Beneath the things that we usually notice, our planet is made of rock.  A rock looks solid and static, but our planet is dynamic.  Rocks are still accumulating or eroding, and the large tectonic plates the surface consists of are slowly moving.  Europe/Africa and the Americas are moving apart by about 2cm a year with lava filling the gap to form the mid-Atlantic ridge.  As the lava solidifies, the little ferro-magnesian crystals form first and point north.  But as you examine the rocks further away they point south, then north and so on showing that the earth’s magnetic field regularly reverses its polarity.  Where the plates come together there is usually a subduction zone with one plate going under the other forming the oceanic trenches with an arc of volcanoes behind.  Sometimes the sediment on the sea floor is pushed up into a chain of mountains such as the Alps and Himalayas as two plates come together which is why you get marine shells at the top of Everest.  These movements mean that the rocks under our feet were probably formed at a different latitude and climate zone than they are in now. 

Sedimentary rocks, the clays, sandstones and limestones, were usually deposited under water although some are desert sandstones or glacial moraine.  There are volcanic rocks formed from lava or ash, and also from magma that has been intruded into the earth’s crust without reaching the surface until eroded later such as Dartmoor and the Whin sill.  And lastly there are metamorphic rocks like slate, marble, schist and gneiss that have been changed by heat and/or pressure.

What are the rocks in your local area? How and where were they formed? And what are they useful for?

Rocks

Rocks
are not just
out there,
they are living memories
of our planet’s past,
still moving, changing,
forming.

We are not
separate from them.
They affect
our landscape, our soil,
our plants, our food,
our bodies.

This is humankind’s
oldest relationship.