Evidence of evolution from the past. Fossil records Biogeography Molecular Evidence Comparative anatomy

Best Conditions For Fossil Formation Reduce the effects of scavenging animals Reduce the effects of decomposers by having :Low oxygen levels Low temperatures Low moisture levels Reduce the action of wind and water

Example 1. Organism undergoes rapid burial by sediment. This action reduces the harmful effects of scavenging animals. It also reduces the activity of bacteria and protects the organism from erosion. Rapid burial by sediment is likely to occur in areas prone to flooding as well as many marine environments.

Why would organisms sinking to the bottom of a deep lake be a likely place for fossils? Low oxygen levels Low temperature Disturbance from wind and water minimised especially if coverage by sediments occurs

What about caves and glaciers?

Fossilisation During the process of fossilisation, in the original organic matter that makes up the organisms is chemically altered and turned into stone. Fossilised wood, for example, is much heavier than normal wood since it is composed of stone. However, the fossilised wood shows the structural details of the original wood from which it was derived.

Example Fish dies and sinks to the sea floor Water currents cover dead remains with sand before scavengers reach it. Depth of sea floor and burial sand reduce oxygen availability for decay, bacteria Weight of water and sediments apply pressure to dead remains, replacing hard tissue such as bones with minerals.

How old is the that fossil? We can determine this in a number of ways: Dating the absolute age of rock layers above and below the fossil to give the upper and lower range of its possible age Knowing the age of indicator fossils or deposits found with the fossil that have been date from similar sites elsewhere Dating the fossils absolute age

Relative age based on stratigraphy The principle of superposition states that older layers of rock are at the bottom of a sequence and the successively higher layers are progressively younger. Fossils aren’t found in igneous rock, but because we can date this rock with radiometric methods, we can determine the upper and lower ages.

Index fossils Index fossils are geologically short lived species with a limited occurrence so that they are restricted to a particular strata. The evidence of such fossils in a particular strata, even in widely separated regions, are used to infer the strata as being the same age.

Absolute Age Radiometric dating is used to determine the age of a rock. 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 or fossil. Carbon-14 (Half-life: 5730 years) is used to date objects younger than 50,00 years. Potassium – 40 (Half-life: 8,400 years) can be used to date object that are millions of years old

Geological time This time scale was developed in the nineteenth century when geologists observed that particular rocks where characterised by distinctive groups of fossils. Names were based on areas where they were first recognised or on the distinctive nature of the rocks. For convenience the geological time scale divided the Earths history into hierarchical intervals. The most widely used time intervals are Periods. The time interval predating the appearance of the first abundant fossils is called the Precambrian.

The Precambrian Era The oldest rock 4600 to 570 million years old Contains the fewest fossils The earliest fossils include stromatolites, which are found in the Pilbara of Western Australia and are dated at 3.3 to 3.5 billion years old and are evidence of the evolution of early prokaryotic organsims.

Stromatolites

The Palaeozoic Era Known as ancient time 570 to 230 million years old Marked by the appearance of a diversity of animals. Trilobites were the most common marine, multicellular animals of the early Cambrian era. The era ended with the formation of on singles super continent, called Pangaea. This caused reduced rainfall, extremes of temperature and the mass extinction of many species. Known as the Permian period.

Trilobites

The Mesozoic Era Known as ‘middle life’ 250 to 65 million years ago Includes Triassic, Jurassic and Cretaceous periods Often described as the age of reptiles At the end of the period there was a mass extinction. 70% of animal species were lost, including almost all large reptiles.

Dinosaurs

The Cenozoic Era Known as the beginning of modern life 65 million years ago to present Many more flowering plant and mammal fossils During the Cenozoic period, monkeys and apes also evolved, including in the last 3 million years our genus Homo.

Biogeographical Evidence Biogeography is the study of the distribution of organisms. Distribution patterns give clues to the evolutionary history of organisms and the Earth itself. Such studies reveal that many organisms, which appear to have a common evolutionary origin, are know found in widely separated parts of the world.

Observations Galaxiid fishes (freshwater) are present in Australia, New Zealand, New Caledonia, South America and South Africa. Different but related species of boabab trees are found in Africa, Madagascar and Western Australia. Various species of waratah are native to Australia, South America and New Guinea. Different species of flightless birds are native to Australia, New Guinea, New Zealand, South America and Africa.

Explanation The theory of continental drift explains this phenomenon: The continents are parts of crustal plates that make up the Earth’s rocky surface and these plates move in relation to one another. More than 135 million years ago, the landmasses of Australia, New Zealand, Antarctica, India, Africa, Madagascar and South America formed a single super continent called Gondwana. Movement of crustal plates, also called tectonic plates, has resulted in the break-up of this supercontinent. Over the last 65 million years, Australia separated from Antarctica The shapes of the continent also show contours that reflect how they may have once fitted together.

Gondwana- southern super continent

Conclusion Ancestral species of different organisms that already existed became isolated on their respective continents and continued to evolve (change) to their present forms.