Transcript Historical Geology

Ch. 1 Dynamic and Evolving
Earth
ESCI 518
Fall 2004
Earth is a Dynamic and
Evolving Planet
• changes in its surface
• changes in life
Historical Geology
• in historical geology we study
– changes in our planet
– how and why past events happened
– implication for today’s global ecosystems
• 3 main ideas of historical geology
– plate tectonics
– evolution
– uniformitarianism
Plate Tectonic Theory
• Lithosphere is broken into individual pieces
called
plates
• Plates move over the asthenosphere
– as a result of underlying convection cells
Theory of Organic Evolution
• provides a framework for understanding
the history of life
• Darwin’s On the Origin of Species by
Means of Natural Selection, published
in 1859
• revolutionized biology
Central Thesis of Evolution
• all present-day organisms
– are related
– descended from organisms that lived
during the past
• Natural Selection is the mechanism that
accounts for evolution
– results in the survival to reproductive age
of those organisms best adapted to their
environment
History of Life
• Fossils are the remains or traces of onceliving organisms
– demonstrate that Earth has a history of life
– most compelling evidence in favor of
evolution
Geologic Time
• human perspective
– seconds, hours, days, years
• ancient human history
– hundreds or even thousands of years
• geologic history
– millions, hundreds of millions, billions of
years
Geologic Time Scale
• resulted from the work of many 19th
century geologists who
– pieced together information from numerous
rock exposures
– constructed a sequential chronology based on
changes in Earth’s biota through time
• the time scale was subsequently dated in
years
– using radiometric dating techniques
Geologic Column and the
Relative Geologic Time Scale
Absolute
ages (the
numbers)
were
added
much
later.
Geologic
Time Scale
Uniformitarianism
• Uniformitarianism is a cornerstone of geology
– present-day processes have operated throughout
time
– physical and chemical laws of nature have
remained the same through time
• to interpret geologic events
– we must first understand present-day processes
and their results
How Does the Study of Historical Geology
Benefit Us?
• survival of the human species depends on
understanding how Earth’s various subsystems work
and interact
– how we consume natural resources and interact with the
environment determines our ability to pass on this standard
of living to the next generation
– our standard of living depends directly on our consumption
of natural resources that formed millions and billions of years
ago
• study what has happened in the past, on a global
scale, to try and determine how our actions might
affect the balance of subsystems in the future
Latest Precambrian / Early
Paleozoic
Supercontinent Rodinia, centered
about the south pole, breaks
apart. North America (Laurentia),
Baltica, and Siberia moved
North.
Marine Invertebrates.
North America: arc on the south.
Baltica and Siberia moved in
from the SE.
Texas (505-570 Ma): Flat plain;
remnants of eroded collisional
belt (Llano). Shallow marine seas
across much of Texas. Sandy
sediment onshore, limestone
offshore. Trilobites, brachiopods.
http://vishnu.glg.nau.edu/rcb/globaltext.html
Latest Precambrian / Early
Paleozoic
Supercontinent Rodinia
continues to break apart. Pieces
move north.
-Fish.
-Glaciation.
North America: Numerous plates
and continental blocks move in
from the south and east. The
Taconic arc collides, forming the
Taconic orogeny.
Texas 438-505 Ma: Shallow
marine seas across much of
inland Texas. Warm-water
limestone. Corals, brachiopods.
http://vishnu.glg.nau.edu/rcb/globaltext.html
Middle / Late Paleozoic
Remains of Rodinia (Gondwana)
move northward to collide with
Laurasia -- creating the super
continent Pangaea and the Tethys
Ocean.
First land-plants.
Baltica collides with North America
in the Caledonian-Acadian orogeny.
Texas 403-438 Ma: Shallow marine
seas across much of west Texas limestone. Corals, brachiopods.
http://vishnu.glg.nau.edu/rcb/globaltext.html
Middle / Late Paleozoic
Most drifting Rodinia blocks
assembled into the super continent of
Laurussia.
Amphibians. Fish really get going.
Ferns.
Glaciation.
North America: Caledonian-Acadian
orogeny marks assemblage of
Laurussia. Gondwana closed in from
the south. An arc formed along
western North America.
Texas 360-408 Ma: shallow marine
sandstones and limestones in west
Texas.
http://vishnu.glg.nau.edu/rcb/globaltext.html
Middle / Late Paleozoic
Gondwana, with a large,
developing glacier, nears
southern Laurussia.
Fern-forests.
North America: The Antler arc
collides with western North
America creating the Antler
orogeny.
Texas 320-360 Ma: shallow
marine seas inland. Shales and
limestones.
http://vishnu.glg.nau.edu/rcb/globaltext.html
Middle / Late Paleozoic
Rodinia blocks of Laurussia and
Siberia collide to form Laurasia.
Reptiles.
North America: Gondwana
collides from the south. The
resulting Appalachian, Ouachita,
Marathon, Ural, Variscan, and
Hercynian orogenies formed some
of the largest mountains of all
time. The Ancestral Rockies form.
Texas 286-320 Ma: Ouachita
Mountains. Collision formed inland
basins filled by seas. Limestone,
sandstone, shale.
http://vishnu.glg.nau.edu/rcb/globaltext.html
Latest Paleozoic / Early
Mesozoic
The supercontinent Pangeae
dominates the Permian Earth, lying
across the equator.
Extinctions! Trilobites go away.
North America: A new arc
approaches western North America.
A new spreading center forms as
Cimmeria rifts from Gondwana and
opens the Tethyian Ocean.
The western fringe of Pangaea lay
along the eastern margin of the
Pacific "ring of fire” subduction zone.
Texas 245-286 Ma: Shallow marine
inland of mountains. Reefs.
Evaporites. Red shales.
http://vishnu.glg.nau.edu/rcb/globaltext.html
Latest Paleozoic / Early
Mesozoic
Mammals.
North America: Arc collision along
western edge forms the Sonoman
orogeny.
As the Tethys Ocean expands,
Cimmeria (Turkey, Iran, and
Afghanistan) move
northward towards Laurasia.
Texas 208-245 Ma: shales and
sandstones in NW. Start opening
the GOM - red sandstone, shale,
evaporites.
http://vishnu.glg.nau.edu/rcb/globaltext.html
Middle Mesozoic
Pangaea rotates; different
components at different rates / in
different directions -- rifts form.
Birds.
North America: Southern North
Atlantic Ocean opens, continuing
west into the Gulf of Mexico.
The Cordilleran arc develops along
Pacific margin.
Arc forms on western side. Nevadan
orogeny begins. Cimmeria begins
collision with Laurasia - Cimmerian
orogeny.
Texas 144-208 Ma: Change in
sediment direction. Shallow water
deposition / evaporites in GOM.
http://vishnu.glg.nau.edu/rcb/globaltext.html
Middle Mesozoic
The Atlantic continues to expand
as Pangaea breaks up.
The Cimmerian orogeny
continues.
North America: Arcs and micro
continents slam into western
region. Laramide orogeny in
Rockies.
Texas 66-144 Ma: Influx of
sediment from Rockies. Shallow
Cretaceous sea way across Texas.
Shallow liestones, shales.
http://vishnu.glg.nau.edu/rcb/globaltext.html
Late Cretaceous / Present
Rifts separate Africa and South
America and then India,
Australia, Antarctica. North
America rifts from Europe.
Old Gondwana lands(Africa,
India, Australia) move north
toward Eurasia, closing the
Tethys Ocean and forming the
Alpine-Himalayan mountains.
The Atlantic lengthens / widens,
the Sevier orogeny continues,
and the Caribbean arc forms.
Texas 65-144 Ma: continuing
shallow limestone and shale
deposition to the southeast (from
Rockies).
http://vishnu.glg.nau.edu/rcb/globaltext.html
Paleocene / Eocene
Himalayan Orogeny. Alps and
Pyrenees form.
The modern patterns of Planet
Earth appear.
Atlantic continues to open. Rocky
Mountains grow.
Texas 65 - 35 Ma: shale and
sandstone in southeast region
prograde shoreline (from the
Rockies). Volcanic activity in
Panhandle.
http://vishnu.glg.nau.edu/rcb/globaltext.html
Oligocene and Miocene
Orogeny continues in
the Mediterranean region and
India nears its junction with
southern Asia.
Antarctica isolated.
Southwestern North America
intercepts the East Pacific Rise
and a great extensional event, the
Basin and Range orogeny begins.
Texas 35-5 Ma: continued
sandstone/shale deposition and
progradation of shoreline (erosion
of Rockies)
http://vishnu.glg.nau.edu/rcb/globaltext.html
Present
Note:
Best data set available.
http://vishnu.glg.nau.edu/rcb/globaltext.html
Fossils
• Fossils are the remains or traces of prehistoric organisms
– Any evidence of past life
• Most common in sedimentary rocks
– and in some accumulations of pyroclastic materials, especially
ash
• They are extremely useful for determining relative ages
of strata
– geologists also use them to ascertain environments of deposition
• Fossils provide some of the evidence for organic
evolution
– many fossils are of organisms now extinct
How do Fossils Form?
• Remains of organisms are called body fossils
– mostly durable skeletal elements such as bones, teeth and
shells
– rarely we might find entire animals
preserved by freezing or
mummification
Trace Fossils
• Indications of organic activity including tracks,
trails, burrows, and nests are called trace fossils
• A coprolite is a type of trace fossil consisting of
fossilized feces that may provide information
about the size and diet of the animal that
produced it
Trace Fossils
• A land-dwelling
beaver, Paleocastor,
made this spiral
burrow in Nebraska
Trace Fossils
• Fossilized feces (coprolite) of a carnivorous
mammal
– specimen measures about 5 cm long and contains
small fragments of bones
Body Fossil Formation
• The most favorable conditions for preservation of body
fossils occurs when the organism
– possesses a durable skeleton of some kind
– and lives in an area where burial is likely
• Body fossils may be preserved as
– unaltered remains, meaning they retain their original composition
and structure,by freezing, mummification, in amber, in tar
– altered remains, with some change in composition or structure by
being permineralized, recrystallized, replaced, carbonized
Unaltered Remains
• Insects in
amber
• Preservation in
tar
Unaltered Remains
• 40,000-yearold frozen
baby
mammoth
found in
Siberia in
1971
– hair around
the feet is
still visible
Altered Remains
• Petrified tree
stump in
Florissant Fossil
Beds National
Monument,
Colorado
Altered Remains
Carbon film of a palm frond
Carbon film of an insect
Fossil Record
• The fossil record is the record of ancient life
preserved as fossils in rocks
• The fossil record is very incomplete because of:
–
–
–
–
bacterial decay
physical processes
scavenging
metamorphism
• In spite of this, fossils are quite common