Earth structure: The origin of the Earths structure 3.1.2
Navigate to resources by choosing units within one of the unit groups shown below.
Delivery guides are designed to represent a body of knowledge about teaching a particular topic and contain:
- Content: A clear outline of the content covered by the delivery guide;
- Thinking Conceptually: Expert guidance on the key concepts involved, common difficulties students may have, approaches to teaching that can help students understand these concepts and how this topic links conceptually to other areas of the subject;
- Thinking Contextually: A range of suggested teaching activities using a variety of themes so that different activities can be selected which best suit particular classes, learning styles or teaching approaches.
|(a)||the bulk composition of the Earth and how it is inferred from the composition of meteorites (chondrites) and the Sun
||To include the use of normalised diagrams displaying element concentrations (qualitative only).
||a qualitative explanation of the nebular hypothesis for the formation of the solar system and the Earth
||To include the evidence for protoplanetary discs, and impact craters on the Earth and other bodies in the solar system.
||the transfer of geothermal energy from:
(i) heat of formation by the Earth
(ii) radioactive decay within the Earth
||the Goldschmidt classification of elements into four groups and a qualitative understanding of the preferred formation of states of substances (oxides and sulfides)
||Lithophile, siderophile, chalcophile, atmophile.
Learners are not required to study enthalpy changes or free energy.
||the differentiation of the Earth into layers of distinct composition and density by the partitioning of each of the Goldschmit groups between the crust, mantle, core, and atmosphere and hydrosphere
||To include: evidence for meteorites as a possible source of rare siderophiles in the crust, crustal abundance and concentration factor.
the geochemical layered structure of the Earth as defined by the mineral composition of the layers and how the composition of these layers is inferred from direct evidence.
|To include evidence from rocks and seismology: deep mines and boreholes, ophiolites, kimberlite pipes, mantle xenoliths, and the Lehmann, Gutenberg and Moho discontinuities.|
This topic equips learners with the tools of geochemistry to support them when learning about the composition of the Earth and many other applications in future modules. Through this topic learners also consider resources and the sustainable use of these could be critically analysed. Learners should consider the challenges associated with finding out the chemistry of the Earths layers and why sampling of meteorites is so important. The Goldschmidt system should be seen as a helpful tool to allow predictions about why certain elements will be found in different mineral settings. For direct evidence of the geochemical nature of the Earth for example ophiolites or kimberlite pipes, examples of locations using maps, photographs and evidence will help to build up the evidence picture.
Common misconceptions or difficulties students may have:
Some learners may be concerned at the chemistry content of the topic if they do not feel secure in their chemistry knowledge and understanding from GCSE. To help to build from pre-existing knowledge start with the periodic table and learners could discuss what it could tell them, where are metals/non-metals found, gaseous elements, most reactive etc. Goldschmidt could be introduced as another technique for dividing up the elements and it should be helpful as it means we don’t have to remember the typical behaviour of elements we can predict it from its position in the table.
Conceptual links to other areas of the specification – useful ways to approach this topic to set students up for topics later in the course:
The learner’s skills in geochemistry will be developed further and applied at numerous stage of the course, in particular when considering generating magmas by partial melting in 3.2.2, and linking magma properties to eruption styles. In topic 5.5.1 learners will investigate Bowen’s reaction series and consider continuous and discontinuous reaction series. The chemistry of the minerals involved in these graphs explains what happens as they melt and crystallise. Later in topic 5.5.1 learners consider the formation of chalcophile cumulates in layered intrusion. The geochemical processes that occur at hydrothermal vents requires learners to consider how massive sulfide ores form.
This topic lends itself towards considering the evidence that supports the theories on the composition of the Earth. The link below is for an activity where learners consider many pieces of evidence about the core, they must decide what is relevant and eventually come up with conclusions from the data. The topic of the nebular hypothesis is vast and there is so much information available, short clips that summarise this and then link to the source of the heat of formation of the Earth are useful. Although radioactive decay is covered at GCSE in science the activity below where students can collect and plot some decay data and measure a half-life could be a useful reminder.
With current research being carried out on the behaviour of the mantle and the core mantle it would be of interest for learners to put together some recent findings on the topic and present them in a creative way.
OCR’s resources are provided to support the teaching of OCR specifications, but in no way constitute an endorsed teaching method that is required by the Board and the decision to use them lies with the individual teacher. Whilst every effort is made to ensure the accuracy of the content, OCR cannot be held responsible for any errors or omissions within these resources. We update our resources on a regular basis, so please check the OCR website to ensure you have the most up to date version.
© OCR 2017 - This resource may be freely copied and distributed, as long as the OCR logo and this message remain intact and OCR is acknowledged as the originator of this work.