Earth History, Earth Interior

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Chapter Outline

11.1

Earth Formation
11.2

Deep History: Geologic Time
11.3

Anatomy of a Planet: Earth’s Internal Structure
11.4

Geographic Perspectives: Earth’s Heat and the Biosphere

Thick clouds of toxic steam rich with hydrochloric acid are produced as incandescent lava spills into the sea on Hawai‘i.

(© Sami Sarkis/Photographer’s Choice RF/Getty Images)

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LIVING PHYSICAL GEOGRAPHY

How did Earth form?
How did the atmosphere and oceans form?
Why doesn’t the hot interior of Earth melt the crust?
How long would it take to drive to the center of Earth?

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THE BIG PICTURE

Earth formed 4.6 billion years ago. The planet’s hot interior is structured in layers. Heat energy moves Earth’s hot interior and its outer crust.

LEARNING GOALS

After reading this chapter, you will be able to:

11.1

Explain the origin of Earth and its atmosphere and oceans.
11.2

Describe the major divisions of geologic time and explain how the age of ancient Earth material is determined.
11.3

Describe the planet’s internal structure and understand the importance of lithospheric plate movement.
11.4

Assess the connection between Earth’s internal heat and life on Earth.

THE HUMAN SPHERE:

The Anthropocene

THERE ARE JUST OVER 7 BILLION PEOPLE ON EARTH TODAY, and by midcentury, there will likely be about 9 billion. No other single species in Earth’s history has been such a pervasive force of change in Earth’s physical systems as humans are now.

Many scientists believe that the extent of human environmental impacts is sufficient to warrant a new geologic epoch in Earth history. This new epoch, called the Anthropocene, or the “Age of Humans,“is the age of human transformation of Earth’s physical systems (Figure 11.1).

Figure 11.1

Tokyo, Japan. Tokyo is the largest city in the world with a population of 13.2 million people. The surrounding metropolitan region has an additional 22 million people. Like many regions on Earth, this city and the area surrounding it have been completely transformed by people.

Anthropocene

(pronounced an-THROP-a-seen) The age of human transformation of Earth’s physical systems; generally seen as starting in 1800.

The beginning of the Industrial Revolution, around 1800, is often cited as the beginning of the Anthropocene. At that time, human activity began changing the chemistry of the atmosphere. Atmospheric carbon dioxide levels began rising as people burned coal, and then petroleum, for energy (see Section 6.3). The increased concentration of CO₂ in the atmosphere led to an anthropogenic greenhouse effect. Atmospheric warming has caused sea level to rise about 20 cm (8 in) in the last century as Earth’s ice sheets and glaciers have melted and seas have warmed and expanded (as we will see in Section 17.5). In addition, the oceans are becoming more acidic as they absorb CO₂ from the atmosphere (see Section 10.1).

Many of the world’s major rivers have been dammed, and about half the world’s freshwater runoff is used by people. Nearly 40% of Earth’s land surface not covered by glaciers is used to grow food for people. Globally, people move more sediment and rock using bulldozers and other earth-moving equipment than is moved naturally by weathering and erosion. About 90% of all mammal biomass is made up of people and domesticated animals, such as cows and sheep. About 10,000 years ago, the proportion of mammal biomass made up of people and domesticated animals was only 0.1%.

The proposed Anthropocene is one of many divisions of geologic time that mark Earth’s extensive history. This chapter investigates how Earth was formed, how scientists divide Earth’s history into geologic time periods, and how Earth’s interior is structured. This chapter also explores the connection between the planet’s internal heat energy and the biosphere.

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