Development of the Biosphere
Investigate evidence for the origin of organic molecules on the Earth, including:
Urey and Miller’s experiments:
Geologists and palaeontologists found very old sedimentary rocks, often in remote places with extreme climates, which enabled them to assemble a timeline for some of the major steps in the history of life
Stromatolites indicated a much longer history for life on Earth than Charles Darwin and his contemporaries ever imagined, Similarly, the 3.8 billion year old black siliceous mudstones discovered at Isua in Greenland contain such high concentrations of the light carbon isotope that it is thought that microbial life must have evolved by this time
Proteins are essential for functioning cells
Stanley Miller and Harold Urey at the University of Chicago in the early 1950’s were investigating the general idea that the atmospheric and physical conditions of early Earth enabled or even promoted the formation of amino acids
To do this, Miller placed a mixture of methane, ammonia, water and hydrogen into an apparatus that enabled these materials to circulate around a sealed loop of glass tubing
Miller reported that the water turned pink after one day, and red by the end of the week. The experiment had synthesised a number of amino acids, including glycine, alpha-alanine and beta-alanine
This work demonstrated that nearly all of the 20 naturally occurring amino acids form spontaneously if the right mixture of starting materials is present
At the beginning of the 20th century, abiotic synthesis of the essential organic components of life seemed to be highly improbable, but the work of Miller, Urey and other scientists suggests that, given time, it is possible
Miller and Urey’s work was the first to demonstrate that abiotic processes could generate the primary, essential components that are required for living organisms to evolve
Scientists have also looked at whether organic molecules on early Earth could have formed on carbonaceous chondrite meteorites and comets and survived long-distance journeys through space. This work has demonstrated that there is a more diverse range of abiotic organic compounds in carbonaceous chondrite meteors than was originally thought by mid-20th-century scientists
Many people hypothesise that organic life occurs everywhere in the universe and the original precursor materials or micro-organisms that led to life developing on Earth arrived from space on comets and meteorites rather than developing on Earth from abiotic precursors
In the 1960’s, scientists proposed that mid-ocean ridges composed of young, recently erupted basalts and near surface magma chambers would generate submarine hydrothermal flow systems
Hydrothermal vents are the underwater equivalent of terrestrial geothermal systems like New Zealand’s hot springs
They are often located on the deep sea floor, near active mid-ocean ridges and submarine volcanoes where jets of very hot seawater are ejected. In a manner similar to the heating of groundwater by cooling volcanic rocks and bodies of subsurface magma, the sea water ejected by submarine hydrothermal vents is heated by a convective system that circulates cold sea water through basalts that were erupted at the axis of the mid-ocean ridge
Some of the hot water precipitates instantly as the streaming jet of hot water cools down suddenly once it mixes with cold, deep oceanic sea water. This process usually builds vertical, chimney-like tubes composed of layers of sulphide or sulfate minerals and silica above the vent
The convective circulation of seawater that builds sulphide chimneys starts with cold seawater seeping into natural fractures in lower levels of the ridge. The water gradually flows through fractured hot rock above the ridge’s magma chamber where it heats up to 350-400ºC, and is returned into the ocean
As the seawater is heated in the layers of fractured seafloor basalt, it cools the young ocean-ridge basaltic rocks that form the ridge and reacts with the basalts. These reactions leach a variety of materials out of the basalt’s pyroxenes, feldspars, oxides and sulphide minerals
Chemosynthetic microbes generate carbohydrates that support a range of species that are adapted to survive the high concentrations in seawater. These specialised species include barnacles, bivalve molluscs, crustacea, crabs and gastropods
Some mussels, clamps, tubeworms and shrimp live in symbiotic relationships with chemosynthetic bacteria where they host colonies of the bacteria inside or on the surface of their bodies
Hydrothermal vent ecosystems are special because their food supply is not generated by photosynthesis. The energy that sustains these deep water communities is entirely sourced from Earth’s internal heat and their food webs support carnivores that feed on consumers supported by chemosynthetic primary producers
Serpentinisation is the reaction between seawater and rock where peridotites is converted into a material called serpentinite
This generates highly alkaline sea water that contains large amounts of hydrogen and sulphur, as well as dissolved silica, calcium, magnesium, nickel, iron and carbonate ions
Investigations have shown that the interaction of alkaline hydrothermal fluids with the Archean’s acidic seawater could have provided just the right conditions for iron-nickel-sulphide catalyst reactions to produce organic molecules. These molecules could have included sugars, self-replicating molecules and possibly membrane-enclosed cells in the vent chimneys and towers, which are often porous and sponge-like rather than completely solid
These scientists hypothesise that alkaline hydrothermal vents could be where organic life arose on Earth during the early Archean
Stanley Miller and Harold Urey replicated Hadean conditions to observe how life was formed
Accepted that water arrived from outgassing
Gases such as Methane (CH4), Hydrogen (H2) and Ammonia (NH3) were thought to be abundant on Earth
Early Earth would’ve had many energy sources such as the Sun, Geothermal Heat and Lightning
Through a series of reactions, complex molecules such as Amino acids were produced in the oceans
Communities Around Black Smokers:
Abiogenesis: Life could have formed from non-life through abiogenesis
Cells require organic molecules for structure and function
Simple chemicals in the environment could react to form those organic molecules
Life may have started in the oceans based on building block chemicals such as amino acids that formed from spontaneous reactions triggered by lightning strikes between the gases in the early atmosphere (primordial soup)
People assumed that if they left food out, maggots and rats would suddenly appear, called spontaneous generation
“Life only comes from life.”
Simple molecules could evolve into living cells
Early ocean was was a rich collection of complex molecules that were produced by chemical reactions (primordial soup)
Black smokers (hydrothermal vents) are an alternative site for the possible origin of organic molecules
Black smokers were only discovered in the 1970’s during deep sea research dives in the Pacific Ocean
They have since been found in volcanically active areas of the sea floor worldwide
Organic molecules could form by reactions between simple molecules such as carbon dioxide and metal sulphides, in the chemical rich and high temperature environment
The base of the food web around black smokers are chemosynthetic bacteria that use sulphur compounds and dissolved carbon dioxide to produce glucose without light (it’s too deep and dark down there for photosynthesis)
These extremophile bacteria are considered evidence that the first cells, archaea, may have been able to survive in these environments
Communities around black smokers, which are found deep in the ocean, don’t prove the origin of organic molecules, but they show us that life can exist in extreme conditions and make organic compounds using chemicals from the vents
This helps us understand how life might have started on Earth in harsh environments
Meteorites/Panspermia:
Panspermia: Life came from meteorites and asteroids
Abiogenesis: Life came from non-life
Meteorites are the solar system’s leftovers. They are material that did not get incorporated into forming planets or the debris left after a space collision. These leftovers can tell us a lot about Earth’s formation
Meteoroids = Rocks in space
Meteors = Space rocks falling through the atmosphere (‘shooting stars’)
Meteorites - Space rocks that have landed on Earth’s surface
Meteorites hit the Earth with great force and large ones leave impressive craters that are much larger than the rock itself
Rare carbonaceous chondrite meteorites contain organic molecules
These organic molecules were delivered to Earth from space - a key idea in panspermia
Murchison meteorite landed in Victoria, 1969. Contains carbon rich chemicals such as amino acids (needed for proteins), purines and pyrimidines (needed for DNA)
Earth was heavily bombarded by meteorites 4.1 - 3.8 billion years ago that could have delivered building block chemicals needed for cells to develop
Abiogenesis:
Organic Molecules from Earth
Chemical reactions on early Earth
Simple chemicals available
Energy sources
Modelled by Urey and Miller
Alternative site could be black smokers
Vs
Panspermia:
Organic molecules arrive from space
Carbon rich meteorites (e.g. Murchison)
Contained organic molecules (e.g. Amino Acids)
Investigate the evidence for the development of photosynthetic life, including cyanobacteria and stromatolites
Organisms living on early Earth obtained nutrients by chemosynthetic processes such as those found around hydrothermal vents. It was not until organisms could use the energy of sunlight to photosynthesise and release free oxygen molecules into the atmosphere that life on Earth started to evolve into the modern day
Stromatolites that exist now are bacterial colonies
Stromatolites survive in their challenging environmental conditions because, rather than being single organisms, they are self-contained microbial ecosystems consisting of prokaryotic, photosynthetic producers and consumers
Slimy material is generated from consumer microbes, including species of anaerobic bacteria. This slime accumulates sediment very efficiently and the stromatolite grows upwards towards the light as layer after layer of sediment is trapped. This process generates the distinctive internal structure and layer geometry of domes, cones and wavy layers that enable geologists and palaeontologists to identify ancient Proterozoic and Archean stromatolites
Most of the stromatolites that have been found are extinct forms preserved as fossils in sedimentary rocks. Stromatolites are relatively commonly identified in Proterozoic rocks and late Archean rocks that are 600-2500 million years old, but some colonial organic structures are 3500 million years old
The oldest stromatolites of known organic origin are the abundant domical, conical and wavy stromatolites found in Strelley Pool cherts in WA. These stromatolites are about 3.4 billion years old. Their internal layering, particularly the conical forms, are generally accepted to be a result of the stromatolite accreting successive layers by growing towards the light
Cyanobacteria are a group of single-celled, photosynthetic prokaryotic microbes that occur in most Earth environments that receive sunlight. All modern cyanobacteria use chlorophyll to produce oxygen by photosynthesis
Cyanobacteria are probably one of the most important groups of organisms that has ever inhabited Earth. They are considered to be largely responsible for changing the composition of the atmosphere
During most of the Precambrian time, the atmosphere was dominated by CO2, nitrogen and water
Some marine biologists consider cyanobacteria to be very important components of modern day ocean plankton, which makes them a significant group of organisms both environmentally and ecologically
Some cyanobacteria form microbial mats like those that build the Shark Bay stromatolites. It is possible that they are responsible for building many, perhaps nearly all, of the stromatolites that have been identified in the geological record
Photosynthesising microbes have been present on Earth for most of geological time. Evidence for this is the long and continuous presence of stromatolites in the geological record and the isotopic composition of preserved organic patter in stromatolitic deposits
Palaeontologists want to know how long cyanobacteria have been on Earth. However, there aren’t enough unmetamorphosed sediments of Archean age to determine this
The evidence currently available demonstrates that cyanobacteria have been part of Earth’s biota for at least 2600 million years and that their ancestors must have arisen by 2700 million years ago
A modern day stromatolite is a mound that is made up of bacterial colonies
Stromatolites are made up mostly of cyanobacteria though they also contain purple bacteria
Photosynthetic cyanobacteria, having made up stromatolites, has created the oldest fossils which are commonly identified in Proterozoic and late Archean rocks
Earth’s first stromatolites were found in Western Australia, they are about 3.4 billion years old
Cyanobacteria date back to the Precambrian Era on the fossil record
Stromatolites became widespread between the Precambrian and Proterozoic Eras, though they are far more common in the Precambrian
Stromatolites were most common during the Precambrian, specifically the Archaean, as they became less common throughout the Proterozoic
Photosynthesis:
Stromatolites can be found in Shark Bay. The fossils are found in the Pilbara Craton, Strelley Pool, with evidence of life including Stromatolite fossils
Photosynthesis is the process where organisms take carbon dioxide in the atmosphere, in the presence of water, and uses sunlight to produce sugars such as glucose and oxygens
Some organisms, such as the ancestor cyanobacteria, was able to produce oxygen about 2.5 - 3 billion years ago
The first organisms may have used photosynthesis to produce oxygen
As the cyanobacteria grew and spread, they were able to impact the atmosphere by making oxygen through photosynthesis
The Great Oxygenation Event (GOE) marked the beginning of the Proterozoic
Anything that lived before the GOE would have died as they found oxygen toxic, meanwhile, life that needed oxygen started to flourish
Layer on the top uses the atmosphere to grow, layer underneath uses the end result of the top layers photosynthesis to grow
The stromatolites and their distinct organic layering is a direct consequence of photosynthesis, proving evidence of this process
Anoxygenic Photosynthesis uses light and produces electrons by using hydrogen sulphide, sulphur, iron or nitrite. These follow a simple molecular pathway to produce an electron to then form a chemical food supply. No oxygen is produced, anoxic environment
Oxygenic photosynthesis uses light and water in a complex molecular pathway to produce an electron to form a chemical food supply. It is 10 times more productive than anoxygenic photosynthesis and oxygen is the byproduct. Oxic environment
The anoxygenic photosynthesis done by cyanobacteria might have led to the GOE
Oxygenic photosynthesis originated in an ancestor of Cyanobacteria when an anoxygenic photosystem gave rise to a water-splitting photosystem
Interactions between the spheres:
Oxygen-producing photosynthesis has dramatically changed the composition of the atmosphere and the conditions on the surface of Earth at least three times during the planet’s 4.56-billion-year-long geological history
They have done this by consuming CO2, and reducing the amount of CO2 in the atmosphere, as they released oxygen into the oceans and the atmosphere as a by-product of generating carbohydrate and organic carbon by photosynthesis.
The Great Oxygenation Event was when the abundance of photosynthetic organisms led to an increase of oxygen in Earth’s atmosphere
Atmospheric oxygen rose 10-20% of present-day levels
The second oxygenation event was at the end of the Protezoic
There is a third oxygenation event but it wasn’t formally named as the increase in Earth’s atmosphere wasn’t permanent
CO2 was removed from the atmosphere during these events, though it is unclear whether it was form the increase in oxygen, and impacted the behaviour of the biosphere and hydrosphere
The iron oxides that accumulated in the iron-rich layers are thought to have precipitated when sea water that was low in oxygen but high in dissolved reduced iron, upwelled from the deep ocean
This mixed with the shallow sea water that was rich in cyanobacteria and oxygen was produced
Oxygen started to accumulate in the atmosphere 2400 million years ago
Pyrite, uraninite and siderate is evidence for this as they stopped being deposited in terrestrial sandstones and conglomerates
It took about 500 million years for the photosynthetic cyanobacteria to generate enough oxygen to permanently oxygenate the oceans and then change the composition of the atmosphere
This is due to the enormous amount of dissolved iron oxide in the global ocean
It is known that this process took about 500 million years because most of Earth’s marine banded iron formations were deposited between 2500 million and 2000 million years ago
Because of this, the GOE is sometimes known as the Rusting of the Earth
Evaluate the evidence for the origin of multicellular life and resulting changes to ecosystems, for example, the Ediacaran and Cambrian fauna
Includes all of the animals and plants that live in the sea and on land - and fungi and algae (not bacteria, archaea and some protists because they are unicellular)
Determining the steps on the evolutionary pathway between single-celled and multicellular life has proven difficult
The ancient transition of organisms is hard to track due to most being microscopic or soft-tissues organisms that tend not to fossilise well - these occurred during the early and middle phanerozoic eon, while the oceans were sulfide rich - this limited the amount of oxygen available to help drive biochemistry
The increase of oxygen in the atmosphere significantly reduced the amount of methane, leading to the Earth cooling due to the drastic reduction of greenhouse gases
Multicellular organisms are composed of more than one cell, with groups of cells differentiating to take on specialised functions
Archaea, then cyanobacteria, then eukaryotic cells, then colonial organisms then multicellular organisms
Fossil site representing the Ediacaran Period were found in Ediacara Hills, Flinders Ranges, in South Australia
Changes to Ecosystems:
Follows a major ice age
Increases in oxygen levels, nutrient rich oceans
Soft sediment and microbial mats on sea floor
How were organisms interacting:
Stationary organisms anchored to sea floor, filter feeding nutrients from the water
Moving over the seafloor consuming microbial mats - primary consumers (herbivores)
Possible development of sexual reproduction, similar to how corals reproduce releasing reproductive cells into water
Ediacaran had soft bodied organisms, Cambrian had hard-shelled organisms
Evaluate the Evidence:
Soft-bodied organisms are less common in the fossil record as they are more easily destroyed before preservation
Mould fossils form an imprint of the organisms - evidence of body plan
Trace fossils show evidence of movement or feeding traces
Size groupings based on age - sexual reproduction
The Ediacaran biota may have undergone evolutionary radiation in a proposed event called the Avalon explosion, 575 million years ago
This was after the Earth had thawed from the Cryogenian periods’ extensive glaciation (snowball Earth)
Avalon Explosion:
In 1946, Regional Sprigg discovered jellyfish-like fossils in a stratum of rock more than 550 million years old
At that time, 540 million years old fossils had been found
Suggested that multicellular life was present and more diverse before the Cambrian Explosion
Charnia fossils had a clearly organised structure, marking it as a living thing, was found in rocks up to 600 million years old
There were thousands of Ediacaran Fossils found in Mistaken Point, Canada
Rangeomorphs were found, some of the earliest fossils from the Ediacaran Period. They were thin and shaped like the front of a plant but were not plants as they lived too deep in the ocean to be able to photosynthesise. Instead, they held fast to the sea-floor and probably absorbed nutrients in the water
Rangeomorphs grew by branching fractally, making they repeated a single basic pattern over and over again as they developed, each branch was just a smaller version of the whole
Some Precambrian organisms - like Tribrachidium - had three symmetrical sections that spiralled (trilateral symmetry), whereas today, organisms have bilateral symmetry
Unsure what they are related to in the modern day, could be related to stem animals, algae, fungi or protists, could also be an entire, separate kingdom of life that has gone extinct. They were likely the first metazoans - animals with differentiated body plans and specialised cells
Haootia was one of the first Cnidarians, a group that exists today (soft bodied organisms such as Jellyfish), also contains the first evidence for muscle like cells
Kimberella was a soft bodied, squishy mollusk like creature with a distinct pattern
Spriggina was a long, segmented creature which had a crescent-shaped head with evidence of rudimentary sensory and is thought to be ancestral to trilobites
About 635 million years ago, a long period of intense cold that had enveloped the world, known as the Cryogenic period, had ended
Glaciers retreated, huge amounts of nutrient-rich water from the melting ice flooded the oceans, causing mass blooms of oxygen-producing cyanobacteria
Video Info:
There needs to be a big enough organism so some cells can focus on different aspects (such as being a brain)
The jump from simple to complex life begins 2.4 billion years ago
Caused by an accidental mutation, photosynthesis
Cyanobacteria was the first to use photosynthesis
All they needed was sunlight for food
The waste product of photosynthesis, oxygen, was toxic to almost all other life at the time
Most life was killed off by oxygen, but the creatures that survived were able to evolve to use oxygen
Oxygen was able to give more energy to the life that could breathe it, allowing them to grow and evolve more rapidly
Some single-celled microorganisms teamed up in communities, causing them to eventually function as a single organism, leading to multicellular life
As the amount of oxygen in the air increased, it reacted with the atmosphere and removed greenhouses such as methane, causing a rapid cooling of the Earth’s climate (snowball earth, lasing for 200 million years)
Likely the first climate catastrophe after life evolved on earth
Eventually, volcanoes were able to release enough greenhouse gases for Earth to recover
Cambrian Fauna:
End of Ediacaran Period leading into the paleozoic era - Explosion
In the fossil record, we see a whole variety of different and unusual organisms
Sudden appearance of multiple animal phyla - mollusks, arthropods, etc, in the Cambrian rocks
Trilobites only lived in the Cambrian period, if their fossil is found, the rock dates back to the Cambrian
Key aspect - the development of Chitinous exoskeletons - hard parts
Other parts appear - mouth, eyes, stomachs - new to previous fossils
Unique organisms - anomalocaris, hallucigenia, trilobites
Environment (entirely marine, Benthic (on the seafloor) and Pelagic (jellyfish, could move))
Characterised by an increase in bilateral symmetry
Anomalocaris, Trilobites
Ediacaran Fauna:
Fossil evidence of Ediacara fauna has been found in volcanic ash deposits and sandstones at more than 30 sites around the world
Ediacaran animals are soft-bodied organisms ranging from a few millimetres to about a metre across
They present several levels of complexity ranging from jelly-like globules (Kimberella) to quilted feathered fronds (Charniodiscus), radial-ribbed discs (Tribichadium) to the worm or arthropod-like suspected predator (Spriggina)
These species lived in shallow marine environments and had complex structures that probably required sufficient oxygen to grow several different types of cell, which makes them metazoans
The Ediacaran lasted from 635 million years ago to the beginning of the Cambrian 541 million years ago, but most of the large Ediacaran animals appeared about 565 million years ago
Fossil impressions generated by Dickinsonia, a flat sheet-like creature up to 50cm long, suggest that it may have been capable of movement on the seabed. This would have required it to have an organised musculature and a simple nervous system to coordinate movement
Their extinction was probably due to competition from the emergence of invertebrate animals. These bilaterians had evolved more complex body plans, including eyes and mouths and armour that enabled them to hunt and consume Ediacarans
Cambrian Explosion:
The sudden appearance of animals and the apparently extremely rapid diversification event that established the animals kingdom is so significant that palaeontologists call it the Cambrian Explosion
About 650 million years ago, the supercontinent Pannotia began to break apart into two large continents, Laurasia and Gondwana. The temperature of the atmosphere significantly rose to an average of 22ºC
Ice sheets receded and ocean levels rose, which led to continental flooding and erosion and eventuated in a change in the chemistry of ocean water, including an increase in oxygen and vital nutrients such as phosphorus for ATP synthesis
An ozone layer formed, shielding earth from harmful ultraviolet rays
The most important factor was probably oxygenation of the oceans and atmosphere because reliable high concentrations of oxygen are required to support the metabolisms of active animals
Evidence from fossils also provides clues about the other main driver of the Cambrian explosion - competition between the evolving animals
Animals had also begun to live in burrows. A surge in the complexity and depths of burrowing in the earliest Cambrian sediments suggests some animals were probably hiding from predators, while others were probably ambushing unsuspecting victims from camouflage hides
Lightly armoured animals became more robustly armoured and bigger. Predators developed large jaws and stronger teeth. Many groups of animals developed sophisticated eyes
Invasion of Land:
It was a surprisingly short period between the Cambrian explosion and the colonisation of terrestrial environments by plants and animals
It may have only been 50 million years before some groups of the large, complex invertebrate animals that appeared 520 million years ago during the Cambrian explosion started to explore the land
The earliest accepted plant fossils are 470 million years old
They are embryophyte spores, which suggests that the first terrestrial plants depended on fungi to obtain their nutrients and that symbiotic relationships were a key aspect of the early terrestrial colonisers
The earliest accepted evidence for animals occupying terrestrial environments are the footprints and tracks of myriapods such as millipedes and eurypterids. These trace fossils become relatively common from about 450 million years ago and suggest that invertebrates colonised the land long before our vertebrate ancestors
Terrestrial Vertebrates:
The first fossil evidence for terrestrial vertebrates dates from about 365 million years ago. This is long after the first arthropods and plants colonised the land in the Silurian period
During this period, vertebrate fish diversified and became a dominant group of oceanic animals
The tetrapod (four footed) descendants of the lobe-fins emerged from rivers and lakes and moved onto the land during the middle and late Devonian
This terrestrial group of lobe-fins includes the amphibians, followed by the reptiles and then the birds and mammals and they have dominated the other terrestrial species ever since their expansion during the Carboniferous
It used to be thought that terrestrial vertebrates had evolved from a fish that had managed to survive on land after being stranded by a falling tide or a receding flood. But the transition from fish to the first tetrapods that walked on the land was much more gradual - it took 15 million years
Really, it was fish with legs rather than truly terrestrial animals. These species’ had scales and gills as well as a special air sac or second stomach
By 355 million years ago, at the end of the Devonian, fully terrestrial tetrapods were abundant, but these species all relied on water for reproduction. They had to lay their eggs in conditions where they wouldn’t dry out
The first tetrapods that were fully terrestrial appeared about 315 million years ago, during the late Carboniferous - they are called amniotes and they laid water-tight eggs