, most of the rock seen on the surface is sedimentary
• The two main features that best classify rocks are texture and mineral assemblage
• Texture is the overall appearance of a rock, resulting from the size, shape, and arrangement of its mineral grains
• Mineral assemblage is the kinds and relative amounts of minerals present

Regolith

• Rock exposed at Earth’s surface is susceptible to alteration by the action of water, wind, and other agents that physically and chemically break it apart and alter it
• This broken-up, disintegrated rock matter is called the regolith
• Literally "blanket rock,” the regolith forms a layer draped over most of Earth’s surface
• Three categories describe most of the various materials of the regolith: saprolite, sediment, and soil
• Saprolite is rock that is weathered in situ
• Sediment is loose rock and mineral particles
• Clastic sediment is broken particles
• Chemical sediment is dissolved material
• Soil contains organic matter mixed with minerals and can support rooted plants