Past is the key to the present 1) The geologic processes now at work were also active in the past 2) The present physical features of Earth were formed by these same processes, at work over long periods of time.
Geologists who came up with the concept of uniformitarianism
General definition of a rock
a group of minerals bound together in some way
formed by the cooling and hardening of hot molten rock from inside Earth
Hot molten rock from inside Earth
formed by hardening and cementing layers of sediments
consist of rock fragments, plant, and animals remains, or chemicals that form on lake and ocean bottoms
formed when rocks that already exist are changed by hear and pressure into new kinds of rocks
Igneous rocks formed underground from cooled magma also known as intrusive
Most are felsic
Igneous rocks formed when lava cools on the surface also known as extrusive
Most are mafic
Light colored, high-silica, formed from thick and slow flowing magma
Most plutonic rocks are felsic
Dark colored, low-silica, formed from thinner, hotter magma
Most volcanic rocks are mafic
depends on the size, shape, and arrangement of its mineral crystals. most important is crystal size though
determined from the speed magma hardens and the amount of gas dissolved in the magma. Slower=larger More gas=crystals grow more quickly
common igneous rock, large crystals, intrusive or plutonic
very quickly cooled magma
becomes glassy because there's no time for crystals to form ex. obsidian (smooth as glass)
igneous rock that has two distinctly different textures: large crystals surrounded by a fine-grained mass of rock
Cools first at great depth and then nearer to the surface
Much like obsidian but has a mafic composition
Volcanic glass of the granite family
contains many of the same minerals as granite and other light colored rocks, but is dark brown or black. and hard and brittle.
Formed from felsic lava the hardened while steam and other gases were still bubbling out of it.
Most common rock of the gabbro family.
ranges from dark green to black
most common rock formed from flows of lava
large ares of basalt exist in places like Iceland, the Hawaiian islands, etc.
Because it is formed while steam and gases bubble out of felsic lava, it has many small holes in it and is sometimes light enough to float on water
About the same composition as basalt, but since its's cooled slowly deep underground it is coarse grained.
dark in color
similar to Diabase in composition which has a finer texture
Similar in composition to gabbro and basalt
Finer in texture than gabbro but coarser than basalt
Formed from felsic magma
Includes different textures but all similar chemical compositions.
Formed from mafic magma
Mainly dark minerals (plagioclase feldspar, augite, olivine, hornblende, biotite)
More dense than granite family
Composition and color between granite and gabbro families
general name for any light-colored, fine-grained rock in the granite family
Ex. Rhyolite, fine-grained, light gray to pink rock
Glassy: cooled quickly at the surface of earth, examples
With Quartz: Obsidian, Pumice
Without Quartz: Obsidian, Basalt glass, Scoria
Fine-grained: cooled slowly at or near surface, examples
With Quartz: Ryolite (Felsite)
Almost No Quartz: Trachyte
Without Quartz: Andesite, Basalt, Diabase
Coarse-grained: cooled very slowly, usually at great depths, examples
With Quartz: Granite, Pegmatite
Almost No Quartz: Syenite
Without Quartz: Diorite, Gabbro
Without Quartz or Feldspar: Peridotite, Pyroxenite, Dunite
How geologists explained the origin of landforms before James Hutton
Before Hutton, most geologists thought that the physical features of Earth had been formed by sudden spectacular events. In their view, these catastrophes caused the formation of mountains, canyons, waterfalls, and almost all landforms.
Two principles of Uniformitarianism
1) the geologic processes now at work were also active in the past
2) The present physical features of Earth were formed by these same processes, at work over long periods of time.
Three main groups of rocks
Difference between Magma and Lava
Magma is below the Earth's surface, lava has reached the surface.
Igneous rock formed under Earth's surface
Also known as plutonic
Igneous rock formed above the Earth's surface
Also known as Volcanic
Rocks formed from fragments of other rocks
Ex. Shale, Sandstone, Conglomerate
Rocks formed from mineral grains that fall out of a solution (precipitate) by evaporation or chemical action.
Ex. Rock salt and some limestones
Rocks formed from the remains of plants and animals
Ex. Coal, Limestones
Three main kinds of sedimentary rock
Natural cements in water (examples)
Silica (SiO2) - gray or white
Calcite (CaCO3) - gray or white
Iron Oxide (FeO) - red, brown, or rust-colored
Ways sediments become rock
Pressure from overlying sediments is sometimes enough to make fine sediments (clay or silt) stick together
Naturals cements found dissolved in water
Effects of Natural cements
Give own colors to rocks
Bind fragments together
Transform loose sediments into firm, cemented rock
Limestones of chemical origin
Formed from grains of calcite deposited from bodies of water
Gray to tan in color
Compact and dense in appearance, smooth to the touch
The natural form of common table salt
occurs in thick layers
Almost pure halite
Occurs in layers like rock salt does
Most common chemical sediments
the property of moving in circles (for planets and comets being observed)
what did the greeks think the elements were?
They thought there were 4 elements: Fire Air Water Earth
explain how something works
explain why something works
Claudius Ptolemy (90-168)
-years of previous models, data -tweaked the models to fit data better -geocentric
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