geosci 110 exam 4

what type of rock does radiometric dating use?

igneous rock

What are radioisotope systems used to date?

igneous rocks and volcanic ash beds

What is radiocarbon dating? (14C)

a method of determining the age of materials by measuring the amount of radioactive decay of the element of carbon 14 in once living material.
-activated upon death of organism
-short half life of only 5,730 years
-NOT a parent-daughter ratio, rather simply the measure of 14C/12C

What is radiocarbon dating (14C) used for? (which materials)

organic and inorganic carbon (NOT igneous rocks)
-Example: if the 14C fraction of total carbon in a pine tree sample is 25%, then age is two half-lives old, so 2 x 5,730 = 11,460 years

what does short half life mean?

materials older than 50k years no longer contain measurable amounts of 14C

What is an isotope?

atoms with the same number of protons but different number of neutrons

What is radioactive decay?

give off a particle and/or radiation and are fundamentally changed (the parent atom becomes the daughter atom)

What is radiometric dating?

Radiometric dating uses the decay rate of radioactive material to date objects.

What defines an element?

number of protons

what is radioisotope half-life

the amount of time it takes for one-half of the radioactive isotope to decay

What are parent-daughter isotope ratios? How are they used to calculate radiometric ages?

when parent atoms decay, daughter products remain

the ratio of parent to daughter after one half-life will be 1:1

measuring the relative amounts of parent and daughter isotopes in them can determine when the rock was crystallized

How do geologists figure out the numeric age of a rock?
(what two things do they need to know)

they need to know
1) ratio of parent to daughter atoms in a sample
2) rate of decay for parent isotope

Who was Clair Patterson?

-he dated age of Earth at 4.55 billion years old
-used the concept of a half-life to calculate the age of the earth
-used uranium-lead decay to determine age of Earth
-passionate humanitarian and environmentalist, we have lower lead counts in our blood bc of him

What is the half life of 238U

4.5 billion years

Why did Clair have to use meteorites to find the age of Earth?

1/2 of uranium-238 was converted to lead in meteorites

how far back in time can radiocarbon dating be applied?

500-50,000 years

how does radiocarbon (14C) differ from other radioisotope systems?

not a parent-daughter ratio

What is the chemical composition of Earth's early (Archean) atmosphere?

SOOOOO much carbon dioxide, and a bit of methane and ammonia

What was the Miller-Urey experiment?

demonstrated that amino acids and basic building blocks of nucleic acids can be synthesized from inorganic molecules in oxygen-free

Significance of Murchison meteorite and its chemical composition

contains all 20 amino acids used by life and nucleotide bases that make RNA and DNA

Its high water content indicated that it broke off a passing comet

Molecules to microbes

compound synthesis, phospholipid bilayer, replication (RNA, ribozymes)

what is compound synthesis

assembling the first proto-cells, origin of life

what are mechanisms for concentrating organic molecules?

mineral grains
clay minerals are abundant
-long linear crystal structures
-chemically attractive
-huge surface area

What is the phospholipid bilayer?

Cell membrane made of 2 layers of lipid molecules

in order to be viable, a cell must have a way to isolate its internal chemistry from the external environment

what is replication of RNA and ribozymes

RNA can replicate WITHOUT enzymatic mediators

what are the precursors of life?

concentrated, synthesized compounds of nucleotides and amino acids

what are the three domains of life?

Bacteria, Archaea, Eukarya

what is molecular phylogeny based on?

DNA sequences for the ssrRNA

what is ssRNA

Positive-strand RNA virus

What about deep-sea hydrothermal vents?

1. mid ocean ridges
2. form along Mid-Ocean ridges, no sunlight, ultimate source of energy is heat from Earth's interior (shallow magma chambers)
3. hot effluent discharged from black-smoker chimneys contains hydrogen sulfide
4. chemosynthetic microbes thrive in absence of sunlight

Where could have life gotten its start?

deep sea hydrothermal vents
- provide a variety of warm envirs
- abundance of dissolved organic and inorganic compounds

what were the earliest signs of life?

Archean-aged terrane/rocks of Pilbara Craton, Australia (i.e. Dresser Formation)

What are stromatolites? How old are they?

mats of blue-green algae that grew in mounds up from the sea floor

formed by prokaryotes that are photosynthesized

first found in archean period

3.5 Ga years old

What is cyanobacteria? How old is it?

Bacteria that can carry out photosynthesis

discovered by William Schopf

3.4 billion years old

what is a geyserite? what is evidence that hot springs on land may have been where early life got its start on earth

wrinkled rocks that have orange and white layers

because the Dresser Formation contains a rock/mineral called geyersite that only forms in modern hot springs

How old and where is the Dresser Formation?

3.48 billion years old, Pilbara area of Australia

How do stromatolites form?

formed by cyanobacteria doing oxygenic photosynthesis as a source of free molecular oxygen

what is oxygenic photosynthesis?

CO2 + H2O => CH2O + O2

When did the "Great Oxygenation Event" (GOE) happen?

circa 2.5-2.3 Ga

When did eukaryotes first appear in the fossil record?

the exact timing is difficult to pinpoint due to poor fossil preservation and definition of what a fossil eukaryote looks like
if we use cell size (>60 microns) then they are common in the fossil record around 2 billion years ago

What are acritarchs?

organic-walled cysts of early eukaryotic algae
first appeared in the fossil record during the Proterozoic at ~2 Ga.

when were prokaryotes and eukaryotes formed?

Pro: 3.5ish Ga
Euk: 2ish Ga

what allowed the evolution of metazoans (multicellular animals) with active lifestyles?

the secondary rise in atmospheric oxygen levels near the end of the Proterozoic Eon, which established "modern-like" atmospheric O2 levels

What is the Ediacara Fauna? When did they evolve?

-soft-bodied, preserved as impressions
-first multicellular animals
-occur world-wide
-relationships uncertain
600 Ma
first discovered in Australia

What was the Cambrian explosion?

all major phyla with hard parts appear before and during this event

marine invertebrates with hard parts such as shells and exoskeletons

Burgess Shale Fossils (Fossil Lagerstaaten)

incredible array of fossils, brand new animals with eyes. every modern phyla is present in these fossils. 525-151 million years ago.

example is the Anomalocaris (large predator)

What are representative organisms of the "Cambrian Evolutionary Fauna"?

trilobites, archaic mollusks, primitive echinoderms, weird inarticulate brachiopods, etc.

What is the Great Unconformity?

Global surface above which sediment is deposited on crystalline basement rocks

How does the Great Unconformity relate to changing seawater chemistry and the Cambrian Explosion of Life?

it is a very prominent geomorphic surface that juxtaposes old rocks (formed billions of years) with relatively young Cambrian sedimentary rock. During the Cambrian, shallow seas eroded surface rock to uncover the older rock within the Earth's crust, and that rock released ions that changed the seawater chemistry. Those old rocks were covered by Cambrian sediment.

Why did so many different kinds of animals evolve shells and exoskeletons during the Cambrian?

As animals began feeding on other animals, protective body armor became a distinct advantage

What did the immense magnitude (amount of missing time) of the Great Unconformity indicate?

the Precambrian terranes were intensely weathered

what conditions/processes are thought to have helped foster the Cambrian Explosion?

-increased predation, a type of "ecological arms race"
-increased O2 levels
-change in ocean chemistry

Who are likely ancestors of the earliest land plants?

marine green algae (eukaryotes)

Timeline for land-plant evolution

ordovician
silurian
devonian
devonian
carboniferous Period

ordovician land plants

seedless, non-vascular mosses

silurian land plants

seedless plants with primitive vascular system (Cooksonia)

devonian land plants

First Forests were made mostly of lycopod plants (seedless, vascular)

late devonian land plants

Primitive gymnosperms and seed ferns (seed plants) first appear

Carboniferous period

vast, widespread "coal swamps" dominated by seedless lycopod trees

what are lycopods

seedless vascular plants

difference between vascular and non-vascular plants

vascular arteries transport water and food to all plant areas

examples of important seedless (spore bearing) plants common to the Paleozoic Era

club mosses and horsetails

why is the evolution of seeds important?

allowed plants to decrease their dependency upon water for reproduction

What are gymnosperms?

plants that produce seeds without flowers (conifers and cycads)

How did the evolution and spread of land plants affect organic carbon burial rates, atmospheric greenhouse gas (CO2) levels, and climate during the Carboniferous Period?

-Plants accelerate the hydrological cycle through evapotranspiration and stimulate rainfall
-increased atmospheric oxygen to present levels

When do the first jawless fish appear?

In the in the Cambrian and Ordovician periods

When do the first fish with jaws appear?

the Silurian period

Why is the Devonian Period also known as the "Age of Fishes"?

the diverse, abundant, and, in some cases, bizarre types of these creatures that swam Devonian seas.

Significance of lobe-finned fishes

during the devonian period
lungfish and coelocanths, extinct Rhipidistians

What are coelacanths?

lobefins that were thought to be extinct until 1938 when they were found

What are Rhipidistians?

an extinct group of lobefin fish
the rhipidistians had evolved nostrils and internal air passages that are used by all land-dwelling tetrapods to breathe

what do fossil records of the late devonian period contain?

transitional forms from lobe-finned fishes to tetrapods
homologous features of the fish and tetrapod

what is ichthyostega?

the first amphibian
found in freshwater deposits

Lines of morphological evidence linking rhipidistian fishes and earliest tetrapods like Ichthyostega?

the shoulder/limb bones and teeth

both have labrynthidont teeth

what is the reproductive biology of amphibians?

strongly tied to aquatic habitats, they lay their eggs in water

when did the first land animals actually appear? what were they?

the silurian period
insects such as Trigonotarbid bugs

what is tetrapod radiation and when did it happen?

happened in carboniferous period

What were Temnospondyls?

the largest and most diverse group of early Amphibians
first appeared in the earliest Carboniferous and descended from Ichthyostega
most common Late Paleozoic amphibians and survived into the Cretaceous

When did first reptiles appear in the fossil record?

the late carboniferous

What is a reptilian reproductive evolution?

the amniotic egg

Why is evolution of amniotic egg important?

made it possible for Life to colonize drier habitats within the continental interiors during Late Paleozoic

what are synapsids?

1 opening, mammal-like reptiles

what are diapsids?

2 openings, dinosaurs, birds, crocodiles, snakes, lizards

What are pelycosaurs?

Fin back reptiles
- eventually get replaced by therapsids
early permian

what are therapsids?

-mammal like reptiles (synapsid)
-permian period

what criteria is used to differentiate background extinction from a mass extinction?

Background: typical process of turnover and replacement (small ones that don't matter that much)
mass: BIG ones, late ordovician, late devonian, end permian, end triassic, KT

When were the FIVE major mass extinctions of the Phanerozoic Eon?

Ordovician-silurian Extinction: 440 million years ago.
Devonian Extinction: 365 million years ago.
Permian-triassic Extinction: 250 million years ago.
Triassic-jurassic Extinction: 210 million years ago.
Cretaceous-tertiary Extinction: 65 million Years Ago.

when was the "great dying"?

250 million years ago
brought an end to the Paleozoic Era

what was the magnitude of the Permo-Triassic mass extinction?

~52%

who died from permo-triassic mass extinction?

lots of marine invertebrates, trilobites, sea scorpions, coral, brachiopods

Kill mechanism

Siberian Traps Flood Basalts emitted massive quantities of volcanic CO2 into ocean-atmosphere system Thermal combustion of Carboniferous coal via intrusion of Siberian Traps

Environmental Impacts

CO2 induced global warming, ocean deoxygenation, ocean acidification

What is pH?

it is the NEGATIVE log of hydrogen ion concentration -log[H+], express the free hydrogen ion concentration in a solution (i. e. seawater)

what happens when pH values decrease?

seawater [H+] increase, meaning acidification

What is oceanic acidification?

dynamic relationship between rising CO2 levels and lowering of ocean pH. CO2 bonds with H2O to make a weak acid called carbonic acid (H2CO3)

Why do many scientists consider the "Great Dying" at Permo-Triassic Boundary to be an ancient analog for future climate change?

it is the only extinction that has affected diversity so much

what caused the great dying at the end of the Paleozoic era?

Massive release of carbon dioxide (CO2 )
Global warming
Ocean acidification
Ocean deoxygenation (dead zones)