Quick questions on Energy flow through Earth's spheres: HSC Earth and Environmental Science Module 5

The internal source is heat. Some is primordial heat left over from the planet's violent formation and core formation, but most of the ongoing supply is radiogenic heat, produced by the decay of long-lived radioactive isotopes of uranium, thorium and potassium in the mantle and crust. This heat drives the deep processes: convection, plate motion, volcanism and metamorphism.

Convection is the transfer of heat by the bulk movement of material. In the mantle, hot rock near the core is less dense and rises slowly; cooler rock near the surface is denser and sinks. These convection currents, acting over millions of years on solid but ductile rock, drag the overlying plates and so power continental drift, sea-floor spreading and subduction. Convection also operates in the atmosphere (rising warm air forms clouds and storms) and in the oceans (warm and cold water masses circulate).

The spheres are not separate boxes; energy flowing through one moves matter into another. Solar heating of the ocean (hydrosphere) evaporates water into the atmosphere, which falls as rain onto rock (geosphere), weathering it and washing sediment and dissolved ions back to the sea. Plants (biosphere) draw carbon dioxide from the atmosphere and nutrients from the soil. A volcanic eruption transfers material from the geosphere into the atmosphere and hydrosphere at once.

Australia sits near the centre of the Indo-Australian Plate, far from the convection-driven plate boundaries that produce most of the world's earthquakes and volcanoes. This makes it one of the most geologically stable and ancient landmasses, which is why deep weathering (a solar-powered surface process) has had hundreds of millions of years to shape its flat, deeply weathered landscapes and lateritic soils. The continent still moves north-east at around seven centimetres a year, carried by mantle convection, fast enough that GPS and mapping datums must be periodically corrected. The strong, reliable solar resource across inland Australia, the basis of the country's large-scale solar energy expansion, is the same external energy flux that drives its surface processes.

Distinguish between the internal and external energy sources that drive Earth's processes, giving one process powered by each. [3 marks]

Explain how convection links heat transfer in the mantle, the atmosphere and the oceans. [4 marks]