Understanding Earth Chapter 1: THE EARTH SYSTEM Grotzinger • Jordan Sixth Edition Chapter 1: THE EARTH SYSTEM © 2011 by W. H. Freeman and Company

Chapter 1: The Earth System

About the Earth System All parts of our planet and all of the interaction of those parts comprise the Earth System. Earth system is an open system. Geosystems include: climate, plate tectonics, and the geodynamo.

Lecture Outline The scientific method 2. Geology as a science 3. Earth’s shape and surface 4. Discovery of a layered Earth 5. Earth as a system of interacting components 6. Overview of geologic time

1. The Scientific Method The goal: explain how the universe works

1. The Scientific Method Observation and experimentation Development of an hypothesis or multiple hypotheses as tentative explanation(s) Testing (challenging) and experimentation to eliminate hypotheses or revise them Scientific theory – a coherent set of hypotheses that explains some aspect of nature Scientific model – based on many hypotheses and theories

Thought questions for this chapter How does science differ from religion as a way to understand the world? If no theory can be proved true, why do almost all geologists believe strongly in Darwin’s theory?

2. Geology as a Science Major questions in geology involve processes that operate on large scales and over long time periods. Field observations are supplemented by laboratory experiments. There are many subfields of geology, including: Oceanography, Ecology, Geophysics, Geochemistry, and Geobiology. In addition, there are others, including Planetary Science.

2. Geology as a Science A special aspect: probing Earth’s long history – studying the geologic record

Principle of uniformitarianism: 2. Geology as a Science Principle of uniformitarianism: The present is the key to understanding the past.

2. Geology as a Science Process comparison: slow versus rapid

R A P I D S L O W The most recent layer of sediment is about 250 million years old. The explosive impact of a meteorite created this 1.2-km-wide crater in just a few seconds. R A P I D S L O W The rocks at the bottom of the Grand Canyon are 1.7–2.0 billion years old.

3. Earth’s Shape and Surface Geodesy – study of Earth’s shape and surface Ancient Greek scholar Eratosthenes’ work showed that the Earth was spherical. Modern research shows that the Earth is not a perfect sphere. Earth’s topography (surface elevation) ranges nearly 20 km from highest to lowest. Sea level – reference level for all Earth surface and seafloor elevations.

Eratosthenes’ work

Topography

4. Discovery of a Layered Earth Seismic waves – illuminate Earth’s interior • Compression and shear waves behave differently and are bent or absorbed at layer boundaries within the Earth. Earth’s interior is layered according to density • Surface rock density is less than 3.5 g/cm3. • Whole Earth density is 5.5 g/cm3. • Core density must be about 8 g/cm3.

4. Discovery of a Layered Earth

Crust

Mantle Crust

Mantle Crust Liquid iron outer core

Mantle Crust Liquid iron outer core Solid iron inner core

4. Discovery of a Layered Earth The crust: continents are made of lighter rock and thus literally “float” on material of higher density. 0 (km) Oceanic crust (3.0 g/cm3) Continental crust (2.8 g/cm3) 10 20 30 Mantle (3.4 g/cm3) Moho discontinuity 40 50 Horizontal distance not to scale

Less dense continental crust floats on denser mantle. 0 (km) Oceanic crust (3.0 g/cm3) Continental crust (2.8 g/cm3) 10 20 30 Mantle (3.4 g/cm3) Moho discontinuity 40 50 Horizontal distance not to scale

Less dense continental crust floats on denser mantle. is less dense than oceanic crust. 0 (km) Oceanic crust (3.0 g/cm3) Continental crust (2.8 g/cm3) 10 20 30 Mantle (3.4 g/cm3) Moho discontinuity 40 50 Horizontal distance not to scale

4. Discovery of a Layered Earth Abrupt changes in density between Earth’s major interior layers are caused by changes in the chemical composition of those layers.

Thought questions for this chapter Imagine you are a tour guide on a journey from Earth’s surface to the center. How would you describe the material that your tour group encounters on the way down? Why is the density of material always increasing as you go down?

5. Earth as a System of Interacting Components Earth system – all parts of Earth and the interactions of the parts • climate system • plate tectonics system • geodynamo system Earth is an open system. • exchanges mass and energy with the rest of the cosmos

Earth system: Interactions of the climate, plate tectonic, and geodynamo systems.

The plate tectonics system: How does the heat energy inside the Earth move and thus affect the crustal plates?

cooled plate is dragged under… Convection causes hot water to rise… ...where it cools, moves laterally, sinks,… Hot matter from the mantle rises,… …causing plates to form and diverge. Where plates converge, a cooled plate is dragged under… Plate Plate …sinks, warms, and rises again. …warms, and rises again.

The geodynamo system: Rapid motion of the liquid outer core stirs up electrical flow in the solid (iron) inner core – causing Earth’s magnetic field.

Earth is an open system. Sun

The Sun drives Earth’s external engine.

Sun The Sun drives Earth’s external engine. Solar energy is responsible for our climate and weather. Sun

Sun The Sun drives Earth’s external engine. Solar energy is responsible for our climate and weather. Earth’s internal engine is powered by trapped heat… Sun

Sun The Sun drives Earth’s external engine. Solar energy is responsible for our climate and weather. Earth’s internal engine is powered by trapped heat… …and radioactivity in its interior. Sun

Sun The Sun drives Earth’s external engine. Solar energy is responsible for our climate and weather. Earth’s internal engine is powered by trapped heat… …and radioactivity in its interior. Sun Heat radiating from Earth balances solar input and heat from interior.

Sun The Sun drives Earth’s external engine. Solar energy is responsible for our climate and weather. Earth’s internal engine is powered by trapped heat… …and radioactivity in its interior. Sun Heat radiating from Earth balances solar input and heat from interior. Meteors move mass from the cosmos to Earth.

Thought questions for this chapter How does viewing the Earth as a system of interacting components help us to understand our planet? Give an example of an interaction between two or more geosystems that could affect the geologic record? In what general ways are the climate system, the plate tectonic system, and the geodynamo system similar? In what ways are they different?

Thought questions for this chapter Not every planet has a geodynamo. Why not? If Earth did not have a magnetic field, what might be different about our planet? Based on the material presented in this chapter, what can we say about how long ago the three major global geosystems began to operate?

6. Overview of Geologic Time

6. Overview of Geologic Time 4.6 billion years ago – formation of solar system 3.5 billion years ago – formation of geodynamo; first known fossils (bacteria) 2.7 billion years ago – oxygen begins to build up in atmosphere 2.5 billion years ago – large continents in crust 2.0 to 1.0 billion years ago – more complex life like algae evolved

6. Overview of Geologic Time

6. Overview of Geologic Time 600 million years ago – first animals 542 million years ago – evolutionary “big bang” 443 million years ago – first mass extinction of life 420 million years ago – first land mammals 359, 251, and 200 million years ago – mass extinctions of life 125 million years ago – first flowering plants

6. Overview of Geologic Time 65 million years ago – last mass extinction (death of the dinosaurs and many other species) 5 million years ago – appearance of first hominids 200,000 years ago – appearance of Homo sapiens

6. Overview of Geologic Time

Key terms and concepts Climate Climate system Convection Core Crust Asthenosphere Climate Climate system Convection Core Crust Earth system Fossil Geodynamo Geologic record Geology Geosystem Inner core Lithosphere

Key terms and concepts Mantle Outer core Plate tectonic system Magnetic field Mantle Outer core Plate tectonic system Principle of uniformitarianism Scientific method Seismic wave Topography