Lecture 3-5 Flashcards
What do absolute dates come from?
Radiometric dating of igneous rocks
What does relative dating come from?
Relationships between rocks
What are the three types of rocks?
Igneous, sedimentary, metamorphic
What is an igneous rock?
Fire formed
Formed through the cooling and solidification of magma lava
We can date most accurately igneous rocks (absolute dates)
What is a sedimentary rock?
Formed from chemical precipitates or fragments of earlier formed rocks
Sedimentary rocks
What is a metamorphic rock?
Formed by application of heat and pressure to either igneous or sedimentary rocks
Transformed into other rocks tell us mostly about the relative order in which events occurred
How do we know how old a rock is?
Radiometric dating
The radioactive decay of an isotope is a natural clock
Once magma/lava, it’s radiometric clock begings
Some isotopes decay over time –> we can measure the decay for carbon dating purposes
When the number of parent atoms decrease, the number of daughter atoms increase
What is an isotope?
All atoms of a precise mass for a given element
Different elements have different masses (isotopes)
E.g. carbon 12 (stable), carbon 13 (stable), carbon 14 (unstable)
Unstable isotopes undergo decay (half life = rates of decay)
Why does radiocarbon dating not always work
We can measure the amount of carbon 14 to determine how old something is. This is called radiocarbon dating. But this only works for things that are up to 50,000 years old.
Most rocks are way older than 50,000 years old
What is a solution to radiocarbon dating limitations?
Measuring the decay of other elements found within a rock to determine an absolute age
Minerals found within rocks contain trace amounts of unstable isotopes
What is a parent isotope?
The starting isotope during radioactive decay
What is a daughter isotope?
The new element produced as a result of radioactive decay
Explain isotopic dating of rocks
Determines the ratio of parent to daughter atoms
This is assuming that when a rock forms it contains an unstable isotope and none of the daughter isotope
Also assuming that over geologic time the rock remains a closed system (no parent or daughter enters or leaves the rock)
That rock can be accurately dated by determining th eratio of parent to daughter atoms
What is relative dating?
Inferring the sequences in which older to younger events (recorded in rocks) occurred
In sedimentary rocks, the older rocks are the layers at the bottom. The younger rocks are the layers above them.
What is the principle of superposition?
Sedimentary rock is produced from the gradual accumulation of sediment on the surface. Therefore, newer sediment is continually deposited on top of previously deposted or older sediment.
How can fossils contribute to relative dating
Different organisms throughout history have left their remains as fossils in sedimentary rocks
Geologists can study the order in which fossils appeared/disappeared through time and rocks
Fossils can help to match rocks of the same age, even when you find those rocks a large distance apart
Rocks in different places can be put into separate time sequences. Fossils in some of the rocks can be correlated to help combine these sequences into longer ones.
Where are fossils most abundant?
In marine sedimentary rocks. They are generally not found in igneous or metamorphic rocks.
Why is using fossils not always clear-cut?
A large river may dump a large amount of sediment into the sea. But rocky stretches of coast may see very little sediment accumulation
Far offshore, in the deep-sea, sediment accumulation is much slower
On beaches, a powerful storm can remove meters of sediments in a single event
So we cannot use the thickness of sedimentary layers to estimate how much time any layer represents.
How did Earth form and approximately how long ago?
4.54 billion years ago out of a solar nebula (a swirling cloud made up of bits and pieces left over from old stars that have exploded.
Earth formed when the force of gravity pulled swirling gas and dust in to become the third planet from the Sun.
What does the Goldilocks Zone refer to?
It refers to the habitable zone around a star where the temperature is just right (not too hot and not too cold) for liquid water to exist on a planet.
Based on the amount of energy (i.e. heat) the planet receives from the sun.
What was Earth like during the Hadean Eon?
Initally molten
Constantly bombarded by asteroids and comets
Formation of the moon
How was the moon formed?
A small planet collided with the Earth and most of its mass joined the Earth. However, a small mass was ejected and went into orbit around the Earth; this become the Moon.
What impact did the late heavy bombardment on Earth have?
Smaller bodies resembling present-day meteros and comets bombarded the Earth, heating it.
This heating was also increase by gravitational contraction.
This lead to partial/total melting of Earth, creating a magma ocean. The iron-rich fraction of this liquid was heavier and it settles to Earth’s center (creating its core).
This melting drove off any H, He-rich primordial atmosphere
What was the Earth composed of 4.4 Ga (4.4 billion years) ago?
A solid iron core
An outer core of liquid iron
A partly molten mantle (a siliceous, SiO2-rich, magma)
Perhaps a “thin” skin of solid rock (the earliest crust) at its surface (like the stuff floating on the top of soup)
When did the Earth cool enough that rocks and oceans began to form?
The end of the Hadean
Steam in the atmosphere cooled down and fell as rain on the Earth to create oceans
FIrst continents began to form (rocks in early oceans)
What was the earliest piece of the planet’s crust composed of?
Zircon crystals from Western Australia have been dated to 4.4 billion years making it the oldest rocks on earth.
- This suggests that within the first 100-200 million years of our planet, there was enough cooling to form a crust.
Ratio of O isotopes within this zircon crystal indicates that it likely formed in a cool, wet process at the Earth’s surface
- This suggests that parts of Earth may have been covered with liquid water
What are the defining characteristics of the Archean?
Archean – meaning “beginning, origin”
Liquid water was prevalent
Emergence of life on Earth (first evidence)
Onset of plate tectonics
What is a plate tectonic?
All of the crust on Earth moves around like floating slabs of rock (about 96km thick) on top of hot, mushy rock in the mantle, the hotter part of the Earth between us and the Earth’s iron core.
The Earth is chewing itself up, melting itself down, and making itself anew (a way that the Earth recycles itself)
Made up of rigid cool lithosphere (the rocky crust of the ocean floor and continents, down to the upper mantel)
What is the theory of Continental Drift?
Alfred Wegener in 1915
Idea that the Earth’s continents have moved over geologic time relative to each other, thus apearing to have “drifted” across the ocean bed
Explained why look-alike animal and plant fossils, and rock formations, are found on different continents (fossil evidence)
What are alternative evidence to Continental Drift for fossils on different continents ?
The species evolved independently on separate continents contradicting Darwin’s theory of evolution
They swam to the other continents in breeding pairs to establish a second pop.
What is the geological evidence for Continental Drift?
Rocks of the same age across the ocean
What was the theory of continental drift replaced by?
Plate tectonic theory
What are the three main layers of the Earth?
Core
- rich in iron
- solid inner core
- liquid outer core (source of Earth’s magnetic field)
Mantle: very hot rocks
- rich in silicon and oxygen (SiO2)
- becomes hot enough to become ductile and weak, behaves “plastically”
Crust: cooler, stiffer rocks
- rich in silicon and oxygen (SiO2)
What are the two different kinds of crust on Earth?
Oceanic crust:
- thin (7 km)
- dense (sinks under continental crust) –> nk
- young
Continental Crust
- thick (10-70 km)
- buoyant: less dense than oceanic crust
- mostly old
Density differences due to chemical differences; when it interacts with continental crust it tends to sink
- Continental crust has more aluminum, silicon, less magnesium, iron
- Oceanic crust has more magnesium, iron, less aluminum and silicon
What does the movement of plate tectonics do?
Earth’s crust is divided into 12 major plates which move in various directions
Plate motion causes them to collid, pull apart or scrape against each other
Each type of interaction cuases a characteristic set of Earth structures or tectonic features (e.g. volcanoes, mountains, ocean trenches)
The word tectonic refers to the deformaiton of the crust as a consequences of plate interaction
What causes plates to move?
Stiff tectonic plates are carried along the top of the mantles as if they were on giant conveyor belts
Convections causes the movement
What are plate boundaries?
Zones of contact between plates. They do not correspond to those of the continents.
What are the three types of plate boundaries?
Divergent: moving away from one another
Convergent: moving toward one another
Transform: moving up against one another
Divergent boundaries
The space created can be filled with new crustl material sourced from molten magma that forms below (the magma comes up in space created by divergent boundaries)
Divergent boundaries form within continents to produce rifts in continental crust. When the rift opens wide enough, it will form the thin rocky floor of a new ocean.
Some rifts failed to open, and created long-lasting valleys where major rivers run
Iceland being slowly torn apart is an example of continental rifting
What are mid-oceanic ridges?
Underwater mountain systems
Most active divergent plate boundaries are between oceanic plates. As plates move apart, small amounts of magma rise to the seafloor and add new crust (seafloor spreading – ocean is growing wider)
Where is the oldest sea floor found?
Near the continents
The age of seafloor increases relative to oceanic rifts
What are black smokers, what do they do, and where are they found?
Also known as hydrothermal vents, they are sea-floor hot springs. Molten hot magma heats up the water and pushes it up through the vent.
Entirely different ecosystem of organisms that we never knew about.
We discovered organisms at these vents get their energy from the vent itself and not from sunlight (chemotrophs) –> beginning of life on the planet?
Convergent boundaries
Refer to plates colliding. Typically the denser plate is subducted underneath the less dense plate. The plate being forced under is eventually melted and destroyed.
3 types of convergent boundaries:
- continent-continent collision
- continent-oceanic collision
- ocean-ocean collision
Explain continent-continent collision
Continental crust meets continental crust
Both continental crusts are too buoyant (light) to subduct so a continent-continent collision occurs, creating especially large mountain ranges
Explain continent-oceanic collision
Continental crust meets oceanic crust
The denser oceanic plate is subducted, often forming a mountain range on the continent
When do subduction zones occur?
Occur when one of both of the tectonic plates are composed of oceanic crust. Leads to oceanic crust being recycled.
Explain ocean-ocean collision
Ocean crust meets oceanic crust
Two oceanic plates collid; one oceanic plate is eventually subducted under the other
Formation of really deep trenches such as the Mariana Trench which is 11 km deep
Transform boundaries
Plates slide past one another
As plates rub against each other, huge stresses are set up that can cause portions of the rock to break, resulting in earthquakes.
Places where these breaks occur are called faults
Lithosphere is neither created nor destroyed
How fast do plates move?
Plate motions are on the order of a few centimeters per year
Along their edges, most paltes either converge of diverge
How do plate tectonics affect the evolution of life?
Plate tectonic movements affect geography (create mountains, give birth to new oceans, produce volcanoes that spew gases into the atmosphere), they could in turn affect food supply, climate, and the diversity of life
Mountain ranges form a physical barrier that allows isolation of gene pools
Ex. When the Grand Canyon formed, squirrels and other small mammls that had once been part of a single pop. could no longer contact and reproduce with each other across this new geographic barrier
Describe Pangea
Supercontinent that assembled from earlier continents approximately 335 million years ago, and it began to break apart about 175 million years ago.
How did Pangea promote biodiversity?
Plate tectonics has been one of the main driving forces promoting the biodiversity of organisms
Terrestrial organisms were able to migrate across all the continents and were only limited by their biotic potential.
As Pangeo began to separate, it created physical barriers such as seas
Species were separated and became exposed to different physical (i.e. climate) and biotic (i.e. changes in predators) conditions, each species adapts differently and eventually forms new species on the newly separated continents
New habitats were created due to a change in biotic and abiotic factors such as climate (temp. and moisture)
What is weathering and how does it impact nutrient distribution?
The breakdown of minerals in rocks at or near the Earth’s surface – releasing nutrients
Weathering is caused by chemical and physical interactions with air, water and living organisms
Nutrients in the oceans ultimately come from weathering and erosion of rocks on the continents
When weathering and erosion rates increase for extended periods, more nutrients are supplied to the oceans
How are plate tectonics and weathering connected?
When tectonic plates collide, mountains are pushed upwards and erosion causes an increase in nutrients in the oceans
How are plate tectonics and habitability connected?
Plate tectonics helps regulate the planet’s temperature, recycles nutrients and many other important functions.
Of all planets, Earth is the only one known to have plate tectonics. It is also the only one known to harbour life.
Some research argues that plate tectonics might be necessary for the evolution of advanced species. Dry land on continents is necessary for species to evolved the limbs/hands that allow them to grasp/manipulate objects, and that a planet with oceans, continents and palte tectonics maximizes opportunities for speciation and natural selection
What are the characteristics of single celled organism?
Consumes and produces energy
Reproduces
Non-motile
Considered life
What are the characteristics of single-cells below the seafloor?
Collect sediment cores that are meters to kms below the seafloor
Deep sea sediments contain lots of single-celled organisms (mostly bacteria)
- dormant for years
- lifespan can be very different from life on the surface (average cell may divide once in 1000 years)
What are the characteristics of a bacteriophage (virus)?
Virus that infects and replicates within bacteria
Has DNA or RNA (contains building blocks of life)
Needs host to reproduce
Cannot make their own energy
Debate whether considered life or not since they cannot reproduce without a living host
What is the definition of Life?
No single accepted definition
NASA def: Life is a self-sustaining chemical system capable of undergoing Darwinian evolution
(according to NASA, viruses would then be considered life)
What are the requirements of be “alive”?
Maintain internal homeostasis: must have a mechanism to maintain its internal envr separately and independently of its exterior envr.
- membranes
Respond to external stimuli: must respond to its envr.
- Movement or chemistry
Consume and produce energy: must be able to process energy
- electrochemical gradients
Reproduce and have a form of heredity: must have a way of passing on info between generations and individuals
- DNA and RNA
Explain the requirement to be alive: maintain homeostasis
The inside of a living thing is different than the external environment (distinct thermal and chemical makeup). Cell must be able to maintain this interior in the face of changing external condition.
Organisms regulate their internal envr. to maintain the relatively narrow range of conditions needed for cell function (internal temp., pH, concentration of proteins and solutes)
What is homeostasis maintained by?
Cell membrane barriers that protects cell
Transport across membranes allow cell to bring things in or push things out in a controlled way (maintains concentrations of ions)
Explain the requirement to be alive: response to external stimuli
External stimuli: a change in the environment.
Responses can be physical (ex. movement) or chemical (ex. hormones)
Everything from complext multicellular organisms to single cells respond to external stimuli
- single-celled organisms may migrate toward a source of nutrient or away from a noxious chemical
Explain the requirement to be alive: consume and produce energy
Living things must use energy and consume nutrients to carry out the chemical reactions that sustain life (e.g. replicating or repairing DNA< synthesizing new proteins)
- Metabolism
What is metabolism?
The sum total of the biochemical reactions occuring in an organism
How do organisms get energy?
Heterotrophs (breaking down organic carbon compounds) –> humans, animals
Autotrophs (light/chemical reactions) –> algae, plants, certain microbes
What is ATP and how is it generated?
Cellular energy currency for all cells –> all life on Earth uses ATP
Energy is moved around the cell as adenosine triphosphate (ATP)
Protons accumulate on one side of a membrane establishing an electrochemical potential energy gradient (like water in a dam)
Movement of the ions back across the membrane is used to do work (generates energy in the form of ATP through these membranes)
- proton gradient from high (in) to low (out)
Explain the requirement to be alive: reproduction and heredity
All life must have a mechanism for reproduction
Reproduction is the process by which living things give rise to offspring and transmit hereditary info
What are the two types of reproduction?
Asexual: single organism creates clone of itself. Most species on the planet reproduce asexually (including all bacteria, archaea, many plants and even some animals) –> much more common than sexual reproduction
Sexual: cells from new parents unite to form first cell of new organism. Offspring is different from parent
How are organisms able to pass on hereditary info?
Living things are able to pass on their traits through genes (a sequences of DNA or RNA) that are passed from parent to offspring each generation
What is DNA and RNA?
A complex code made up of nucleotides
Allows for incredible flexibility in the info recorded
When is it theorized that life first evolved on earth?
During the Archean, from at least 3.5 billion years ago
What are the necessary ingredients for life?
Chemical building blocks: O, H, C, N, S, P
Energy source: UV light from sun, electrical energy from lightning, and chemical energy
What are the four macromolecule building blocks of all life?
Carbohydrates
Lipids
Proteins
Nucleic acids
What is a macromolecule?
A large biological molecule made up of smaller subunits or monomers
What are the monomers that formed the 4 main macromolecules?
Proteins
- Amino acids
Lipids
- Fatty acids
- Sugar residues –> glycerol
Carbohydrates
- Sugar residues –> mono-saccharides
DNA or RNA
- Sugar residues –> monosaccharides –> nucleotides
- nucleobases –> nucleotides
What is LUCA and what is the evidence?
The “last universal common ancestor”: suggests that all current life evolved from a single common ancestor
Does not necessarily mean that life only evolved once on Earth
- Other forms of life could have gone extinct very early in evolutionary history and left no record in modern-day life for us to find
Evidence: all extant life has:
- carbon based
- similar enzymes with similar gene recipes
- enzymes for most basic biological functions are the same across very different species
- passes heredity info through DNA or RNA
- Amino acids and nucleic acids are found in two different configurations (left handed and right handed –> same compound they are mirror images)
–>all extant life has ONLY left-handed amino acids and right handed nucleic acids
What is the Primordial Soup Theory?
Based heavily on the idea that the early earth environment consisted of high concentrations of compounds and elements known to be abundant in life (C, H, water vapour, ammonia)
What are the four steps to the primordial soup theory?
1) Early Earth had a chemically reducing atmosphere
- very low levels of gaseous oxygen
- high levels of reducing gases (e.g. carbon monoxide)
- oxygen was found on earth, but almost all bound in minerals. Essentially inert and unavailable
2) This atmosphere, exposed to energy in various forms produced simple organic compounds (monomers)
- energy may have come from lightning or the sun (UV)
3) These compounds accumulated in a “soup”, which may have been concentrated at various locations (shorelines, oceanic vents, etc.)
4) Concentration led to the eventual formation of complex organic compounds (polymers)
- life eventually arose from these complex polymers
- early cells then broke down these organic molecules to generate ATP –> heterotrophy
What is the Miller-Urey Experiment?
Experimental support to the primodial soup theory
Test for production of monomers under early primitive Earth conditions
Results:
- Found that 25 different amino acids had been produced (the basic building blocks of proteins)
Conclusion: if free oxygen is present, no organic compounds are formed
- Assumes that amino acids formed first and would eventually connect somehow to form proteins
What are the main issues with issues with the Primordial Soup Theory?
No mechanism for the generation of complex polymers from simple monomers
No mechanism for the evolution of cells from monomers and polymers
Need sustained energy for life to develop (not one time “spark”)
What is the RNA World Theory?
RNA formed first
Proliferation of RNA eventually lead to DNA and protein formation
RNA can store replication info (like DNA), can replicate itself, can act as an enzyme –> ribozyme, could have provided heredity and catalyzed reactions before the evolution of DNA and proteins
Does not necessarily preculde the primordial soup theory (theories are not mutually exclusive)
- organic molecules were the precursors to nucleotides
What is the experimental and observational support for the RNA World theory?
Experimental: Nucleic acid precursors and nucleotides have been produced in the lab from simple compounds common on early earth (hydrogen cyanide, hydrogen sulfide) and UV light
Observational: Some viruses contain RNA only. Viruses generally considered to be ancient form of life
What are the issues with the RNA World theory?
How does a combination of DNA, RNA and proteins lead to cell formation
How are membranes produced?
Attemps to create self-replicating RNA under plausible early-Earth conditions have failed
- RNA is not very stable in water
Does not make sense since viruses need a cell to infect
What is the deep sea hydrothermal vent theory?
First theory to seriously challenge the primordial soup theory
Involves the generation of electrochemical gradients and metal-containing enzymes as the first precursors to life
- allowed for the generation of chemical energy
Once energy could be reliably generated
- organic monomers and polymers would be formed naturally
- RNA, DNA, and proteins would follow
- Eventually all would combine behind a membrane which could safely leave the vent, colonize the rest of the ocean and eventually the planet
What is a hydrothermal vent?
Small cracks on the seafloor from which geothermally heated water issues
Called black of white smokers
Found in the mid-ocean ridges where seafloor is spreading (magma reaches the ocean)
- at divergent plate boundaries
The deep sea hydrothermal vents have very unique chemistry
- alkaline water from vents meets slightly acidic oceanic water (OH- and H+) –> creates a natural proton gradient (creation of energy ATP)
How are chimney-like structures near hydrothermal vents created and what are their characteristics?
Porous geological structures produced by chemical reactions between solild rock and water
Hot hydrothermal fluids mix with near-freezing seawater. These minerals solidify as they cool, forming chimney-like structures (chimneys are very porous)
Chimney structures can be porous and act as a primitive semi-permeable membrane
- Worked well enough to create different proton concentrations in different locations
- energy would be generated when a proton went with the gradient
What is the experimental and observational evidence of the deep sea hydrothermal vent theory?
Experimental: articial hydrothermal vents have generated proton gradients under laboratory conditions
Observational: many of the oldest enzymes contain iron or sulfur in their complexes. Reconstruction of proteins from ancestral bacteria show high heat stability (i.e. they evolved in a warm/hot place)
What are the issues with the deep sea hydrothermal vent theory?
No clear mechanism yet for how biomolecules eventually developed
Could some building blocks of life have come from outer space?
Perhaps, meteorites such as Tagish Lake Meteorite have been shown to contain an abundance of organic materials including amino acids.
Another example is Murchison that has been estimated to be nearly 4.95 billions years old. It contained organic compounds including amino acids as well as purine and pyrimidine compounds. Both purines and pyrimidines are needed to form RNA and DNA
What is the panspermia theory?
Life is actually everywhere in the universe
Microbes which can survive the effects of space can become trapped in debris ejected into space after collisions between planets and small Solar System bodies that harbor life.
What does the panspermia theory require?
1) that organic molecules originated in space
2) that life originated from these molecules extraterrestrially
3) that this extraterrestrial life was transported to Earth
- this is improbable –> temperatures surviving in outer space and entering our orbit does not make very much sense since it is too hot for microbes to survive
What are the conditions of the early Archean Earth?
THere was a reducing atmosphere of methane, ammonia, and other gases which would be toxic to most life on our planet today. No free oxygen (O2) was present
No ozone O3 layer to shilef Earth from UV radiation, and other solar and cosmic radiation
High rates of metero bombardment
What is a biosignature?
A sign of life (proof that life was present)
Any substance–such as an element, isotope, or molecule–that provides evidence of life.
What are different types of biosignatures?
Fossils
Chemical fossils
Isotopic signatures
What are fossils (micro and macro)?
Remains or traces of ancient life that have been preserved by natural processes
Can include anything ranging from sea shells, imprints of microbes, to large skeletons
In the context of early life, it was an imprint of a microbe (cells)
What are chemical fossils?
Molecular biological markers (biomarkers) are natural products that can be traced to a particular biological origin
The most effective biomarkers are compounds with specific biological sources, whose structures can be preserved through geologic time
Lipids are the most stable macromolecules and are an example of chemical fossils. They are preserved in sedimentary rocks and can offer insights into Earth’s history (different organisms make different lipids –> can trace them back in time)
What do stable and unstable isotopes tell us about a compound?
Unstable isotopes can tell us about the age of a compound
Stable isotopes tell us about the source (e.g. biotic or abiotic)
- how molecule was made
How can we measure isotopic signatures and what do they reflect?
By measuring the amount of the ratio of carbon-12 to carbon-13
Different processes have different stable carbon isotopic signatures
Stable carbon isotopic signatures will reflect unique biological processes
- organic compounds can have unique isotopic signatures
Isua, Greenland (3.8 Ga)
Banded Isua rocks are the oldest known metamorphosed sediments
These rocks have graphite in them
- graphite = pure carbon
- graphite is not a biosignrature, but it can form by cooking organic matter
- graphite can keep most of the original stable carbon isotopes
Isotopic signatures suggested that this carbon originated possibly photoautotrophic microorganisms
- Hypothesis was that microbes using sunlight to make their own carbon. Carbon was consistent with some photosynthetic process rather than abiotic production (HOWEVER, this was disproved)
Apex Chert, Australia (3.5 Ga)
Apex Chert is part of the Pilbara Craton: an old and stable part of the continental lithosphere
One of the few places on the planet where geological evidence of early Earth has been preserved, largely because it has not been subjected to geological processes that would have altered it, like burial and extreme heating due to tectonic activity
Theory: evidence of life because it looked like certain bacteria. This was argued that this could also look like minerals. The microbe theory was proved to be right
Isotopic signature showed that they were consistent looking. Stable carbon isotopic compositions confirmed that microscopic fossils discovered in a nearly 3.5 Ga rock from Apex Chert are the earliest direct evidence of life on Earth
Stromatolites as evidence of early life
Stromatolites are the least controversial evidence of early life
Stromatolites are rocklike structures made up of layers of bacteria and sediment, found in shorelines
Found throughout Archean rocks and become more common later in the Archean.
How are stromatolites formed?
Created through the trapping, binding and cementation of grains of sediment by microbial mats (i.e. biofilms)
Mucus secreted by the bacteria collects grains of sediment, and these grains and cells become stuck together with calcium carbonate also from the bacteria (grow over long timescales)
In modern environments, stromatolites are found in coastal regions or areas submerged in water
When are the oldest accepted stromatolites?
From 3.5 Ga ago from the Warrawoona Group (Western Australia)
Where are modern stromatolites found?
They are usually found in hypersaline lakes and marine environments where the extreme salt level prevents animals such as snails from grazing on them.
Modern stromatolites’ size in non-hypersaline environments tend to be smaller since snails graze on them
What kind of bacteria make modern stromatolites?
Cyanobacteria:
- autotroph (makes its own food)
- photosynthetic (obtain energy through photosynthesis)
- found in almost every terrestrial and aquatic habitat (oceans, lakes, ponds, rivers, etc.)
What are microbial mat structures?
Can be composed of diatoms, cyanobacteria, purple sulfur bacteria, sulfate- reducing bacteria
Microbial mats can contain more than just autotrophs
There are lots of other microorganisms that live in and on them
For example, cyanobacteria excretes glucose that can be a food source for other heterotrophic microbes –> first microscale ecosystem
Stromatolites were actually micro-scale ecosystems
What is anoxygenic photosynthesis?
Photosynthesis without the production of oxygen
Does not use water as an electron donor, but rather can use a variety of substrates including sulfide, iron, and hydrogen
CO2 + 2H2A + light energy –> Ch2O + 2A + H2O
What are some examples of early anoxygenic phototrophs?
Purple sulfur bacteria
Green sulfur bacteria
Purple nonsulfur bacteria
We think that the dominant microbes during the Archean were anoxygenic microbes due to sulfur
What other kinds of bacteria existed during the Archeae?
Sulfate reducing microbes
- heterotrophs
- live in anaerobic environments (low or no O2)
- Use sulfate as an electron acceptor instead of oxygen
Explain the Great Oxidation Event
Also called the oxygen catastrophe, oxygen crisis, oxidation resolution
The bioloigcally induced appearance of dioxygen (O2) in teh Earth’s atmosphere through the activity of oxygenic phototrophic microorganisms (cyanobacteria)
In other words, cyanobacteria oxidized the planet –> induced detectable O2 into the atmosphere
Why did it take so long for the oxygen to build up in the atmosphere?
Not entirely sure
There are many sinks for oxygen
- O2 being produced is balanced by sinks and respiration
- Microorganisms learned to use O2 expansion of aerobic microorganisms
- banded iron formations and red beds as O2 sinks
How do aerobic metabolisms work?
Require oxygen as electron acceptor
Oxygenic photosynthesis : CO2 + H2O –> glucose + oxygen
Heterotrophic respiration is the contrary, and produces ATP as well
What are banded iron formations?
Alternating layers of iron-rich material (commonly magnetite) and silica (chert).
Each layer is relatively thin, varying in thickness from a mm or so up to several cm
When did BIFs occur?
Around the time of the Great Oxidation Event
BIFs are abundant in Proterozoic rocks ranging in age from 1.8-2.5 billion years old
Appear on all continents
Huge deposits, km thick and 1000s of km^2 wide
Most common rock mined for iron
What is the connection of BIFs to oceans?
BIFs are thought to have formed through the caputre of O (released by photosynthetic processes) by iron dissolved in ancient ocean water
- sedimentation of biomass and iron minerals
- free iron in ocean consumed oxygen
Once nearly all the free iron was consumed in seawater, oxygen could gradually accumulate in the atmosphere, allowing an ozone layer to form
Where does the banded structure of BIFs come from?
The banded structure is thought to occur from fluctuating densities (or blooms) of cyanobacteria in the ocean
The periodic process might have been due to seasonal fluctuations or storm surges or factors that we don’t know about
Layers of iron and sediment
What are red beds?
Red beds form when iron is weathered out of rock in the presence of oxygen
Red in colour due to the presence of ferric oxides (iron and oxygn interact to form ferric oxides)
Earliest confirmed redbeds are thought to have formed about 2.2 Ga ago. For several million years BIFs and red beds overlap indicating the presence of low levels of atmospheric oxygen.
How did Earth’s oceans and atmosphere became oxygenated?
Once production exceeded consumption/sinks, O2 could accumulate in the atmosphere
By 2 Ga, O2 levels began to build up in the atmosphere
The presence of O2 had a profound impact on life on Earth
- O2 is toxic to organisms that don’t have protective mechanisms; many died as O2 levels built up
- many anaerobic organisms survive (even today) only in environments with little to no O
- some organisms developed means to use O2 in respiration to extract more energy from foods (aerobic respiration)
The formation of the ozone layer (O3) soon after oxygenation of the atmosphere provided protection from UV radiation and allowed life to expand to regions at and near the Earth’s surface
How did the Great Oxidation Event participate in diversity?
Towards the end of the Great Oxygenation Event: diverse microfossils of bacteria become more common in sedimentary rock
Their sizes (<10 micrometers) suggest that most were prokaryotes –> simple single-celled organisms (probably needed very little O)
What is a eukaryote?
Have a membrane bound organielles (prokaryotes do not)
- Eukaryote cells are more large and complex compared to prokaryote cells
DNA within membrane-bound nucleus; linear chromosomes
Cytoskeleton: protein filaments in cell membrane provide structural framework
Complex organelles: some organelles (mitochondria and chloroplasts) contain their own DNA and replicate independently
Compare prokaryotes to eukaryote cells
Prokaryote only: nucleotid, circular DNA
Both: Cells, cell membrane, ribosomes
Eukaryote only: nucleus, organelles, linear DNA
What is the oldest accepted eukaryotic biosignature found?
1.9 Ga in Gunflint Chert, North America
Sequences of rocks that are exposed in Minnesota and Ontario
Why did eukaryotes evolved so long after prokaryotes?
No clear answer, could be because of eukaryotes’ need for oxygen
The use of O as an electron acceptor provides substantially more energy to a cell (way more ATP generated, eukaryotes have higher cellular needs?)
