Part 2-Lesson 1

The Environment of the Phanerozoic eon

Part 2-Lesson 1

Conditions for life on EarthThe Earths atmosphere began to change around the beginning of the Proterozioc. (Mark this on your timelines) Cyanobacteria were becoming more abundant and adding more and more oxygen to the atmosphere through photosnythesis.

Conditions for life on EarthThe oxygen cyanobacteria produced reacted with iron dissolved in the oceans and was taken out of the atmosphere and ended up on the bottom of the ocean. (precipitation) This is how BIFs formed.

Conditions for life on EarthEventually the dissolved iron was used up and oxygen began to accumulate in the atmosphere. As the oxygen accumulated it began to form a very important layer. The ozone layer.

Conditions for life on EarthThe ozone layer is in the lower part of the stratosphere (10-50km above the surface). This layer blocks out 93-99% ultra violet radiation from the sun.

Conditions for life on EarthThe energy from the sun causes oxygen molecules to split. The single atoms of oxygen react with other oxygen molecules in a process called photolysis to produce Ozone O3.

Conditions for life on EarthThis reaction absorbs some of the UV radiation which would otherwise reach the Earths surface. How would this affect early life on Earth?

Conditions for life on EarthThe first organisms evolved in very hostile environments on Earth. Until the ozone layer, ultraviolet radiation from the sun would have made living on land impossible.

Conditions for life on EarthAs the oxygen concentrations increased, the ozone concentrations increased blocking more and more UV radiation. Organisms were now faced with new living conditions. They could now evolve to live on land and use this new gas (oxygen) to produce energy instead of chemosynthesis.

Conditions for life on Earth The ozone layer allowed organisms to evolve and live in terrestrial environments around 500 million years ago, this marks the start of the Phanerozoic Eon. (find this on your timeline)

HomeworkRead page 71 HSC Spotlight TextUpdate electronic vocab listComplete To Think About SET 2 pg 73 HSC Spotlight TextComplete DOT Points 2.1-2.4 pg 33-34

The Cambrian ExplosionPart 2-Lesson 2Dating the Cambrian ExplosionThe Cambrian period marks the start of the Phanerozoic Eon. This is when environmental conditions allowed new life to form and evolve and become more complex than it had in the Archaean and Proterozoic.

Dating the Cambrian ExplosionFossils around the world provide us with evidence about what these times were like and the organisms that lived during them.

Dating the Cambrian ExplosionFinding fossils can be easy but determining how old they are is not. Because fossils are found in sedimentary rocks we can get a relative age based on the fact that the layers below are older than those on top. This is called the law of superposition and is the basis of relative dating.

Dating the Cambrian ExplosionBy using the law of superposition and stratigraphic sequences, geologists can construct a geological time scale. This then allows scientists to break the large eons into smaller periods.

ActivityRead pages 11-12 A snapshot handout from the TAFE Environments Through Time ModuleUnderline key words and phrasesComplete the Dating Game Activity on page 13Dating the Cambrian ExplosionTo determine the exact age of a rock or fossil geologists use radiometric dating. This method measures the radioactive decay of isotopes. These isotopes come from the minerals that make up rocks. What does this mean for sedimentary rocks?

Dating the Cambrian ExplosionWe know that minerals form in igneous rocks, so the minerals and sediments that make up sedimentary rocks are likely to have formed millions of years before. Radiometric dating therefore cannot be used to date fossils or sedimentary rocks.

Dating the Cambrian ExplosionRelative dating can give us accurate information for determining the order in which life forms appeared on Earth. Once this order is established, then absolute dating of available igneous rocks provide an exact age for the fossils.HomeworkRead pages 75 HSC Spotlight TextUpdate Electronic Vocabulary Complete DOT Point 3.1

Radiometric DatingPart 2-Lesson 3Radiometric DatingRelative dating is based on position in a strategraphic column as well as a comparison of the lithology of the rocks and their fossils. To determine an absolute date of a rock or fossil, scientists use radiometric dating.Radiometric DatingRD is based on the radioactive decay of isotopes to measure age. Radioactive decay happens when the unstable parent isotope breaks down into a more stable daughter isotope. Radiation and DecayBelow is a list of other examples of atoms decaying to become more stable :Uranium-235 to lead-207Thorium-232 to lead 208Rubidium-87 to strontium-87Potassium-40 to argon-40Carbon-14 to nitrogen-14

In these examples, the unstable atoms on the left are called the parent material and the more stable atoms on the right are called the daughter product or remnant isotope. Determining ages from half-livesThe time taken for each of the parent atoms to decay to their daughter products varies from millions of years to minutes.

KEY CONCEPT:The time taken for half of the parent material to decay into its daughter product is know as the Half Life of that parent material. Determining ages from half-livesThe half-life for each radioactive element remains the constant. For example it takes 5370 years for half a sample of carbon-14 to decay to nitrogen-14

Determining ages from half-livesIt will take another 5370 years for half the remaining carbon-14 to decay into nitrogen-14. This is known as the second half-life.

This means it has taken 10740 years for of the original carbon-14 to decay. (two half-lives)

Determining ages from half-livesThis diagram shows the relationship between half-life and amount of radioactive parent material

Dating RocksKEY CONCEPT:Using the half-lives from radioactive elements to calculate age is known as radiometric dating.

Dating rocks using radioactive elements can indicate a particular time of formation.

Dating RocksWhen minerals in igneous rocks are first formed after cooling, the amount of each radioactive mineral present at this time is 100%

Immediately after formation these unstable radioactive minerals begin to break down

Dating RocksThink about this:

If you were given two samples of rock, one sample containing 95% of the original radioactive parent element and the other sample had 30% of the same original radioactive parent element, which of these rocks do you think would be oldest? Why?Dating the oldest rocks in AustraliaRadiometric dating methods have enabled scientists to determine the time of mineral formation of some of the oldest rocks on Earth.

The oldest minerals ever dated in Australia are zircon crystals found in quartzite rock at Mt. Narryer in the Murchison region of Western Australia. These minerals are dated at 4.15byoDating the oldest rocks in Australia

Methods Used to Date Precambrian RocksThe correct types of radiometric isotopes have to be used to date Precambrian rocks. Precambrian time starts about 4.7 billion years ago when the Earths crust began to form to the start of the Cambrian about 542 million years ago.

Methods Used to Date Precambrian RocksBecause the Precambrian dates back to far, uranium/lead isotopes are used to date rocks within this period of time. Naturally occurring uranium contains two radioactive isotopes both with very long half-lives.

Uranium usually occurs as trace elements in minerals such as zircon.

HomeworkRead pages 76-77 HSC Spotlight TextUpdate electronic vocabularyComplete Activity 2.7 pg 77 HSC Spotlight TextComplete DOT Point 3.3

The Cambrian EventPart 2-Lesson 4The Cambrian EventThe appearance of numerous and varied fossils separates the Precambrian from Cambrian. We know that life existed well before the Cambrian but was not preserved as fossils. During the Cambrian, existing life evolved very rapidly in the oxygen rich environment which allowed more complex evolution to occur.

The Cambrian EventFor example, more complex organisms began reproducing sexually versus asexually which had happened up until this period in time. Sexual reproduction allows individuals to pass on genetic material to their offspring. This mixing of genetic material means that the offspring were not identical to their parents.

The Cambrian EventGenetic variations happen because of mutations. If such mutation is beneficial to the organism, it can then be passed through the population by sexual reproduction.

The Cambrian EventIf a new population is separated from the original population by geographical isolation or other isolating mechanism, over many generations they can evolve into a new species.

The Cambrian EventOrganisms with hard parts and shells did not exist before the Cambrian period (Precambrian). A well known fossil site for these soft bodied organisms is in Ediacara, South Australia. This site is very important geologically because fossils of these organisms are very rare.

SprigginaDickinsoniaThe Cambrian EventThe first hard-bodied organisms had an advantage over their soft bodied competitors. They could use this to hide from predators and for protection against environmental elements.

Do you think it allowed them to colonise new environments?

The Cambrian EventThese organisms with hard parts have a much greater chance of being preserved as a fossil than those that were soft. The most famous fossil site for Cambrian organisms is the Burgess Shale in British Colombia.

The Cambrian EventMan of the late Cambrian organisms such as brachiopods and trilobites had very specialised armour to protect them from predators. These organisms also evolved long spines which allowed them to burry themselves in the sand to prevent being washed around by currents.

The Cambrian EventThese hard bodied organisms became more abundant and still exist today. Examples include molluscs and crustaceans.

ActivityComplete activity 2.8 and 2.9 pg 79 HSC Spotlight Text in class.HomeworkRead pages 78 HSC Spotlight TextUpdate electronic vocabulary Complete DOT Points 3.4, 3.5, 3.7Science SkillsPart 2-Lesson 5Science Skills ActivityRead and discuss the bottom of page 79

Complete To Think About pg 80-81

Complete any outstanding homeworkEvolutionPart 2-Lesson 6The theory of evolutionEvolution is organisms changing over time. Fossils provide evidence of these changes. Charles Darwin (1809-1882) proposed a theory to explain why evolution occurs.

The theory of evolutionDarwin believed that evolution occurred because of natural selection. Certain traits passed on from generation to generation make certain organisms more likely to survive and reproduce. Those better suited to survive will do just that, and those who arent, die and do not pass on their genetics to others.

The theory of evolutionAn observable example of such evolution occurred in the United Kingdom during the industrial revolution. The peppered moth can exist in light and dark colours. During the industrial revolution, trees and forests were covered in soot which gave the darker moth an advantage because it was better able to hide from predators. In just a few generations the majority of the moths were dark.

The theory of evolutionThe four points of Darwins theory of evolution are:Genetic variation can occur in any population and individuals within a species are not identical.Offspring do not always survive to adults. As they die, the characteristics they posses are not passed on.The offspring that do survive and reproduce pass on favourable genetic variations as they are well adapted to the environment.These favourable genetic variations are passed on to offspring and become more common in the population.The theory of evolutionScientists studying organisms today can see similarities between certain species and are able to trace these characteristics to distant relatives.

The theory of evolutionToday scientists have a number of lines of evidence to support the theory of evolution. This includes:AnatomyPhysiologyBiogeographyEmbryonic developmentBiochemistryActivityRead and discuss pages 83-88 HSC Spotlight TextHomeworkUpdate electronic vocabularyComplete To Think About page 89-91 HSC Spotlight Text