LSU GEOL 1003 Luther Exam 2 Spring 2025

Hadean Eon

- Hades

- magma ocean boiling at the surface

- oldest time period

Events that shape the Hadean

1. Differentiation of Earth's interior

2. Formation of the crust

3. Differentiation changes composition of crust

Accretion

- the process of adding material to a tectonic plate or landmass

- heavy (dense) sinks and lighter rises

Differentiation

- materials separate into distinct layers or compositions

- occurs over tens of millions of years

Earth's layers- seismic wave analyses

- increase in density > increase in wave velocity

Earliest crust

- earliest crust forms

- made of komatiite- ultramafic

- very rare and fine grained

- peridotite: ultramafic

- oceanic crust- basalt

Earliest composition of Earth

- felsic: continental crust

- mafic: current oceanic crust

Earth's oldest rocks

1. Jack Hill's zircon: oldest mineral

2. Acasta Gneiss Complex: oldest presumed rock- 4 billion years old

3. The Nuvvuagittuq Greenstone Belt

Jack Hill's Zircon

- oldest mineral

- 4.404 Ga

- commonly form in granite

- found in a sedimentary rock

- 150 my > crust differentiates

- oxygen isotopes

- heavy and cool enough for oceans to be present

Acasta Gneiss- Slave Craton

- craton: stable interior of continent > no tectonism for 1 Ga

- shield: exposed craton

- platform: craton covered with sediments

Acasta Gneiss

- oldest rock

- gneiss is an igneous rock

- 3.92-4.02 Ga

- crust must exist for this to intrude

The Nuvvuagittuq Greenstone Belt

- oldest oceanic crust

- mafic and ultramafic volcanic rocks

- erupted in an ancient ocean- presence of lava pillows

- cut by 3.77 Ga rocks- actual age unknown

Earth's oldest fossils?

- also found in NGB

- 2017 traces of life found in seds of the NGB

- microscopic small tubes made of the iron mineral hematite

- same shape and size of those made by bacteria in modern hydrothermal vent environments

- discovered the mineral graohite composed entirely of carbon

- formed by metamorphism of organic material

O2 in the atmosphere

- earth cooled: atmosphere formed mainly from gases spewed from volcanoes

- hydrogen sulfide, methane, and ten to two hundred times as much carbon dioxide as today's atmosphere

- after about half a million years, Earth's surface cooled and solidified enough for water to collect on it

Miller and Urey Experiment (1953)

- demonstrated that organic compounds could be made by simulating conditions on early Earth

- methane, ammonia, water vapor and hydrogen- no oxugen

Formation of the oceans

- origin of water still up for debate

- most astronomers believe water came from comets

- salt > free

- salt comes from weathering of rocks

- Earth reached current salinity by the end of the Archean

Major Proterozoic events

- increase in atmospheric oxygen

- BIF's stop forming and red beds begin

Onset of typical plate tectonics

- arcuate belts of tectonic activity

Proterozoic Supercontinents

- Rodinia: formed at 1.6 bya and broke up at 1 bya

- Grenville orogenic belt: an arcuate orogenic region, 1.3 to 1.0 Ga, extensive area of present-day North America and adjacent regions

Supercontinent cycles

- a tectonically driven cycle defined by the assembly of a supercontinent and later fragmentation and dispersal of its pieces

- begins with the collision and welding of tectonic plates to form an enormous mass of continental crust

- ends with the breakup and dispersal of fragments of the supercontinent

- proterozoic eon witnessed at least 2 cycles

Gondwana

- late Paleozoic continent that formed the southern portion of Pangaea, consisting of all or parts of present-day South America, Africa, Australia, India, and Antarctica

Late proterozoic sea level related to plate tectonics

- breakup of supercontinent near the end of proterozoic

- high rifting rates: large volume of warm expanded oceanic lithosphere

- high sea levels lasted until the Cambrian

Snowball Earth

- entire Earth frozen

- 3 different events Neo (720-660)(645-640)(580)my

Evidence for snowball Earth

- glacial striations: tilites- sediment in ice melted

- tillites (rocks with glacial sediment) and diamictites

- dropstones

Why scientists believe snowball Earth was global

- glaciers at low altitudes

- paleomagnetism: past magnetic field and determines rock location at time

Snowball Earth stage one

- continents near equator develop large carbonate deposits along their continental shelves

- this may have increased when Rodinia began to split up

- carbon dioxide levels drop and greenhouse reduced > Earth cools

Snowball Earth stage two

- cooling Earth develops sea ice cover and continental glaciers

- increased albedo reflects sunlight, enhances cooling

- formation of carbonate stops

- CO2 no longer removed from atmosphere

Snowball Earth stage three

- Earth completely covered in ice

- surface temperature from 0 to negative forty degrees C

- volcanoes continue to erupt

- CO2 levels rise in the atmosphere but biological activity takes time to recover

Snowball Earth stage four

- lag in biological production of limestone and removal of CO2

- CO2 reaches 100 times normal level to form greenhouse

- glaciers and sea ice melt rapidly, greenhouse accelerates

- holthouse earth develops massive carbonate deposits

- carbonate formation reduces CO2, starts cycle again

Archean eon

- 4.0-2.5 billion years ago

- formation of protocontinents and greenstone belts

- no free oxygen

- life begins: stromatolites and other bacteria/archeabacteria

How can we determine when plate tectonics began?

1. Blueschists

2. Parallel strips of metamorphic rocks

Blueschists

- Metamorphic rocks formed under high pressure, low temperature

Greenstone- old oceanic crust

- greenstone belts formed- elongate area in a shield with metamorphic and deformed volcanic and sed-rich rocks

- chlorite-rich greenstone- green rocks unique to the precambrian & more mafic than modern rocks

- old oceanic crust

Early continental crust

- formed during the mobile crust phase when plates were moving quickly

- many subduction zones adjacent to protocontinents

Typical archean rocks

- no siliciclastic rocks

- chert

- BIFs

- stromatolites

Archean cherts

- marine

- plankton death

- no clastic rocks due to no land exposed above sea level

- continents are dense

Banded Iron Formations (BIF)

- interlayered chert and iron rich materials (hematite, magnetite)

- unique to precambrian

- times when there was no oxygen in the atmosphere

- main ore for human use- steel (Fe)

Conglomerates

- later archean

- mountain building

- environment- fast moving stream

Detrital pyrite

- sedimentary pyrite- clastic

- today would be oxidized- proves that oxygen levels were too low

Pillow basalt

- lava spill on ocean floor

- oceanic crust

Greenstones

- greenschist

- medium temperature and medium to low pressure

Autotrophs

- organisms that produce their own food

- earliest organisms

- chemosynthesis

- photosynthesis

- all feeding strategies are gained prior to end of precambrian

Heterotrophs

- Organisms that depend on other organisms for their food

- no heterotrophs before the precambrian

Chemosynthesis

- process in which chemical energy is used to produce carbohydrates

Photosynthesis

- Conversion of light energy from the sun into chemical energy

Fossils in early Proterozoic

- early proterozoic life is still fossil poor until the Ediacaran (late proterozoic)

First Fossils

- simple burrows

- horizontal, near surface

Early Paleozoic

- cambrian and ordovician

- (542-444 Ma)

Middle Paleozoic

- Silurian and Devonian

- (444-359Ma)

Late Paleozoic

- Carboniferous and Permian

- (359-251 Ma)

Cambrian Explosion

1. appearance of numerous taxonomic groups (all marine)

2. Diversity

3. First good fossil record

- most phyla appear at this time: most animals can be traced back to this time

- about 40 Ma: which is not that much time for the amount of diversity

Cambrian Explosion Organisms

- vertebrates: jawless fish (Cambrian)

- phylum chordata: has a spinal cord- armored fish that appear later in early paleozoic are dominant vertebrates

Trilobites

- strong swimmers

- active burrowers for food

- opportunistic- eat anything they can find

- make it all the way through paleozoic

Cambrian Fossils

- first set of organisms with hard parts

- shells with keratin are better fossilized

1. biomineralized animals

2. non mineralized animals

3. trace fossils

Biomineralized Fossils

- original material replaced with phosphite

- most shells made of calcite: plankton, teeth

Nonbiomineralized Fossils

- skeletons of large animals

Trace Fossils

- increase in diversity of trace fossils and increase of amount of trace fossils

- new hunting strategies, new homes, new niches

- burrowing deeper

- complex branching from burrows

Burgess Shale

- famous outcrop with first fossilized soft parts and numerous shelly fossils

Cambrian Paleogeography

- rifting of supercontinent

- platea are pulling apart and creating new oceans

Ordovician Paleogeography

- closure of the Iapetus ocean

- future Atlantic ocean

- huge volcanic eruptions

Taconic Orogeny

- in early paleozoic

- Taconic orogeny: first of three mountain building events in Paleozoic

- creation of Appalachian mountains

- subduction of current East coast

- creating of Taconic Arc- volcanic islands

- arc eventually collides with North America

- a lot of sediment and end of volcanism

- taconic mountains

- wide range of metamorphic grade

Orogeny

- mountain building event

- look for:

1. eroded roots of mountains

2. sedimentary basins

Sedimentary Basins

- sequence of turbidites

- underwater basins

- grades beds of shales

Terrestrial Sediments

- shed off the mountains

- red beds

- this sedimentary sequence is common

Early Paleozoic Marine Reorganization

- sea level rise > more living space

- changes in ocean chemistry: increase in oxygen > more organisms can survive there

- nutrients from weathering

Predator-prey Relations

- arms race

- increase radiation

- example: anomalocaris and trilobites

- organisms become more efficient at escape: become faster at swimming, swimming backwards, hiding more efficiently

- development of spines and thicker skeletons

Ordovician (Or) Sea Level

- sea level is high at the beginning of Ordovician

- sea level drops and then rises- pretty high for most of period: caves > filled with petroleum

- major sea level drop at the end

Life on the Land

- plants are beginning to take root

Ordovician Glaciation and Extinction

- sea level drop

- glaciation on Gondwana

- 2nd most significant extinction event (Permian was the largest event)

- numerous tropical animals die out: brachiopods, corals, trilobites

- 2 stage event

First stage of Ordovician Glaciation and Extinction

- cooling stage

- drop exposes continental shelves

Second stage of Ordovician Glaciation and Extinction

- any species that ***

Paleomagnetism and Latitude of glaciers

- the latitude indicates that glaciers were present at the equator

- if glaciers are present at the equator (should be warmest) than the whole Earth is covered in snow

Limestone CaCO3

- reduces carbon dioxide in atmosphere

- colder climate

Modern Plate Boundary Rocks

- blueschists

- high pressure low temp rock related to subduction

Greenstone

- determine if there were plate tectonics in the Archean specifically

- super mafic rock that has been metamorphosed

Middle Paleozoic

- Silurian and Devonian

- 444 Ma-359 Ma

1. Evolution of land plants

2. Acadian Orogeny

3. Age of Fishes

Approximate Paleogeography of middle Paleozoic

- warm and wet

- Laurentia is south of equator

- shallow sea in Laurentia

- mountain range similar to Andes

Land Plants in middle Paleozoic

- plants are small

- no roots, no leaves, no seeds (spores), no woody tissue

- late Devonian- huge forests with huge trees

- 30 cm > 30 m

- root systems, seeds, woody tissue, leaf canopy present

- seeds can travel long distances: protected in colder weather

Old vs Modern Forests

- finger-like roots and not able to support super tall trees

- hollow inside

Late Devonian Plants

- development of larger leaf canopy

Significance of Leaf Canopy

- provides shade and shelter

- protects organisms (insects)

- creates leaf litter: habitat for bacteria and fungi

Affect on Streams

- roots stabilize the ground surface

- braided streams: wide stream channels

- many small channels in a wide area

- streams get localized and deeper

Black Marine Shales

- black shales in Appalachian basin

- forrests linked to black marine shale

- black in color due to organic materials

- due to amount of soil created, Nitrogen and Phosphorous get dumped in ocean

- encourages algae growth

- sea water becomes anoxic and toxic to marine life which eventually is killed off > organic material in shales

Forest and Coal Deposits

- plant material

- quiet environment > swamp

Changes in Climate and Atmosphere

- CO2 drops dramatically

- cooling event

Number of Predators vs Prey

- predators are 3 times more prevalent than prey

- arthropods: initially not much food available for herbivores

Acadian Orogeny

- second event leading to formation of the Appalachians and Pangea

- nearly identical to Taconic

- thrust faulting, metamorphism

Extension

- extension when pulling apart

- no extension in mountain building events

Age of Fishes

- Devonian: middle paleozoic

- must numerous vertebrates on Earth today

- huge diversity of fish at this time

Jawless Fish

- during Cambrian explosion

- lampreys and hagfishes: modern jawless fish

- ostracoderms: extinct due to slow swimming, ate plankton off sea floor

Jawed fish

- jawed fish

1. bony fish

- most fish we see today

2. cartilaginous

- have bones

- sharks

3. placoderms

- went extinct

Bony Fish

- difference in location of bones

- lobe-finned fish- evolve into amphibians

- lobe- bones are throughout the fin

- ray-finned- bones are just adjacent to fin

- most fish today are ray-finned

Cartilaginous Fish

- went extinct quickly

- rays, sharks, sawfish, skates: modern cartilaginous fish

Placoderms

- top predators in middle Paleozoic seas

- first armored head

- biggest predators for awhile

- go extinct by the end of middle paleozoic

Late Devonian Mass Extinction

- protracted event: lasts a long amount of time for an extinction event

- 25 million years: 8-10 pulses of extinction

- mostly hits marine life

- lots of marine invertebrates: clams, nonfish (no spinal chord)

- reefs almost completely disappear

- some explanations relate to plants including ocean anoxia (low oxygen), global cooling

- other explanations include volcanism

Practice Question: What are the 3 main types of fossils that made their debut in the Cambrian period?

- three main types of fossils

1. biomineralized fossils: small shelly fossils replaced by phosphorus

2. non biomineralized fossils: have not been replaced by another mineral e.g. skeleton of an organism

3. trace fossils- complex burrowing patterns

Practice Question: How does carbon in rocks versus the atmosphere effect the climate and rock record?

- calcium carbonate in rocks: low CO2 in the atmosphere

- effect on climate: atmosphere gets colder

- calcium carbonate in atmosphere: higher CO2 in atmosphere

- effect on climate: atmosphere gets warmer

- more limestone

Practice Question: Difficulties when studying Archean life

- not many organisms

- do not fossilize well due to the presence of only hard parts which are rare

- fossils would be destroyed by metamorphism

Practice Question: 2 Stages of Ordovician Extinction Event

- first: global cooling which kills of tropical marine life

- second: warming quickly after the cooling > kills off organisms that adapted to the cold

Practice Question: First Vertebrates to Move to Land

- tetrapods (amphibians)- Tiktaalik

- live in the water as juveniles and move to land as adults

- evolved from lobe-finned fish