Lesson 1 Reading Guide - KC What is the theory of plate tectonics? What evidence do scientists use to support the theory of plate tectonics? How do the forces created by plate motion change Earth’s surface? Plate Tectonics

Lesson 1 Reading Guide - Vocab plate tectonics continental drift convergent boundaryconvergent boundary divergent boundarydivergent boundary Plate Tectonics transform boundarytransform boundary subduction zonesubduction zone compression tension shear

Hypothesis A possible explanation about an observation that can be tested by scientific investigations. Theory An explanation of observations or events based on knowledge gained from many observations and investigations. Theory vs. hypothesis A theory is an explanation. The validity of a theory rests upon its ability to explain phenomena. Theories may be supported, rejected, or modified, based on new evidence. Gravitational theory, for example, attempts to explain the nature of gravity. Cell theory explains the workings of cells. Evolutionary theory explains the history of life on Earth. A hypothesis is a testable idea. Scientists do not set out to “prove” hypotheses, but to test them. Often multiple hypotheses are posed to explain phenomena and the goal of research is to eliminate the incorrect ones. Hypotheses come and go by the thousands, but theories often remain to be tested and modified for decades or centuries. In science, theories are never hunches or guesses and to describe evolution as “just a theory” is inappropriate.

Lesson 1-1 The theory of plate tectonics states that Earth’s crust is broken into rigid plates that move slowly over Earth’s surface.plate tectonics The rigid plates are called tectonic plates. North America is part of the North American Plate. Plate Motion

Lesson 1-1 The movement of one plate is described as either moving away from or toward another plate, or sliding past another plate. Plates move at speeds of only a few centimeters per year. At this rate, it takes moving plates millions of years to make new continents, new mountain ranges, or other landforms. Plate Motion (cont.)

Lesson 1-1 Long before geologists proposed the theory of plate tectonics, they discovered evidence of continental movement. Plate Motion (cont.) Photo by G.K. Gilbert, U.S. Geological Survey

Lesson 1-1 In 1912, before the Theory of Plate Tectonics came to be, Alfred Wegener developed the hypothesis that continents move, called continental drift.continental drift Plate Motion (cont.)

Wegener used different types evidence to back up his hypothesis: Geological evidence and Fossil evidence This evidence can be used to show where the continents were connected at different times of Earth’s history –Pangaea is the name for the infamous supercontinent that existed in the late Paleozoic and early Mesozoic eras, this is over 2225 million years ago! –After Pangaea broke up, Laurasia and Gondwana were formed, two separate supercontinents (we will be focusing on evidence from Gondwana) this happened 200 million years ago!

Look at how the continents have changed over time… And even now they are still changing. What will they look like in another 100 million years???

Lesson 1-1 One piece of evidence is the shape of Earth’s continents. The outlines of South America and Africa match up like pieces of a puzzle. Plate Motion (cont.)

Lesson 1-1 Fossil and rock evidence from the Gondwana continents also supports the hypothesis of continental drift. Plate Motion (cont.)

Lesson 1-1 Geologists have discovered the same types of fossils on continents that are now separated by vast oceans.

Lesson 1-1 Scientists have also found geological evidence. Rocks that are made of similar substances and mountains that formed at similar times are present on continents that are now far apart. Plate Motion (cont.)

Lesson 1-1 Wegener’s hypothesis of continental drift was not accepted for more than 50 years after it was proposed. The main reason for this was because he could not explain how the continents could move. Plate Motion (cont.)

So how did they Hypothesis of Continental Drift, become the Theory of Plate Tectonics? Harry Hess made it happen!!! Harry Hess was a geologist and Navy submarine commander during WWII In 1960, he proposed that the continents move due to sea-floor spreading (we will come back to this later) This provided the evidence Wegner’s original hypothesis lacked, this proved HOW the continents were moving!!!

Lesson 1-1 Plate Motion (cont.) Convection is the circulation of particles within a material caused by differences in thermal energy and density Convection affects the mantle underneath tectonic plates. Hotter mantle rises toward Earth’s surface and cooler mantle sinks deeper into the mantle.

Lesson 1-1 Plate Motion (cont.) As the Earth’s mantle moves, it pushes and pulls tectonic plates over Earth’s surface. This is what causes sea-floor spreading! As the convection currents in the mantle move the molten material, the lithosphere moves on the surface of Earth

Lesson 1-2 The edges of tectonic plates are called plate boundaries. –A convergent boundary is where two plates move toward each other.convergent boundary –A divergent boundary is where two plates move apart from each other.divergent boundary –A transform boundary is where plates slide horizontally past each other.transform boundary Tectonic Plate Boundaries

Lesson 1-2 Convergent Boundaries When two plates come together, the denser oceanic plate usually is forced down into the mantle and the less dense continental plate remains on Earth’s surface. The area where one plate slides under another is called a subduction zone. subduction zone

Lesson 1-2 When two continents collide at a plate boundary, both continents remain on the surface. As two continents push together, the crust rises up and large mountains form. Convergent Boundaries

Lesson 1-2 When plates move apart at divergent boundaries, a rift forms between the two plates. A rift can form within continents when continental crust moves in opposite directions. Divergent Boundaries

Lesson 1-2 A rift also can form at divergent boundaries on the ocean floor. As plates separate, molten rock can erupt from the rift. As the molten rock cools, it forms new crust. Divergent Boundaries

Lesson 1-2 Tectonic plates slide past each other at transform boundaries. The two sides of the boundary move in opposite directions. This can deform or break features such as fences, railways, or roads that cross the boundary. Transform Boundaries

Lesson 1-3 Forces within Earth cause plates to move. The three types of plate boundaries experience different types of forces. Forces Changing Earth’s Surface

Lesson 1-3 The squeezing force at a convergent boundary is called compression. compression The pulling force at a divergent boundary is called tension.tension The side-by-side dragging force at transform boundaries is called shear. shear

Lesson 1-3 Even though plates move slowly, the forces at plate boundaries are strong enough to form huge mountains and powerful earthquakes. Tensional forces pull the land apart and form rift valleys and mid-ocean ridges. Compressional forces form mountains. Forces Changing Earth’s Surface (cont.)

Lesson 1 - VS Evidence of continental drift includes fossils, mountain ranges, rock types, and the shapes of continents. Earth’s crust is broken into pieces called tectonic plates. Convection currents in the mantle cause the plates to move.

Lesson 1 - VS There are three types of tectonic plate boundaries. Movement occurs at all three boundaries.

Lesson 1 – LR1 Which boundary is between two plates moving toward each other? A.convergent B.divergent C.subduction D.transform

Lesson 1 – LR2 A.convergent B.divergent C.subduction D.transform Which zone describes the boundary where one plate slides under another plate?

Lesson 1 – LR3 A.shear B.tension C.compression D.continental drift Which is the side-by-side dragging force at transform boundaries?

Lesson 1 - Now 1.Continents do not move. 2.Earth’s mantle is liquid. Do you agree or disagree?