Earth structure: The physical structure of the Earth 3.1.1
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|(a)||the layered structures of the Earth as defined by the rheological properties of the layers
||To include how each layer deforms in response to an applied force.
how the variation in P and S wave velocities provides indirect evidence to identify layers within the Earth and how their paths through the Earth produces the P wave and S wave shadow zones
To include how the state and depth of the inner and outer core of the Earth can be determined.
the lithosphere as a rigid, brittle layer made of the crust and part of the upper mantle, which is divided into plates
how evidence from gravity anomalies and isostasy provides indirect evidence to determine the behaviour of the lithosphere and asthenosphere
To include: gravity anomalies (free air and Bouguer), isostatic equilibrium and isostatic rebound.
how indirect evidence from electromagnetic (EM) surveys may be used to identify the lithosphere and asthenosphere at mid-ocean ridges
To include the relationship between conductivity and partial melting.
the nature of the asthenosphere as a rheid, plastic layer with 1–5% partial melting
To include the role of the asthenosphere in plate tectonics.
how the density of the whole Earth and the rocks at the surface provide indirect evidence to infer the density of the core and mantle rocks
the probable geodynamo origin of the Earth’s magnetic field which provides indirect evidence for the subdivision of the core.
To include convection in a rotating conducting fluid.
This topic is all about the physical structure of the Earth, the topic includes how layers are defined and behave, and the evidence used to support our current understanding. This topic is underpinned by the physics and chemistry knowledge learners bring from GCSE (9-1) science. Learners may find parts of this topic challenging (e.g. gravity anomalies) but if you remind them of their pre-existing knowledge as a starting point then they can refer back to this as the topic develops to make it accessible to them. The topic includes a series of sources of evidence for the Earth structure which operate across a range of scales and within the Earth where they cannot be seen. This can be challenging for learners however there are many opportunities to use models, video clips and diagrams to support topics including programs which reconstruct pathways of seismic waves. The topic of partial melting is critical to understand, introducing it by modelling a melting mixture of gravel and wax may be helpful to some learners.
Common misconceptions or difficulties students may have:
Learners pre-existing knowledge is likely to include the chemical boundaries within the Earths structure between crust, mantle and core, they may get mixed up with the physical boundaries of lithosphere and asthenosphere and think that boundaries will be in the same place.
The nature of the asthenosphere as a rheid plastic layer with 1-5% partial melting may be challenging for learners to visualise as they may struggle to picture everyday examples. Past teaching may have described it as fully solid and some films may portray the upper mantle as a liquid. Learners will be familiar with solid crystalline materials that are able to flow over long periods of time like potty putty or glacier ice. The behaviour of glass is not analogous as it is an amorphous solid which is brittle below the glass transition temperature but rubbery above it. Experiments on 20 Ma amber from Costa Rice have proved that glass does not flow, but crystalline solids like rock do within the Earth, just very, very slowly.
Conceptual links to other areas of the specification – useful ways to approach this topic to set students up for topics later in the course:
This topic prepares learners for 3.2.1 and 3.2.2 the plate tectonics theory as the understanding of the physics of the Earths structure is critical when considering the details of lithospheric plates, including driving forces, boundary types. Topic 5.3.1 Igneous petrology builds on the understanding of partial melting by quantifying it in the continuous and discontinuous reaction series. 6.1 Geohazards topic considers the risk of the physical behaviour of the Earth and the impact of earthquakes and other geohazards on life and the built environment.
The physical structure of the Earth topic is built on considering indirect evidence and using it to support suggested theories and ideas, the topic could be approached in a how science works context. Learners could consider what is known about the physical structure of the Earth today and analyse the various routes of investigation that have come before. Learners also could consider the priorities for the future scientific investigations, this could be integrated by looking at up to date research on topics such as harmonic tremors in predicting volcanoes or gravity anomalies on the Moon.
Learners could be asked to present information in many different formats for different purposes, the example below explains the Earth’s magnetic field through a comic book.
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