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