Читать книгу The Dangerous Book for Boys - Conn Iggulden - Страница 16

HALF A BILLION YEARS ago there was no life on land and only worms, snails, sponges and primitive crabs in the seas. When these creatures died, their bodies sank into silt and mud and were slowly covered. Over millions of years, the sea bottom hardened into rock and the minerals of the bones were replaced, molecule by molecule, with rock-forming minerals such as iron and silica.

Eventually, this process turns the bones into rock – and they become known as fossils, a slowly created cast of an animal that died hundreds of millions of years ago. Other fossils are formed when dying animals fall into peat bogs or are covered in sand. As each new sedimentary layer takes millions of years to form, we can judge the age of the fossils from their depth. You can travel in time, in fact, if you have a spade. You can reach Roman times in just six or seven feet down in some places. To reach levels millions of years ago, you’ll need to find a cliff where the layers are already revealed – like Lyme Regis and Charmouth in Dorset or the Lake District in Cumbria.

Those sea animals can move a long way in the time since they were swimming in dark oceans! Geological action can raise great plates of the earth so that what were undersea fossils can be found at the peak of a mountain or in a desert that was once a valley on the sea floor.

In parts of New Zealand, you can see the fossilised remains of ancient prehistoric forests in visible black bands on the seashore. This particular compressed material is coal and it burns extremely well as fuel. Oil too is a fossil. It is formed in pockets, under great pressure, from animals and plants that lived three hundred million years ago. It is without a doubt the most useful substance we have ever found – everything plastic comes from oil, as well as petrol for our planes and cars.

By studying fossilised plants and animals, we can take a glimpse at a world that has otherwise vanished. It is a narrow view and the information is nowhere near as complete as we would like, but our understanding improves with every new find.

Even the commonest fossils can be fascinating. Hold a piece of flint up to the light and see creatures that last crawled before man came out of the caves – before Nelson, before William the Conqueror, before Moses. It fires the imagination. Here are some of the classic forms of fossils.

Ammonite. A shelled sea creature that died out at the KT boundary 65 million years ago (see Dinosaurs). Sizes vary enormously, but they can be attractively coloured.

Trilobite. These are also a fairly common find, though the rock must usually be split to see them. Fossil hunters carry small hammers to tap away at samples of rock.

Sea urchin. Fossilised sea urchins and simple organisms like starfish are all very well, but remnants of woolly mammoths have been found in the south of England, as well as remnants of Jurassic period great carnivores and herbivores. However, you are likely to find a few ammonites on the Dorset coast in a single afternoon, while a Jurassic skeleton would be the find of a lifetime. That said, if you don’t look, you won’t find.