Introduction to Earth Science PDF

1. UNDERSTANDING SCIENCE Learning Objectives By the end of this chapter, students should be able to: Contrast objective versus subjective observations, and quantitative versus qualitative observations. Identify a pseudoscience based on its lack of falsifiability....

1. UNDERSTANDING SCIENCE Learning Objectives By the end of this chapter, students should be able to: Contrast objective versus subjective observations, and quantitative versus qualitative observations. Identify a pseudoscience based on its lack of falsifiability. Contrast the methods used by Aristotle and Galileo to describe the natural environment. Explain the scientific method and apply it to a problem or question. Describe the foundations of modern geology, such as the principle of uniformitarianism. Contrast uniformitarianism with catastrophism. Explain why studying geology is important. Identify how Earth materials are transformed by rock cycle processes. Describe the steps involved in a reputable scientific study. Explain rhetorical arguments used by science deniers. 1.1 What is Science? Scientists seek to understand the fundamental principles that explain natural patterns and processes. Science is more than just a body of knowledge, science provides a means to evaluate and create new knowledge without bias. Scientists use objective evidence over subjective evidence, to reach sound and logical conclusions. An objective observation is without personal bias and the same by all individuals. Humans are biased by nature, so they cannot be completely objective; the goal is to be as unbiased as possible. A subjective observation is based on a person’s feelings and beliefs and is unique to that individual. Another way scientists avoid bias is by using quantitative over qualitative measure- ments whenever possible. A quantitative measurement is expressed with a specific numerical value. Qualitative observations are general or relative descriptions. For example, describing a rock as red or heavy is a qualitative observation. Determining a rock’s color by measuring wavelengths of reflected light or its density by measuring the proportions of minerals it contains is quantitative. Numerical values are more pre- Figure 1.1: This is Grand Canyon of the Yellowstone in Yellowstone National cise than general descriptions, and they can be analyzed using statistical calculations. Park. An objective statement about this This is why quantitative measurements are much more useful to scientists than qual­ would be: “The picture is of a waterfall.” A subjective statement would be: “The itative observations. picture is beautiful.” or “The waterfall is there because of erosion.” 2 | UNDERSTANDING SCIENCE Establishing truth in science is difficult because all scientific claims are falsifiable, which means any initial hypothesis may be tested and proven false. Only after exhaustively eliminating false results, competing ideas, and possible variations does a hypothesis become regarded as a reliable scientific theory. This meticulous scrutiny reveals weaknesses or flaws in a hypothesis and is the strength that supports all scientific ideas and procedures. In fact, proving current ideas are wrong has been the driving force behind many scientific careers. Falsifiability separates science from pseudoscience. Scientists are Figure 1.2: Canyons like this, carved in the deposit left by the wary of explanations of natural phenomena that discourage or avoid May 18th, 1980 eruption of Mt. St. Helens is sometimes used falsifiability. An explanation that cannot be tested or does not meet by purveyors of pseudoscience as evidence for the Earth scientific standards is not considered science, but pseudoscience. being very young. In reality, the unconsolidated and unlithified volcanic deposit is carved much more easily than Pseudoscience is a collection of ideas that may appear scientific but other canyons like the Grand Canyon. does not use the scientific method. Astrology is an example of pseudoscience. It is a belief system that attributes the movement of celestial bodies to influencing human behavior. Astrologers rely on celestial observations, but their conclusions are not based on experimental evidence and their state- ments are not falsifiable. This is not to be confused with astronomy which is the scientific study of celestial bodies and the cosmos. Science is also a social process. Scientists share their ideas with peers at conferences, seeking guidance and feedback. Research papers and data submitted for publication are rigorously reviewed by qualified peers, scientists who are experts in the same field. The scientific review process aims to weed out misinformation, invalid research results, and wild speculation. Thus, it is slow, cau- tious, and conservative. Scientists tend to wait until a hypothesis is supported by overwhelming amount of evidence from many independent researchers before accepting it as scientific theory. Figure 1.3: Geologists share information by publishing, attending conferences, and even going on field trips, such as this trip to the Lake Owyhee Volcanic Field in Oregon by the Bureau of Land Management in 2019. Take this quiz to check your comprehension of this section. If you are using an offline version of this text, access the quiz for section 1.1 via the QR code. An interactive H5P element has been excluded from this version of the text. You can view it online here: https://pressbooks.lib.vt.edu/introearthscience/?p=66#h5p-1  UNDERSTANDING SCIENCE | 3 1.2 The Scientific Method Modern science is based on the scientific method, a pro­ The Scientific Method as an Ongoing Process cedure that follows these steps: Formulate a question or observe a problem Apply objective experimentation and observation Think of Interesting Analyze collected data and Interpret results Questions Devise an evidence-based theory \ wtl:,«tN lnillll ·,·~-- W IIOm o,oA Submit findings to peer review and/or publication Refine, Alter, Expand, or Reject Hypotheses / This has a long history in human thought but was first fully --- ---~.,, / formed by Ibn al-Haytham over 1,000 years ago. At the forefront of the scientific method are conclusions based on objective evidence, not opinion or hearsay. -------- Figure 1.4: Diagram of the cyclical nature of the scientific method. Step One: Observation, Problem, or Research Question The procedure begins with identifying a problem or research question, such as a geological phenomenon that is not well explained in the scientific community’s collective knowledge. This step usually involves reviewing the scientific literature to understand previous studies that may be related to the question. Step Two: Hypothesis ,,,,. Once the problem or question is well defined, the scientist proposes a possible answer, a hypothesis, before conduct- \.. ' ing an experiment or field work. This hypothesis must be ~ 'I~ - _,._ _ 1.Af/1"... ~ ~ specific, falsifiable, and should be based on other scientific work. Geologists often develop multiple working hypothe­ ses because they usually cannot impose strict experimental , ~ ~ ~ controls or have limited opportunities to visit a field location... -~ r~........... ,......... ,. ~ ,, ~....... ~...... , '""'- - TH & J-1::::. ::Q~OTIOH ·--&l.l.lZ CI.A.";D~1t,· o... l>1 LSL...IVJ> -,AIIPO i>,.-o_,11,y Q 9:°1'1M,ra - olA~"o" Uw 11t.lo.o\"1ot,.,.l,:...l-.. lr.f.. -· :.:':SJ. "-'-,, '. ;.·, --- - ·- - Figure 1.5: A famous hypothesis: Leland Stanford wanted to know if a horse lifted all 4 legs off the ground during a gallop, since the legs are too fast for the human eye to perceive it. These series of photographs by Eadweard Muybridge proved the horse, in fact, does have all four legs off the ground during the gallop. 4 | UNDERSTANDING SCIENCE Step Three: Experiment and Hypothesis Revision The next step is developing an experiment that either supports or refutes the hypothesis. Many people mistakenly think experiments are only done in a lab; however, an experiment can consist of observing natural processes in the field. Regardless of what form an experiment takes, it always includes the systematic gathering of objective data. This data is interpreted to determine whether it contradicts or supports the hypothesis, which may be revised and tested again. When a hypothesis holds up under experimentation, it is ready to be shared with other experts in the field. Step Four: Peer Review, Publication, and Replication Scientists share the results of their research by publishing articles in scientific journals, such as Science and Nature. Reputable journals and publishing houses will not publish an experimental study until they have determined its methods are scientifically rigorous and the conclusions Figure 1.6: An experiment at are supported by evidence. Before an article is published, it undergoes a rigorous peer review the University of Queensland by scientific experts who scrutinize the methods, results, and discussion. Once an article is has been going since 1927. A petroleum product called published, other scientists may attempt to replicate the results. This replication is necessary to pitch, which is highly viscous, confirm the reliability of the study’s reported results. A hypothesis that seemed compelling in drips out of a funnel about one study might be proven false in studies conducted by other scientists. New technology can once per decade. be applied to published studies, which can aid in confirming or rejecting once-accepted ideas and/or hypotheses. Step Five: Theory Development In casual conversation, the word theory implies guesswork or speculation. In the lan- guage of science, an explanation or conclusion made in a theory carries much more weight because it is supported by experimental verification and widely accepted by the scientific community. After a hypothesis has been repeatedly tested for falsifia- bility through documented and independent studies, it eventually becomes accepted as a scientific theory. While a hypothesis provides a tentative explanation before an experiment, a theory is the best explanation after being confirmed by multiple independent experiments. Confirmation of a theory may take years, or even longer. For example, the continen- tal drift hypothesis first proposed by Alfred Wegener in 1912 was initially dismissed. After decades of additional evidence collection by other scientists using more advanced technology, Wegener’s hypothesis was accepted and revised as the the- ory of plate tectonics. The theory of evolution by natural selection is another example. Originating from the Figure 1.7: Wegener later in his life, ca. 1924-1930. work of Charles Darwin in the mid-19th century, the theory of evolution has with- stood generations of scientific testing for falsifiability. While it has been updated and revised to accommodate knowledge gained by using modern technologies, the theory of evolution continues to be supported by the latest evidence.  UNDERSTANDING SCIENCE | 5 Take this quiz to check your comprehension of this section. If you are using an offline version of this text, access the quiz for section 1.2 via the QR code. An interactive H5P element has been excluded from this version of the text. You can view it online here: https://pressbooks.lib.vt.edu/introearthscience/?p=66#h5p-2 _ _ _ _ I 1.3 Early Scientific Thought Western scientific thought began in the ancient city of Athens, Greece. Athens was governed as a democracy, which encouraged individuals to think independently, at a time when most civilizations were ruled by monarchies or military conquerors. Foremost among the early philosopher/scientists to use empirical thinking was Aristotle, born in 384 BCE. Empiricism emphasizes the value of evidence gained from experimentation and observation. Aristotle studied under Plato and tutored Alexander the Great. Alexander would later conquer the Persian Empire, and in the process spread Greek culture as far east as India. Aristotle applied an empirical method of analysis called deductive reasoning, which applies known principles of thought to establish new ideas or predict new outcomes. Deductive reasoning starts with generalized principles and logically extends them to new ideas or specific conclusions. If the initial principle is valid, then it is highly likely the conclusion is also valid. An example of deductive reason­ ing is if A=B, and B=C, then A=C. Another example is if all birds have feathers, and a sparrow is a bird, then a sparrow must also have feathers. The problem with deduc­ Figure 1.8: Fresco by Raphael of Plato (left) tive reasoning is if the initial principle is flawed, the conclusion will inherit that flaw. and Aristotle (right). Here is an example of a flawed initial principle leading to the wrong conclusion; if all animals that fly are birds, and bats also fly, then bats must also be birds. This type of empirical thinking contrasts with inductive reasoning, which begins from new observations and attempts to discern underlying generalized principles. A conclusion made through inductive reasoning comes from analyzing mea- surable evidence, rather making a logical connection. For example, to determine whether bats are birds a scientist might list various characteristics observed in birds–the presence of feathers, a toothless beak, hollow bones, lack of forelegs, and externally laid eggs. Next, the scientist would check whether bats share the same characteristics, and if they do not, draw the conclusion that bats are not birds. Both types of reasoning are important in science because they emphasize the two most important aspects of science: observation and inference. Scientists test existing principles to see if they accurately infer or predict their observations. They also analyze new observations to determine if the inferred underlying principles still support them. 6 | UNDERSTANDING SCIENCE Greek culture was spread by Alexander and then absorbed by the Romans, who help further extend Greek knowledge into Europe through their vast infrastructure of roads, bridges, and aqueducts. After the fall of the Roman Empire in 476 CE, scientific progress in Europe stalled. Scientific thinkers of medieval time had such high regard for Aristotle’s wisdom and knowl- edge they faithfully followed his logical approach to understanding nature for centuries. By contrast, science in the Middle East flourished and grew between 800 and 1450 CE, along with culture and the arts. Near the end of the medieval period, empirical experimentation became more common in Europe. During the Renaissance, which lasted from the 14th through 17th centuries, artistic and scientific thought experienced a great awakening. European scholars began to criticize the traditional Aristotelian approach and by the end of the Renaissance period, empiricism was poised to become a key component of the scientific revolution that would arise in the 17th century. An early example of how Renaissance scien- Figure 1.9: Drawing of Avicenna (Ibn Sina). He is among the first tists began to apply a modern empirical to link mountains to earthquakes approach is their study of the solar system. and erosion. In the second century, the Greek astronomer Claudius Ptolemy observed the Sun, Moon, and stars moving across the sky. Applying Aristotelian logic to his astronomical calculations, he deductively reasoned all celestial bodies orbited around the Earth, which was located at the center of the universe. Ptolemy was a highly regarded mathematician, and his mathematical calculations were widely accepted by the scientific community. The view of the cosmos with Earth at its center is called the Figure 1.10: Geocentric drawing by Bartolomeu geocentric model. This geocentric model persisted until the Renaissance Velho in 1568. period, when some revolutionary thinkers challenged the centuries-old hypothesis. By contrast, early Renaissance scholars such as astronomer Nicolaus Copernicus (1473-1543) proposed an alternative explanation for the perceived movement of the Sun, Moon, and stars. Sometime between 1507 and 1515, he provided cred- ible mathematical proof for a radically new model of the cosmos, one in which the Earth and other planets orbited around a centrally located Sun. After the invention of the telescope in 1608, scientists used their enhanced astronomical observa- tions to support this heliocentric, Sun-centered, model. Two scientists, Johannes Kepler and Galileo Galilei, are credited with jump- starting the scientific revolution. They accomplished this by building on Coper- nicus work and challenging long-established ideas about nature and science. Johannes Kepler (1571-1630) was a German mathematician and astronomer who expanded on the heliocentric model—improving Copernicus’ original cal- culations and describing planetary motion as elliptical paths. Galileo Galilei (1564 – 1642) was an Italian astronomer who used the newly developed tele- scope to observe the four largest moons of Jupiter. This was the first piece of direct evidence to contradict the geocentric model, since moons orbiting Jupiter could not also be orbiting Earth. Figure 1.12: Copernicus’ heliocentric model.  UNDERSTANDING SCIENCE | 7 Galileo strongly supported the heliocentric model and attacked the geocentric model, arguing for a more scientific approach to determine the credibility of an idea. Because of this he found himself at odds with prevailing scientific views and the Catholic Church. In 1633 he was found guilty of heresy and placed under house arrest, where he would remain until his death in 1642. Galileo is regarded as the first modern scientist because he conducted experiments that would prove or disprove falsifiable ideas and based his conclusions on mathematical analysis of quantifiable evidence—a radical departure from the deductive thinking of Greek philosophers such as Aristotle. His methods marked the beginning of a major shift in how scientists studied the natural world, with an increasing number of them relying on evidence and experimentation to form their hypotheses. It was during this revolutionary time that geologists such as James Hutton and Nicolas Steno also made great advances in their scientific fields of study. Figure 1.11: Galileo’s first mention of moons of Jupiter. Take this quiz to check your comprehension of this section. If you are using an offline version of this text, access the quiz for section 1.3 via the QR code. An interactive H5P element has been excluded from this version of the text. You can view it online here: https://pressbooks.lib.vt.edu/introearthscience/?p=66#h5p-3 8 | UNDERSTANDING SCIENCE 1.4 Foundations of Modern Geology As part of the scientific revolution in Europe, modern geologic principles developed in the 17th and 18th centuries. One major contributor was Nicolaus Steno (1638-1686), a Danish priest who studied anatomy and geology. Steno was the first to propose the Earth’s surface could change over time. He suggested sedimentary rocks, such as sandstone and shale, originally formed in horizontal layers with the oldest on the bottom and progressively younger layers on top. In the 18th century, Scottish naturalist James Hutton (1726–1797) studied rivers and coast- lines and compared the sediments they left behind to exposed sedimentary rock strata. He hypothesized the ancient rocks must have been formed by processes like those producing the features in the oceans and streams. Hutton also proposed the Earth was much older than previously thought. Modern geologic processes operate slowly. Hutton realized if these processes formed rocks, then the Earth must be very old, possibly hundreds of millions of years old. Hutton’s idea is called the principle of uniformitarianism and states that natural processes Figure 1.13: Illustration by Steno operate the same now as in the past, i.e. the laws of nature are uniform across space and showing a comparison between time. Geologist often state “the present is the key to the past,” meaning they can understand fossil and modern shark teeth. ancient rocks by studying modern geologic processes. Prior to the acceptance of uniformitarianism, scientists such as German geologist Abraham Gottlob Werner (1750-1817) and French anatomist Georges Cuvier (1769-1832) thought rocks and landforms were formed by great catastrophic events. Cuvier championed this view, known as cata­ strophism, and stated, “The thread of operation is broken; nature has changed course, and none of the agents she employs today would have been sufficient to produce her former works.” He meant processes that operate today did not operate in the past. Known as the father of verte­ brate paleontology, Cuvier made significant contributions to the study of ancient life and taught at Paris’s Museum of Natural History. Based on his study of large vertebrate fossils, he was the first to suggest species could Figure 1.14: Cuvier’s comparison of modern elephant go extinct. However, he thought new species were introduced by special and mammoth jaw bones. creation after catastrophic floods. Hutton’s ideas about uniformitarianism and Earth’s age were not well received by the scientific community of his time. His ideas were falling into obscurity when Charles Lyell, a British lawyer and geologist (1797-1875), wrote the Principles of Geology in the early 1830s and later, Elements of Geology. Lyell’s books promoted Hut- ton’s principle of uniformitarianism, his studies of rocks and the processes that formed them, and the idea that Earth was possibly over 300 million years old. Lyell and his three-volume Principles of Geology had a lasting influence on the geologic community and public at large, who eventually accepted uniformitarianism and millionfold age for the Earth. The principle of uniformitarianism Figure 1.15: Inside cover of Lyell’s Elements of Geology. became so widely accepted, that geologists regarded cata- strophic change as heresy. This made it harder for ideas like the sudden demise of the dinosaurs by asteroid impact to gain traction.  UNDERSTANDING SCIENCE | 9 A contemporary of Lyell, Charles Darwin (1809-1882) took Principles of Geology on his five-year trip on the HMS Beagle. Darwin used uniformitarianism and deep geologic time to develop his initial ideas about evolution. Lyell was one of the first to publish a reference to Darwin’s idea of evolution. The next big advancement, and perhaps the largest in the history of geology, is the theory of plate tectonics and continental drift. Dogmatic acceptance of uniformitar­ ianism inhibited the progress of this idea, mainly because of the permanency placed on the continents and their positions. Ironically, slow and steady movement of plates would fit well into a uniformitarianism model. However, much time passed and a great deal of scientific resistance had to be overcome before the idea took hold. This hap- pened for several reasons. Firstly, the movement was so slow it was overlooked. Sec- ondly, the best evidence was hidden under the ocean. Finally, the accepted theories were anchored by a large amount of inertia. Instead of being bias free, scientists resisted and ridiculed the emerging idea of plate tectonics. This example of dog- matic thinking is still to this day a tarnish on the geoscience community. Plate tectonics is most commonly attributed to Alfred Wegener, the first scientist to compile a large data set supporting the idea of continents shifting places over time. Figure 1.16: J. Tuzo Wilson. He was mostly ignored and ridiculed for his ideas, but later workers like Marie Tharp, Bruce Heezen, Harry Hess, Laurence Morley, Frederick Vine, Drummond Matthews, Kiyoo Wadati, Hugo Benioff, Robert Coats, and J. Tuzo Wilson benefited from advances in sub-sea technologies. They discovered, described, and analyzed new features like the mid-ocean ridge, alignment of earthquakes, and magnetic striping. Gradually these scientists intro- duced a paradigm shift that revolutionized geology into the science we know today. Take this quiz to check your comprehension of this section. If you are using an offline version of this text, access the quiz for section 1.4 via the QR code. An interactive H5P element has been excluded from this version of the text. You can view it online here: https://pressbooks.lib.vt.edu/introearthscience/?p=66#h5p-4 10 | UNDERSTANDING SCIENCE 1.5 The Study of Geology Geologists apply the scientific method to learn about Earth’s materials and processes. Geology plays an important role in soci- ety; its principles are essential to locating, extracting, and manag- ing natural resources; evaluating environmental impacts of using or extracting these resources; as well as understanding and miti- gating the effects of natural hazards. Geology often applies information from physics and chemistry to the natural world, like understanding the physical forces in a land­ slide or the chemical interaction between water and rocks. The term comes from the Greek word geo, meaning Earth, and logos, meaning to think or reckon with. 1.5.1 Why Study Geology? Figure 1.17: Girls into Geoscience inaugural Irish Fieldtrip. Geology plays a key role in how we use natural resources—any naturally occurring material that can be extracted from the Earth for economic gain. Our developed modern society, like all societies before it, is dependent on geologic resources. Geologists are involved in extracting fossil fuels, such as coal and petroleum; metals such as copper, aluminum, and iron; and water resources in streams and underground reservoirs inside soil and rocks. They can help conserve our planet’s finite supply of nonrenewable resources, like petroleum, which are fixed in quantity and depleted by consumption. Geologists can also help manage renewable resources that can be replaced or regenerated, such as solar or Figure 1.18: Hoover Dam provides hydroelectric energy and wind energy, and timber. stores water for southern Nevada. Resource extraction and usage impacts our environment, which can negatively affect human health. For example, burning fossil fuels releases chemicals into the air that are unhealthy for humans, especially children. Mining activities can release toxic heavy metals, such as lead and mercury, into the soil and water- ways. Our choices will have an effect on Earth’s environment for the foreseeable future. Understanding the remaining quantity, extractability, and renewability of geologic resources will help us better sustainably manage those resources. Figure 1.19: Coal power plant in Helper, Utah.  UNDERSTANDING SCIENCE | 11 Geologists also study natural hazards created by geologic processes. Natural hazards are phenomena that are potentially dan- gerous to human life or property. No place on Earth is completely free of natural hazards, so one of the best ways people can protect themselves is by understanding geology. Geology can teach peo- ple about the natural hazards in an area and how to prepare for them. Geologic hazards include landslides, earthquakes, tsunamis, floods, volcanic eruptions, and sea-level rise. Finally, geology is where other scientific disciplines intersect in the concept known as Earth System Science. In science, a system is a Figure 1.20: Buildings toppled from liquefaction during a 7.5 magnitude earthquake in Japan. group of interactive objects and processes. Earth System Science views the entire planet as a combination of systems that interact with each other via complex relationships. This geology textbook provides an introduction to science in general and will often reference other scientific disciplines. Earth System Science includes five basic systems (or spheres), the Geosphere (the solid body of the Earth), the Atmosphere (the gas envelope surrounding the Earth), the Hydrosphere (water in all its forms at and near the surface of the Earth), the Cryosphere (frozen water part of Earth), and the Biosphere (life on Earth in all its forms and interactions, including humankind). Rather than viewing geology as an isolated system, earth system sci­ entists study how geologic processes shape not only the world, but all the spheres it contains. They study how these multidisciplinary spheres relate, interact, and change in response to natural cycles and Figure 1.21: Oregon’s Crater Lake was formed about 7700 human-driven forces. They use elements from physics, chemistry, years ago after the eruption of Mount Mazama. biology, meteorology, environmental science, zoology, hydrology, and many other sciences. 1.5.2 Rock Cycle The most fundamental view of Earth materials is the rock cycle, which describes the major materials that comprise the Earth, the processes The rock cycle that form them, and how they relate to each other. It usually begins Magma C~talUtatlon with hot molten liquid rock called magma or lava. Magma forms Meltln11: under the Earth’s surface in the crust or mantle. Lava is molten rock Textural and/or chemkal damage that erupts onto the Earth’s surface. When magma or lava cools, it Metamorphic Igneous rocks rocks solidifies by a process called crystallization in which minerals grow Additional within the magma or lava. The rocks resulting rocks are igneous chemlc;II or te,ctural change hhumahonor tock back to Weatherin1 rocks. Ignis is Latin for fire. Tel(tural and/or Earth's surface chemical damase Sediment Igneous rocks, as well as other types of rocks, on Earth’s surface are Transport and exposed to weathering and erosion, which produces sediments. Sedimentary depa~ition Weathering is the physical and chemical breakdown of rocks into rocks Bllrialand llthiflc tlon smaller fragments. Erosion is the removal of those fragments from their original location. The broken-down and transported fragments or Figure 1.22: Rock cycle showing the five materials (such as grains are considered sediments, such as gravel, sand, silt, and clay. igneous rocks and sediment) and the processes by which These sediments may be transported by streams and rivers, ocean one changes into another (such as weathering). currents, glaciers, and wind. 12 | UNDERSTANDING SCIENCE Sediments come to rest in a process known as deposition. As the deposited sediments accumulate—often under water, such as in a shallow marine environment—the older sediments get buried by the new deposits. The deposits are compacted by the weight of the overlying sediments and indi- vidual grains are cemented together by minerals in groundwater. These processes of compaction and cementation are called lithification. Lithified sediments are considered a sedimentary rock, such as sandstone and shale. Other sedimentary rocks are made by direct chemical precipitation of minerals rather than eroded sediments, and are known as chemical sedi­ mentary rocks. Figure 1.23: Mississippian raindrop impressions over wave ripples from Nova Scotia. Pre-existing rocks may be transformed into a metamorphic rock; meta- means change and -morphos means form or shape. When rocks are subjected to extreme increases in temperature or pressure, the mineral crystals are enlarged or altered into entirely new minerals with similar chemi- cal make up. High temperatures and pressures occur in rocks buried deep within the Earth’s crust or that come into contact with hot magma or lava. If the temperature and pressure conditions melt the rocks to create magma and lava, the rock cycle begins anew with the creation of new rocks. 1.5.3 Plate Tectonics and Layers of Earth Figure 1.24: Metamorphic rock in Georgian Bay, Ontario. The theory of plate tectonics is the fundamental unifying principle of geology and the rock cycle. Plate tectonics describes how Earth’s layers move relative to each other, focusing on the tectonic or lithospheric plates of the outer layer. Tectonic plates float, col- lide, slide past each other, and split apart on an underlying mobile layer called the asthenosphere. Major landforms are created at the plate boundaries, and rocks within the tectonic plates move through the rock cycle. Plate tectonics is discussed in more detail in chapter 2. Figure 1.25: Map of the major plates and their motions along boundaries. Earth’s three main geological layers can be categorized by chemical composition or the chemical makeup: crust, mantle, and core. The crust is the outermost layer and composed of mostly silicon, oxygen, aluminum, iron, and magnesium. There are two types, continental crust and oceanic crust. Continental crust is about 50 km (30 mi) '° 20 30 40 so 60 70 thick, composed of low-density igneous and sedimentary Figure 1.26: The global map of the depth of the moho. rocks, Oceanic crust is approximately 10 km (6 mi) thick and made of high-density igneous basalt-type rocks. Oceanic crust makes up most of the ocean floor, covering about 70% of the planet. Tectonic plates are made of crust and a portion the upper mantle, forming a rigid physical layer called the lithosphere.  UNDERSTANDING SCIENCE | 13 The mantle, the largest chemical layer by volume, lies below the crust and extends down to about 2,900 km (1,800 mi) below the Lithosphere thick (crust and upper- most solid mantle) Earth’s surface. The mostly solid mantle is made of peridotite, a Mantle high-density composed of silica, iron, and magnesium. The upper part of mantel is very hot and flexible, which allows the overlying tectonic plates to float and move about on it. Under the mantle is the Earth’s core, which is 3,500 km (2,200 mi) thick and made of iron Core and nickel. The core consists of two parts, a liquid outer core and solid inner core. Rotations within the solid and liquid metallic core generate Earth’s magnetic field (see figure 1.27). Figure 1.27: The layers of the Earth. Physical layers include lithosphere and asthenosphere; chemical layers are crust, mantle, and core. 1.5.4 Geologic Time and Deep Time 2 Ma: 230-66 Ma: First Hominins 4550 Ma: Non-avian dino urs ~Formation of the Earth Hom1nins ammals c. 380 Ma: nd plants First vertebrate land animals imals ·cellular life 4527 Ma: C. 530 Ma: ormation of the Moon C. 4000 Ma: End of the 750-635 Ma: Late Heavy Bombardment; / first life C. 3200 Ma: C. 2300 Ma: Atmosphere becomes oxygen-rich; first Snowball Earth Figure 1.28: Geologic time on Earth, represented circularly, to show the individual time divisions and important events. Ga=billion years ago, Ma=million years ago. 14 | UNDERSTANDING SCIENCE “The result, therefore, of our present enquiry is, that we find no vestige of a beginning; no prospect of an end.” (James Hutton, 1788) One of the early pioneers of geology, James Hutton, wrote this about the age of the Earth after many years of geological study. Although he wasn’t exactly correct—there is a beginning and will be an end to planet Earth—Hutton was expressing the difficulty humans have in perceiving the vastness of geological time. Hutton did not assign an age to the Earth, although he was the first to suggest the planet was very old. Today we know Earth is approximately 4.54 ± 0.05 billion years old. This age was first calculated by Caltech professor Clair Patterson in 1956, who measured the half-lives of lead isotopes to radiometrically date a meteorite recovered in Arizona. Studying geologic time, also known as deep time, can help us overcome a perspective of Earth that is limited to our short lifetimes. Compared to the geologic scale, the human lifespan is very short, and we struggle to comprehend the depth of geologic time and slowness of geologic processes. For example, the study of earthquakes only goes back about 100 years; however, there is geologic evidence of large earthquakes occurring thousands of years ago. And scientific evidence indicates earthquakes will continue for many centuries into the future. EON ERA PERIOD EPOCH Ma Holocene Eons are the largest divisions of time, and from oldest to youngest are Quaternary l - - -- - -~ -- -+-0.0 11 - Pleistocene >--- --+- 0.8 1 - - - - ~- 2.4 - -+-- - - - - - + -~,-'----t- named Hadean, Archean, Proterozoic, and Phanerozoic. The three old- II Pliocene '-=- --+- 3.6 - u i 1------+---..- ~ -+- S.3 - est eons are sometimes collectively referred to as Precambrian time. 0 r -==-+- 1 1.2 - u l!lC II..., z Miocene !----;;=ic=+ 16.4 - 1---l~ ~ - - ~ ~i-;c~L-+ 23.0 -.....c:>l:'e""..-j- 28.S - Life first appeared more than 3,800 million of years ago (Ma). From 3,500 I.a;=-._.+- 3 4.0- Ma to 542 Ma, or 88% of geologic time, the predominant life forms were 41.3 - 49.0- SS.8 - single-celled organisms such as bacteria. More complex organisms 61.0 - 6S.S - appeared only more recently, during the current Phanerozoic Eon, u ·s u Cretaceous r---.=:.::-- - - - --,- 99.6 - f - - - - - -+--r:''2------+ 14S - which includes the last 542 million years or 12% of geologic time... 1 Jurassic ~==~~~~~==========~!~! = 0 N II C II The name Phanerozoic comes from phaneros, which means visible, and f - - - - - - --1---..;::::;=o- - - - --+- 200 - "' &. 0. :E Triassic ~==~~~~§::::::::::~~!~ : zoic, meaning life. This eon marks the proliferation of multicellular ani- f--+------+ - ~'2-- - - --+ 2S1 - I -- == - - - - --+- 260 - mals with hard body parts, such as shells, which are preserved in the r----,i,:;;c;"=--------t- 271 - f--- - - - ---1--..=:;..:o------+- 299 1 - ~ - - - - - - - - + - 306 - - geological record as fossils. Land-dwelling animals have existed for 360 3 11 - million years, or 8% of geologic time. The demise of the dinosaurs and 318 - i::------t- 326 - subsequent rise of mammals occurred around 65 Ma, or 1.5% of geologic 34S - 3S9 - time. Our human ancestors belonging to the genus Homo have existed 38S - 397 - since approximately 2.2 Ma—0.05% of geological time or just 1/2,000th 416 - 419 - the total age of Earth. 423 - 4 28 - 444 488 - - The Phanerozoic Eon is divided into three eras: Paleozoic, Mesozoic, - ~ ~ = - -- - - -+- S01 - and Cenozoic. Paleozoic means ancient life, and organisms of this era S13 - S42 - included invertebrate animals, fish, amphibians, and reptiles. The Meso­ 1000- zoic (middle life) is popularly known as the Age of Reptiles and is charac- 1600 - terized by the abundance of dinosaurs, many of which evolved into birds. 2S00 - The mass extinction of the dinosaurs and other apex predator reptiles marked the end of the Mesozoic and beginning of the Cenozoic. Ceno­ 3200- zoic means new life and is also called the Age of Mammals, during which 4000 - mammals evolved to become the predominant land-dwelling animals. Fossils of early humans, or hominids, appear in the rock record only dur- ing the last few million years of the Cenozoic. The geologic time scale, Figure 1.29: Geologic time scale showing time period names and ages. geologic time, and geologic history are discussed in more detail in chap- ter 7 and chapter 8.  UNDERSTANDING SCIENCE | 15 1.5.5 The Geologist’s Tools In its simplest form, a geologist’s tool may be a rock hammer used for sampling a fresh surface of a rock. A basic tool set for fieldwork might also include: Magnifying lens for looking at mineralogical details Compass for measuring the orientation of geologic features Map for documenting the local distribution of rocks and minerals Magnet for identifying magnetic minerals like magnetite Dilute solution of hydrochloric acid to identify carbonate-containing minerals like calcite or limestone. In the laboratory, geologists use optical microscopes to closely examine rocks and soil for mineral composition and grain size. Laser and mass spectrometers precisely measure the chemical composition and geological age of minerals. Seismographs record and locate earthquake activity, or when used in conjunction with ground pen- etrating radar, locate objects buried beneath the surface of the earth. Scientists apply computer simulations to turn their collected data into testable, theoretical models. Figure 1.30: Iconic Archaeopteryx Hydrogeologists drill wells to sample and analyze underground water quality and lithographica fossil from Germany. availability. Geochemists use scanning electron microscopes to analyze minerals at the atomic level, via x-rays. Other geologists use gas chromatography to analyze liquids and gases trapped in glacial ice or rocks. Technology provides new tools for scientific observation, which leads to new evidence that helps scientists revise and even refute old ideas. Because the ultimate technology will never be discovered, the ultimate observation will never be made. And this is the beauty of science—it is ever-advancing and always discovering something new. Take this quiz to check your comprehension of this section. If you are using an offline version of this text, access the quiz for section 1.5 via the QR code. An interactive H5P element has been excluded from this version of the text. You can view it online here: https://pressbooks.lib.vt.edu/introearthscience/?p=66#h5p-5 16 | UNDERSTANDING SCIENCE 1.6 Science Denial and Evaluating Sources One or more interactive elements has been excluded from this version of the text. You can view them online here: https://www.youtube.com/watch?v=8MqTOEospfo Video 1.1: Science in America. If you are using an offline version of this text, access this YouTube video via the QR code. Introductory science courses usually deal with accepted scientific theory and do not include opposing ideas, even though these alternate ideas may be credible. This makes it easier for students to understand the complex material. Advanced students will encounter more controversies as they continue to study their discipline. Some groups of people argue that some established sci­ entific theories are wrong, not based on their scientific merit but rather on the ideology of the group. This section focuses on how to identify evidence based information and differentiate it from pseudoscience. 1.6.1 Science Denial Figure 1.31: Anti-evolution league at the infamous Tennessee v. Scopes trial. Science denial happens when people argue that established sci- entific theories are wrong, not based on scientific merit but rather on subjective ideology—such as for social, political, or economic reasons. Organizations and people use science denial as a rhetorical argument against issues or ideas they oppose. Three examples of science denial versus science are: 1) teaching evo- lution in public schools, 2) linking tobacco smoke to cancer, and 3) linking human activity to climate change. Among these, denial of climate change is strongly connected with geology. A climate denier specifically denies or doubts the objective conclusions of geologists and climate scientists. Figure 1.32: 2017 March for Science in Washington, DC. This and other similar marches were in response to funding cuts and anti-science rhetoric.  UNDERSTANDING SCIENCE | 17 Science denial generally uses three false arguments. The first argument tries to undermine the credibility of the scientific conclusion by claiming the research methods are flawed or the theory is not universally accepted—the science is unsettled. The notion that scientific ideas are not absolute creates doubt for non-scientists; however, a lack of universal truths should not be confused with scientific uncertainty. Because science is based on falsfiabiity, scientists avoid., claiming universal truths and use language that conveys uncertainty. This., V C., ·;;;., E -~ V> ·;::; allows scientific ideas to change and evolve as more evidence is uncovered.., ,ii ] ::, £.,., ~., C" The second argument claims the researchers are not objective and motivated C "O ·e £ C by an ideology or economic agenda. This is an ad hominem argument in which "O 4i E ·;..,E"' 0 a person’s character is attacked instead of the merit of their argument. They => C u claim results have been manipulated so researchers can justify asking for more funding. They claim that because the researchers are funded by a federal grant, they are using their results to lobby for expanded government regulation. Figure 1.33: Three false rhetorical arguments of The third argument is to demand a balanced view, equal time in media cover- science denial. age and educational curricula, to engender the false illusion of two equally valid arguments. Science deniers frequently demand equal coverage of their proposals, even when there is little scientific evi- dence supporting their ideology. For example, science deniers might demand religious explanations be taught as an alter- native to the well-established theory of evolution. Or that all possible causes of climate change be discussed as equally probable, regardless of the body of evidence. Conclusions derived using the scientific method should not be confused with those based on ideologies. Furthermore, conclusions about nature derived from ideologies have no place in science research and education. For example, it would be inappropriate to teach the flat Earth model in a modern geology course because this idea has been disproved by the scientific method. The formation of new conclusions based on the scientific method is the only way to change scientific conclusions. The fact that scientists avoid universal truths and change their ideas as more evidence is uncovered shouldn’t be seen as meaning that the science is unsettled. Unfortunately, widespread scientific illiteracy allows these arguments to be used to suppress scientific knowledge and spread misinformation. In a classic case of science denial, beginning in the 1960s and 20-Year Lag Time Between Smoking and Lung Cancer for the next three decades, the tobacco industry and their sci- Cigarettes Lung Smoked Cancer entists used rhetorical arguments to deny a connection Per Person Deaths between tobacco usage and cancer. Once it became clear Per Year (Per 100,000 scientific studies overwhelmingly found that using tobacco 4000 People) Cigarette dramatically increased a person’s likelihood of getting cancer, ConsuO\ption their next strategy was to create a sense of doubt about on the (men) Lung science. The tobacco industry suggested the results were not 3000 cancer yet fully understood and more study was needed. They used (men) this doubt to lobby for delaying legislative action that would warn consumers of the potential health hazards. This same 2000 tactic is currently being employed by those who deny the sig- nificance of human involvement in climate change. 1000 1900 1920 1940 1960 1980 - - - - -- - - Year - -- - -- -- Figure 1.34: The lag time between cancer after smoking, plus the ethics of running human trials, delayed the government in taking action against tobacco. 18 | UNDERSTANDING SCIENCE 1.6.2 Evaluating Sources of Information In the age of the internet, information is plentiful. Geolo- gists, scientists, or anyone exploring scientific inquiry must Central U.S. discern valid sources of information from pseudoscience 1000 Earthquakes 00 1973 - 2016 and misinformation. This evaluation is especially important ~ Cll ::, in scientific research because scientific knowledge is _g- 800 t: respected for its reliability. Textbooks such as this one can Cll w aid this complex and crucial task. At its roots, quality infor- M 600 mation comes from the scientific method, beginning with ~ 0 the empirical thinking of Aristotle. The application of the