sign in sign up
<<
Home , Age of Earth, Principles of Geology, Theory of the Earth

Chapter 1 The Science of An Introduction to Geology

• Geology - the science that pursues an understanding of planet • 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 “If there is an interesting place you want to go, there is Earth and its development interesting geology that you can study there” through time Mersin ophiolite, (Cappadocia, Central Turkey). Turkey

The Science of Geology The Science of Geology 1.3: satellite image of Mt. Vesuvius, Italy. • Some historical views • Geology, people, and the environment of the Earth • Many important relationships exist between • , 300 BC; people and the • James Ussher, ca. 1600, ‘Earth was created in Problems and issues 4004 BC;’ addressed by • geology include • Earth’s features formed through • Natural hazards, sudden and violent resources, changes. ‘The Dog population growth, of and environmental Pompeii’ issues Dwelling in Goreme, Cappadocia

The Science of Geology Hutton, Kelvin, and the great Earth debates. • The beginnings of modern geology “All natural processes that affect the Earth’s crust (, deposition, • ca. 1780, James Huton’s volcanic eruptions, faulting, glaciation ; etc.) operate with the same intensity • : “the and under the same set of physical processes that operate constraints now as in the geologic past.” today have operated in “(as to the ) we see no the past.” vestige of a beginning, no prospect of • a uniformitarian view of an end.” Earth requires a vast These points are incorrect - why? amount of time…. , 1726-1797

1

Hutton, Kelvin, Twain and the Hutton, Lyell, Kelvin, and the great Earth debates. great Earth debates.

C. Lyell: ’’ Lord Kelvin, the greatest physicist of "The present is the key to the his day… “Earth cannot be more than past." (T&L p. 4) 100 million years old [on the basis of a simple convective cooling model].” Uniformitarianism today: Earth’s geological history can be Mark Twain, satirist and writer of the interpreted through processes time: “Scientific research has shed we see operating today. We can considerable darkness on the subject of also understand Earth’s present the Age of the Earth, and if they by interpreting its past. continue at their present pace, we’ll Sir , soon know nothing about it!” 1797-1875

The Geologic time geologic time • and the scale • Relative dating means that dates are placed in their The principle of proper sequence or order faunal without knowing their age in years; succession is useful for • of pre-existing , such as this fish and dividing amphibian, are important markers of relative time. time.

Figure 1.8

Geologic time

• are now able to assign fairly accurate dates to events in Earth history (better than + 1% with ANIMAL). Auburn Noble Mass Analysis Lab

A N I M A L Figure 1.8

2

Geologic The of time scientific inquiry

• The magnitude of • Science assumes the natural geologic time world is consistent and • Involves vast times predictable – millions or billions of years • A goal of science is to discover • An appreciation for patterns in nature and use the the magnitude of geologic time is knowledge to make predictions important because • Scientists collect data through many processes are observation and measurements very gradual

Figure 1.8

The nature of The nature of scientific inquiry… scientific inquiry methods of science

• How or why things happen is • The ‘Scientific method’ involves explained using a • Gathering facts through • Hypothesis – a tentative (or observations untested) explanation • Formulation of hypotheses and • Theory – a well-tested and theories, and laws. widely accepted view that the scientific community agrees best • There is no fixed path that explains certain observable facts scientists follow that to • Scientific Laws provide brief - scientific knowledge, yet the paths usually mathematical - statements to describe nature. begin with inquiry and are guided by logic Scientific laws are not ‘superior’ to theories.

A view of Earth Earth as a system

Earth System Science • Earth’s four spheres • Aims to study Earth as a system composed of numerous interacting • Hydrosphere parts or subsystems • Atmosphere • Employs an interdisciplinary approach to solve global • environmental problems • Solid Earth Systems have ‘negative’ and ‘positive’ feedback mechanisms (p.15)

3

The hydrologic cycle is one of Earth’s many subsystems Earth as a system

• The Earth system is powered by: o Solar energy drives most external processes in the • Atmosphere • Hydrosphere • At Earth’s surface

o of (U234, U235, K40, etc.) drives processes in Earth’s interior c.f. figure 1.13 o Lithosphere, Asthenosphere, Mesosphere, Core

Early of Earth Early evolution of Earth • Origin of planet Earth • Most researchers believe • Origin of planet Earth that Earth and the other planets formed at • Nebular hypothesis essentially the same time – Assumes a flat, disk • Nebular hypothesis shape with the protosun (pre-Sun) at – Rotating cloud called the center the solar nebula – Inner planets begin to – Composed of form from metallic hydrogen and and rocky substances – Nebula began to – Larger outer planets contract about 5 began forming from billion years ago 1.15 fragments of ices (H O, CO , and 2 2 1.15 *We see nebula today, and earth’s interior has the others) same composition as early materials.

*Samples of the Early Solar System Early evolution of Earth • Chondrites - contain spherical aggregates of high-temperature (olivine and • Formation of Earth’s layered structure pyroxene, in ‘chondrules’); condensed from • Metals (especially Fe and Ni) sank to the center the solar nebula with some ‘pre-solar’ grains • Molten rose to produce a primitive crust • Fe-Ni • Chemical segregation established the three basic • Lunar samples divisions of Earth’s interior: core, , and • Martian meteorites crust; • Primitive atmosphere evolved from gases in Earth’s interior Chondrites generally give radiometric ages of ~ 4.5 Ga 1 mm Chondrule

4

Prior to 2005, scientists felt that the bulk composition Earth’s of rocks in Earth’s interior was the same; Structure Main • using spectrometers more precise than previously Divisions: available, in 2005 scientists discovered important Crust; chemical differences between the bulk Earth and the Mantle; chondrites. Core.

the simple model Geophysical that Earth separated Divisions: from a uniform solar Lithosphere; nebula and then Asthenosphere; changed only by Mesosphere; simple ‘segregation’ Outer Core; is incorrect. Inner Core. 1 mm Chondrule c.f. 1.16

How do we know anything Earth’s internal structure about Earth’s interior? “We have never • Layers defined by composition sampled the • Crust mantle directly…. • Mantle “We have been able • Core to examine slivers of the uppermost • Layers defined by physical properties mantle and • Lithosphere overlying oceanic • Asthenosphere crust … in Cyprus, (Turkey,) • Mesosphere Newfoundland and • Inner and Outer Core Oman (p. 23).”

c.f. 1.16

Oceanic Crust section, Antakya, Turkey (Syrian Antioch) The face of Earth -

Note the shields… platforms… mountain belts 1.18

5

The face of Earth - basins 1.17

James Hutton, ~1780 ‘Theory of the Earth’

Note abyssal plains, spreading ridges, seamounts, and trenches… The rock cycle c.f. 1.23

Rocks and the rock cycle Rocks and the rock cycle • Basic rock types • Igneous rocks • Basic rock types • Cooling and solidification • Sedimentary rocks of magma (molten rock) • Accumulate in layers at Earth’s surface • Examples include granite • Sediments are derived and basalt from of preexisting rocks • Examples include sandstone and limestone

Rocks and the rock cycle • Basic rock types • Metamorphic rocks • Formed by “changing” preexisting igneous, sedimentary or other metamorphic rocks • Driving forces are increased heat and pressure (Chapter 2) • Examples include gneiss and marble

6