visualizing earth history by loren e. babcock chapter 1 introduction to earth system history

VISUALIZING EARTH HISTORYBy Loren E. Babcock

Chapter 1

Introduction to Earth System History

What is Earth History?

Distinguish Earth history from Earth dynamics.

Geology is the science of the Earth.

Geology studies the composition, structure, origin, life forms,

physical and chemical processes affecting it, and its history.

The science of geology is divided into two broad but overlapping

subdisciplines referred to as:

Earth dynamics (or physical geology) and

Earth history (or historical geology).

What is Earth History?Explain the meaning of a scientific theory.

Geology is based on facts or observations about nature.

The Scientific Method – is a scientific investigation involving an iterative process of empirical observation,

hypothesis building (with a predictive or retrodictive component), and testing.

What is Earth History?Explain the meaning of a scientific theory.

A scientific theory is a unifying idea that incorporates a number of provisionally accepted hypotheses.

The popular meaning of “theory” is speculative, an idea in need of testing, and one that is

not necessarily widely accepted by scientists.

Scientific theory is a scientific concept that is tantamount to fact.


The theories of plate tectonics and biological evolution.

Two important scientific theories are central to an understanding of Earth history:

plate tectonics and biological evolution.

http://www.youtube.com/watch?v=QDqskltCixA

The Early Earth and Plate Tectonics


The theories of plate tectonics and biological evolution.

Plate tectonics theory is the great unifying idea of geology.

It states that the Earth’s outer shell (the lithosphere), which

consists of the crust and upper mantle, is cracked and

composed of pieces that float on a hot, deformable

asthenosphere.

The pieces move in various directions, and may slowly

spread apart, collide, or slip past one another.

What is Earth History?The theories of plate tectonics and biological evolution.

Evolutionary theory is the great unifying idea of biology.

It is the process by which biological species give rise to other species by way of genetic changes.

What is Earth History?The theories of plate tectonics and biological evolution.

Plate tectonics and evolutionary theories provide a sound, consistent framework within which to interpret the past

and present, and both ideas are well tested and supported by an overwhelming amount of evidence.

What is Earth History?Composition of the Earth’s Crust

Crust - The outermost layer of the Earth, defined by density, composition (Si, O), and a seismic velocity difference

from the underlying mantle. Oceanic: 5-10km, continental: 33km.Mantle – It’s composed of Si, O, Mg and Fe.

It extends to 2900km depth.

Lithosphere - Outer, relatively rigid layer of the Earth, approximately 100 km thick, overlying the asthenosphere.

It includes the entire crust plus the upper mantle.Asthenosphere - Layer within the upper mantle and

below the lithosphere where rocks are relatively ductile and easily deformed.

Overview of Earth Systems

Explain what parts of the Earth system geologists study.

The systems approach to studying the Earth is a way of

breaking down large, complex problems into smaller

components while remaining mindful of the

connections between the components.

Earth system - The sum of the physical, chemical, and

biological processes operating on and within the Earth.



A change in one component in a system commonly has

effects in other components and its systems.

The usage of oil increases carbon dioxide, water vapor,

and other gaseous chemicals to the atmosphere;

these gases limit heat loss from the Earth’s thin

atmosphere and promote an increase in temperature.

Overview of Earth SystemsIdentify the major geologic processes operating on Earth.

Earth is a planet that differs markedly from others in the Solar System.

Three important processes have substantially modified the Earth’s surface over time:

1, tectonics,

2, the action of water in various forms

3, biological processes,

Overview of Earth SystemsIdentify the major geologic processes operating on Earth.

1, tectonics, which involves the movement of lithospheric plates across the planet’s surface, and which is responsible

for the recycling of rocks;

2, the action of water in various forms (liquid, ice, and water vapor), which plays a major role in weathering and erosion,

and in the formation of rocks; and

3, biological processes, living organisms are source of profound

change on Earth surface, and their effects alter surface and subsurface areas, water systems, and the atmosphere.


The roles of water, carbon, and oxygen in Earth systems.

Key elements of the Earth system are the cycles of essential

ingredients for life and some of the forces of change:

water, carbon, oxygen, and other chemicals.



The water cycle is used to describe the endless

exchange of water among the atmosphere, oceans, lakes, streams, through living organisms, and through the ground.



Water, carbon, oxygen, and other nutrients are cycled

through atmospheric, biological, and geological systems.

Carbon and oxygen from the atmosphere may be used by

living organisms.

Oxygen is used for respiration by animals, and carbon dioxide is

used by plants and some bacteria for photosynthesis.



Sediments or derivative rocks may be exposed

to weathering and erosion, and the elements

may be released to continue cycling through

the Earth systems.

Earth is not entirely a closed set of systems.

Biological processes depend heavily on both the

presence of liquid water from Earth, and a constant

stream of radiation from the Sun.

Principles of Earth History

Seven important principles guide our interpretation of

Earth history, and provide a way of deciphering historical

events in their correct relative time sequence:

uniformitarianism,

superposition,

original horizontality,

lateral continuity,

cross-cutting relationships,

included fragments,

and biotic succession.


Explain Hutton’s principle of uniformitarianism.

Uniformitarianism - The principle that processes acting upon the Earth today have also operated in the geologic past.

The concept of uniformitarianism, which is often expressed in the phrase “the present is the key to the past.”


Describe Steno’s three principles of stratigraphy.

Stratigraphy, the science of layered rocks, developed

from three principles first stated by Niels Stenson (1638-1687),

who latinized his name to Nicolaus Steno.

Steno was the first to formally recognize the importance

of stratification, or horizontal layering.

Stratification of sediments occurs as the result

of differences in particle size and density.



The principle of Original Horizontality

Steno’s principle of original horizontality states that sedimentary

layers were deposited nearly horizontally and parallel to the

Earth’s surface.



The principle of Lateral Continuity

Steno’s principle of original lateral continuity states that at the

time of deposition, strata extended continuously in all

directions until they terminated by thinning at the edge of a

basin, ended abruptly at a barrier to sedimentation, or graded

laterally into a different sediment type.


Explain Lyell’s two principles of stratigraphy.

Lyell provided interesting illustrations of the concept of

uniformitarianism, and provided cogent explanations for

geological phenomena that countered the prevailing

geological philosophy of the time—catastrophism.

Catastrophism (rooted in biblical scriptures) was a paradigm

that attempted to explain the development of erosional

surfaces and the extinction of species by violent, rapid,

calamities, like giant floods.


Explain Lyell’s two principles of stratigraphy.

Lyell also introduced two other general principles of geology:

Principle of cross-cutting relationships – States that

a rock unit, sediment body, or fault that cuts another

geologic unit is younger than the unit that was cut.

Principle of included fragments - States that

fragments of rock within a larger rock unit

are older than the rock in which they

are enclosed.


Understand Smith’s principle of biotic succession.

Principle of biotic succession - The principle that body

fossils occur in strata in a definite, determinable order.

This final major principle used to interpret the

relative ages of strata was proposed by the

English engineer and surveyor, William

(“Strata”) Smith (1769–1839).


Understand Smith’s principle of biotic succession.

visualizing earth history by loren e. babcock chapter 1 introduction to earth system history

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