Life On Earth

Part 2

The fossil record provides information about the subsequent evolution of living things

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identify the major stages in the evolution of living things, including the formation of:

- organic molecules- membranes- procaryotic heterotrophic cells- procaryotic autotrophic cells- eucaryotic cells- colonial organisms- multicellular organisms

Organic molecules

- The first stage of the evolution of life was the creation of organic

molecules, either through synthesis from inorganic molecules, or from

outer space

- These organic molecules began to clump together in a “soup”

Membranes

- A membrane had to be developed to protect the internal environment of

the large organic molecule

- The internal environment, i.e. the contents began to evolve into nucleic

acids and the primitive cell could now replicate

- RNA was thought to be the first genetic material

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Procaryotic heterotrophic cells

- The first and simplest types of cells, like bacteria

- No membrane-bound nucleus or membrane-bound organelles

- These consumed other organic molecules to provide energy (heterotrophic)

Procaryotic autotrophic cells

- Some of the heterotrophic procaryotic cells developed pigments

- These pigments allowed them to use the energy from the sun to create

food: Euglena

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Eucaryotic cells

- These cells had membrane-bound nuclei and organelles

- Examples include animals, fungi, plants

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Colonial organisms

- Colonial organisms are groups or colonies of similar cells, eg,

stromatolites

- All the cells in the colony have the same function; no differentiation

- They form when daughter cells from cell division become bound together

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Multicellular organism

- These are groups of cells, where some cells have differing functions from others

- Each cell has its own specialised function and all cells depend on each other

- The organism functions as a coordinated whole

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describe some of the palaeontological and geological evidence that suggests when life originated on Earth

- Fossils are found in sedimentary rocks, the oldest of which are 3800 million years old

- The earliest fossils are of 2 types:

Microfossils, these are similar to present day unicellular, anaerobic (does not need oxygen) procaryotic organismsStromatolites, layered clumps of photosynthetic cyanobacteria

- Modern stromatolites are found in Western Australia, Shark Bay

- Microfossil and stromatolite fossils are found in 3 places:

3400 – 3500 mya rocks from Warrawoona Group, Western Australia2800 – 3000 mya rocks from Fig Tree Group, South Africa2000 mya rocks from Gunflint Chert rocks, Lake Superior, North America

Stromatolite Fossil

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Stromatolites in Shark Bay WA today

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Geological evidence

- The first primitive cells were heterotrophic: they obtained energy by consuming other organic compounds.

- Then cells containing pigments developed. These cells were able to capture light energy from the Sun and use it to convert carbon dioxide to more complex organic compounds for their own use—in other words, they photosynthesised. As a by-product of this process, oxygen was produced.

- The evolution of photosynthesis had a dramatic effect on the environment of Earth. It led to an explosion in the abundance of photosynthetic organisms. These organisms used up carbon dioxide which gradually reduced the levels present in the atmosphere.

- The oxygen produced did not at first build up in the atmosphere but was taken up by rocks. These oxidised rocks can be seen today in the ancient banded iron and red bed rock formations.

- When all oxidisable surface rock had been saturated with oxygen, oxygen began to build up as a gas in the atmosphere.

- Ultraviolet radiation from the Sun reacted with some of the oxygen gas to form ozone.

- As the amount of oxygen in the atmosphere increased, more and more could be converted to ozone, until an ozone layer formed around the Earth, high in the atmosphere.

- This ozone layer acted as a shield, absorbing ultraviolet radiation so that less reached the surface of Earth.

- Banded iron formations (BIFs)BIF stands for banded iron formation. At the time of the formation of these deposits the atmosphere did not contain free oxygen and the sea contained large amounts of dissolved iron. When the first organisms began to photosynthesise they gave off oxygen as a waste product.This oxygen was immediately bonded with dissolved ferrous ions (iron (II) ions ) and formed insoluble ferric oxide (iron oxide). This is the same process that we call rusting. The sediments fell to the bottom and the banded iron formations were formed by alternative layers of iron rich material and silica-rich chert.

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explain why the change from an anoxic to an oxic atmosphere was significant in the evolution of living things

- The conditions needed for life as we know it are:Available liquid waterProtection from ultraviolet (UV) radiationFree oxygen in the atmosphere

- Water was already readily available; it was everywhere- When all oxidisable rock had been saturated with oxygen, due to the increase of

photosynthetic organisms, the atmosphere began to fill with oxygen- Firstly, the oxygen reacted with the UV radiation, and created ozone- When enough ozone was created, it formed an ozone layer- This protection from UV rays by the ozone layer enabled more sensitive

organisms to develop on Earth- Oxygen began to build up and the atmosphere was changed from anoxic (no

oxygen) to oxic (has oxygen)- The significance was that anaerobic organisms declined, and aerobic organisms

thrived- The number of photosynthetic organisms rose sharply- Today, anaerobic organisms only live in places of low oxygen concentration;

swamps and bogs, deep underground, etc.

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- The protection provided by the ozone layer enabled organisms to live on land

- Aerobic organisms took advantage of the abundant oxygen by evolving a system of producing energy that lies on the presence of oxygen: respiration

- The energy efficiently produced in respiration enabled organisms to increase in size and in their complexity

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process and analyse information to construct a timeline of the main events that occurred during the evolution of life on Earth

Timeline of evolution

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discuss the ways in which developments in scientific knowledge may conflict with the ideas about the origins of life developed by different cultures

- Science: Evolution; all organisms are constantly changing, not created, but evolved.

- Christians: They believe in Biblical creationism; all organisms created as they are by God, no change over time

- Chinese: Believe the first organism was P’an Ku, who evolved in a giant cosmic egg. All elements of the universe were in the egg, all mixed. In the egg, he separated the opposites, then 18,000 years later the egg hatched, and P’an Ku died from the effort of creation.

- Aboriginals: Dreamtime; great supernatural beings existed in the dreamtime and created the Earth and everything in it

- Greek: Aristotle’s ideas that the whole universe had a hierarchy and that it started from rocks, up through plants and animals, to humans, and finally to God.

- Romans: Lucretius, a Roman philosopher believed there was no God, because the universe was so imperfect. It was made of particles all squeezing together.

- As you can see, science contradicts with the belief of many people.

gather first-hand or secondary information to make observations of a range of plant and animal fossils

Brachiopod

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Fish

Glossopteris

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Ammonites

Trilobite

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identify data sources, gather, process, analyse and present information from secondary sources to evaluate the impact of increased understanding of the fossil record on the development of ideas about the history of life on Earth

- As new technology becomes available there is a development in the understanding of the origin of life and evolution of living things. As it became possible to identify chemicals and molecular structure this gave evidence to support the action of organic compounds.

- Other changes in technology have made it possible to accurate date fossils and piece together a more complete picture. These include: electron microscopes spacecraft deep sea exploration vessels carbon dating molecular clock.

Electron microscopes

- The invention of the electron microscope has meant that microfossils within rocks can now be seen. This has extended the evidence of live on Earth and also may identify fossils from other planets.

Spacecraft

- Sending spacecraft to other planets makes it possible to examine conditions on these planets to compare to the conditions on early Earth.

Deep sea exploration vessels

- The presence of deep-sea vents was unknown until vessels were developed that could travel to the depths of the oceans. Once this occurred it was discovered that there were many unknown organisms living on the vents and using the energy from the vents as a basis for an ecosystem.

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Radioactive carbon dating

- When rocks are dated, their ages are referred to as either numerical or relative. Numerical age refers to a specific number of years, such as 200 million years ago (mya). Numerical age is sometimes called absolute age. Relative age provides a comparison between rocks, in other words it states whether one rock formation is older than another rock formation.

- The numerical age of a rock comes from the decay of radioactive isotopes, resulting in new (daughter) isotopes that are more stable. This process of change is called radioactive decay. The unstable radioactive element is also called the parent material, and the stable

- non-radioactive element produced from the decay of the parent material is known as the daughter product. Therefore uranium will decay to lead and potassium will decay to argon.

- Using the known behavior of many isotopes, the age of rock can be calculated using two methods:

- counting the number of new (daughter) isotopes

- using the known decay rate to calculate the length of time required to produce a specific number of new isotopes.

- Another way of determining the numerical age of rocks is by using carbon-14 (an isotope of the element carbon). It is a radioactive isotope that is continually produced in the atmosphere by the action of cosmic rays breaking down atmospheric nitrogen.

- The carbon combines with oxygen to form carbon monoxide or carbon dioxide. It is then absorbed by living things, so that all living things containing some carbon-14.

- While an organism is alive, the decaying radiocarbon is continually replaced. This means that the ratio of carbon-12 to carbon-14 remains constant. When the organism dies, the amount of carbon-14 decreases as it decays into nitrogen-14. The age of a sample is derived by comparing the proportions of carbon-12 to carbon-14.

- This method of dating has been adopted for determining the ages of samples from the last small fraction of geologic time as the amount remaining eventually is too small to determine.

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The molecular clock

- Another technological advance that has had a huge impact on scientific thinking is the molecular clock. Biologists use a number of molecules, such as DNA, to determine similarities and differences between organisms. The differences in the molecules can be said to measure how long the organisms have been evolving independently of each other. This method of comparison assumes however, that the rate of molecular change is constant and measurable.

- These claims are based on the assumption that the molecular clock, the rate of genetic change any given species undergoes, is relatively constant over time.

- Thus, a measurement of the genetic difference between any pair of species would reveal how long ago their ancestral lineages went their separate ways.

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