Chapter 4 Our Dynamic Earth

Lesson 1 Plate Tectonics

What are Earth’s Layers? Earth is divided into 4 main parts. The crust is the outermost layer of the Earth. The crust is the thinnest layer. At the mountains, the crust is thicker. At the oceans the crust is thinner. The layer just below the crust is the mantle. The mantle is mostly made out of hot, melted rock. The mantle is the thickest layer of the Earth, around 1,802 miles.

The very center of the Earth is the core. The core is divided into the inner and outer core. The inner core is made of solid metals. The outer core is made of liquid metals. These metals are iron and nickle.

The hydrosphere is all of Earth’s liquid and solid water. Geological features are found on the Earth’s surface. A geological feature is a physical structure on Earth’s surface. In Tennessee, you will see mountains, plateaus, valleys, rivers, lakes, and caves.

Quick Check From which layer of Earth do people get most of their resources? From the crust Why do you think it would be difficult to travel to the center of the Earth? The top part is made from solid rock which would be hard, the mantle is made of melted rock which would be hot, the outer core is melted metal which is extremely hot, and the inner core which is solid metal is extremely hard.

What do you notice when looking at our continents?

Are the continents moving? A geologist is a scientist who examines rocks to find out about Earth’s history and structure. Geologist think that millions of years ago the continents were joined together and a force pulled them apart to where they are today. This is called theory of continental drift.

The supercontinent was called Pangaea. In the middle of the Atlantic Ocean, there is a underwater mountain chain. On both sides of the mountain chain, the ocean floor is moving.

Pangaea

Quick Check Is it possible that the animals that became fossils swam across the ocean to the other continent? No, the distance between the two continents is too far from an animal to swim.

What cause the ocean floor to move? Plate tectonics explain how forces deep within Earth can cause ocean floors to spread and continents to move. The crust is made of huge plates of solid rock. The melted rock below causes solid rock to move.

Where the plates are moving apart, magma is pushed up to the surface. Magma is hot, melted rock. Sea floor spreading is when the ocean floor moves apart and separates the plates. Mid-ocean ridges are the underwater mountain ranges that are caused by sea floor spreading.

Seafloor Spreading

Mid-Atlantic Ridge Mountain Range

Quick Check Look at pg. 200 at how the plates are moving.

What forces change Earth’s crust? The same forces that move continents can also change their shapes Transform boundary – where plates slide past each other Earthquakes form along these boundaries. San Andreas Fault

Convergent boundary – where plates collide The collision squeezes the rock together. Convergent boundaries can form mountains. Earthquakes and volcanic activity can also occur here. The Alps were formed by a convergent boundary

Divergent boundary – where plates move apart Sea floor spreading occurs at divergent boundaries. Faults also occur at divergent boundaries. A fault is a break or crack in the rock of the crust along which movements take place.

Types of Faults Strike-slip fault – produced at transform boundaries where plates slide past one another. Reverse fault – produced at convergent boundaries where rock above the fault moves upward. Normal fault – produced at divergent boundaries where rock above the fault moves down and the plates pull apart

Reverse Fault

Reverse Fault

Normal Fault

Normal Fault

What are the different types of mountains? Folded mountains – rock layers are folded together by compressions The Great Smoky Mountains are folded mountains.

Fault-block Mountains – made by huge, tilted blocks of rock separated from the surrounding rock by faults Sierra Nevada mountains are fault-block mountains.

Lesson 2 Volcanoes

What are volcanoes? A volcano is an opening in Earth’s crust. Most volcanoes are found where plates meet. Volcanoes have a magma chamber underneath the rock.

Sometimes the pressure is too great and the magma rushes upward toward Earth’s surface. When magma reaches Earth’s surface, it is called lava. Over time a cup-shaped depression is formed around a volcano vent. This is called a crater. When the magma chamber is emptied, the volcano may collapse inside itself. This is called a caldera.

Caldera

Where are most volcanoes found? The Ring of Fire is a circle of volcanoes that surrounds the Pacific Ocean.

How does magma form geological features? A dike forms when magma hardens in vertical or nearly vertical cracks. A sill forms when magma hardens between horizontal layers of rock. A laccolith is when a sill does not spread horizontally, but it pushes upward and forms a dome.

Dike

Sill

Laccolith

A batholith is a huge and irregularly shaped underground magma formation. When lava comes out of a vent, it is liquid. Lava will form solid rock layers as it hardens building up the height of a volcano. An active volcano is a currently erupting or has recently erupted. A dormant volcano is one that has not erupted for some time.

An extinct volcano is one that has stopped erupting. There are different types of active volcanoes: shield, cinder-cone, and composite.

Shield Volcano Shield volcanoes are built by thinner fluid lava that spreads over a large area. Shield volcanoes have a broad base and gently sloping sides.

Cinder-Cone Volcano Cinder-cone volcanoes are built by thick lava that is thrown into the air and falls as chunks or cinders. Cinder-cone volcanoes form as cone shapes with a narrow base and steep sides.

Composite Volcano Composite volcanoes are built by layers of ash and cinders sandwiched between layers of hardened lava.

How do volcanoes build islands? Island chain is a line of volcanic mountains. The Hawaiian Islands are an island chain. Hawaii rests on top of a slowly moving tectonic plate. As the plate moves, it passes over hot spots which are stationary pools of magma.

Over time the mountain grew taller and moved away from the hot spot Over time the mountain grew taller and moved away from the hot spot. And a new island began to form. An island arc is a string of volcanic islands made from melted rock rising up from beneath the sea floor. This happens when one ocean plate is pushed under another ocean plate so it melts.

Lesson 3 Earthquakes

What is an earthquake? An earthquake is a sudden movement of Earth’s crust. Earthquakes happen when layers of rocks on a fault are stuck together and suddenly slip. Earthquakes usually occur below the Earth’s surface.

The earthquake’s focus is where the slipping begins. Waves ripple out from the focus. When the waves reach the Earth’s surface, they spread out from a point directly above the focus. This is called the epicenter.

The amount of damage of an earthquake depends on the amount of energy released at the earthquake’s focus. Earthquakes happen along the boundaries of tectonic plates.

What waves do earthquakes make? A seismometer is an instrument that detects and measured waves produced by an earthquake. There are 3 kinds of waves: primary waves (P waves), secondary waves (S waves), and surface waves (Lg waves).

Primary waves Move the fastest Pass through both liquid and solid Earth layers Move back and forth as rocks squeeze together and spread apart

Secondary waves Move only in the solid layers of the mantle Move up and down

Surface waves Slowest moving waves Move across Earth’s surface Move like waves of the ocean Causes the most damage

How is an earthquake measured? Magnitude is a measure of the amount of energy released by an earthquake. Richter scale measures magnitude at the epicenter. Richter scale rates the earthquake from the weakest to strongest starting with 1.

Mercalli scale measures what people felt and what happened to objects at the specific locations. Mercalli scale rates the earthquakes in Roman numerals from I to XII. Aftershocks are earthquakes with lesser magnitude. Aftershocks are sometimes felt after the main earthquake.

Tsunamis are huge waves that come on land that are caused by underwater earthquakes. Earthquakes push the water at very high speeds and when the waves reach the shore they are pushed up into the air. Read pg. 226 on how to prepare for an earthquake!

Lesson 4 The Atmosphere

What are weather and climate? The layer of gases that surrounds Earth is called the atmosphere. The atmosphere consists mostly of nitrogen and oxygen. The layer of gases closest to the Earth’s surface is the troposphere. Weather is the condition of the troposphere at a particular time and place.

Climate is the average weather of a place. Average temperatures and average precipitation are important variables in determining climate. Latitude has a strong effect on climate. Latitude is the distance north or south of the equator.

How do oceans affect temperatures on land? Climate is usually milder in places near oceans. Temperature of the land increases faster than the temperature of the water. The movement of air from the water to the land is called a sea breeze. The movement of air from the land to the water is called a land breeze.

How do mountains and ocean currents affect climate? A current is a constant movement of ocean water. Land near cool currents have cool temperatures. Land near warm currents have warmer temperatures. Altitude is a measure of how high a place is above sea level.

The higher the altitude the cooler the climate. Mountain ranges affect rain patterns. One side of the mountain gets all of the rainfall. On this side there will be lots of vegetation. This side of the mountain is called the windward side. The other side receives very little rain and is very dry.

This is called the leeward side. The dry area on the leeward side of the mountain is called a rain shadow.

Rain Shadow

What is El Nino? El Nino is the change in weather conditions caused by the sinking of cold currents in the Pacific Ocean. Higher tides, heavy rains, and storms occur along the coasts of North and South America. Read more about El Nino on page 238.