Earth as a system

• The Earth system is powered by energy from the sun that drives the external processes in the

• Atmosphere

• Hydrosphere

• Biosphere

• Geosphere (lithosphere)

• Earth system is also powered by internal processes driven by heat flow within earth. What are some sources of heat?

Figure 1.4

Was this rock formation the result of internal or external processes?What had to occur for this arch to form?

• Can you think of one or more internal processes that are of interest to geologists?

• Can these processes be explained?

Two views of PakistanCharakusa Valley, Karakorum Range

Muzzaffarabad

Natural Hazards

• One important reason to study geology and be able to predict processes is to prevent threats to humans

• A natural hazard is just that – natural process. It only becomes a hazard when humans put themselves in harm’s way.

The Science of Geology

• Geology - the science that pursues an understanding of planet Earth

• GEO=earth OLOGY = study of• Physical geology - examines the materials

composing Earth and seeks to understand the many processes that operate beneath and upon its surface • Historical geology - seeks an

understanding of the origin of Earth and its development through time

The Science of Geology

• Some historical notes about geology

• The nature of Earth has been a focus of study for centuries

• Catastrophism

• Uniformitarianism and the birth of modern geology

James Hutton: Theory of the Earth Late 1700s – birth of modern Geology

The nature of scientific inquiry

• Science assumes the natural world is consistent and predictable

• Goal of science is to discover patterns in nature and use the knowledge to make predictions

• Scientists collect data through observation and measurements

The nature of scientific inquiry

• How or why things happen is explained using a

• Hypothesis – a tentative (or untested) explanation • Theory – a well-tested and widely accepted

view that the scientific community agrees best explains certain observable facts

Box 1.2 Do glaciers move? (pg. 11)Rhone Glacier, Switzerland, 1874-1882

credit: L. Agassiz

The nature of scientific inquiry

• Scientific method involves• Gathering facts through observations• Formulation of hypotheses and theories

• There is no fixed path that scientists follow that leads to scientific knowledge

Solar Nebular Hypothesis

Is this hypothesis created by direct or indirect observation?

How do you think this model was made?

Early evolution of Earth

• Origin of planet Earth • Nebular hypothesis – Assumes a flat, disk shape with the protosun

(pre-Sun) at the center

– Inner planets begin to form from metallic and rocky substances

– Larger outer planets began forming from fragments of ices (H2O, CO2, and others)

Early evolution of Earth

• Origin of planet Earth • Most researchers believe that Earth and the

other planets formed at essentially the same time • Nebular hypothesis – Rotating cloud called the solar nebula

– Composed of hydrogen and helium

– Nebula began to contract about 5 billion years ago

Figure 1.9A

How did the moon form? Do scientists agree?

Speaking of models…how did this diagram become a model of earth?

Early evolution of Earth

• Formation of Earth’s layered structure • Metals sank to the center• Molten rock rose to produce a primitive

crust• Chemical segregation established the three

basic divisions of Earth’s interior • Primitive atmosphere evolved from gases in

Earth’s interior

Earth’s internal structure

• Layers defined by composition • Crust• Mantle• Core

• Layers defined by physical properties• Lithosphere• Asthenosphere• Mesosphere• Inner and Outer Core

Figure 1.16

Earth’sLayered

structure

Figure 2.29

Figure 1.5

The second frame of reference for geologic time is absolute dating – Absolute dating results in specific dates for rock units or

events expressed in years before the present

Radiometric dating is the most common method of obtaining absolute ages – Such dates are calculated from the natural rates of decay

of various natural radioactive elements present in trace amounts in some rocks

Concept of Geologic Time