Building the Crust with Rocks

13

416

Chapter Outline

  • 13.1

    Minerals and Rocks: Building Earth’s Crust

  • 13.2

    Cooling the Inferno: Igneous Rocks

  • 13.3

    Layers of Time: Sedimentary Rocks

  • 13.4

    Pressure and Heat: Metamorphic Rocks

  • 13.5

    Geographic Perspectives: Fracking for Shale Gas
This sandstone formation is part of the Bungle Bungle Range in Purnululu National Park, Western Australia. The sandstone was formed from sediments deposited in layers by streams in a valley about 375 million years ago. Through time, the sediments were turned to rock, then erosion slowly exposed and rounded the rock into these domes.
(© Manfred Gottschalk/Lonely Planet Images/Getty Images)

417

LIVING PHYSICAL GEOGRAPHY

  • Why is ice classified as a mineral?

  • How are rocks formed?

  • What is coal?

  • What is fracking and why is it controversial?

418

THE BIG PICTURE

Plate tectonics drives the rock cycle that creates and transforms rocks. Natural gas deposits within layers of sedimentary rock are a controversial energy source.

LEARNING GOALS

After reading this chapter, you will be able to:

  • 13.1

    List the main mineral groups that make up rocks and discuss how rocks are formed, transformed, and recycled.

  • 13.2

    Describe the different types of igneous rocks and where they form.

  • 13.3

    Explain the three types of sedimentary rocks, where they form, and how they provide information about Earth’s history.

  • 13.4

    Explain where metamorphic rocks form and how they are categorized.

  • 13.5

    Assess the pros and cons of extracting natural gas trapped in shale through hydraulic fracturing.

THE HUMAN SPHERE:

People and Rocks

OUR SUCCESS AS A SPECIES IS DIRECTLY LINKED TO EARTH’S ROCKS. About 2.6 million years ago in eastern Africa, our early hominid ancestors began chipping and grinding rocks into tools. Those tools were not used for hunting. Instead, they were used for cutting and scraping meat from animal carcasses and breaking the bones for their marrow.

Through time, as humans evolved, so did their use of rocks and an increasingly wide range of Earth materials. In more recent prehistoric times, Paleolithic humans used materials derived from Earth’s crust in a wide range of applications, ranging from spear tips to pigments for cave murals like those in Figure 13.1.

Figure 13.1

Cave of Altamira. This painting of a now-extinct species of bison was found in the Cave of Altamira, located near Santander, Spain. Some of the images in this cave were made about 35,600 years ago and are among the earliest known cave paintings in Europe. Stone tools were used to grind various Earth materials, including iron oxides and ochre from rocks, to make the paints. These bison were hunted using stone-tipped spears.
(© Heritage Images/Getty Images)

Earth materials continue to be prominent in the lives of humans today. Earth materials such as copper and gold are used in electronics manufacturing. Diamonds and rubies are carefully cut and polished to make jewelry. Uranium, a mineral found in many rocks in Earth’s crust, is used in applications ranging from nuclear energy to atomic weaponry. Pencil lead (graphite), electronic circuitry (silicon and quartz), wallboard and concrete (gypsum), baby powder (talc), plant fertilizer (sulfur), soap (borax), and toothpaste (calcite) are all products of minerals and rocks derived from the crust. Coal has been among the most economically important rocks for the last century and a half. Coal fueled the Industrial Revolution and continues to power a large portion of the modern global economy. Humans could not have followed the path of increasing technological advancement without rocks, and our modern economy would not exist without fossil fuels, such as coal, from the ground.

This chapter explores how rocks are formed, the major rock types in Earth’s crust, and the tectonic context of rock formation. We also examine a growing controversy around a procedure that extracts natural gas from the ground.

419