SUMMARYSUMMARYSUMMARYGEOL 1301 Fall 2014Mini Exam # 1 Study Guide (August 21st – August 28th)Chapter 1 The Earth System This chapter gives a broad picture of how geologists think. It starts with the scientific method, the observational approach to the physical universe on which all scientific inquiry isbased. We will illustrate how the scientific method has been applied to discover some of Earth’s basic features—its shape and its internal layering. We will introduce the study of our complex natural world as an Earth system involving many interrelated components.SUMMARYWhat is geology? Geology is the study of Earth—its history, its composition and internal structure, and its surface features.How do geologists study Earth? Geologists, like other scientists, use the scientific method. They develop and test hypotheses, which are tentative explanations for natural phenomena based on observations and experiments. They share their data and test one another’s hypotheses. A coherent set of hypotheses that have survived repeated challenges constitutes a theory. Hypotheses and theories can be combined into a scientific model that represents a natural system or process. Confidence grows in those hypotheses, theories, and models that withstand repeated tests and are able to predict the results of new observations or experiments.What is Earth’s shape? Earth’s overall shape is a sphere with an average radius of 6370 km that bulges slightly at the equator and is slightly squashed at the poles due to the planet’s rotation. Its topography varies by about 20 km from the highest point on its surface to the lowest point. Its elevations fall into two main groups: 0 to 1 km above sea level over much of the continents and 4 to 5 km below sea level for much of the ocean basins.What are Earth’s major layers? Earth’s interior is divided into concentric layers of different compositions separated by sharp, nearly spherical boundaries. The outer layer is the crust, made upmainly of silicate rock, which varies in thickness from about 40 km in the case of continental crust to about 7 km for oceanic crust. Below the crust is the mantle, a thick shell of denser silicate rock that extends to the core-mantle boundary at a depth of about 2890 km. The core, which is composed primarily of iron and nickel, is divided into two layers: a liquid outer core and a solid inner core, separated by a boundary at a depth of 5150 km. Jumps in density between these layers are caused primarily by differences in their chemical composition.How do we study Earth as a system of interacting components? When we try to understand a complex system such as the Earth system, we find that it is often easier to focus on its subsystems (which we call geosystems). This textbook focuses on three major global geosystems: the climate system, which involves interactions among the atmosphere, hydrosphere, cryosphere, biosphere, and lithosphere; the plate tectonic system, which involves interactions among Earth’s solid components; and the geodynamo, which involves interactions within Earth’s core. The climate system is driven by heat from the Sun, whereas the plate tectonic system and the geodynamo are driven by Earth’s internal heat.What are the basic elements of plate tectonics? The lithosphere is broken into about a dozen large plates. Driven by convection in the mantle, these plates move over Earth’s surface at rates of afew centimeters per year. Each plate acts as a rigid unit riding on the ductile asthenosphere, which isalso in motion. Hot mantle material rises at boundaries where plates form and separate, cooling and becoming more rigid as it moves away. Eventually, most of it sinks back into the mantle at boundaries where plates converge.What are some major events in Earth’s history? Earth formed 4.56 billion years ago. Rocks as old as 4.3 billion years have survived in Earth’s crust. Liquid water existed on Earth’s surface by 3.8 billion years ago. Rocks about 3.5 billion years old show evidence of a magnetic field, and the earliest evidence of life has been found in rocks of the same age. By 2.7 billion years ago, the oxygen content of the atmosphere was rising because of oxygen production by early organisms, andby 2.5 billion years ago, large continental masses had formed. Animals appeared suddenly about 600 million years ago, diversifying rapidly in a great evolutionary explosion. The subsequentevolution of life was marked by a series of extreme events that killed off many species, allowing new species to evolve. A dramatic example was the impact of a large meteorite 65 million years ago. Our species, Homo sapiens, first appeared about 200,000 years ago.KEY TERMS AND CONCEPTSAsthenosphere: The weak, ductile layer of rock that constitutes the lower part of the upper mantle (below the lithosphere) and over which the lithospheric plates slide. (From the Greek asthenes, meaning “weak.”)Climate: The average conditions of Earth’s surface environment and their variation.climate system: The global geosystem that includes all the components of theEarth system and all the interactions among these components needed to determine climate on a global scale and how it changes over time.Convection: The mechanical transfer of heat energy that occurs as a heated material expands, rises, and displaces cooler material, which is itself heated and rises to continue the cycle.Core: The dense central part of Earth below the core-mantle boundary, composed principally of iron and nickel. (See alsoinner core; outer core.)Crust: The thin outer layer of Earth, averaging from about 8 km thick under the oceans to about 40 km thick under the continents, consisting of relatively low-density silicates that melt at relatively low temperatures.Earth system: The collection of Earth’s open, interacting, and often overlapping geosystems.Fossil: A trace of an organism that has been preserved in the geologic record.Geodesy: The science of measuring the shape of Earth and locating points on its surface.Geodynamo: The global geosystem that produces Earth’s magnetic field, driven by convection in the outer core.geologic record: Information about geologic events and processes that has been preserved in rocksas they have formed at various times throughout Earth’s history.Geology: The branch of Earth science that studies all aspects of the planet: its history, its composition and internal structure, and its surface features.Geosystem: