Geologic Time Scale

Cenozoic Era

Quaternary Period - 2.5 million years ago (man)

Tertiary Period - 65 million years ago (grazing and carnivorous mammals)

Mesozioic Era

Cretaceous Period - 136 million years ago (primates, flowering plants)

Jurassic Period - 195 million years ago (birds)

Triassic Period - 225 million years ago (dinosaurs, mammals)

Paleozoic Era

Permian Period - 280 million years ago

Carboniferous Pennsylvanian Period - 320 million years ago (reptiles)

Carboniferous Mississippian Period - 345 million years ago (fern forests)

Devonian Period - 395 million years ago (amphibians, insects)

Silurian Period - 430 million years ago (vascular land plants)

Ordovician Period - 500 million years ago (fish) 

Cambrian Period - 570 million years ago (shellfish)

Precambrian Era (algae, cells)

Formation of the Earth - 4.65 billion years ago



Igneous: made of molten material (magma, which comes to the surface as lava)

                Falsic (contains feldspar and quartz)

                                Grantie: contains large quartz and feldspar particles

                                Rhyloite: small-grain granite

                Mafic (contains magnesium and iron)

                                Gabbro: contains large pyroxene and olivine crystals

                                Basalt: the most common volcanic rock

Metamorphic: rocks that have been changed by high temperature or pressure

                Mica: minerals aligned perpendicular to maximum pressure

                Slate: fine, thin layers caused by foliation at low pressure

                Schist: coarse foliation at medium pressure

                Gneiss: very coarse foliation at high pressure

Sedimentary: rocks formed when loose fragments harden

                Clastic: form from broken fragments of current rocks

                                Sandstone: made from sand

                                Shale: made from mud

                Chemical: formed when minerals precipitate from solution;  evaporites

                                Gypsum: used in plaster and wallboard

                                Halite: used in table salt

                Organic: made from animal and plant remains

                                Limestone: made from calcium carbonate of coral and shellfish skeletons

                                Coal: made from swamp plant remains



Hematite Fe2O3

Magnetite Fe3O4

Bauxite Al2O3

Cassiterite SnO2

Periclase MgO

Silica SiO2

Iron pyrites FeS2

Cinnabar HgS

Rock salt NaCl

Sylvite KCl

Carnallite KCl*MgCl2

Limestone CaCO3

Magnesite MgCO3

Dolomite MgCO3*CaCO3

Gypsum CaSO4*2H2O

Epsom salts MgSO4*7H2O

Barite BaSO4



Steel: iron and 0.8% carbon and 0.5% manganese

Brass: copper and zinc

Bronze: copper and tin

Amalgams: include mercury


History of Geology

Aristotle's student Theophrastus wrote an essay about stones.

Georgius Agricola (Saxon, 1556) wrote De Re Metallica.

James Ussher (English, 1600s) estimated from the Bible that the Earth is 6000 years old.

Comte de Buffon (French, 1700s) estimated from iron ball cooling rates that the Earth is 75,000 years old.

James Hutton (English, 1700s) formulated uniformitarian theory, and is known as the father of geology.

Charles Lyell (Scottish, 1800s) advocated uniformitarianism and wrote Principles of Geology.

Georges Cuvier (French, 1800s) advocated catastrophism.

Alfred Wegener (German, 1912) proposed Continental Drift and the Pangaea supercontinent, which split

into Laurasia and Gondwanaland.

Eduard Seuss (Austrian, 1900s) named Gondwanaland.

Vine and Matthews (British, 1900s) proposed their magnetic stripes hypothesis.

J. Tuzo Wilson (Canadian) and Jason Morgan (American) proposed plate tectonics in the 1960s, saying that

lithosphere plates move over less rigid asthenosphere and sink at subduction zones.



The Law of Superposition states that more recent fossils are in layers of Earth closer to the surface.

Stratigraphy is the study of the Earth's crust, and biostratigraphy studies it through fossils.