What is ¹ .geology?

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Basalt

This dense igneous rock forms the bedrock of the ocean floors. It erupts as molten lava from oceanie volcanoes.

tGeology is the science of rocks—how they are created and destroyed, and how they have formed our planet. This lnvolves studying minerals, which are the natural \ Chemical compounds that form rocks, as well as k looking at the forces that drive geological processes.

The rock cycle

01: Igneous rocks are madę of minerals formed by the cooling of molten rock erupting from below Earth’s crust.

02: These rocks are worn down into tiny particles (sediments), which are carried into the sea.

03: Over millions of years, the sediments are compressed to form sedimentary rocks.

04: Earth movements push these rocks up so that they become land and start wearing down.

Geological time

When geologists first began studying rocks, they had no way of knowing how old they were. They figured out which rocks were the same age by comparing the minerals and fossils within them.

Groups of rocks are named after areas where they were studied or after an obvious feature. So Devonian rocks get their name from rock in Devon, England, while Carboniferous rocks include seams of coal, which is mostly carbon.

Older rock layers usually lie beneath younger ones, sińce they formed earlier. Devonian rocks are normally below carboniferous rocks, so are older. Permian rocks mainly lie above carboniferous rocks, so are younger.

These names are used to describe divisions of relative geological time. The Devonian, Carboniferous, and Permian are the three periods that led up to the age of the dinosaurs.

i Geologists can now datę rocks in millions of years, to give absolute geological time.

4,540 million

The number of years ago that Earth formed

4,030 million

The dating (in years) of the oldest-known rock on Earth’s surface—the Acasta gneiss of northwest Canada

3,460 million

The age (in years) of the oldest fossils of living things—algal colonies called stromatolites in the rocks of Pilbara,

Western Australia

230-65 million

The number of years ago that dinosaurs roamed Earth

3.6 million

The datę (in years) of the first evidence of our human i ancestors walking upright

WHAT’S IN A NAME.

^poloqy is known as an

_E?rthscience_FTheword

translates as Earth talk

in Greek, and sińce the “talk" tescientificdiscussion,

geology does literally ntean ^y “Earth science.

ock types

Granite

A very hard igneous rock, granite is mostly glassy quartz and feldspar, which often forms colorful crystals.

Sandstone

Many rocks are sedimentary— rock fragments bound together by other minerals. Sandstone is composed of sand grains.

Limestone

Another sedimentary rock, most limestones are madę of the skeletons of millions of microscopic sea organisms.

Schist

Earth’s oldest rocks have been squeezed and melted by massive forces to form metamorphic rocks, such as schist.

I don’t I believe it ■

Geologists can datę rocks by measuring the amount of radioactive minerals (like uranium) that they contain. Over time, these turn into different minerals; by measuring this process, the rock can be dated.

(c) 2011 Dorling Kindersley. Ali Rights Reserved.