Tag Archives: plate tectonics

Energy transformations

I mentioned a couple of weeks ago that I am teaching thermodynamics at the moment [see ‘Conversations about engineering over dinner and a haircut‘ on February 16th, 2022].  I am using a blended approach [see ‘ Blended learning environments‘ on November 14th, 2018] to deliver the module to more than 300 first year undergraduate students with one hour in the lecture theatre each week while the students follow the components of the MOOC I developed some years ago [see ‘Free: Energy! Thermodynamics in Everyday Life‘ on November 11th, 2015, and ‘Engaging learners online‘ on May 25th, 2016].  I have found that first year undergraduates are reluctant to participate in the online discussions that are part of the MOOC and so last year I asked them to discuss each topic in small groups with their academic tutor.  I got some very positive feedback from tutors who had interesting and stimulating discussions with their students.  We are repeating the process again this year.  The first discussion is about energy transformations: noting that energy is always conserved but constantly transformed into different forms, each student is asked to start from an energy state of their choice and to trace the transformations backwards until they can go no further.  In the lecture preceding the discussion with their tutor I provide some examples for starting states, including breakfast cereal, a pole vaulter in mid-jump and a bullet train.  I also describe the series of transformations from the Big Bang to tectonic plate movement: after the initial expansion caused by the Big Bang, the universe cooled sufficiently to allow the formation of sub-atomic particles followed by atoms of hydrogen and some helium and lithium that gravity caused to coalesce into clouds which became the early stars, or solar nebula.  A crust formed on the solar nebula which broke away to form planets.  Our planet has a molten core with temperatures varying from 4,400 to 6000 degrees Celsius, compared to around 5,500 degrees on the surface of the sun.  The temperature variation in the Earth’s core cause thermal currents which drive the movement of tectonic plates and so on [see ‘The hills are shadows, and they flow from form to form, and nothing stands‘, on February 9th, 2022].  Most chains of energy transformation lead backwards to the sun and forwards to dissipation of energy into some unusable form which we might call ‘entropy’ [see ‘Life-time battle‘ on January 30th, 2013].

The hills are shadows, and they flow from form to form, and nothing stands

Decorative aerial view of hillsThe title of this post comes from two lines in ‘In Memoriam A.H.H.‘ by Alfred, Lord Tennyson.  The theory of plate tectonics evolved about fifty years ago so it is very unlikely that Tennyson was thinking about the hills as waves of rock flowing across the landscape.  However, we now understand that Earth’s crust is divided into plates that are moving as a result of currents in the liquid magna beneath them.  For example, the African plate is moving northwards crashing into the Eurasian plate causing the edges of the plate to buckle and flow forming the Alps and Pyrenees along the edge of the Eurasian plate.  At the same time, the Eurasian plate is moving eastwards very slowly at a speed of about 2.5 cm per year, or about 2 metres in an average human lifetime.  So, nothing stands still.  Everything is a process.  It’s just that some processes are quicker than others [see ‘Everything is in flux but it’s not always been recognised‘ on April 28th, 2021].


Helen Gordon, Notes from deep time, London: Profile Books, 2021.