"Nothing in biology makes sense, except in light of evolution,” Theodosius Dobzhansky, Geneticist 1. Evolution EL:
Before we begin…. • Spend the next ten minutes writing down how you think evolution works – i.e. how would you explain it to a non-biologist? • Write your name on it and hand it in.
The evolution of evolution • Biological evolution describes the change over time in the genetic composition of a population of organisms • The evidence from the fossil record and genetics is overwhelming but the theoryis itself ever-evolving
Erasmus Darwin (1794) • All living organisms originate from common ancestor – gave no mechanism
Lamarck (1809) • Proposed a mechanism for how changes in a species could come about • Changes acquired in a lifetime could be passed on to their offspring, causing a gradual change in the species Read his views on snakes – pg 507
Darwin and Wallace (1859) Theory of evolution by natural selection (or survival of the fittest) • Organisms produce more offspring than can survive • Offspring show variation. Some variations more suited to environment than others • Those individuals with favourable characteristics more likely to survive and produce more offspring • Successive generations will become modified over time – eventually becoming a new species Page 508-514 http://www.youtube.com/watch?v=2d_Qqknr6SU
Mendel (1865) • Model of inheritance largely ignored for 30 years • In 1900 rediscovered and accepted
August Weismann (post 1896) • Neo-Darwinism combines Darwin’s theory of natural selection with population genetics and theory of inheritance
Demonstrating Natural Selection • Frog selection game
Activity and homework • Watch http://media.smh.com.au/news/science/the-origin-of-life-replay-3390621.html?rand=1340240614371 – take summary notes and submit first lesson next week • Ch 14 quick check qu 1-3 • Ch 14 ch review qu 14&15
Reflection • How does Darwin’s explanation (slide 6) compare with your pre-knowledge of evolution • What learning was new today? • What learning was revision or built on what I already know? • What did I find most challenging and what strategies will I put in place to help me? • What percentage of the class did I spend on task and how can I improve this if needed?
2. Evolution EL:
Geological Time • This time scale was developed in the nineteenth century when geologists observed that particular rocks were characterised by distinctive groups of fossils. • Names where based on areas where they were first recognised or on the distinctive nature of the rocks. • Geological time scale divided into Eras (e.g. Precambrian), Periods (e.g. Proterozoic) and Epochs. • The most widely used time intervals are Periods. • The time interval predating the appearance of the first abundant fossils is called the Precambrian.
Activity and homework • As a class we are going to complete activity 14.1, part A
Three Rock Types • Igneous Rocks- formed from molten rock. • Sedimentary Rocks – formed from the compaction of various sediments (sand, mud and clay) under heat and pressure. Sediments vary in size and are deposited under water or by wind. • Metamorphic Rocks- these are sedimentary or igneous rocks that have been changed due to the action of extreme heat and pressure.
A Dynamic Planet • Earth is constantly changing in: • the position of the continents • global temperature and climate • sea levels • the number of species that make up the biosphere. • These changes are both: • natural (e.g. earthquakes, tsunami and volcanic activity) and • human induced (e.g. climate change).
Plate Tectonics • The Earth’s crust is fragmented into a number of plates that move on the fluid mantel that overlies the Earth’s core. • Land masses – the continents are carried on those plates. • Over time these plates move, driven by convection currents generated by the heat in the Earth’s core. • The movement is about as fast as your fingernails grow! http://www.youtube.com/watch?v=QDqskltCixA
Plates side by side • The San Adreas Fault in California USA, is an example of a transform plate boundary. • Here the American Plate and the Pacific Plate are sliding past one another. • At times the plates get stuck. This causes pressure to build up. • When the pressure is finally released earthquakes result.
When Plates Collide • When two plates converge, one plate is forced under the other plate in what is called a subduction zone. • The Nazca Plate is being forced under the South American Plate. The Andes is the result of this action. Many peaks in the Andes are volcanically active.
When Plates Move Apart • New crust forms from molten material that rises up when plates move apart. • Divergent plate boundaries are responsible for rift valleys and new ocean floors and mid ocean islands. • The great rift valley of East Africa is a young divergent plate boundary.
The African plate will continue to move northwards, slowly closing the Mediterranean sea and driving up mountain ranges in Southern Europe. • Australia will continue to move north (about 5cm/year) colliding with SE Asia. • America will continue to move away from Europe and Africa as the Atlantic Ocean widens.
Biogeography • Biogeography is the study of the geographical distribution of plants and animal species based upon their evolution and dispersal. • The world is divided into biogeographical regions that roughly correspond to the continents. • Provides evidence for plate techtonics and continental drift.
Take a walk through Geological Time The Present 200 Mya 542 Mya
The Dating Game • How do we determine the ages of rocks and fossils? • Relative time • Stratigraphic correlation • Absolute time
Relative Time The Principal of Rock Succession “in an undisturbed sequence of layered rocks, the oldest layers lie at the bottom and the successively high layers are progressively younger”. This principal can be applied to any fossils that are contained in the layers. A rock succession
Stratigraphic Correlation – Using Index Fossils • Index fossils are geologically short lived species with a limited occurrence so that they are restricted to a particular sedimentary strata. • The presence of such fossils in a particular strata, even in widely separated regions, are used to infer the strata as being of the same age. Location 1 Location 2
Stratigraphic Correlation – Using Index Fossils Look at page 521 Figure 14.16. Which is the oldest of these strata? Why? Which is the youngest? Why?
Absolute Time • Reliable technique that assigns a numerical date to the sample. • Techniques include radiometric dating, electron spin resonance and luminescence • Radiometric dating is the most common technique.
Radiometric dating • The method is based upon the radioactive decay of unstable atoms to a more stable atom. • In a certain period of time, called the half life, half of the unstable atoms will have decayed into the more stable atom. • By measuring the ratio of unstable to stable decay products, the time that has elapsed since the decay began can be calculated. This is equivalent to the age of the rock.
Radiometric dating • Carbon 14 – (HL: 5,730 years) used to date objects younger than 70,000 years. http://www.youtube.com/watch?v=udkQwW6aLik&feature=related
Radiometric dating Carbon dating is not useful for organic material older than about 60 000 years ago. However, another technique of dating, known as electron-spin resonance (ESR), is useful for ages from about 50 000 years ago to 500 000 years old.
Activity • Chapter 14 quick check qu 4-8 • Ch 14 ch review qu 8, 9, 11
Reflection Look at figure 15.27 on page 584. Which dating technique would you use on Homo fossils? How is this different to dating Australopithecus fossils? • What learning was new today? • What learning was revision or built on what I already know? • What did I find most challenging and what strategies will I put in place to help me? • What percentage of the class did I spend on task and how can I improve this if needed?
3. Evolution EL:
Evidence for Evolution WebQuest • http://www.pbs.org/wgbh/evolution/educators/lessons/lesson3/act2.html
The Fossil Record • Fossils are the remains or traces of pre-existing life forms preserved in rocks. • Usually only the hard parts (shells or skeletons) are preserved. • Trace fossils are the signs or remains of an organism’s activities such as footprints, bite marks, burrows and coprolites. • Fossil remains have been found across 3,500 million years of Earth’s history, but there are gaps in the fossil record. • The fossil record is evidence of biological evolution.
Fossilisation • Fossils are formed when an organism dies and the body or part of the body is preserved in some way. • Usually, the body needs to be rapidly buried in sediments. • Rapid burial prevents destruction of the organism by predators, bacterial or weathering.
Fossilisation • Burial can occur: • on the bottom of the sea, rivers, and lakes • on land by blowing sand or volcanic ash, • by the entrapment of the organism in some sticky substance such as tar or tree sap (amber).
Fossilisation • After burial, fossils may undergo a variety of physical and/or chemical changes depending upon the environment of the enclosing sediment. • As successive layers of sediment build up, the fossil may be flattened and distorted as the sediment is hardened into rock by heat and pressure.
Fossilisation • Chemical changes occur as the original hard parts are progressively replaced by other minerals such as quartz or opal in a process called petrification. • Or the hard parts may be dissolved away completely, so that an impression or a natural mould of them remains in the rock.
Types of Fossils • When an organism decays it leaves a cavity known as a mould. • When the cavity is later filled by other material a cast is formed. Impression of the hard exoskeleton of a trilobite that lived during the Cambrian Period, about 500 mya.
Types of Fossils • Thin tissue is sometimes preserved as a carbon film or impression in a rock.
Types of Fossils • Ammonoid fossil shell from the Jurassic Period (England). The shell has been replaced with iron sulphide (pyrite). • Cockle shell replaced with opal from Cretaceous Period, Cooper Pedy, SA.
Types of Fossils • Petrified tree trunk in Arizona. • Plant material is replaced with mineral salts that petrified the tissue – the tree literally turns to stone.
Types of Fossils • A human cast formed in volcanic ash at Pompeii.
Types of Fossils Fossils are not only found in rock! • Animals have been trapped in natural tar pits. • Mammoths and other animals have been trapped in ice or frozen underground, so that flesh and stomach contents have been preserved. • Extinct insects have been found in amber (tree sap). Insect preserved in amber from the Baltic Region dated from the Oligocene Period
What the fossil record shows…. http://faculty.icc.edu/easc111lab/labs/labf/geologicalscaleclock/geologicscale_clock.html
Making Connections: Transitional Fossils • Fossils that are intermediate between the ancestral form and a new species. • If birds have evolved from reptiles the fossil record could show a fossil that has characteristics of both reptiles and birds. e.g. Archaeopteryx
First Life Forms • Prokaryotic life forms existed ~3.5 billion years ago. • Stromatolites are structures formed by primitive e photosynthetic cyanobacteria communities. • The structures are made up of many fine concentric layers of a hard limestone-like substance deposited by the bacteria. • The stromatolites are the most notable fossil of the Precambrian. Right: Shark Bay, Western Australia