Geo Chapter 1

Front 1

What is Geology?

Back 1

Geology is the science that deals with Earth – its history, its composition and internal structure, and its surface features

Front 2

How do geologists study Earth?

Back 2

Geologists, like other scientists, use the scientific method. They share the data that they develop and check one another’s work. A hypothesis is a tentative explanation of a body of data. A set of related hypotheses confirmed by other data and experiments may be elevated to a theory. A theory may be abandoned or modified when subsequent observations show it to be false. Confidence grows in those theories that withstand repeated tests and are able to predict the results of the new experiments.

Front 3

What is Earth’s size and shape?

Back 3

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, owing to the planet’s rotation. Its solid surface has topography that deviates from this overall shape by about 10 km. elevations fall into 2 main groups 0-1 km above sea level for much of the land surface and 4-5 km below sea level for much of the deep oceans.

Front 4

What are Earth’s major layers?

Back 4

Earth’s interior is divided into concentric layers of different compositions, separated by sharp, nearly spherical boundaries. The outer layer is the crust, which varies from about 40 km thick beneath continents to about 8km thick beneath oceans. Below the crust is the mantle, a thick shell of denser rock that extends to the core-mantle boundary at a depth of 2900km. the central core, which is composed primarily of iron and nickel, is divided into 2 layers: a liquid outer core and a solid inner core, separated by a boundary at a depth of 5150 km.

Front 5

How do we study Earth as a system of interacting components?

Back 5

When we try to understand a complex system such as Earth, we find it is often easier to break the system down into subsystems (geosystems) to see how they work and interact with one another. There are three major global geosystems: the climate system, which mainly involves interactions among the atmosphere, hydrosphere, and biosphere; the plate tectonic system, which mainly involves interactions among Earth’s solid components (lithosphere, asthenosphere, and deep mantle); and the geodynamo system, which mainly involves interactions within Earth’s central core. The climate system is driven by heat from the Sun, wheras the plate tectonic and geodynamo system are driven by Earth’s internal heat.

Front 6

What are the basic elements of plate tectonics?

Back 6

The lithosphere is not a continuous shell; it is broken into about a dozen large plates. Driven by convection in the mantle, plates move over Earth’s surface at rates of a few centimeters per year. Each plate acts as a rigid unit, riding on the asthenosphere, which also is in motion. The lithosphere begins to form from rising hot mantle material where plates separate, cooling and becoming more rigid as it moves away from this divergent boundary. Eventually, it sinks into the asthenosphere, dragging material back into the mantle at boundaries where plates converge.

Front 7

What are some major events in Earth’s history?

Back 7

Earth formed as a planet 4.56 billion years ago. Rocks as old as 4 billion years have survived in Earth’s crust. Liquid water existed on Earth’s surface by 3.8 billion years ago, and the geodynamo was generating a magnetic field by 3.5 billion years ago. The earliest evidence of life has been found in rocks of this latter age. By 2.5 billion years ago, the oxygen content of the atmosphere was rising because of oxygen production by early plant life, and the geologic processes at Earth’s surface were very similar to those operating today in plate tectonics. Animals appeared suddenly about 600 million years ago, diversifying rapidly in a great evolutionary explosion. The subsequent evolution of life was marked by a series of mass extinctions, the last caused by a large meteorite impact 65 million years ago, which killed off the dinosaurs. Our species, Homo sapiens, first appeared about 160,000 years ago.