Geology Stuff

Fact

Confirmed Observation

Hypothesis

Testable if then idea

Theory

Well supported explanation, not a guess

Relative dating

Puts events in order, no calendar year required

Absolute dating

Gives a number, usually a radioactive decay

Carbon 14

Useful for wood bone and charcoal, even cloth younger than 50,000 years, even dinosaurs too

Six rules to keep

Superposition, Horizontality,  Inclusion, continuity, unconformity, cross-cutting

Superposition

Bottom is older if not overturned

Cross-cutting

The cutter is younger

Horizontality

Tilted beds were tilted later

Inclusions

Pieces that are older than the host

Continuity

Matching layers across a gap are the same layer

Uncomformity

A gap, time is missing

Four families of clocks

Radiometric, Luminescence, Tree rings, Varves

Radiometric

Unstable atoms become stable atoms at a fixed rate

Luminescence

Quartz and feldspar store a light signal that resets in sunlight or heat

Tree rings

 One ring per year. Exact calendar years on wood

Varves

One light, dark pair per year in some lakes and glacial ponds, count the years.

Silicate

Silicon and oxygen, most of the crust, quartz and feldspar, mica and olivine, pyroxene and amphibole

Non-silicate

No si-o backbone, fewer of them, often the useful ones, calcite and halite, gypsum and hematite, carbonate and ore, salt and evaporites

Granite

Silicate, continent, quartz and feldspar with mica, silica rich melt, light and coarse

Quartz

Silicate, harder than glass, no cleavage, does not fizz, sand and granite

Calcite

Non-Silicate, softer than glass, rhomb cleavage, fizzes in acid, limestone

Three boundaries

Divergent, Convergent, Transform

Divergent

New curst, divert from each other, Mid Atlantic Ridge, East African rift

Convergent

crust goes down or is pushed together, Andes, Japan, Himalaya

Transform

neither created nor destroyed, San Andreas, oceanic fracture zones

How a mineral forms

From melt, from water, from other solids

Minerals form from melt

Magma or lava cools, crystals grow, quartz in granite, olivine in basalt

Minerals formed from water

Ions in solution come together, halite from evaporated brine, calcite from seawater

Minerals formed from other solids

Heat and pressure rebuild the structure, new minerals in metamorphic rock

Plate Tectonic

The crust moves, the lithosphere is not one shell, it’s broken into plates that move a few centimeters, fingernail speed per year for millions of years.

Plate

A rigid piece of lithosphere, continent, ocean floor, or both

Boundary

Where two plates meet, almost all of the violence in here

Interior

Collision builds mountains, mid-ocean ridges sit on the push apart edges

Earthquakes

Concentrate in narrow belts. The belts are the boundaries

Volcanoes

Same belts, plus a few spots in the middle of plates (later).

Plate Boundaries

Lithosphere, Edges, Ohio, Two crusts

Lthosphere

Broken into plates, continent, ocean floor or both

Edges

Earthquakes and most volcanoes mark the boundaries, not random

Ohio

Plate interior, quiet, our limestone is a moved tropical area

Two crusts

Oceanic, thin dense and can sink, continental thick, light, piles up

law of faunal succession

 different fossils are found in different layers in order

Index fossils

it is the relative age of the rock layers, easy to recognize, good for matching rocks

Cleavage

Not on Quartz but on Calcite, breaks on flat planes, structure showing or how a mineral breaks