Earth Science Unit 2
What is the definition of lava ?
fluid rock ejected from Earth's surface
Most volcanoes are found at
plate boundaries, where tectonic plates either push together or pull apart. The plate movements cause processes that send plumes of magma to the surface to form volcanic mountains.
A __________________ may be found at the edge of a continent where the oceanic plate and continental plate collide.
volcanic arc
Which statements correctly describe the relationship between Earth's plates and earthquakes?
- Divergent plate boundaries are usually are associated with relatively weak earthquakes - The most severe earthquakes usually are associated with subduction zones
Which of the following provide evidence that South America, Africa, Antarctica, and Australia were once together as one supercontinent? Select the three correct answers.
- Fossils of marsupials were originally the same across South America and Australia. - Glacial deposits and scratches in the bedrock from an ice sheet match in distant regions. - Cratons match across the edges of continents.
Mario is creating a poster that explains how Earth's landmasses move and form, and he wants to contrast the theory of continental drift on one side of the poster with the theory of plate tectonics on the other side. What explanations should he include to support the theory of plate tectonics? Choose all correct answers.
- The seafloor spreads apart at the mid-ocean ridges where magma flows out and cools into new crust. - Earth's lithosphere is made up of plates that move relative to each other due to mantle convection.
Convergent Boundary
- creates subduction zones - high pressure and temperature melting rock to form magma chambers
Which features would you look for to classify a volcano? Select the three correct answers.
- height - steepness - type of lava
Wegener searched for data to support his theory of continental drift. He was looking for evidence of plant and animal life and geographic features that were similar between continents even though the continents were far apart. He found supporting evidence for the following:
- jigsaw fit - geological fit - glacial deposits - fossil evidence
Divergent Boundary
- plates pulling apart along the Mid-Atlantic Ridge - magma rises to the surface, cools and becomes new crust
Scientists continued to modify and revise Wegener's theory after his death. New technologies that allowed new data to be collected ignited interest in the theory again in the 1950s. Over the next few decades, scientists found new evidence to support continental drift, such as the following:
- seafloor spreading - hotspots - transform faults - mantle convection
Which processes are important in the formation of volcanic arcs at the edge of continental plates? Select the two correct answers.
- subduction - uplift
Which information is needed to construct a geomagnetic time scale? Select the two correct answers.
- the age of rocks along the surface of Earth - the magnetic direction of rocks along the surface of Earth
There are three known types of tectonic plate boundaries. The different ways plates interact at boundaries help to connect the ideas of plate tectonic theory. They answered questions about how different landforms, such as mountains, are created and what causes geological events, such as earthquakes. Tectonic plate boundaries and their movements can be summarized as follows:
1. Plates move past each other at transform boundaries. 2. Plates move away from each other at divergent boundaries. 3. Plates push against each other at convergent boundaries.
Wegener presented several types of geological evidence, such as glacial deposits, for his theory—the theory of continental drift. He used maps to show how
Earth's continents—in different places, long ago—once fit together like pieces of a giant jigsaw puzzle.
What is the definition of the theory of plate tectonics ?
Earth's lithosphere is divided into plates that move over the mantle, changing Earth's surface.
Earthquakes occur when
Earth's plates move against or past each other at their boundaries. This movement releases energy in waves that cause the ground to shake. About 90 percent of the world's earthquakes occur in the "Ring of Fire," an area surrounding the Pacific Ocean where the Pacific Plate collides with several other plates. The Ring of Fire, which stretches for 40,435 km (25,000 mi.), includes more than 450 (mostly undersea) active volcanoes.
What evidence supported Wegener's idea that South America and Antarctica had once been connected?
Fossils of the same species can be found in both Brazil and West Africa. There are glacial deposits on Antarctica and the southern part of South America. Wegener believed they supported his idea.
Not every earthquake has a(n) [blank], but every earthquake has [blank] that occur in [blank] the mainshock
Not every earthquake has a(n) [foreshock], but every earthquake has [aftershocks] that occur in [in the same place as] the mainshock
What is the difference between P waves and S waves?
P waves compress and expand (shake) the ground in the same direction and in the opposite direction that they are moving. They are weaker but faster than S waves. S waves deform the ground perpendicular to the direction they are moving. They are stronger and slower than P waves.
How are satellites useful in monitoring volcanoes?
Satellites can be used along with GPS to monitor deformation of the land surrounding a volcano and to produce images that show emission of gases and flow of lava.
How do scientists use fossils to unlock mysteries about the past?
Scientists study fossils to determine what forms of life existed on Earth at different times in Earth's history.
Geologist discovered fossils of identical spider mites from the same time period but on opposite sides of the ocean from each other. What conclusion is supported by the discovery of these fossils?
The locations of the fossils were once much closer to each other.
Why do ancient rocks have different magnetic directions?
The magnetic direction of the rocks depends on the direction of Earth's magnetic field when the rocks formed. Magnetic iron pieces within lava align with the Earth's magnetic field when the lava cools to form solid rock.
One common plate boundary feature is the
volcanic arc . Often volcanic arcs form at the edges of continents, where an oceanic plate and a continental plate collide. Oceanic plates are denser than continental plates, and, as a result, subduction occurs. The denser oceanic plate slips under the lighter continental plate, causing uplift of the continental plate on top of it. The leading edge of the oceanic plate then undergoes partial melting when it meets intense heat about 60 miles down in the mantle. The melted crust forms hot magma, which is less dense than the solid crust above and surrounding it. Some of this magma rises through passageways toward the surface, where it bursts forth to form volcanic mountains.
What clues indicated that the Parícutin volcano was about to erupt?
Villagers noticed the rumbling of deep earthquakes followed by ground swells, a crack in the land, a sulfur smell, and eventually emission of smoke and flaming rock fragments.
Can volcanoes form away from plate boundaries? If so, where would they form, and how?
Yes. Volcanoes can form away from plate boundaries. Volcanoes can form at hotspots under the ocean or on land. Hotspot volcanoes, like those of Hawaii, form from plumes of magma that rise up from unusually hot areas under the crust. The magma breaks through openings in the crust and can build over time into a volcano.
One of simplest types of volcanoes is
a cinder cone, also known as a scoria cone. Compared to other types of volcanoes, cinder cones are usually much smaller and might form in just a few months or years. The name cinder cone refers to the single, symmetrical cone at the top of a steep hill or mountain and the chunks of lava, called cinder, that are ejected during an eruption and quickly cool.
At which type of boundary is new oceanic crust created?
a divergent plate boundary
Most earthquakes happen at
a fairly shallow depth in Earth's crust—about 80 km (50 mi.) below the surface—but they can occur as deep as 750 km (400 mi.) below the surface. Some earthquakes have one or more foreshocks, which are smaller earthquakes that happen before the mainshock, or main earthquake. All main earthquakes have aftershocks, which are smaller earthquakes that happen after the mainshock. Foreshocks and aftershocks happen in the same place as the mainshock.
What is the definition of island arc ?
a line of volcanoes in the ocean near a convergent plate boundary
What is the definition of volcanic arc ?
a line of volcanoes on land near a convergent plate boundary
What is the definition of pyroclastic flow ?
a mass of hot gases, rock, and ash that moves down the sides of an erupting volcano
What is the definition of hotspot ?
a place on Earth's surface which is fed by underlying mantle that is hotter than surrounding mantle a hot area under a plate that creates plumes of magma that form volcanoes
A volcano is
a rupture in Earth's crust where lava and gases can burst out onto the surface. The mountain formed by a volcanic eruption is also known as a volcano.
What is the definition of transform fault ?
a tectonic plate boundary where plates slip past each other
Alfred Wegener was one of these scientists. In 1912, he theorized that
all of the continents had been part of one big supercontinent, which he called Pangaea.
For example, the Juan de Fuca plate is located off the western coast of North America. As it moves northeast at four centimeters per year, it subducts below the North American plate. Paleomagnetic evidence reveals some of the history of the Juan de Fuca plate. The broken alignment ofN/A the magnetic stripes indicates that the plate fractured along a transform fault during a large-scale seismic event that likely involved a series of earthquakes. Scientists can use the striping pattern to determine
approximately when the earthquakes took place.
The oldest of Hawaii's volcanic islands are those that
are the farthest distance from the hotspot.
At which type of plate boundary do tectonic plates slide past each other?
at conservative plate boundaries
Iceland is an example of
volcanism at a divergent plate boundary. Iceland straddles the dividing line between the North American Plate to the west and the Eurasian Plate to the east. It is a place where the mid-Atlantic ridge comes to the surface and the plate boundary becomes visible on land. There is also a reservoir of magma beneath Iceland. This reservoir, plus the natural upwelling of magma at a divergent boundary, has created many volcanoes on Iceland.
Many scientific theories and discoveries begin with observation. Observations that eventually led to the theory of plate tectonics began as early as the 1500s when
cartographers began drawing maps of the world. These world maps gave people a picture of what the continents looked like and where they were located. It did not take long to see that the outlines of the continents around the Atlantic Ocean were very similar. Soon, cartographers, philosophers, and other scientists were speculating that the continents had once been joined. It would take a few hundred more years, but these observations were the beginning of what is known today about Earth's continents and how they move.
Not all volcanoes erupt as violently as Mount St. Helens did in 1980. The type of eruption depends on
where the volcano is and, as a result, the composition of its magma.
With a convergent boundary, two plates
collide. If one of the plates is composed mainly of thinner oceanic crust, it will be forced under the plate composed of mainly continental crust in a process called subduction. Convergent boundaries tend to spawn the strongest earthquakes as the two plates collide, with slightly weaker earthquakes occurring as one plate continues to move under the other.
Divergent boundaries also occur on
continents. One example is Africa's Great Rift Valley, where the African Plate and the Somali Plate are pulling away from each other. The result is a long, narrow rift valley dotted with volcanoes and often shaken by earthquakes.
The location of the San Andreas __________________ is one reason California is so prone to earthquakes.
fault
The __________________ of an earthquake can be found inside Earth's crust underneath the epicenter.
focus
What evidence did Alfred Wegener gather to support his theory of continental drift?
fossil evidence, jigsaw fit, glacial deposits, geological fit
Similar animal __________________ found in two different continents helped form Alfred Wegener's theory that continents used to be joined.
fossils
Some of Wegener's strongest evidence was linked to
fossils . He found several types of plant and animal traces and remains that seemed to prove the continents have moved over time. Proof of drifting continents was an early step toward understanding that Earth's surface is composed of a number of interlocking, movable plates.
A volcanic __________________ can form islands such as those found in Hawaii.
hotspot
While many scientists agreed with the evidence Wegener provided for the theory of continental drift, one part of his theory was disputed. Scientists did not agree with Wegener's idea about
how the continents had actually moved.
Wegener was not deterred and proposed that the gravitational pull of the moon could cause the continents to move. This, too, was shown by scientists to be
impossible. Scientists also had other ideas about how to explain some of the evidence for continental drift. Some suggested that animals had moved from one continent to another by land bridges that had since disappeared.
Where would you be most likely to find the oldest rocks on Earth?
in the middle of the continents
When scientists construct maps showing the magnetic direction of rocks found at different distances from mid-oceanic ridges, they find patterns of
irregular, alternating magnetic stripes. The stripes are mirror images on either side of the ridge. Scientists can use the pattern to determine how fast new rock is forming at the ridge, as well as how fast landforms supported by the plate move along Earth's surface.
Over time an __________________ of underground volcanoes can break the surface of the water to form new land.
island arc
When plates collide on the ocean floor, an
island arc can form. Subduction also occurs at these boundaries. Lava plumes formed by melting of the leading edge of the subducted plate rise through the ocean floor, slowly building volcanic mountains. Over long periods of time, the mountains can break the ocean's surface to become chains of volcanic islands. Just as with volcanic arcs on land, trenches can form in the subduction zones next to island arcs.
A volcano is classified as active if
it has erupted within the past 10,000 years and as dormant if it has not. An extinct volcano is never expected to erupt again.
What is the definition of focus ?
location in Earth's crust at which an earthquake begins
__________________ is similar to heating water in a tea kettle where the warmer parts of Earth's material move up and the cooler parts move down.
mantle convection
Jigsaw puzzles were originally used to teach geography. Today, puzzles have any number of images on them, but in the eighteenth century, they were made using
maps. It should come then as no surprise that scientists began wondering if the continents would fit together like puzzle pieces.
A kangaroo with its iconic pouch is a well-known type of __________________.
marsupial
Divergent boundaries form
mid-ocean ridges such as the Mid-Atlantic Ridge, an undersea mountain range that formed at the boundary between the North American Plate and the Eurasian Plate. It extends through the Atlantic Ocean from the Arctic Ocean to the tip of Africa. At the top of the ridge is a rift, or valley, where molten rock bubbles up from the mantle and forms new crust, pushing the plates away from each other. Over 100 to 200 million years, this divergent boundary has made the Atlantic Ocean into the immense expanse of water it is today.
What is the definition of mantle convection ?
movement in the mantle in which cooler parts move down and warmer parts move up
As the flipbook explains, skewed magnetic directions in continental rock layers help scientists understand continental drift. Rocks on the ocean floor that record large reversals in Earth's magnetic field also provide valuable
paleomagnetic evidence that supports tectonic plate theory.
Scientists specializing in __________________ might use their skills to draw maps that determine how fast new rocks are forming.
paleomagnetism
There are large and small plates that are part of the lithosphere of Earth. The lithosphere rests on and moves across the asthenosphere beneath it, which is made of molten rock. Scientists still aren't completely certain how this works, but the plates interact at
plate boundaries. These interactions have shaped and continue to shape Earth's surface.
Two plates pushing into each other is one thing that could happen at a __________________.
plate boundary
Paleomagnetic patterns also help scientists know when
plates fractured or changed their movement relative to one another. In this way, scientists can piece together the geologic history of a tectonic plate, which also supports tectonic plate theory.
What is the definition of epicenter?
point on Earth's surface directly above where an earthquake begins
The __________________ from the erupting volcano destroyed everything in its path, partially due to its extremely fast speed.
pyroclastic flow
Earthquakes at all three types of plate boundaries can
reshape mountains and create valleys and lakes. They can change how groundwater flows, and they can cause mudslides and landslides that change Earth's surface.
What main process do all volcanoes have in common, regardless of the specific ways they form?
rising magma
__________________ was a theory proposed by Harry Hammond Hess to explain how continents moved apart as new oceanic crust was formed.
seafloor spreading
Like Mesosaurus , fossils of Cynognathus were also found in South America and Africa. Cynognathus was a land reptile about 3 feet in length that lived during the Triassic Period. The areas where fossils of this reptile were found are now
separated by thousands of miles of ocean.
Evidence from many parts of the world strengthened Wegener's argument. It showed that
similar animal species lived long ago on continents that today are separated by vast distances.
With a transform boundary, two plates
slip or grind past each other horizontally. Earthquakes of middle strength tend to occur at transform boundaries, with somewhat weaker earthquakes occurring when the transform boundary is underwater (as most are). The many faults in the San Andreas Fault Zone in California are examples of transform boundaries—in this case, between the Pacific Plate and the North American Plate.
Mesosaurus was a small reptile that lived in fresh water. Mesosaurus fossils were found in two places—
southern Africa and eastern South America. Because Mesosaurus is a freshwater animal, it does not have the ability to swim across a large body of salt water such as the Atlantic Ocean.
The three main types of volcanoes are
stratovolcanoes, shield volcanoes, and cinder cone volcanoes. The different types are distinguished by their shape, whether they have explosive or quiet eruptions, and the type of lava that flows from them.
More than half of the volcanoes on Earth are
stratovolcanoes. These tall volcanoes have a gentle slope near the base rising to steep sides and a narrow cone at the top. They may also have vents at various places along the sides of the volcano. Stratovolcanoes are also known as composite volcanoes because of their layers of lava, ash, and rock. The magma of a stratovolcano is viscous, causing it to build up underground with increasing pressure until it suddenly explodes with a dangerous eruption. The thick lava from a stratovolcano flows slowly and quickly hardens to produce the steep sides of the volcano.
Parts of Canada and Alaska have a __________________, which gives them very long and cold winters.
subarctic climate
__________________ is the process when two plates meet and one is forced below the other.
subduction
Many of the islands of Southeast Asia contain volcanoes that formed due to
subduction at convergent boundaries on the ocean floor. Some of these volcanoes have produced historically large eruptions. They include composite volcanoes Krakatoa and Tambora, in Indonesia. Krakatoa ripped its island apart in 1883 with an eruption so powerful that it could be heard 2,800 miles away. Even earlier, in 1815, Tambora erupted with an explosion 100 times more powerful than that of Mount St. Helens.
Convergent boundaries don't always result in
subduction, though. The Indian and Eurasian Plates are both composed of continental crust, so when they collided at a convergent boundary, neither was subducted. Instead, they continued to push against one another, slowly forming the Tibetan Plateau and the towering Himalayan Mountains.
Wegener believed the location of the Mesosaurus fossils proved
that Africa and South America were once joined. His theory was strengthened by the coastlines of the two continents, which seem to fit together. If that were true, the continents must have moved to their present positions—an ocean apart.
Thanks to Alfred Wegener's observation of the shapes of the continents, we know
that's exactly what happened. There's even rock and fossil evidence supporting continental drift. It's the movement deep below Earth's crust that causes earthquakes and volcanoes. Not only do Earth's tectonic plates move, but thanks to invisible patterns on the ocean floor, we also know that the magnetic poles flip! Earth is really always changing, no matter how permanent it seems!
The location and severity of an earthquake are affected by
the composition of the plates involved and the type of boundary between them. Some plates are composed of either thick continental crust or thinner oceanic crust, while other plates are composed of both continental and oceanic crust.
The movements of Earth's plates, including the resultant earthquakes, are responsible for
the formation and alteration of many different types of landforms.
What is the definition of seafloor spreading ?
the formation of new oceanic crust at mid-ocean ridges through the upwelling of magma
In some parts of the United States, earthquakes are a common occurrence. Alaska has
the most earthquakes by far, but earthquakes also occur frequently in California, Hawaii, Nevada, Montana, Oklahoma, and Wyoming. Several million earthquakes occur every year worldwide. Most are too small to be felt by humans, but about 500,000 per year are detectable with instruments. Humans can feel the vibrations caused by about 100,000 of these earthquakes, and about 100 earthquakes per year cause damage.
A shield volcano gets its name from
the resemblance of its wide, dome shape similar to a knight's shield lying on the ground. The magma that forms a shield volcano is less viscous, producing quieter eruptions. The lava flows long distances from the summit or vents along the sides before cooling into thin sheets. The layers of lava give a shield volcano its broad base with gentle slopes to the summit.
The rock on both sides of a fault moves because Earth's plates are always moving. The rough edges of the rocks get caught on each other at the fault. As the plates continue to move, energy builds up where the edges are stuck. An earthquake begins when
the rocks finally move past each other along the fault, at a point called the focus (also called the hypocenter). The contact releases waves of energy that move outward from the focus in all directions and cause the shaking that people feel. The epicenter of the earthquake, which is located directly above the focus at Earth's surface, is often where the most damage takes place. Sometimes, an earthquake causes rock to be thrust above the Earth's surface at the fault line, forming a fault scarp that looks like a giant step.
The ages of rocks along mid-oceanic ridges reveal that
the seafloor spreads outward from the ridge.
What is the theory of continental drift ?
the slow drift of continents apart from each other
Scientists use sensitive instruments called seismographs to measure
the strength of earthquakes
What is the definition of paleomagnetism ?
the study of ancient magnetic fields
Which best describes paleomagnetism?
the study of ancient magnetic fields
Alfred Wegener argued that the coastlines of Africa and South America used to fit together like jigsaw puzzle pieces as part of the __________________.
theory of continental drift
The __________________ helps explain how Earth's surface changes and how volcanoes and mountains form.
theory of plate tectonics
The movement that can be seen when you heat water on the stove is a result of __________________.
thermal convection
Fossils of the Glossoptera plant gave Wegener and his supporters additional evidence. Glossoptera was a fern that grew in subarctic climates . Investigations show that the fossils left behind by the plant during the Paleozoic Era were found in what are now Africa, Australia, India, and South America. Later, an expedition to the South Pole returned with Glossoptera fossils found in Antarctica. The areas where the fossil ferns were found have diverse climates today—not all of them hospitable for the plant. Wegener therefore believed
these lands were grouped in a common climate region in the distant past.
In 1915, Alfred Wegener proposed a unique theory. He wrote that Earth's continents are not stationary—
they move. In fact, over millions of years they have moved long distances across Earth's surface.
Hot Spot is characterized by a
thin spot int he crust
Wegener thought that the rotation of Earth created a centrifugal force that caused Pangaea to break apart and move away from the poles. Scientists, however, did some calculations, and most agreed that
this centrifugal force would not be enough to move continents.
Earth's high mountain ranges and low, flat plains help make up its varied __________________.
topography
What is the definition of fossil ?
traces or remains of past plant and animal life
A conservative plate boundary is also known as a __________________ and is a type of boundary where plates slip past each other.
transform fault
A __________________ can be formed when two plates meet and one is forced below the other.
trench
Continents are made up of stable areas of Earth's crust called a __________________.
craton
When plates are subducted at convergent boundaries, they often form
deep ocean trenches. Subduction can also form mountain ranges. For example, when the oceanic Nazca Plate was subducted under the continental South American Plate, the South American Plate was lifted up. It formed the Andes Mountains.
Earth's oceans are split by
divergent plate boundaries that form a chain of mid-ocean ridges. In several places at these boundaries, upwelling magma has formed volcanoes.
There are three types of boundaries between plates:
divergent, transform, and convergent. When two plates pull apart, they have a divergent boundary. At the point where the plates pull apart, molten rock wells up from the mantle, cools, and forms new, thin crust. The weakest earthquakes occur at divergent boundaries.
During an earthquake people closest to its __________________ may feel stronger movement than those farther away.
epicentre
Geologists discovered that the largest coal deposits were formed around 300 million years ago. How did this observation support the theory of plate tectonics?
Around that time, those regions were located in tropical climates that were partially submerged on the coasts.
What was the relationship of fossils to the theory of continental drift?
Fossils showed evidence that supported continental drift.
What will happen where two continental plates collide at a convergent boundary?
The plates push up, forming a mountain range.
What is the definition of subarctic climate ?
a climate that is harsh, but not as cold as an Arctic climate
Where are the newest parts of Earth's crust located?
at mid-ocean ridges
What is the definition of fault ?
fracture or zone of fractures in Earth's crust
The stream of __________________ flowing down from the erupting volcano destroyed everything in its path.
lava
What is the definition of subduction ?
the forcing of one tectonic plate below another
Scientists wondered how volcanoes could be located so far from tectonic plate boundaries until one proposed the idea of [blank], where the magma is much hotter than the surrounding magma. These are [blank] and do not move with tectonic plates. They are responsible for the creation of [blank] chains.
1. hotspots 2. fixed 3. volcanic
How does evidence from fossils and other sources accumulate to support a new scientific theory?
As scientists learn an increasing amount of information over time from fossils, new research, and advances in the tools available to them, they can often confirm observations and hypotheses to support a new scientific theory.
How are P waves used in earthquake warning systems?
Because P waves are the fastest earthquake waves, seismographs detect them first. Scientists can then send out an earthquake warning alert so people have time to get to a safer area.
How do scientists use the magnetic direction of ancient rocks to explain that continents have moved over time?
Layers within lava rock have slightly skewed magnetic directions. Scientists conclude that the directions are skewed because the plate on which each rock layer formed was moving relative to Earth's magnetic field, which remains relatively stable for long time periods. If the plates move, the continents atop them move, too.
Lystrosaurus was another land reptile common during the Triassic Period. Fossils from this extinct animal were found in India, Africa, and even in Antarctica. Aside from being separated by vast oceans today, these areas have very different climates. Wegener reasoned that it is
Lystrosaurus was another land reptile common during the Triassic Period. Fossils from this extinct animal were found in India, Africa, and even in Antarctica. Aside from being separated by vast oceans today, these areas have very different climates. Wegener reasoned that it is
Describe how magnetic striping patterns near a mid-oceanic ridge help support the theory of plate tectonics.
Magnetic striping patterns help scientists determine how fast new rock is forming at the ridge, and how fast it is causing landforms supported by the plate to move along Earth's surface. This supports the continental drift idea of tectonic plate theory.
Wegener compiled fossil evidence of similar animals that are now on separate landmasses, which at one time could have been joined. One example is
Mesosaurus
Wegener also presented evidence from plants. He studied fossils found on the Svalbard Islands north of Norway. The islands have a cold, harsh climate during much of the year. Interestingly, the fossils Wegener located were of plants native to a much warmer climate. How could fossils of such plants be found north of the Arctic Circle? Wegener's answer:
The Svalbard islands have not always been in their current polar location. Rather, they were once located where the climate was warmer.
As scientists investigated more rocks from the ocean floor, they identified another important source of evidence.
The rocks could be placed in categories according to their magnetic field direction. Some rocks had a north-south direction similar to Earth's current magnetic field (magnetic normal). Other rocks had magnetic fields oriented in the opposite direction (magnetic reverse). Scientists also discovered magnetic patterns in lava rock found on land.
Name two pieces of evidence that Wegener found that suggested Brazil and West Africa had fit together like a jigsaw puzzle millions of years ago.
There is a belt of ancient rocks in Brazil that matches a belt of ancient rocks in West Africa.
Why were the fossil remains of Mesosaurus important to Alfred Wegener?
They suggested that the two continents where they were found could have been joined.
