Chapter 13 Introduction to Geology Space and Earth Science Chapter Review

Introduction to Geology

Adapted from Physical Geology, Beginning University of Saskatchewan Edition (Karla Panchuk) and Physical Geology (Steven Earle)

Figure one.1: Badlands in southern Saskatchewan. Erosion has exposed layers of rock going dorsum more than than 65 million years. Source: Karla Panchuk (2017) CC BY-SA four.0. Click the epitome for more attributions.

Learning Objectives

After reading this chapter and answering the review questions at the end, you should be able to:

• Explicate what geology is, and why we study Earth.
• Draw the kinds of work that geologists practise.
• Explicate what is meant by geological time.
• Explain how the principle of uniformitarianism allows usa to translate observations about Globe today into knowledge nearly how Globe worked in the past.
• Summarize the main idea backside the theory plate tectonics.

What Is Geology?

Geologists study Earth — its interior and its exterior surface, the rocks and other materials around us, and the processes that formed those materials. They study the changes that accept occurred over the vast time-span of Earth'south history, and changes that might take place in the near futurity.

Geology is a science, meaning that geological questions are investigated with deductive reasoning and scientific methodology. Geology is arguably the most interdisciplinary of all of the sciences because geologists must understand and apply other sciences, including physics, chemistry, biology, mathematics, astronomy, and more.

An aspect of geology that is unlike most of the other sciences is the role played by time — deep time — billions of years of it. When geologists study the evidence around them, they are often observing the results of events that took place thousands, millions, and even billions of years in the past, and which may still be ongoing. Many geological processes happen at incredibly slow rates — millimetres per year to centimetres per yr — but considering of the corporeality of time available, tiny changes can result in expansive oceans forming, or entire mountain ranges beingness worn abroad.

Geology on a Grand Scale in the Canadian Rocky Mountains

The height on the correct of the photographs in Figure 1.two is Rearguard Mountain, which is a few kilometres northeast of Mount Robson. Mount Robson is the tallest peak in the Canadian Rockies, at iii,954 m. The large glacier in the middle of the photo is the Robson Glacier. The river flowing from Robson Glacier drains into Berg Lake in the bottom right.

Many geological features are shown here. The rocks that these mountains are made of formed in body of water water over 500 million years ago. A few hundred million years later, the rocks were pushed east for tens to hundreds of kilometres, and thousands of meters upward in a groovy standoff between Earth's tectonic plates.

Over the past two million years this surface area, like most of the rest of Canada, has been repeatedly covered by glaciers that scoured away rocks to form the valley to the left of Rearguard Mountain. The Robson Glacier itself is at present only a fraction of its size during the Little Ice Age of the 15th to 18th centuries. And, similar almost all other glaciers on Earth, it is now receding even more than rapidly because of climatic change. Figure 1.two (right) taken around 1908 past the Canadian geologist and artist Arthur Philemon Coleman, gives an indication of how much the glacier has receded in the last hundred years.

Figure 1.2: Rearguard Mountain and Robson Glacier in Mount Robson Provincial Park, BC. Left: Robson Glacier today, retreating upwardly the valley. Right: Robson Glacier circa 1908. Sources: Left- Karla Panchuk (2017) CC BY-SA 4.0 with photo by Steven Earle (2015) CC By 4.0 view source. Right: A.P. Coleman (c. 1908) Public Domain. Click the image for more attributions.

Geology is about understanding the evolution of Globe through time. Information technology is about discovering resources such as metals and free energy, and minimizing the environmental implications of our use of resources. It is about learning to mitigate the hazards of earthquakes, volcanic eruptions, and slope failures. All of these aspects of geology, and many more, are covered in this textbook.

Why Study World?

Why? Considering Earth is our home — our just home for the foreseeable futurity — and in order to ensure that it continues to be a great place to live, we need to understand how it works. Another reply is that some of u.s.a. tin't help but study information technology because it's fascinating. Simply there is more to it than that.

• Explain what geology is, and why we study Earth.
• Describe the kinds of work that geologists do.
• Explicate what is meant by geological time.
• Explain how the principle of uniformitarianism allows us to translate observations about Earth today into cognition most how Earth worked in the by.
• Summarize the main thought backside the theory plate tectonics.

The Importance of Geological Studies for Minimizing Risks to the Public

Figure 1.iii shows a slope failure that took identify in Jan 2005 in the Riverside Bulldoze area of N Vancouver. The steep bank below the business firm shown gave way, and a slurry of mud and sand flowed downwardly. It destroyed another house below, and killed i person. The slope failure happened after a heavy rainfall, which is a common occurrence in southwestern B.C. in the winter.

Effigy 1.3: Aftermath of a deadly debris flow in the Riverside Drive area of North Vancouver in January, 2005. Source: The Province (2005), used with permission.

A geological study written in 1980 warned the District of North Vancouver that the surface area was decumbent to gradient failure, and that steps should be taken to minimize the risk to residents. Unfortunately, not enough was washed in the intervening 25 years to prevent a tragedy.

What Do Geologists Practise?

Geologists do a lot of different things. Many of the jobs are the things you would expect. Geologists work in the resource industry, including mineral exploration and mining, and exploring for and extracting sources of free energy. They do hazard assessment and mitigation (eastward.thou., assessment of risks from slope failures, earthquakes, and volcanic eruptions). They report the nature of the subsurface for construction projects such as highways, tunnels, and bridges. They use information about the subsurface for water supply planning, development, and management; and to decide how best to incorporate contaminants from waste.

Geologists also exercise the research that makes practical applications of geology possible. Some geologists spend their summers trekking through the wilderness to make maps of the rocks in a particular location, and collect clues about the geological processes that occurred there. Some geologists piece of work in laboratories analyzing the chemical and physical properties of rocks to understand how the rocks volition deport when forces human action on them, or when water flows through them. Some geologists specialize in inventing means to use circuitous instruments to brand these measurements. Geologists study fossils to understand ancient animals and environments, and go to extreme environments to understand how life might accept originated on Earth. Some geologists help NASA understand the data they receive from objects in space.

Geological work tin be washed indoors in offices and labs, only some people are attracted to geology because they like to be outdoors. Many geological opportunities involve fieldwork in places that are equally amazing to encounter as they are interesting to written report. Sometimes these are locations where few people have ever set foot, and where few e'er will over again.

Figure 1.4: Geologists at work on the isle of Spitsbergen, office of the Svalbard archipelago. The islands are located in the Arctic Ocean north of Norway. Source: Gus MacLeod (2007) CC BY-NC-ND 2.0 view source

We Study Earth Using the Scientific Method

There is no single method of enquiry that is specifically the scientific method. Furthermore, scientific research is not necessarily unlike from serious inquiry in other disciplines. The key features of serious inquiry are the following:

• Explicate what geology is, and why nosotros report Earth.
• Depict the kinds of work that geologists practise.
• Explain what is meant by geological fourth dimension.
• Explicate how the principle of uniformitarianism allows us to translate observations nearly Globe today into knowledge about how Earth worked in the by.
• Summarize the main idea backside the theory plate tectonics.

An Example of the Scientific Method at Work

Consider a field trip to the stream shown in Figure 1.five Notice that the rocks in and along the stream are rounded off rather than having sharp edges. We might hypothesize that the rocks were rounded considering equally the stream carried them, they crashed into each other and pieces bankrupt off.

Figure 1.5: Hypothesizing well-nigh the origin of circular rocks in a stream. Source: Steven Earle (2015) CC By four.0 view source

If the hypothesis is right, so the further we become downstream, the rounder and smaller the rocks should be. Going upstream we should find that the rocks are more than angular and larger. If we were patient we could likewise examination the hypothesis past marking specific rocks and so checking back to see if those rocks take become smaller and more rounded as they moved downstream.

If the predictions turn out to be correct, nosotros must still be careful about how much certainty to adhere to our hypothesis. Although our hypothesis might seem to us to be the just reasonable caption, someone could argue that we have the mechanism incorrect, and the rocks weren't rounded past bumping into each other. If our experiment didn't specifically check for the mechanism (e.g., by looking to see if chips fall off the rocks and the rocks are made smoother) so we would have to admit the possibility. Nosotros needn't carelessness the hypothesis as a useful tool for making predictions, but it is necessary to be open to the possibility that other things might exist going on. If someone demonstrates conclusively that our hypothesis is wrong, then we accept to discard the hypothesis and come upward with a better ane.

A expert hypothesis is testable. Someone might fence that an extraterrestrial organization creates rounded rocks and places them in streams when nobody is looking. There is no practical fashion to test this hypothesis to confirm information technology, and there is no way to prove it false. Even if we never encounter aliens at work, we however can't say they haven't been, because according to the hypothesis they only work when people aren't looking. Compare this to our original hypothesis which allows united states to make testable predictions such as rocks getting smaller and rounder downstream. Our original hypothesis gives united states a fashion to see how realistic it is, whereas the conflicting hypothesis gives united states of america no way to know if it makes sense or not.

Theories and Laws

Two other terms appear in discussions of the scientific method: theory and constabulary. A theory starts out as a hypothesis, but over a long period of time and a slap-up many tests, it has never come upwards short. That doesn't hateful it never will, but the odds of that are very unlikely given our present (and conceivable future) state of knowledge. Yous may have heard someone dismiss an thought by saying it is "simply a theory," just they are using the term incorrectly if they hateful to say it'due south a wild and unproven guess.

A law is a clarification of a phenomenon rather than an explanation of it. For example, you could do thousands of tests by dropping an object with known mass and measuring its acceleration and the strength with which it hits the ground. Over again and again your results volition yield the formula force = mass x acceleration. However, that doesn't mean you know what is responsible for the force accelerating it toward the ground. Aye, we say that gravity is pulling information technology toward the Earth'south surface, but why? A law is true regardless of why a phenomenon happens as long as it describes the outcome of that phenomenon.

Iii Big Ideas: Geological Fourth dimension, Uniformitarianism, and Plate Tectonics

In geology at that place are three big ideas that are cardinal to the mode nosotros remember nearly how Earth works. The ideas are like the sound track to a movie- sometimes we might not even discover them, only at the aforementioned time they affect our perception of what is happening. In the rest of this book these ideas may be mentioned explicitly in some cases, but in other cases it will be helpful for you to realize that they are relevant, fifty-fifty if they are not being discussed by name.

Geological Time (Deep Fourth dimension)

Earth is approximately 4.57 billion years old (iv,570,000,000 years), which is a long time for geological events to unfold and changes to happen. The changes themselves might be tiny. For case, over a year, a chemic reaction might eat away a few layers of atoms at the surface of a rock. Simply over time the changes accumulate and accept a great impact. Over hundreds of millions of years the chemical reaction could cause a mount range to crumble into grains of sand, and exist swept away by rivers.

For geologists who study very, very deadening processes, 10 million years might be a curt fourth dimension, and 1 million years might be trivial. For these geologists, intervals of one meg years aren't fifty-fifty useful to consider, considering the changes over that fourth dimension are too small to run across in the rocks that accumulated.

As you read through this book, keep in mind that the well of geologic time is indeed deep, and "ancient" is divers in a whole new way.

Expressing Geological Time in Numbers

Special note is used for geological time because, as you might imagine, writing all those zeroes can go tiresome. Table 1.one shows common abbreviations yous will meet throughout this volume.

Table 1.1: Abbreviations Used to Draw Geological Time

Abbreviation	Meaning	Example
Ga	giga annum or billions of years	Earth is 4.57 Ga one-time.
Ma	mega annum or millions of years	Globe is 4,570 Ma old.
ka	kilo annum or thousands of years	The last glacial cycle concluded eleven,700 years ago, or 11.7 ka.

Expressing Geological Fourth dimension Using the Geological Time Scale

The geological fourth dimension calibration (Figure 1.6) is a way of breaking down geological time co-ordinate to important events in Earth's history. Time is divided into eons, eras, periods, and epochs, and these intervals are referred to past names rather than by years. Giving intervals of geologic time names rather than using numbers makes sense because nosotros won't ever know the age in years (the accented historic period) of a rock or fossil, but we can place information technology in context based on our knowledge of the geological tape. We can describe its relative age by saying that it is older than or younger than another rock or fossil.

Figure 1.6: Geologic Society of America Geologic Time Scale, 2012. Source: Walker, J.D., Geissman, J.W., Bowring, Due south.A., and Babcock, L.E., compilers (2012) Geologic Fourth dimension Calibration v. 4.0: Geological Society of America, doi: 10.1130/2012.CTS004R3C. Download PDF

The catchy affair about the geologic time calibration is that the boundaries are ever changing. Equally our knowledge of the absolute historic period of an event improves with new discoveries, it might be necessary to nudge a boundary earlier or after. Sometimes the original reason for defining a purlieus no longer holds, but we agree to utilise it anyway. For example, the Phanerozoic Eon (the last 542 million years) is named for the time during which visible (phaneros) life (zoi) is present in the geological record, and its start was meant to mark the outset advent of these organisms. In fact, we at present have evidence that large organisms — those that exit fossils visible to the naked eye — have existed longer than that, commencement actualization by 600 Ma at the latest.

An Early on Definition of the Proterozoic

Observe that in Figure i.6 the Proterozoic Eon precedes the Phanerozoic Eon. This was not always the instance. Figure 1.seven shows an extract from a periodical published in 1879, in which the Proterozoic is defined equally covering the Cambrian through Silurian. The author refers to "the virtually extreme adherents of the Murchisonian political party in geology," a reference to the contentious assertion by Scottish geologist Roderick Murchison (1792-1871) that the Silurian Menstruum should encompass the Cambrian and Ordovician periods too.

Effigy one.7: An extract from the journal The Annals and Magazine of Natural History (1879) in which the name "Proterozoic" is assigned to the Cambrian, Ordovician, and Silurian periods instead of to the time preceding the Cambrian. Source: Karla Panchuk (2017) CC Past four.0 Read the volume

A Fashion To Think Nigh Geological Time

A useful mechanism for understanding geological time is to scale it down into one yr. The origin of the solar organisation and World at 4.57 Ga would be represented by January 1, and the present year would be represented by the last tiny fraction of a second on New Twelvemonth's Eve. At this scale, each mean solar day of the year represents 12.five million years; each hr represents about 500,000 years; each minute represents 8,694 years; and each 2nd represents 145 years. Some significant events in Earth's history, as expressed on this time scale, are summarized in Table 1.2.

Table 1.2: Some Important Dates Expressed As If All of Geological Time Were Condensed Into Ane Year. Source: Karla Panchuk (2017) CC Past 4.0, modified after Steven Earle (2015) CC BY iv.0 view original.

Event	Judge Date	Calendar Equivalent
Formation of oceans and continents	four.5 - four.iv Ga	first week of January
Evolution of the start primitive life forms	3.eight Ga	end of Feb
Formation of Saskatchewan'south oldest rocks	3.4 Ga	end of March
Development of the first multi-celled animals	600 Ma	get-go of Nov
Animals first crawled onto state	360 Ma	end of November
Vancouver Island reached North America and the Rocky Mountains were formed	ninety Ma	December sixteen
Extinction of the non-avian dinosaurs	65 Ma	December eighteen
Beginning of the Pleistocene ice age	ii Ma	10:10 p.m., December 31
Oldest radiocarbon engagement from people living in Canada (British Columbia)	13.8 ka	xi:58 p.m., Dec 31
Earliest evidence of human action in Saskatchewan	11.5 ka	48 seconds before midnight, December 31
The last of the glacial water ice retreats from Saskatchewan	6 ka	41 seconds earlier midnight, December 31
Hudson'southward Bay Company establishes a permanent settlement at Cumberland Business firm in northern Saskatchewan	243 years ago	2 seconds before midnight, December 31

Uniformitarianism

Uniformitarianism is the notion that the geological processes occurring on Earth today are the same ones that occurred in the past. This is an important thought considering information technology means that observations we make today about geological processes can be used to interpret and understand the rock tape. While this thought might non seem remarkable today, it was ground breaking and fifty-fifty controversial for its time. Many people who heard nearly information technology for the first fourth dimension thought virtually the age of the Earth in thousands of years, just uniformitarianism required them to retrieve on timescales almost as well vast to comprehend. For some, this implied questioning their most deeply held religious beliefs.

The Scottish geologist James Hutton initially presented the idea in 1785¹. Charles Lyell, likewise a Scottish geologist, paraphrased this idea as "the present is the key to the past" in his book Principles of Geology.^two This is how information technology is often described today.

To be articulate, "the present is the cardinal to the by" can be viewed equally an oversimplification. Not all geological processes occurring today occurred at all times in the geological past. For case, some important chemical reactions that happened on Earth'south surface today crave abundant oxygen in the temper, and could not have occurred prior to Globe developing an oxygen-rich atmosphere. Conversely, there was a time in Globe'southward history when continents as nosotros know them hadn't nonetheless adult. Some events, such equally devastating impacts by objects from space, accept never been witnessed on the same scale past humans. We must be cognizant of the fact that conditions were different at different times in Earth'due south history, and accept that into account when interpreting the rock record.

Despite the dissimilar past weather on Globe every bit a whole, there still exist environments today where some of these conditions are nowadays. These environments are like little samples of what World used to be like. This ways we can yet use nowadays conditions to inform us almost the past, but we have to recollect advisedly almost ways that such environments today differ from the ancient environments that no longer exist.

Plate Tectonics

It is but within the terminal 50 years or so that we accept been able to reply questions like, "How did that mountain range become there?" and "Why practise earthquakes happen where they do?" The theory of plate tectonics- the idea that Earth's surface is cleaved into large moving fragments, called plates- profoundly changed our perspective on how the Earth works. Figure one.8 shows World's xv largest tectonic plates, along with arrows indicating the plates' direction of movement, and how fast they go. (Longer arrows mean faster movement.) In that location are many more than plates on Earth that are also small to show conveniently in Figure 1.eight. A more detailed map of Earth's tectonic plates can be found at hither.

Figure i.8: Earth's fifteen largest tectonic plates. Blackness arrows prove the management of plate motions. The length of the arrow indicates velocity. Red arrows show how plates move relative to each other. Source: Steven Earle (2015) CC BY 4.0. view source Modified after U. S. Geological Survey (1996) Public Domain view original

Prior to plate tectonics, we fabricated observations merely could only guess at mechanisms. Information technology was similar watching the hands on a clock and trying to guess what moves them. Afterwards plate tectonics it was like being able to open the clock and not only spotter the gears turn, but realize for the first fourth dimension that at that place are such things as gears. Plate tectonics non only explains why things have happened, just also allows us to predict what might happen in the futurity.

Plate tectonics is covered in more than detail afterwards, however the key bespeak is that Earth's outer layer consists of rigid plates that are constantly interacting with each other every bit they move around the Earth. The boundaries of plates movement abroad from each other in some places, collide in others, and sometimes only slide past each other (illustrated by the red arrows in Effigy i.8). The plates can move because they are floating on a layer of weak stone that deforms equally the plates travel, much the aforementioned way the filling in a peanut butter and jelly sandwich allows you to slide the top layer of bread across the lesser layer.

Whether the plates motility away from each other, collide, or just slide past each other determines things like the locations of mountain belts and volcanoes, where earthquakes happen, and the shapes and sizes of oceans and continents.

Summary

The topics covered in this chapter can be summarized equally follows:

What is Geology?

Geology is the study of World. Information technology is an integrated science that involves the application of many of the other sciences. Geologists must have into account the fact that the geological features nosotros run into today may take formed thousands, millions, or even billions of years ago, and over very long fourth dimension spans.

Why Study Earth?

Geologists written report Globe out of curiosity and for other, more than practical reasons, including understanding the evolution of life on Earth; searching for resources; understanding risks from geological events such as earthquakes, volcanoes, and slope failures; and documenting past ecology and climate changes so that we tin understand how human activities are affecting Earth.

What Do Geologists Do?

Geologists piece of work in the resource manufacture, and in efforts to protect the environs. Geologists work to minimize the risks from geological hazards (e.1000., earthquakes), and to help the public understand those risks. Geologists investigate Earth materials in the field, in and in the lab.

We Study World Using the Scientific Method

Scientific inquiry requires a conscientious process of making a hypothesis and then testing it. If a hypothesis doesn't pass the test, it'south time for a new one. A theory is a hypothesis that has been tested repeatedly and never failed a test. A law is a description of a natural process.

3 Big Ideas: Geological Time, Uniformitarianism, and Plate Tectonics

Geological time: World is approximately 4,570,000,000 years old; that is, iv.57 billion years or 4.57 Ga or 4,570 Ma. It's such a huge amount of time that fifty-fifty extremely slow geological processes tin have an enormous impact.

Uniformitarianism: Processes that occur today as well occurred in the geologic past. We tin employ our observations of the present to sympathise the processes that shaped the Earth throughout its history.

Plate tectonics: Earth's surface is broken into plates that motion and collaborate with each other. The interactions between these plates are key for understanding the mechanisms backside geologic processes.

Chapter Review Questions

1. How does the element of time make geology different from the other sciences, such equally chemical science and physics?

2. Listing 3 ways in which geologists can contribute to society.

3. The following dates are written with the abbreviations Ga, Ma, and ka. Limited the dates in years. (For example, 2.3 Ma = 2,300,000 years)

   1. two.75 ka
   2. 0.93 Ga
   3. four.2 Ma
   4. 0.2 ka

4. Dinosaurs first announced in the geological record in rocks from about 215 Ma and so about became extinct at 65 Ma. What percentage of geological time does this represent?

5. If sediments typically accumulate at a rate of 1 mm/yr, what thickness of sediment could accumulate over a period of 30 million years?

6. Does uniformitarianism mean that conditions on Earth are uniform, and never change?

7. Summarize the chief idea behind plate tectonics.

Answers to Chapter Review Questions

1. Geology requires that nosotros consider vast amounts of time, and think nigh the effects that accrue over thousands, millions, or even billions of years.

2. There are many means that geologists contribute. Geologists provide information to reduce the hazard of harm from hazards such as earthquakes, volcanoes, and slope failures; they play a critical office in the discovery of important resources; they contribute to our understanding of life and its evolution through paleontological studies; and they play a leading role in the investigation of climatic change, by and present and its implications.

3. Ages in years:

   1. 2.75 ka = 2,750 years
   2. 0.93 Ga = 930,000,000 years
   3. 14.ii Ma = 14,200,000 years
   4. 0.2 ka = 200 years

4. 215 - 65 = 150 Ma. Since the age of the Earth is 4570 Ma, this represents 150/4,570 = 0.033 or 3.iii% of geological time.

5. At one mm/y 30,000,000 mm of sediment would accumulate over that 30 million years. This is equivalent to 30,000 yard or thirty km. Few sequences of sedimentary rock are fifty-fifty close to that thickness because near sediments accrue at much lower rates, more like 0.ane mm/y. Also, over fourth dimension the sediments are compressed.

6. No. Uniformitarianism means that we tin use the processes nosotros detect today to assist us understand what happened in the past.

7. Plate tectonics is the thought that Earth'due south outer layer is broken into rigid plates. The plates motility around and interact with each other along their margins.

References

Cottrell, G. (2006) History of Saskatchewan. Retrieved 26 August 2017. Visit the website

Victoria University Library (2009) A. P. Coleman Exhibition. Retrieved 25 August 2017. Visit the website

fielderbantiong.blogspot.com

Source: https://paleolimbot.github.io/physical-geology/introduction-to-geology.html

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