This feature was first published in August 2024 in My Mensa Weekly, our exclusive newsletter for Mensa members. Find out more about becoming a Mensa member here.
Words: Joanna Cummings
We explore our world of rocks and why we simply couldn’t live without them
Carl Sagan, the famous planetary scientist, once said that we live “on a hunk of rock and metal”. The fact is that, without rocks, we simply wouldn’t exist. From the Stonehenge megaliths right down to that annoying pebble you get stuck in your shoe, rocks and their derivatives underpin our lives and histories. The study of geology, while perhaps considered the least ‘sexy’ science, gives us an insight into the very foundations of life on Earth, helping us understand everything from how our landscapes have formed and why earthquakes happen to predicting volcanic eruptions.
Rocks are like time capsules, formed – and still forming – through an extremely slow process over millennia. The three main types of rocks, each formed due to different yet fascinating physical changes are, of course, igneous, sedimentary and metamorphic. Igneous rocks are formed either deep within the earth (intrusive) or from cooled and solidified lava (extrusive). Sedimentary rocks form when layers of other organic material – rocks or once-living organisms – accumulate on the Earth’s surface and become tightly compacted. If any type of rock is exposed to further intense heat and pressure, they transform into metamorphic rocks, such as marble or slate.
The phrase ‘the only constant is change’ could have been invented for rocks. Not only are individual rocks subject to weathering and erosion, but our very landscape is also in a constant state of flux. That same erosion and weathering has an impact on a much larger scale, and is behind the evolution of our coastlines, valleys and mountains.
Some parts of the world experience this more dramatically than others: in Iceland, one of the most geologically active places on Earth, the landscape is continually reshaped by geysers and volcanic activity – eruptions, such as those in the Reykjanes peninsula, can remove land, destroy agriculture and generally wreak havoc for humans as well as creating new landforms.
In Hawaii in 2018, the eruption of the Kilauea volcano altered the coastline and created new land; the Grand Canyon in the US continues to be deepened by the Colorado River; and reports earlier this year suggest that the tectonic plate under Tibet is splitting in two. Closer to home, 17% of UK coastlines are being affected by erosion, which can cause significant flooding and landslides – rocks come to our aid as ‘rock armour’, being used to absorb the force of waves; or they can form ‘groynes’, which restrict the movement of sediment and lessen the impact of erosive forces.
Back in prehistoric times, our predecessors began deploying rocks as tools, ultimately using them to build homes and early infrastructures. It is in the latter part of the Stone Age that humans are thought to have begun to extract rocks from the Earth; flint mines have been found in the UK and Poland that are thought to date back to around 4000-3000BC. For over 2.5 million years, from the time of human ancestors through to homo sapiens, rocks have proved a handy resource, culminating eventually in the creation of awe-inspiring structures as varied as the Parthenon in Greece (marble), Machu Picchu in Peru (granite) and Neuschwanstein Castle in Germany (limestone). Consider also the massive quantities of sandstone, limestone, granite and slate within the UK and Ireland’s heritage, from Neolithic and Iron Age structures to cottages, castles, soaring cathedrals and city tenements – even the Houses of Parliament.
Rocks have other practical parts to play in our lives too. The types of underlying rock in a region determine its soils and the biodiversity it can support, as well as the potential for humans to grow crops. A rich, loamy soil is ideal for agriculture whereas a clay-rich soil can be difficult to cultivate, though is useful for making bricks and ceramics. (But that is a whole other science story for another day.)
Every time we travel along a road, we are driving or walking over crushed stones and minerals. Highways, bridges, and buildings rely on rocks for strength and stability, and they are also a vital part of many industrial processes – in the manufacture of glass, for example, the use of limestone makes the material easier to handle by improving viscosity and preventing crystallisation. Stone paper – used in much the same way as cellulose-based paper but sturdier – is made from limestone, putting a whole different slant on the game ‘rock, paper, scissors’. And many of the materials used to make smartphones come from minerals. Crystalline rock – the humble salt – both flavours our meals and keeps our roads safe in icy weather.
We also seem to be interested in rocks for their own sake. For people of a more spiritual persuasion, stones and crystals are used in various healing practices and rituals, and it is believed that they can ‘unblock’ or ‘redirect’ trapped energy. Some of us use rocks for meditation or ‘grounding’, simply holding a rock in the palm of the hand and using it to focus attention. You have no doubt slipped a pebble into your pocket at the beach, even if only for its aesthetic appeal or as a holiday keepsake.
So next time you skip that flat stone across the surface of a pond, take a moment to consider its significance. For millennia, rocks have been the unsung heroes of our lives, forming our landscapes, flavouring our meals and providing safe havens – making that pebble in your hand a tiny piece of Earth’s history.
STONE STORIES
Coincidentally, at the time of writing, rocks cropped up in two big news stories:
Stonehenge shocker
A ‘jaw-dropping’ study has found that the largest bluestone megalith at Stonehenge came not from Wales but Scotland, meaning it had been transported around 450 miles – by land or sea? – to the stone circle.
Snowball Earth
Clues hidden in rocks found on islands off the west coast of Scotland have provided the best (and possibly only) record of Earth entering its biggest ever ice age around 720 million years ago.
