Third Rock From the Sun Notes

Precambrian – the oldest and largest

division of geologic time (87% of Earth’s

history) Time Frame – 4600 to 544 million

years ago

Eras

Geologic Time

Organisms –

oldest definite fossils known

prokaryotes (lacking a cell membrane)

Similar to cyanobacteria; (oxygen-producing & underwent photosynthesis)

It was 2 billion years later before the origin of eukaryotes

By the end of this era we had the origin of shell-less invertebrates

Paleozoic Time Frame – 544 to 245 million years ago

Periods – (from oldest) Cambrian,

Ordovician, Silurian, Devonian,

Carboniferous, Permian

Organisms – (referred to as the explosion of life)

At the beginning was the origin of most invertebrates

Then the first vertebrates & first land plants appeared

Around the middle of this era the first amphibians and insects appeared

During the second half of this era the first reptiles appeared.

Mesozoic

Time Frame – 245 to 66 million years ago

Periods – Triassic, Jurassic, and Cretaceous

Organisms –

◦ During Triassic the first mammals & dinosaurs appeared

◦ Jurassic-dinosaurs become dominant

◦ Cretaceous- mammals began to spread out and flowering plants appeared & the dinosaurs became extinct

Cenozoic

Time Frame – 66 million years ago to

the present. Mammals flourished.

Periods –

◦ Tertiary – Paleocene, Iocene, Oligocene,

Miocene, Pilocene

◦Quaternary – Pleistocene, Recent

The Geologic

Time Scale

Based on

*Fossils

*Correlation

Later

*Calibrated with

radiometric

dating

Evidence - fossils

Relative Dating – The age of a fossil

in terms of other fossils around it.

Fossils in layers of sedimentary rocks,

younger are on top & older are in the

lower layers.

◦ Index Fossils – are used to coordinate

the fossils at one location with those at

another. For ex. One island with another

Evidence Cont.

Absolute Dating – age is given in years instead of relative terms ◦ Ex. Radioactive Dating – determines the age of fossils by looking at the isotopes of elements that accumulate with the organisms when they were alive

◦Confirmed the Geologic Time Scale

Newest Technology

Radiometric Calibration

- uses half life of elements for date

estimations.

-computer simulations and sampling is the

newest method for fossil estimations

Imperfection of the Fossil Record

Organisms had to die on the right

place and right time for burial

conditions to favor fossilization

Rock must be exposed for us to see

The fossil record is incomplete

because of this.

Description Fossils are mineralized or petrified

replicas of skeletons, bones, teeth,

shells, leaves and seeds or

impressions of such items; usually

found in sedimentary rock.

Fossils

Types

Remainders – the actual body or

parts of an organism

Petrified – the bone has been

replaced by mineral

Molds/Casts –

◦Molds – bone gets buried and the

sediment turns into rock, and the animal

is dissolved away

◦Casts – if another mineral fills the mold

and hardens in the shape of the old

animal it becomes a cast

Carbonization – if an animal dies and the sediment crushes the animals as fossilization is occurring, you will have a thin black coating on the fossil. Much of this is coal.

Impression – (trace fossil) there is an impression of the fossil, but the fossil is gone

Amber – resin from certain trees that small insects and other organisms get trapped in

Tracks – footprints left in the sediment that solidifies ◦ Ex. dinosaur tracks in Texas

Burrows – an animal like a worm burrows into the mud, then the burrow becomes fossilized

Coprolites – fossil excrement can sometimes give definitive knowledge about the eating habits of the animals

Gastroliths – smooth, polished

stones that are found in the abdominal

cavities of the skeletons of dinosaurs.

They are thought to have helped the

huge animals grind up vegetation in

their stomachs.

Fossil Record Ideal Conditions – quick burial and the

presence of some hard parts

Meaning – tells us the date of the organism

by dating the rock. You can tell what came

before what by superposition; mass

extinctions; pop. explosions.

Support for Evolution – changes over time

can be seen

Examples of Fossil Record

Burgess Shale – Middle Cambrian Period

(505 mya)

◦ Exceptional preservation of soft parts

Jurrasic Solnhofen Limestone (200-245

mya)

Description

Plate tectonics is the theory

explaining the movement of the

plates and the processes that

occur at their boundaries.

GEOLOGIC PROCESSES

The earth is made up of a core, mantle, and crust

and is constantly changing as a result of processes

taking place on and below its surface.

The earth’s interior consists of:

◦ Core: innermost zone with solid inner core and

molten outer core that is extremely hot.

◦ Mantle: solid rock with a rigid outer part

(asthenosphere) that is melted pliable rock.

◦ Crust: Outermost zone which underlies the

continents.

GEOLOGIC PROCESSES

Major features of the earth’s crust and upper mantle.

Figure 15-2

Fig. 15-2, p. 336

Volcanoes

Folded

mountain

belt

Abyssal

floor

Oceanic

ridge

Abyssal

floor Trench Abyssal hills Craton

Abyssal plain

Oceanic crust

(lithosphere) Continental

shelf

Continental

slope

Continental

rise

Continental crust (lithosphere)

Mantle (lithosphere)

Fig. 15-3, p. 337

Spreading center Ocean

trench

Subduction

zone

Oceanic

crust

Continental

crust Continental

crust

Material cools as it reaches

the outer mantle

Cold dense material falls back through

mantle

Hot material

rising through

the mantle

Mantle convection

cell

Two plates move towards each other. One is subducted back into the mantle on a falling convection current.

Mantle

Hot outer

core Inner

core

Collision between

two continents

Oceanic

crust

GEOLOGIC PROCESSES

Huge volumes of heated and molten rack

moving around the earth’s interior form

massive solid plates that move extremely

slowly across the earth’s surface.

◦ Tectonic plates: huge rigid plates that are

moved with convection cells or currents by

floating on magma or molten rock.

The Earth’s Major Tectonic Plates

Figure 15-4

Continental Drift

Wegener proposed

the theory that the

crustal plates are

moving over the

mantle.

Supported by:

Fossil, rock type

evidence and

coastline shapes.

Earth ~200 million years ago

The Continental Drift Hypothesis

Proposed by Alfred Wegener in 1915.

Supercontinent Pangaea started to break up about 200

million years ago.

Continents "drifted" to their present positions.

Pangea is now known to be the latest in a succession

of “super continents”

Continental Drift: Evidence

Geographic fit of South America and Africa

Fossils match across oceans

Rock types and structures match across

oceans

Tight fit of

the continents,

especially

using

continental

shelves.

Continental

Drift:

Evidence

Continental Drift:

Evidence Fossil critters and plants

Continental

Drift:

Evidence

Correlation of

mountains

with nearly

identical

rocks and

structures

Continental

Drift:

Evidence

Glacial features

of the same age

restore to a

tight polar

distribution.

Continental Drift – current

movement While not every plate moves at the same

speed, or even moves at all relative to

every other plate, an overall average

velocity of speed for present-day plates is

about 2.5 cm per year.

The Earth’s Major Tectonic Plates

The extremely slow movements of these plates cause them to grind into one another at convergent plate boundaries, move apart at divergent plate boundaries and slide past at transform plate boundaries.

Figure 15-4

Fig. 15-4, p. 338

Fig. 15-4a, p. 338

EURASIAN PLATE NORTH

AMERICAN

PLATE

ANATOLIAN

PLATE

JUAN DE

FUCA PLATE CHINA

SUBPLATE

CARIBBEAN

PLATE

PHILIPPINE

PLATE

ARABIAN

PLATE AFRICAN

PLATE PACIFIC

PLATE SOUTH

AMERICAN

PLATE NAZCA

PLATE INDIA-

AUSTRALIAN

PLATE

SOMALIAN

SUBPLATE

ANTARCTIC PLATE

Divergent plate boundaries

Convergent plate

boundaries

Transform

faults

The Theory of Plate Tectonics

Earth’s outer shell is broken into thin, curved plates

that move laterally atop a weaker underlying layer.

Most earthquakes and volcanic eruptions happen at

plate boundaries.

Three types of relative motions between plates:

Why do the plates move? Two related ideas are widely accepted:

Slab pull: Denser, colder plate sinks at subduction

zone, pulls rest of plate behind it.

Mantle convection: Hotter mantle material rises

beneath divergent boundaries, forces the cooler

material to sink at subduction zones.

So: moving plates, EQs, & volcanic eruptions are due

to Earth’s loss of internal heat.

Convection Currents

The force responsible for plate movement is __________.

Oceanic Crust is more dense than

Continental Crust.

Continental Crust is thicker than Oceanic

Crust.

Because of this the continental crust

floats on top of the oceanic crust.

Plates move apart from each other at

divergent boundries.

Molten rock flows up the resulting cracks

forming oceanic ridges.

Internal forces push two plates together.

Continental-Continental

◦ The light crusts colliding causes them to push up

and form high mountain ranges like the Himalayas.

Continental-Oceanic

◦ Oceanic is denser and dives under lighter

continental. This causes trenches when the oceanic

dives and mountain ranges when the continental

buckles and folds.

Oceanic-Oceanic

◦ Collision of 2 dense plates causes deep trenches

because they are each trying to dive under the

other. EX. Marianna’s Trench

Plates slide past each other often causing

earthquakes.

◦ Ex. San Andreas Fault (California)

Fig. 15-4b, p. 338

Trench Volcanic island arc Craton

Transform

fault

Lithosphere

Lithosphere Lithosphere

Asthenosphere Asthenosphere Asthenosphere

Divergent plate boundaries Convergent plate boundaries Transform faults

Rising

magma

Plate Boundaries

Divergent Boundary – moving _____

Convergent Boundary – moving ________

Transform Fault Boundary – moving

________________________

apart

together

sideways past each other

Divergent boundaries: Chiefly at oceanic ridges

(aka spreading centers)

Boundaries Divergent – the plates move

apart in opposite directions.

Divergent boundary of two continental plates.

Creates a __________. Example: _____________ rift valley East African Rift

Divergent

boundaries

also can rip

apart (“rift”)

continents

Presumably,

Pangea was

ripped apart by

such continental

rifting & drifting.

Convergent – the plates push together by internal forces. At most convergent plate boundaries, the oceanic lithosphere is carried downward under the island or continent. Earthquakes are common here. It also forms an ocean ridge or a mountain range.

Convergent boundary of two oceanic plates.

Creates an ________ and a _____. Example: _____ island arc trench Japan

Subduction zones form at convergent boundaries

if at least one side has oceanic (denser) material.

Modern examples: Andes, Cascades

Major features: trench, biggest

EQs, explosive volcanoes

Another subduction zone—this one with

oceanic material on both sides.

Modern example: Japan

Boundaries (Continued) Transform – plates

slide next or past each other in opposite directions along a fracture.

California will not fall into the ocean!

Pacific Plate

The Pacific plate is off the coast of

California. Lots of volcanoes and

earthquakes occur here.

“California will fall into the ocean” idea.

It is the largest plate and the location of

the ring of fire.

GEOLOGIC PROCESSES

The San

Andreas Fault

is an example

of a transform

fault.

Figure 15-5

Most transform

boundaries

are in the oceans.

Some, like the one

in California, cut

continents.

The PAC-NA plate

boundary is MUCH

more complex than

this diagram shows.

Transform-fault boundary where the North American

and Pacific plates are moving ____ each other.

Example: ________________ in California

past

San Andreas Fault

Importance

Plate movement adds new land at

boundaries, produces mountains,

trenches, earthquakes and

volcanoes.

Hotspots, such as the one under Hawaii,

have validated plate tectonic theory.

Plate Boundaries Review Places where plates move apart are called _____________

boundaries.

When continental plates diverge a ___________ is

formed.

When two oceanic plates converge what is created?

_________________

The Appalachians formed mainly from continental plate

collisions and therefore are a __________ mountain

range.

The force moving the plates is ____________ .

Convection currents

divergent

rift valley

an island arc and a trench

folded

The Rock Cycle – the interaction

of processes that change rocks

from one type to another

Rock Cycle

Figure 15-8

Fig. 15-8, p. 343

Erosion

Transportation

Weathering

Deposition

Igneous rock

Granite,

pumice,

basalt

Sedimentary

rock

Sandstone,

limestone Heat, pressure

Cooling

Heat, pressure,

stress Magma

(molten rock)

Melting

Metamorphic rock

Slate, marble,

gneiss, quartzite

Steps

Oxygen

The most abundant element in Earth’s

crust.

Nitrogen

The most abundant element in the Earth’s

atmosphere.

Iron

The most abundant element in the Earth’s

core.

Aluminum

The element commercially extracted

from bauxite

Relationships Between All Three

Rocks

All three rocks are being

recycled and converted to all

of the classes

Igneous Description – forms the bulk of the earth’s

crust. It is the main source of many non-fuel mineral resources.

Classification –

◦ Intrusive Igneous Rocks – formed from the solidification of magma below ground

◦ Extrusive Igneous Rocks – formed from the solidification of lava above ground

Rock Classification

Igneous (Continued)

Examples – Granite, Pumice,

Basalt, Kimberlite (Diamond,

Tourmaline, Garnet, Ruby,

Sapphire)

Sedimentary

Description – rock formed from

sediments. Most form when rocks

are weathered and eroded into small

pieces, transported, and deposited in

a body of surface water.

Clastic – pieces that are cemented together by quartz and calcium carbonate (Calcite).

Examples: sandstone (sand stuck together), Conglomerate (rounded & concrete-looking) and Breccia (like conglomerate but w/ angular pieces)

Sedimentary (Continued)

Nonclastic –

◦Chemical Precipitates – limestone precipitates out and oozes to the bottom of the ocean (this is why there is a lot of limestone in S.A.)

◦Biochemical Sediments – like peat & coal

◦Petrified wood & opalized wood

Metamorphic

Description – when preexisting rock is

subjected to high temperatures (which

may cause it to partially melt), high

pressures, chemically active fluids, or a

combination of these

Location – deep within the earth

Examples:

Contact Metamorphism- rock that is next

to a body of magma

Ex. limestone under heat becomes marble

through crystallization

Limestone -> marble

sandstone -> quartzite

shale -> hornfelds (slate)

Dynamic Metamorphism – earth movement crushes & breaks rocks along a fault. Rocks may be brittle- (rock and mineral grains are broken and crushed) or it may be ductile- (plastic behavior occurs.)

Rocks formed along fault zones are called mylonites.

Metamorphic (Continued)

◦Regional Metamorphism – during

mountain building; great quantities of

rock are subject to intense stresses and

heat

Ex. cont. shelves ram together

Progressive Metamorphism – One form of rock changing into another

shale->slate->schist->gneiss

coal->graphite

granite->gneiss