GEL111 Introductory Geology

Overview/Chapter 1

The science of geology

Geology is the science that pursues an understanding of planet Earth

• Physical geology – examines the materials composing Earth and seeks to understand the processes that operate beneath and upon its surface

• Historical geology – seeks an understanding of the origin of Earth and its development through time

Who needs geology? We all do!

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The science of geology

This semester, our study of planet Earth will cover a lot of territory:

- Atmosphere (Air)

- Hydrosphere (Water)

- Geosphere (Materials)

- Biosphere (Life)

The intersection of three spheres The atmosphere, hydrosphere, and the geosphere

Earth as a system

- Earth is a dynamic planet with many interacting parts or spheres

- Parts of the Earth system are linked

- It is characterized by processes that

• Vary on spatial scales from fractions of a millimeter to thousands of kilometers

• Have time scales that range from milliseconds to billions of years

Earth as a system

- The Earth system is powered by the Sun, which drives external processes

• In the atmosphere

• In the hydrosphere

• At Earth’s surface

Earth as a system- The Earth system is also powered from

Earth’s interior

• Heat remaining from the Earth’s formation and heat that is continuously generated by radioactive decay powers the internal processes that produce volcanoes, earthquakes, and mountains

How do we know what we know?

- Geologic writings date back to the Greeks, more than 2,300 years ago! (Not very scientific back then; more philosophical – e.g. Aristotle)

- In the mid 1600s, church leader James Ussher constructed a chronology of Earth based on Biblical interpretation (Not scientific; more personal/Biblical). This idea grew to be called catastrophism.

- In the late 1700s, a physician and farmer named James Hutton put forth the idea of uniformitarianism, which says the physical, chemical, and biological laws that operate today also operated in the geologic past. (“The present is the key to the past.”)

What does this mean for us today?

- First, it means that just because humans weren’t around for certain geologic events doesn’t mean they didn’t happen!

-It also means that geological events operate on different time scales than human lifespans. For example, it is estimated that the North American continent is eroding away at a rate of 3 centimeters every 1,000 years.

-This means in about 100 million years, erosion can weather away a 10,000 foot peak (like Mount Redoubt in Alaska)!

Geologic time

- Geologists are now able to assign fairly accurate dates to events in Earth history. There are two main types of geologic time: relative time and absolute time.

- Relative dating means that dates are placed in their proper sequence or order without knowing their specific age in years (like knowing your mom is older than you without knowing her age).

- Absolute dating is when you can attribute a specific time to an event or specimen (like knowing the exact date you were born helps us know how old you are).

Relative time

- At first, geologists didn’t know what kind of timeline they were working with, so they created logical rules to help date things relatively.

- Law of superposition: In layers of sedimentary rocks or lava flows, the youngest layer is on top and the oldest is on the bottom (assuming nothing has disturbed it since it was deposited).

Relative time

- Principle of Original Horizontality: Layers of sediment are generally deposited in a horizontal position, then moved or upturned.

Relative time

-Principle of Cross-Cutting Relationships:

When a fault cuts through other rocks, or when magma intrudes and crystallizes, we can assume the intrusion/fault is younger than the rocks affected.

Relative time

- Principle of fossil succession: Fossil organisms succeed one another in a definite and predictable order, so any time period can be recognized by its fossil content.

Relative time

-Principle of Inclusions: An inclusion is older than the rock that contains it.

Relative time

-Law of Lateral Continuity: Sediments and lava flows are generally laterally continuous unless something breaks them or they taper off into something else.

The geologictime scale

Activity – Unique and Shared

-Groups will each need one piece of paper and a pen.

- You have 5 minutes to discover as many common traits and qualities members of the group have. Be creative – something like “we are all wearing clothes” is too obvious.

- Now, let’s take another 5 minutes to discover at least one unique trait each group member has that no one else does.

The nature of scientific inquiry

- Science assumes the natural world is consistent and predictable

The goal of science is to discover patterns in nature and use the knowledge to make predictions

Scientists collect facts through observation and measurements

The nature of scientific inquiry

- How or why things happen are 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

- Law – used only when there is only one explanation for a theory

The nature of scientific inquiry

- Scientific method • Scientific method involves gathering facts

through observations and formulation of hypotheses and theories

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

Activity – Come Fly With Me

-Groups will each need one copy of the lab paperwork, one pen, one tape measure, and three different sized airplanes.

- You will each be assigned a role to play in this lab – reader, spokesperson, researcher, scribe, etc.

-Follow the procedures on the lab paperwork. Ask me for help if you have questions.

Wrap Up – Questions?

- Today we have learned about what geology is, how it is organized, and how it affects our lives. Each week this semester we will delve deeper into the various areas of the biosphere, atmosphere, hydrosphere, and lithosphere.

- Our lab this week will cover maps. Please review Chapter 9 in your lab manual. Be thinking of what mapping concepts you might have questions about.

- Also, it’s important that you work on your quarterly homework every week so you don’t get behind.