Fossils and time: Geological time 2.2.2
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(i) the use of radioactive decay rates of the radionuclides in minerals to give a numerical age of those minerals and rocks
(ii) the plotting and interpretation of half-life curves
|To include qualitative historical consideration of other numerical dating methods, the age of the Earth, appropriate minerals, and the dating of sedimentary and metamorphic rocks|
|(b)||the geochronological division of the geological column for the Phanerozoic into eras and systems using a biostratographic relative time sequence
To include basic identification of main invertebrate groups (trilobites, corals, brachiopods, bivalves, gastropods) and an outline of Palaeozoic, Mesozoic and Cenozoic faunas.
Learners are not required to memorise dates
Learners now move on from considering how fossils form and their application in interpreting palaeo-environment to consider the stratigraphic value of fossils and other dating evidence. Learners are introduced to the absolute dating technique of using the proportion of parent to daughter elements to calculate the age of a rock and learners will experience how to deal with this type of data. Other numerical dating methods are considered learners could think about why they may have been more convincing in the past. Learners then look at the structure of the geological column for the Phanerozoic and start to familiarise themselves with the order and divisions. Learners will need to relate eras and periods to the fossil evidence which is found for that time.
Common misconceptions or difficulties students may have:
The main challenge in this topic is likely to be dealing with half-life data, learners may have experience of this from GCSE but may still not be confident in what the graph represents. Various models of radioactive decay rates can be used to support this topic, for example rolling large numbers of dice to collect data, removing dice of a certain number (such as six) to represent a decay and recording after each roll how many dice remain. The results can be plotted a curve drawn and a half-life measured, different sets of students will get slightly different results because of the random nature or both dice rolling and radioactive decay.
Conceptual links to other areas of the specification – useful ways to approach this topic to set students up for topics later in the course:
Learners will develop ideas introduced in this unit when studying relative dating and biostratigraphy 4.2.1 and will further their work on radioactive decay in mid – ocean ridges 5.3.2.
The geological setting of the task is a cross section through an imaginary rock outcrop exposed in the side of a valley. The sequence includes igneous features and a sedimentary sequence. A number of fossils have been identified in the area. Students use the fossils present to discuss how fossils can be used in dating a sequence of rocks.
The resource sheet presents the geological section using the standard set of rock stipples and information for each fossil is summarised in the style of geology top trumps. Appropriate background is provided in the stem of each activity within the Checkpoint task and supplementary detail is given in the glossary. However, learners are not expected to have detailed knowledge of individual fossils or rocks (beyond the fact that some are sedimentary and other igneous).
A ‘Scientific Story’ that explores why if the problem was solved in the 1913 it took until the 1950s to convince most scientists. It also challenges the misconception of this as a battle between science and religion.
One of six geology ‘science stories’ that illustrate how scientific ideas developed over time and challenging the common misconceptions about how science and scientists work. Understanding Earth’s age: early efforts by naturalists and chronologists explores how ideas about the age of the Earth developed from 350BC up to James Hutton.
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