Midhurst Footpath Companions
Walking in Sussex, Hampshire and Surrey.

Walking rocks!


The club has had an email from Steve Peacock, the author of a book about Geology. The book is called  "Geology for Walkers" and if you've ever wondered how chalk, made from seashells, has got to the top of The South Downs, this book will answer that question, and many more. Full of photos, charts and illustrations. Very entertaining!

Can be found here:-  https://www.amazon.co.uk/dp/B091JJTZST

To help understand the enormous amount of time involved, the author has chosen a year to represent the actual 4.56 billion years.

Sample page:-

The Earth 19 THE EARTH “3rd Rock from the Sun” - Title of a 1996-2001 American sitcom - Back in school, no doubt many of us learnt that the Earth has three main layers – the Core, the Mantle and the Crust – but perhaps hadn’t quite appreciated what an absolutely fundamental role that layering plays in shaping why our planet works the way it does.

A DIFFICULT BIRTH On ‘1st January’ (those 4,560 million years ago), our solar system formed from a rotating cloud of cosmic dust and gases, called a nebula. Gravity pulled most of the nebula’s material into its centre, forming our Sun, whilst the remaining orbiting material began to clump together into several large bodies, by a process of gravitational attraction dubbed ‘sticky collisions’. Remarkably – probably in the space of the first day or two of our metaphorical year – the dominant bodies had hoovered up enough surrounding material to resemble the configuration of planets that we recognise today; and, as intense radiation from the early Sun blew away the lighter gases and liquids from those planets accumulating closest to it, it left them as purely rocky bodies, and left our planet as the ‘third rock from the Sun’. Now, building a planet via ‘collisional aggregation’ is a risky process, and around ‘4th January’ the fledgling Earth appears to have been hit by a particularly large object; one about half its size - about as big as Mars! This was a body 100 million times bigger in volume than the asteroid which wiped out the dinosaurs at the end of the Cretaceous, and it struck with an estimated force equivalent to several trillion megatons (for comparison, the power of a modern Trident nuclear warhead is about one-tenth of a megaton). In a wonderful example of understatement, scientists call this event, the ‘Giant Impact’! The collision severely winded the baby Earth, knocking it 23 degrees off its axis - thus giving the planet its current tilt, which generates our seasons - and the shrapnel which was showered into space coalesced to form our Moon - which today stabilises the Earth’s wobble and generates our tides. The intense heat energy generated by the Giant Impact was enough to turn the Earth into a largely molten state. In this state, the heavier elements like iron and nickel preferentially sank toward the centre, forming the Core, whilst the lighter components (containing a large proportion of elements like silicon, oxygen, magnesium, aluminium and calcium) migrated to the outer edge of the spinning planet (a bit like the way light objects would drift toward the edge of a spinning roundabout). As the molten planet cooled, a scab of rocky Crust gradually solidified around the outside – and thus, during the second week of ‘January’, a rudimentary version of today’s layered Earth was already in place, with a Core, a Crust and a large layer of still soft rock between them - called the Mantle. 

In case you're wondering when Homo Sapiens turned up, it was just before midnight on New Years Eve! 

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