FOSSILS Uncovering Clues to the Earth’s Past FOSSILS Fossils form when water replaces the cells of dead animals or plants with minerals. These minerals Uncovering Clues to then petrify into rock to form the fossils we see in museums. the Earth’s Past This process has many risks and only a small This guide provides you with a summary of proportion of living things end up becoming a the program and follow-up questions (along fossil. with their answers). A list of web links leads to further information on the topic. This is especially true for fossils from the earliest The question sheet is designed to be duplicated and longest geological period, the Precambrian. for class distribution. Fossils from this remote time before 1 billion years ago are rare because the so�-cells of the plants and Before Viewing: Give students an overview animals preserved poorly and many rocks that The present geological era is the Cenozoic and this of the program. Use the program summary may have contained good specimens have been period is the Age of the Mammals who were able to help provide this introduction. Select pre- either destroyed or transformed by the process of to survive the mass extinctions of the Mesozoic. viewing discussion questions and vocabulary Plate Tectonics. Of the Cenozoic’s 66 million years, humans have to provide a focus for students when they view dominated for less than the last three million the program. The following period, the Paleozoic, is far be�er years. How long our species remains dominant is represented in the fossil record. This is helped anyone’s guess, but the fossil record shows that A�er Viewing: Use a selection of the follow- due to invertebrate animals evolving hard outer even animals that survive for millions of years can up questions to help review the program shells at this time, along with the evolution of become extinct. and encourage students to research the topic vertebrate animals that le� more tangible remains further with the internet resources provided. in the fossil record. As animals le� the oceans for dry land during this period, fossils are also more Word Check: You can cut and paste text from the pdf ﬁle to widespread. compile your own set of questions or to enter Precambrian, Paleozoic, Mesozoic, Cenozoic, links into a web browser. Petriﬁcation, Invertebrate, Vertebrate. Following a mass extinction at the end of the Paleozoic around 240 million years ago, the reptiles of the Mesozoic came to dominate this next Pre-viewing Questions: geological period. As the Age of the Dinosaur this period is well known although many questions 1. What is a fossil and how do they form? remain; in particular why, around 66 million years ago, another mass extinction occurred which 2. What can fossils tell us about the history of the ASTARTE RESOURCES wiped out the larger species of reptiles. earth? www.astarte.com.au Fossils Chapter 2: The Paleozoic Era 27. Why are dinosaur fossils o�en hard to interpret? QUESTIONS 14. What does Paleozoic mean? 28. What is petriﬁcation? 15. What characterises the beginning of the Chapter 1: The Precambrian Era Paleozoic era? 29. What occurred at the end of the Mesozoic era? 1. What is the oldest geological period to 16. What characteristics did animals evolve at contain life on earth? the beginning of the Paleozoic era? 2. Around how many billions of years ago was 17. What was a common invertebrate animal Chapter 4: The Cenozoic Era the Precambrian era? from the Paleozoic era? 30. What is the current geological era called? 3. Describe what the earth was like during the 18. Describe the stages in which a trilobite Precambrian era? could become a fossil. 31. Which type of animal has dominated this era? 4. What sort of life existed during this era? 19. How is the trilobite an index fossil for the Paleozoic era? 32. What other things also increased in diversity 5. Which modern plants resemble plants from during the Cenozoic era? the Precambrian era? 20. What is a vertebrate animal? 33. How does amber help preserve a fossil 6. Why are fossils from the Precambrian era so 21. What major change to life on earth record? rare? happened during the Paleozoic era? 34. What are hominids? 7. How long a�er the appearance of single 22. What formed the layers of coal that are cell plants did the ﬁrst single cell animals mined today? appear? FURTHER INFORMATION 23. Why do we call some types of fuel such as 8. How long ago did the ﬁrst single cell coal ‘fossil fuels’? ABC Television’s excellent site on Australian fossils: animals appear on earth? h�p://www.abc.net.au/ozfossil/default.htm 24. What happened around 240 million years 9. What is an invertebrate? ago? Museum Victoria’s pages on Dinosaurs & Fossils: h�p://www.museum.vic.gov.au/dinosaurs/ 10. What is a palaeontologist? 11. What are some examples of invertebrates Australia’s famous Riversleigh fossil ﬁeld: Chapter 3: The Mesozoic Era that existed in the Precambrian era? h�p://www.australianwildlife.com.au/features/ 25. How long did the Mesozoic era last? riversleigh.htm 12. Why are invertebrate fossils hard to ﬁnd? 26. The Mesozoic is o�en referred to as the Age Further Australian fossil links: 13. What happened around 570 million years ago? of Reptiles. Why? h�p://www.amonline.net.au/explore/fossils.htm Fossils: ANSWERS 11. Jellyﬁsh and marine worms are some 23. In the case of coal it is literally the fossilised examples of invertebrates from the remains of ancient swamps. precambrian era. 24. Around 240 million years ago there was a Chapter 1: The Precambrian Era 12. Invertebrate fossils are hard to ﬁnd because mass extinction of many species of plants 1. The Precambrian era is the ﬁrst geological animals without hard parts preserve badly. and animals. period to contain life. 13. Around 570 million years ago the ﬁrst Chapter 3: The Mesozoic Era 2. The Precambrian spans the history of the complex animals appeared. 25. The Mesozoic era lasted 174 million years. earth from around 4 billion years ago to Chapter 2: The Paleozoic Era around 1 billion years ago. 26. The Mesozoic is referred to as the Age of (billion = 1000 million years) 14. Paleozoic means ‘ancient life’. Reptiles because of the dominance of reptiles 15. The beginning of the Paleozoic era (around at this time. 3. The Precambrian era occurs a�er the earth’s crust had cooled and the ﬁrst oceans had 570 million years ago) is characterised by 27. Remains of dinosaurs are o�en sca�ered formed. Life in these oceans begins during the appearance of complex animals. or jumbled together into huge communal this time. 16. Animals at this time evolved hard outer burials (by rivers etc.). 4. Life during the Precambrian era consisted of shells to protect their so� inner tissues. 28. Petriﬁcation is when water replaces the cells single cell plants. 17. The trilobite was a common animal from the of bone with minerals that then turn to rock. 5. Algae that today grows in shallow warm Paleozoic era. 29. A mass extinction of marine animals and seas resembles the single cell plants found 18. A�er the so� inner tissues have decayed, dinosaurs took place. in Precambrian fossils. the hard outer shell might be covered with Chapter 4: The Cenozoic Era 6. Fossils from the Precambrian era are rare layers of mud. With time, these layers of because the earth’s rocks are constantly mud become sedimentary rocks and the 30. The current geological era is called the being recyled by Plate Tectonics and many hard outer shell of the trilobite is replaced Cenozoic era. old rocks containing precambrian fossils with other minerals to form a cast. 31. Mammals have dominated the Cenozoic era. have been destroyed or transformed. 19. Because the trilobite was so numerous and 32. Flowering plants, insects and ﬁsh also 7. Single cell animals appeared around 2 because it evolved into diﬀerent shapes increased in diversity during the Cenozoic billion years a�er the appearance of single throughout the Paleozoic, fossils of trilobites era. cell plants. can be used to date rock strata. 33. Insects caught in tree sap that becomes 8. Single cell animals appear around 1.5 billion 20. A vertebrate animal has a backbone. amber are well preserved. years ago. 21. Some Paleozoic animals evolved lungs 34. Hominids are species closely related to our 9. An invertebrate is an animal without a (amphibians) and were able to leave the own. backbone. ocean and colonise the land. 10. A palaeontologist is a person who studies 22. Layers of coal are the remains of Paleozoic fossils. swamps. RADIOACTIVE DATING One of the great by-products of research into RADIOACTIVE radioactivity was the discovery that radioactive atoms decay, or lose electrons, at a set rate. These various clocks, once discovered, revolutionised DATING our ability to date the past. This guide provides you with a summary of For the more recent past the best radioactive clock the program and follow-up questions (along is the Carbon 14 atom. This naturally occurring with their answers). A list of web links leads to isotope of the more common Carbon 12 atom is further information on the topic. absorbed by all living things. At death the unstable Carbon 14 atom begins to decay, while the more The question sheet is designed to be duplicated stable Carbon 12 atom remains unchanged. As for class distribution. we now know that the half-life of Carbon 14 is 5730 years, we can easily measure how long ago Before Viewing: Give students an overview something died. of the program. Use the program summary to help provide this introduction. Select pre- However for dates earlier than 40,000 years, the viewing discussion questions and vocabulary Carbon 14 method of dating is unreliable because to provide a focus for students when they view the remaining amount of Carbon 14 is too small to the program. be accurately measured. A�er Viewing: Use a selection of the follow- For dates older than 40,000 years another atomic up questions to help review the program Word Check: clock is chosen; the Potassium 40 atom. Rather and encourage students to research the topic Isotope, Carbon, Radioactive Decay, than a half-life of a mere 5700 years, the half-life further with the internet resources provided. Photosynthesis, Half-Life, Potassium. of Potassium 40 is one billion, 300 million years. You can cut and paste text from the pdf ﬁle to As we can measure the rate at which Potassium 40 compile your own set of questions or to enter atoms slowly transform into Argon 40, we can date Pre-viewing Questions: links into a web browser. rocks whose age stretches back to the formation of 1. Why have people always yearned to know the earth. how old something is? With both Carbon 14 and Potassium-Argon 2. How did the discovery of a scientiﬁc dating dating, our own human history can be mapped, method aﬀect many professions ranging from along with the much older history of our earth. geologists to archaeologists? ASTARTE RESOURCES www.astarte.com.au Radioactive Dating 13. Why can only organic materials be used for radioactive dating? QUESTIONS 14. At what point does the amount of Carbon 14 become too small to measure accurately? Chapter 1: Carbon 14 Dating Chapter 2: Potassium-Argon Dating 1. Why is Carbon used in radioactive dating? 15. How does the atom Potassium 40 decay? 2. What is the most abundant form of Carbon? 16. What is the half-life of Potassium 40? 3. What isotope of Carbon is rare and unstable? 17. What sort of rocks commonly contain 4. How is Carbon 14 formed? Potassium 40? 5. What happens to a Carbon 14 atom when it 18. How does Potassium-Argon dating work? decays? 19. How is a Mass Spectrometer used in 6. How do animals come to contain both Potassium-Argon dating? isotopes of Carbon? 20. How can Potassium-Argon dating be used 7. What is the ration of Carbon 14 to Carbon 12 to date organic materials? in the atmosphere? 21. How old are the rocks of the moon as 8. In relation to absorbing Carbon atoms, what established by radioactive dating? happens when an animal or plant dies? FURTHER INFORMATION 9. With the death of an animal or plant, what happens to the ratio of Carbon 12 to An on-line calculator to demonstrate how Carbon A look at dating techniques in general: Carbon 14? 14 dating works: h�p://www.mnsu.edu/emuseum/archaeology/ h�p://www.earthsci.org/freewar/C14/Carbon%20 dating/ 10. In relation to the Carbon 14 that was present 14%20Dating%20Calculator.htm when an animal or plant dies, what happens Dating the earth: a�er 5,700 years? For the chemistry behind Carbon 14 dating (along h�p://www.amonline.net.au/geoscience/earth/ with a bit of history): dating.htm 11. Why is 5700 years called ‘the half life of h�p://www.ausetute.com.au/carbon14.html Carbon 14’? Good information of dating methods: A fact sheet on both Carbon 14 and Potassium- h�p://www.earthsci.org/geotime/radate/radate. 12. How then can the amount of Carbon 14 Argon dating from the Museum of Victoria: html present give an indication of age? h�p://www.museum.vic.gov.au/scidiscovery/ radioactivity/radio_dating.asp 7. For every Carbon 14 atom there are Chapter 2: Potassium-Argon Dating about a trillion Carbon 12 atoms. 15. The atom Potassium 40 decays into Calcium 8. When a plant or animal dies, it stops 40 and Argon 40. absorbing Carbon atoms. 16. The half-life of Potassium 40 is one billion, 9. As Carbon 14 is radioactive, it decays 300 million years. while the non-radioactive Carbon 12 17. Igneous rocks commonly contain Potassium remains constant. 40. Potassium-Argon dating is therefore 10. A�er 5700 years only half of the good for dating volcanoes. Carbon 14 that was present at death 18. When fresh lava is formed it has Potassium will be le�. 40 but no Argon 40. As the rock ages the 11. 5700 years is the half life of Carbon 14 level of Potassium 40 will fall and the rate of because every 5700 years the amount Argon 40 will rise at a known rate. Radioactive Dating: ANSWERS of Carbon 14 decreases by one half 19. A Mass Spectrometer is used to measure the (more accurately the half-life of amount of Argon 40 in a sample. Chapter 1: Carbon 14 Dating Carbon 14 is 5730 years). 20. Potassium-Argon dating can be used to date 1. Carbon is used in radioactive dating 12. As Carbon 14 decays at a known rate, the layers of rock that contain fossils of organic because it is abundant in the atmosphere amount of Carbon 14 compared to Carbon materials, thereby dating the fossils. and in all living (and dead) things. 12 will give a date when the plant or animal 21. Radioactive dating showed that the rocks of died. 2. Carbon 12 is the most common form of the moon are four and a half billion years Carbon in the atmosphere. 13. Only something that has been alive will old. As this is the same age as the earth’s have absorbed the necessary Carbon atoms. rocks, the earth and moon were either 3. The isotope of Carbon, Carbon 14, is rare and unstable. 14. At about 40,000 years ago the amount of created together, or the moon has been Carbon 14 becomes too small to measure formed from the earth (scientists believe 4. Carbon 14 is formed in the high atmosphere that the moon was torn oﬀ the earth in the accurately. when Nitrogen atoms are bombarded by early stages of its formation). solar radiation. 5. A Carbon 14 atom loses one electron and reverts into Nitrogen. 6. Plants absorb both isotopes during photosynthesis. When animals eat the plants they too absorb the isotopes of Carbon.