Uncovering Clues to the Pastindd

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Uncovering Clues to the Pastindd Powered By Docstoc
Uncovering Clues to the Earth’s Past
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
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
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
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:
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
     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
     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.

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
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
Radioactive Dating                                   13. Why can only organic materials be used for
                                                         radioactive dating?
                                                     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?
                                                     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?
                                                         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
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
     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.

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