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Simulation

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Simulation

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Explore Tabs

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This is in the techbook for Massachuesetts sci standards

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Theory of Plate Tectonics Flashcards | Quizlet

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Sea Floor Spreading

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*Relative Age of Rocks Flashcards | Quizlet

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Theory of Seafloor Spreading

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Layers of the Earth | #aumsum #kids #science #education #children

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Earth's Interior Isn't Quite What We Thought It Was | TNTM

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It turns out that Earth's interior is way more wild than you probably thought -- there's liquid metal, hidden oceans, and it's hotter than the surface of the sun. So, what's really going on below our feet?

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3 Types of Rocks and the Rock Cycle: Igneous, Sedimentary, Metamorphic - FreeSchool

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Continental Drift and Plate Tectonics Theory for kids

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The secrets buried inside our planet are revealed by recording and studying things called seismic waves. Caused by things like earthquakes, explosions and the movement of our oceans, there are two types of seismic wave - a shear wave, which won't travel through liquid; and a pressure wave, which moves through both liquid and solids. These waves show that the Earth is made from five layers: the inner and outer core, the lower and upper mantle, and the crust.

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The Earth's inner core is a huge metal ball, 2,500km wide. Made mainly of iron, the temperature of the ball is 5,000°C to 6,000°C - that's up to 6,000 times hotter than our atmosphere and scorching enough to make metal melt! The metal at the inner core stays solid because of the incredible pressure surrounding it.

Temperature: 4,000°C - 6,000°C
State: Liquid
Composition: iron, nickel, sulphur and oxygen

This liquid layer of iron and nickel is 5,150km deep. The outer core flows around the centre of the Earth, and the movement of the metals creates our planet's magnetic field.

Lower Mantle

The lower mantle is found between 670km and 2,890km below the surface, and is made from solid rock. The rock is hot enough to melt, but is solid because of the pressure pushing down on it.

Upper Mantle

Temperature: 1,400°C - 3,000°C
State: liquid / solid
Composition: iron, oxygen, silicon, magnesium and aluminium

This layer is up to 670km below the Earth's surface. The lower part of the upper mantle is made from both solid and melted rock (liquid), while the rock in the upper region is stiffer, because it's cooler.

Temperature: Around 22°C
State: Solid
Composition: Oceanic crust made up of iron, oxygen, silicon, magnesium and aluminium.
Continental crust made up of granite, sedimentary rocks and metamorphic rocks.

The Earth's surface is covered by its thinnest layer, the crust. Land is made of continental crust, which is 8km to 70km thick and made mostly from a rock called granite. The layer beneath the ocean bed is made of oceanic crust, which is about 8km thick and made mainly from a rock called basalt.

By studying rocks and meteorites (rocks from space), scientists believe the Earth is about 4.5 billion years old!

Illustration: Getty Images UK

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Structure of the Earth! - National Geographic Kids

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Learn all about the structure of the Earth here at National Geographic Kids! Join us as we explore the different layers - the crust, upper mantle, lower mantle, outer core and inner core...

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Science for Kids: Composition of the Earth

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Kids learn about the science of the composition of the Earth. Different layers and what they do.

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Kids learn about the Earth science subject of plate tectonics including major and minor plates, convergent, divergent, and transform boundaries.

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Kids learn about the Earth science subject of fossils including the ways fossils form, types such as trace and body, fun facts, collecting, and where they are found.

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Kids learn about the science of rocks and the rock cycle. How different types such as igneous, sedimentary, and metamorphic form from minerals with the help of nature.

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Seafloor spreading occurs at divergent plate boundaries. As tectonic plates slowly move away from each other, heat from the mantle's convection currents makes the crust more plastic and less dense. The less-dense material rises, often forming a mountain or elevated area of the seafloor.

Eventually, the crust cracks. Hot magma fueled by mantle convection bubbles up to fill these fractures and spills onto the crust. This bubbled-up magma is cooled by frigid seawater to form igneous rock. This rock ( basalt) becomes a new part of Earth's crust.

Seafloor spreading occurs along mid-ocean ridges-large mountain ranges rising from the ocean floor. The Mid-Atlantic Ridge, for instance, separates the North American plate from the Eurasian plate, and the South American plate from the African plate. The East Pacific Rise is a mid-ocean ridge that runs through the eastern Pacific Ocean and separates the Pacific plate from the North American plate, the Cocos plate, the Nazca plate, and the Antarctic plate. The Southeast Indian Ridge marks where the southern Indo-Australian plate forms a divergent boundary with the Antarctic plate.

Seafloor spreading is not consistent at all mid-ocean ridges. Slowly spreading ridges are the sites of tall, narrow underwater cliff s and mountains. Rapidly spreading ridges have a much more gentle slopes.

The Mid-Atlantic Ridge, for instance, is a slow spreading center. It spreads 2-5 centimeters (.8-2 inches) every year and forms an ocean trench about the size of the Grand Canyon. The East Pacific Rise, on the other hand, is a fast spreading center. It spreads about 6-16 centimeters (3-6 inches) every year. There is not an ocean trench at the East Pacific Rise, because the seafloor spreading is too rapid for one to develop!

The newest, thinnest crust on Earth is located near the center of mid-ocean ridge-the actual site of seafloor spreading. The age, density, and thickness of oceanic crust increases with distance from the mid-ocean ridge.

The magnetism of mid-ocean ridges helped scientists first identify the process of seafloor spreading in the early 20th century. Basalt, the once- molten rock that makes up most new oceanic crust, is a fairly magnetic substance, and scientists began using magnetometers to measure the magnetism of the ocean floor in the 1950s. What they discovered was that the magnetism of the ocean floor around mid-ocean ridges was divided into matching "stripes" on either side of the ridge. The specific magnetism of basalt rock is determined by the Earth's magnetic field when the magma is cooling.

Scientists determined that the same process formed the perfectly symmetrical stripes on both side of a mid-ocean ridge. The continual process of seafloor spreading separated the stripes in an orderly pattern.

Oceanic crust slowly moves away from mid-ocean ridges and sites of seafloor spreading. As it moves, it becomes cooler, more dense, and more thick. Eventually, older oceanic crust encounters a tectonic boundary with continental crust.

In some cases, oceanic crust encounters an active plate margin. An active plate margin is an actual plate boundary, where oceanic crust and continental crust crash into each other. Active plate margins are often the site of earthquakes and volcanoes. Oceanic crust created by seafloor spreading in the East Pacific Rise, for instance, may become part of the Ring of Fire, the horseshoe-shaped pattern of volcanoes and earthquake zones around the Pacific ocean basin.

In other cases, oceanic crust encounters a passive plate margin. Passive margins are not plate boundaries, but areas where a single tectonic plate transitions from oceanic lithosphere to continental lithosphere. Passive margins are not sites of faults or subduction zones. Thick layers of sediment overlay the transitional crust of a passive margin. The oceanic crust of the Mid-Atlantic Ridge, for instance, will either become part of the passive margin on the North American plate (on the east coast of North America) or the Eurasian plate (on the west coast of Europe).

New geographic features can be created through seafloor spreading. The Red Sea, for example, was created as the African plate and the Arabian plate tore away from each other. Today, only the Sinai Peninsula connects the Middle East (Asia) with North Africa. Eventually, geologists predict, seafloor spreading will completely separate the two continent s-and join the Red and Mediterranean Seas.

Mid-ocean ridges and seafloor spreading can also influence sea levels. As oceanic crust moves away from the shallow mid-ocean ridges, it cools and sinks as it becomes more dense. This increases the volume of the ocean basin and decreases the sea level. For instance, a mid-ocean ridge system in Panthalassa-an ancient ocean that surrounded the supercontinent Pangaea -contributed to shallower oceans and higher sea levels in the Paleozoic era. Panthalassa was an early form of the Pacific Ocean, which today experiences less seafloor spreading and has a much less extensive mid-ocean ridge system. This helps explain why sea levels have fallen dramatically over the past 80 million years.

Seafloor spreading disproves an early part of the theory of continental drift. Supporters of continental drift originally theorize d that the continents moved (drifted) through unmoving oceans. Seafloor spreading proves that the ocean itself is a site of tectonic activity.

Seafloor spreading is just one part of plate tectonics. Subduction is another. Subduction happens where tectonic plates crash into each other instead of spreading apart. At subduction zones, the edge of the denser plate subducts, or slides, beneath the less-dense one. The denser lithospheric material then melts back into the Earth's mantle.

Seafloor spreading creates new crust. Subduction destroys old crust. The two forces roughly balance each other, so the shape and diameter of the Earth remain constant.

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June 8, 2015

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Seafloor spreading occurs at divergent plate boundaries. As tectonic plates slowly move away from each other, heat from the mantle's convection currents makes the crust more plastic and less dense. The less-dense material rises, often forming a mountain or elevated area of the seafloor. Eventually, the crust cracks.

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Seafloor spreading Facts for Kids | KidzSearch.com

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At the Mid-Atlantic Ridge (and other places), material from the upper mantle rises through the faults between oceanic plates to form new crust as the plates move away from each other. The new crust then slowly moves away from the ridge. Seafloor spreading helps explain continental drift in plate tectonics.

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Plate Boundary: Divergent (Fast-spreading Ridge)

1min 10s Novice Spanish Chinese

How do mid-ocean ridges form new crust?

Spreading mid-ocean ridges form the longest mountain ranges in the world. New oceanic crust is created at this boundary when basalt magma, formed in the mantle, rises into fractures in the crust and solidifies. Spreading ridges are high elevation because the young oceanic plate at the ridge crest is hot and less dense than the older, colder and more dense plate on the flanks of the ridge. As the plates move away from the boundary, they thicken because underlying mantle rocks cool and add to the bottom of the plate.

CLOSED CAPTIONING: A .srt file is included with the download. Use appropriate media player to utilize captioning.

Keypoints:

Hot mantle rock rises beneath mid-ocean ridges

Melt forms beneath the lithosphere

Magma rises into magma chambers

Lava erupts onto ocean floor building new crust

Plates move apart

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Plate Boundary: Divergent (Fast-spreading Ridge)- Incorporated Research Institutions for Seismology

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New oceanic crust is created at this boundary when basalt magma, formed in the mantle, rises into fractures in the crust and solidifies. Spreading ridges are high elevation because the young oceanic plate at the ridge crest is hot and less dense than the older, colder and more dense plate on the flanks of the ridge.

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Throw your hands up for the Layers of the Earth!

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Throw your hands up for the Layers of the Earth!

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The Earth is not just one big ball that's solid throughout, although it might look that way! But it is made up of different layers, a bit like an onion. Each layer you peel off is made up of different things and they do different things too. Let's get on with it and find all there is to know about the layers of the Earth!

How Many Layers Does the Earth Have

The Earth has 4 layers

Crust - We live on this part

Mantle - Mostly solid rock but parts are hotter and more fluid

Outer Core - Made up of liquid metal and rock

Inner Core - Solid Rock made up of iron and nickel

Its radius is around 6371 km or 1,800 miles

What are the layers of the Earth?

The Earth is made of four layers. Let's start from the outside and move our way in. The top layer, which is what we stand on is the crust, next comes the mantle and finally the core. Some of these layers are made up of even more layers and they're always on the move. The Earth is mostly made of rock and metal. Scientists can't exactly get in a rocket and head right to the middle of the Earth, or the core, so it's difficult to know exactly what's there. But being as clever as they are, they are always coming up with new ideas, and as measuring equipment becomes more advanced so they learn new things all the time.

What is the Crust?

The crust is an outer solid layer and this is where all life exists on earths surface, including us, animals, mountains, sea and soil. It is about 8km thick in the ocean bed, which is called the oceanic crust. The oceanic crust is mostly made from basalt rock.

Then there's the continental crust which is covered by land and is made mostly out of granite. Above that granite is sedimentary rock. Sedimentary rocks form over long periods of time and are made from debris, chemical sediment and broken rocks. It is between 5km to 70km thick.

The crust is the only later on Earth that scientists can study, as they can drill into it. So this is the layer that we know the most about!

But how do they study the crust? Well they watch how waves travel through the Earth, called Seismic waves, which are caused from earthquakes or eruptions and the movement of tectonic plates. They also watch things like pressure and temperature

They use a machine called a seismograph to study the waves.

What is the Mantle?

The next layer that comes is called the mantle and here's all the info you need to understand this layer of the Earth.

The mantle is about 2,900km thick and amazingly it makes up about 85% of the Earth's weight. Wow! That's one heavy layer.

It is made molten, or melted, iron, minerals and other semi-solid rocks that will still flow under pressure.

In this layer the rocks rise. Those clever scientists think that when they rise from the very intense heat, and then cool down again, that they sink back to the core. This movement makes the crust break into plates, or different sections.

What happens when the crust breaks up into plates? Well they move and crash into each other and this causes earthquakes and volcanic eruptions. This movement is how new mountains and sea beds are formed. Wow, that's interesting.

As we mentioned earlier, the oceanic crust is made of basalt, which is a really thick rock, and this can press into the mantle and then fill with water.

This is amazing. The continents were made from lighter blocks that float on the mantle like massive big icebergs.

How do they explore the mantle? This is usually done from the sea bed where the layer is thinner than it is on land. They first explored it back in 1996. But, they actually gave up as they just couldn't get it right. In 2007 they drilled 7,000m below the seabed from a ship. This drilling was three times deeper than any other drillings that they'd done.

What is the Core?

Next up is the core! This is made up of two layers, the inner and the outer core. The Earth was formed 4.5 billion years ago, and when this happened, all the heavy materials sunk to the middle and this became the inner core. The lighter ones like air and water stayed on the top on the crust.

The inner core is kind of like a solid lead ball, which is about 2,400km thick. No wonder it's like a solid lead ball! There's heaps of pressure in the inner core, and that means it actually can't melt. This is unbelievable!

The temperature in the inner core is between 4, 982⁰ and 7,204⁰C. That's seriously hot, and just as hot as the surface of the sun. No wonder they can't explore here, everyone would fry! Have you ever spilt some boiling water on yourself? Well if you have, you know it's seriously sore! That water is 100⁰C. Now compare that to the inner core...can you even begin to imagine how hot it is?

The inner core apparently spins at a different speed to the rest of the planet and this causes the Earth's magnetic field.

It is because of the flow of metals in the inner core that the Earth is magnetic. The effect of this magnetic field spreads way beyond the Earth and goes off far into space. It actually forms a barrier that helps protect the Earth from the Sun's destructive solar winds. Wow that's interesting.

The second layer of the core is made of liquid iron and nickel and is about 2,300km thick. As we don't really know for sure, there are some people who think that it is 5,150km thick and between 3,982⁰C to 4,982⁰C hot! Whoa!

Some Other Interesting Facts

The mantle of the earth is solid rock, but amazingly it can be moulded, just like play dough. This certainly isn't the type of play dough you'd want to play with; your fingers would burn as it's so crazy, mad hot!

The inner core and the outer core of the Earth are as big as Mars! Now that's something.

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Earths Layers - Layers of the Earth Facts for Kids

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The Earth is not just one big ball that's solid throughout, although it might look that way! But it is made up of different layers, a bit like an onion. Each layer you peel off is made up of different things and they do different things too.

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Worksheets for Kids & Free Printables | Education.com

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Award-winning educational materials like worksheets, games, lesson plans, and activities designed to help kids succeed. Start for free now!

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This topic explains the inner layers of the earth's crust and how the earth looks like on both the inside and the outside. This is a product of Mexus Education Pvt. Ltd., an education innovations company based in Mumbai, India. http://www.mexuseducation.com, http://www.ikenstore.in

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Have you ever wondered why a bottle of soda fizzes - and sometimes bubbles over - when you open it? The answer is pressure. A bottle of soda contains high pressure. Leave the cap on and nothing happens. As soon as you take the cap off, though, some of the liquid soda escapes and becomes a gas. This is why it fizzes.

The inside of the Earth also contains a lot of pressure. After the Earth was made, it began to cool. The outer shell became a hard crust of rock. The inside of the Earth is still unbelievably hot because of nuclear reactions that are still going on. The temperature of the rock here is much hotter than molten lava, but it isn't liquid. It remains a solid because of the pressure.

Fun Facts About the Layers of Earth for Kids

The very center of the Earth is the core, which is mostly iron and nickel. The inner core is solid and measures 1,516 miles in diameter.

The outer core of the Earth is liquid metal - also mostly nickel and iron. Together, the inner core and outer core are about as large as Mars. The outer core is 1,408 miles in diameter.

Meteorites often contain bits of nickel and iron. Scientists believe they may be pieces from other planets which exploded.

The mantle of the Earth is solid rock, but it's not completely hard. Because of the intense heat, the mantle is moldable, like play dough. The mantle slowly moves. This movement causes earthquakes and volcanic eruptions.

The mantle is 1,800 miles deep.

The crust of the Earth is made of granite and other solid rock. Sand, soil and crushed rock sit atop the crust. The crust ranges in depth from 3 to 43 miles.

Earth's Layers Vocabulary

1. Pressure: Force applied to an area divided by the size of the area

2. Crust: Outermost layer of a planet

3. Nuclear: Involving atomic energy

4. Molten: Melted; glowing red-hot

5. Meteorites: Metallic or stony objects that are the remains of meteors

6. Mantle: Layer of the Earth between the core and the crust

7. Diameter: Straight line through the center of a circle that runs between two points on the outside (circumference) of the circle.

All About Earth's Layers Video for Kids

Check out this cool video about the Structure of Earth for kids:

Layers of the Earth Q&A

Question: How do scientists know about the Earth's layers?

Answer: Scientists learn about the Earth by studying other planets, earthquakes and volcanoes and even by drilling into the Earth.

Enjoyed the Easy Earth Science for Kids all about Earth's Layers info? Take the FREE & fun Earth's Layers quiz and download FREE Earth's Layers worksheet for kids. For lengthy info click here.

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Have you ever wondered why a bottle of soda fizzes - and sometimes bubbles over - when you open it? The answer is pressure. A bottle of soda contains high pressure. Leave the cap on and nothing happens. As soon as you take the cap off, though, some of the liquid soda escapes and becomes a gas.

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Have you ever watched a pot of soup simmering on the stove? Steam in the pot rises. Put a lid on the pot and the steam and water may actually boil over. Turn the heat down, though, and the water and steam drop too. Deep beneath the Earth, heat rises from the core through the mantle to the surface. The heat rises slowly, but it moves the mantle. The mantle rises beneath the Earth's crust before spreading sideways and cooling. Once the mantle cools, it sinks again.

This slow, but constant movement has broken the lithosphere in many places, dividing the Earth's crust into tectonic plates. This movement happens over millions of years and it's called continental drift. 250 million years ago, all the continents were joined together to make a giant continent called Pangaea.

Fun Facts about Tectonic Plates for Kids

In some places, the plates are pulling apart. New crust is pushed up from below. These are called divergent boundaries and they create rifts or valleys. Large lakes sometimes form in rifts.

In other places the plates are pushing against each other, creating mountains. These areas are known as convergent boundaries. Sometimes one crust is dragged beneath - or subducted - below another one. Ocean plates are heavier than continental plates so these plates are always dragged beneath.

A transform boundary happens when plates slide past each other but neither collide nor rip apart. The San Andreas Fault in California is a transform boundary.

The Red Sea formed where the African and Arabian plates pulled apart. This rift is getting larger and the Red Sea will eventually form an ocean.

Tectonic Plates Vocabulary

1. Simmer: when liquid bubbles during cooking

2. Lithosphere: the area where the Earth's crust and mantle bond together

3. Pangaea: a super continent that broke apart over 200 million years ago to form smaller continents

4. Divergent boundaries: when two fault lines pull apart

5. Convergent boundaries: when two fault lines push against each other

6. Subduct: when one plate is dragged beneath another one

7. Transform boundary: when plates slide past one another

All about the Tectonic Plates Video for Kids

Check out this cool video all about tectonic plates for kids:

A kid's video that discusses about tectonic plates and what it causes and creates.

Tectonic Plates Q&A

Question: Will the continents suddenly change?

Answer: The plates' movement happens very slowly. For example, the Atlantic Ocean began as a rift 160 million years ago. The rift expands at the rate of 1 inch per year. You are not likely to notice major changes in your lifetime. Stick around for a million years or so, though, and you might see a difference.

Enjoyed the Free Geography Kids online resources all about Tectonic Plates info? Take the FREE & fun Tectonic Plates quiz and download FREE all about Tectonic Plates worksheet for kids. For lengthy info click here.

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Have you ever watched a pot of soup simmering on the stove? Steam in the pot rises. Put a lid on the pot and the steam and water may actually boil over. Turn the heat down, though, and the water and steam drop too.

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Sedimentary rock forms in layers over millions of years. If you look at a cliff made from sedimentary rock, you'll notice distinct layers that may even be different colors. Changes in the environment cause changes in the rocks. For example, a volcanic eruption may create a layer made of hardened ash. The oldest layers of rock are at the bottom. Newer layers are at the top.

Sometimes, the layers are twisted or tilted because of the movement of the Earth's tectonic plates. Rocks on a fault line may snap or break. Scientists study these layers to learn more about the Earth's history. Radiometric dating measures radioactive elements in the rocks. Scientists can learn exactly how old a rock is by using radiometric dating.

Fun Facts about Layers of Rocks for Kids

The Earth is about 4.6 billion years old. We are now in the Quaternary Period.

By studying sedimentary rock, scientists learn a lot about each period of Earth's history.

Scientists make geological maps that show how old rocks are in a certain place.

Layers of Rocks Vocabulary

1. Sedimentary rock: rock that forms from soft sediment

2. Volcanic eruption: when a volcano explodes or erupts

3. Radiometric dating: method of reading radioactive elements in rock

All About Layers of Rocks Video for Kids

This is the best video we found for kids to learn all about Layers of Rocks:

This is a video presentation about how rock layers, or strata, can fold within the earth. Sedimentary rocks start out in horizontal layers.

Layers of Rocks Q&A

Question: What are rock layers called?

Answer: Rock layers are known as strata.

Enjoyed the Easy Geography for Kids all about Layers of Rocks info? Take the FREE & fun all about Layers of Rocks quiz and download FREE all about Layers of Rocks worksheet for kids. For lengthy info click here.

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Sedimentary rock forms in layers over millions of years. If you look at a cliff made from sedimentary rock, you'll notice distinct layers that may even be different colors. Changes in the environment cause changes in the rocks. For example, a volcanic eruption may create a layer made of hardened ash.

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Types Of Rocks | The Dr. Binocs Show | Learn Videos For Kids

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Why is Mount Everest so tall? - Michele Koppes

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Fun Facts About Fossils | Nat Geo Kids Dinosaurs Playlist

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Discover the very best dinosaur videos YouTube has to offer - brought to you by National Geographic Kids! ➡ Subscribe for more National Geographic Kids videos: http://bit.ly/SubscribeToNatGeoKids ➡ Watch more Dinosaurs: http://bit.ly/NGKDinosaursPlaylist More National Geographic Kids: Check out "Weird But True!" during Xploration Station on most FOX broadcast stations!

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Fossils & Evidence For Evolution | Evolution | Biology | FuseSchool

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Sea Floor Spreading | 100 Greatest Discoveries

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Sea Floor Spreading & Plate Tectonic Evidence

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Seafloor Spreading - Cover of "Let It Go" from "Frozen"

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Seafloor spreading is a geologic process where there is a gradual addition of new oceanic crust in the ocean floor through a volcanic activity while moving the older rocks away from the mid-oceanic ridge. The mid-ocean ridge is where the seafloor spreading occurs, in which tectonic plates-large slabs of Earth's lithosphere -split apart from each other.

Seafloor spreading was proposed by an American geophysicist, Harry H. Hess in 1960. By the use of the sonar, Hess was able to map the ocean floor and discovered the mid-Atlantic ridge (mid-ocean ridge). He also found out that the temperature near to the mid-Atlantic ridge was warmer than the surface away from it. He believed that the high temperature was due to the magma that leaked out from the ridge. The Continental Drift Theory of Alfred Wegener in 1912 is supported by this hypothesis on the shift position of the earth's surface.

The Process of Sea Floor Spreading

The mid-ocean ridge is the region where new oceanic crust is created. The oceanic crust is composed of rocks that move away from the ridge as new crust is being formed. The formation of the new crust is due to the rising of the molten material (magma) from the mantle by convection current. When the molten magma reaches the oceanic crust, it cools and pushes away the existing rocks from the ridge equally in both directions.

A younger oceanic crust is then formed, causing the spread of the ocean floor. The new rock is dense but not as dense as the old rock that moves away from the ridge. As the rock moves, further, it becomes colder and denser until it reaches an ocean trench or continues spreading.

It is believed that the successive movement of the rocks from the ridge progressively increases the ocean depth and have greater depths in the ocean trenches. Seafloor spreading leads to the renewal of the ocean floor in every 200 million years, a period of time for building a mid-ocean ridge, moving away across the ocean and subduction into a trench.

The Subduction Process

The highly dense oceanic crust that is formed after a progressive spreading is destined to two possible occurrences. It can either be subducted into the ocean deep trench or continue to spread across the ocean until it reaches a coast.

Subduction is the slanting and downward movement of the edge of a crustal plate into the mantle beneath another plate. It occurs when an incredibly dense ocean crust meets a deep ocean trench. On the other hand, if the ocean crusts continuous to move along the ocean and not found a trench, no subduction will occur. It will continue to spread until a coast is found and literally pushing it away towards its direction.

Two possible things could happen in the subduction of ocean crust. Once the subduction occurs, a melting happens due to a tremendous friction. The ocean crust is then melted into magma. The magma could either go back into the mantle for another convection currents leading again to another sea floor spreading or it could burst through a crack in a continental crust and creates a volcano.

Subduction and sea-floor spreading are processes that could alter the size and form of the ocean. For instance, the Atlantic Ocean is believed to be expanding because of its few trenches. Due to this, continuous Seafloor spreading occurs and makes Atlantic Ocean floor to be connected to other continental crust making the ocean gets wider over the time.

On the other hand, the Pacific Ocean has more trenches that lead to more subduction of ocean crusts rather than the formation of the mid-ocean ridge. The Pacific Ocean is believed to be continuing to shrink.

Evidence of Sea Floor Spreading

Harry Hess's hypothesis about seafloor spreading had collected several pieces of evidence to support the theory. This evidence was from the investigations of the molten material, seafloor drilling, radiometric age dating and fossil ages, and the magnetic stripes. This evidence however was also used to support the Theory of Continental drift.

1. Molten material

Hess's discovery on the warmer temperature near the mid-Atlantic ridge when he began the ocean mapping, led to his evidence about the molten material underneath the ocean. The condition on the mid-oceanic ridge was substantially different from other surfaces away from the region because of the warmer temperature. He described that the molten magma from the mantle arose due to the convection currents in the interior of the earth.

The convection current was due to the radioactive energy from the earth's core that makes the materials in the lower mantle to become warm, less dense and rise. The flow of the materials goes through the upper mantle and leaks through the plates of the crust. This makes the temperature near the mid-oceanic ridge becomes warm and the other surface to become cold because as the molten magma continues to push upward, it moves the rocks away from the ridge.

2. Seafloor drill

The seafloor drilling system led to the evidence that supports the seafloor-spreading hypothesis. The samples obtained from the seafloor drill reveals that the rocks away from the mid-oceanic ridge were relatively older than the rocks near to it. The old rocks were also denser and thicker compared to the thinner and less dense rocks in the mid-oceanic ridge.

This means that the magma that leaks from the ridge pushes the old rocks away and as they increasingly become distant, they more likely become older, denser, and thicker. On the other hand, the newest, thinnest crust is located near the center of the mid-ocean ridge, the actual site of seafloor spreading.

3. Radiometric age dating and fossil ages

By the use of radiometric age dating and studying fossil ages, it was also found out the rocks of the sea floor age is younger than the continental rocks. It is believed that continental rocks formed 3 billion years ago, however the sediments samples from the ocean floor are found to be not exceeding 200 million years old. It is a clear evidence that the formation of rocks in the sea floor is due to reabsorption of materials.

4. Magnetic stripes

In the 20th century, the magnetic survey was conducted in the Mid-ocean ridge in order to investigate evidence of sea-floor spreading. By using the magnetometer, the magnetic polarity will be shown through a timescale that contains the normal and a reverse polarity. The minerals contained in the rocks are oriented opposite to the magnetic field. The patterns of the magnetic field will then be compared to the rocks to determine its approximate ages.

The investigation of the mid-ocean-ridge, using the magnetic stripes resulted in the three discoveries. First, stripes of normal and reversed polarity were alternate across the bottom of the ocean. Second, the alternate stripes of normal and reversed polarity formed a mirror image to the other side of the ridge. The third is the abrupt ending of stripes when it reached the edge of the continent or an ocean trench. It was concluded that the sea floor is composed of different rocks according to ages and that they are positioned equally in opposite directions. This records that there is a constant movement and spreading of rocks on the ocean floor.

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Theory and Evidence of Seafloor Spreading | Earth Eclipse

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The Theory of Seafloor Spreading Seafloor spreading is a geologic process where there is a gradual addition of new oceanic crust in the ocean floor through a volcanic activity while moving the older rocks away from the mid-oceanic ridge. The mid-ocean ridge is where the seafloor spreading occurs, in which tectonic plates-large slabs of Earth's lithosphere-split apart from each other.

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seafloor spreading and magnetic striping

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seafloor spreading and magnetic striping

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Rising magma assumes the polarity of Earth's geomagnetic field before it solidifies into oceanic crust. At spreading centres, this crust is separated into parallel bands of rock by successive waves of emergent magma. When Earth's geomagnetic field undergoes a reversal, the change in polarity is recorded in the magma, which contributes to the alternating pattern of magnetic striping on the seafloor.

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Sea-floor spreading is the process in which the ocean floor is extended when two plates move apart. Plates are huge slabs into which the crust as well as the upper part of the mantle (the intermediate zones between the Earth's crust and core) is divided.

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Some engineers have created an interactive map to navigate the overwhelming amount of data created by the Paleobiology Database, a massive collection of information about fossils and related research. The map essentially plots the location of every fossil ever found by scientists, from early mammals to dinosaurs.

To search the map, you can click on different geologic eras, the strata that the organism was found in, or search the specific taxonomy you're looking for. The map shows the continents as they are today by default, but when you click on a different geological era they rearrange themselves, showing how dramatically tectonic plates have shift over millions of years.

If you aren't looking for any specific creature, just click around randomly and see what pops up. You can zoom in on any part of the world and see what kinds of fossils have been found there. For example, through the map we learned that Pleistocene-era mollusks have been found in Manhattan. What roamed the Earth where you live millions of years ago?

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Check Out An Interactive Map of Every Dinosaur Fossil Found On Earth

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Some engineers have created an interactive map to navigate the overwhelming amount of data created by the Paleobiology Database, a massive collection of information about fossils and related research. The map essentially plots the location of every fossil ever found by scientists, from early mammals to dinosaurs.

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Last Sunday, May 24, marked the 109th birthday of geologist Harry Hammond Hess, who discovered the primary mechanism of plate tectonics. That's the process through that determined how the shape of continents came to be. But long before his birthday, people wondered how it was that the sea and the land were formed.

When the first European map of America was published in 1507, naturalists noted that the coastline of South America seemed to fit into the coastline of Africa. In 1620, the English philosopher Francis Bacon claimed in his Novum Organum that "it's more then a curiosity," but couldn't provide any explanation. In 1658, Francois Placet, a monk, published a small booklet entitled The break up of large and small world's, as being demonstrated that America was connected before the flood with the other parts of the world. He argued that the two continents were once connected by the lost continent of "Atlantis" and that the destructive currents of the Biblical flood later separated them. The Biblical flood will remain a very popular explanation for the next 250 years.

It wasn't until the the 18th century that the first primitive geological theories were formulated. Politician and naturalist Benjamin Franklin explained the existence of marine fossils found on the summits of mountains in a letter to French geologist Abbé J. L. Giraud-Soulavie in 1782 as follows:

Such changes in the superficial parts of the globe seemed to me unlikely to happen if the earth were solid to the center. I therefore imagined that the internal parts might be a fluid more dense, and of greater specific gravity than any of the solids we are acquainted with, which therefore might swim in or upon that fluid. Thus the surface of the earth would be a shell, capable of being broken and disordered by the violent movements of the fluid on which it rested.

French zoologist Jean-Baptiste Lamarck (better known for his theory of evolution) developed his own geological theory to explain these things. To explain the discovery of fossil marine animals on dry land, he proposed that the continents "move" slowly around the globe in a very peculiar manner. The eastern coastlines of the single continents are eroded by the sea, but in the same time new sediments were deposited on the western coasts, so the continents apparently move around the globe and the sea becomes land. Lamarck self-published work explaining this, Hydrogéologie, was published in 1802. It was a financial disaster and bankrupted him.

In the early 19th century another geological theory became very popular. American geologist James Dwight Dana (1813-1895) proposed that the cooling earth ( volcanoes are quite efficient in dispersing earth´s inner heat) was also shrinking. Like on an old and dry apple, on a smaller earth fissures - or oceans- and wrinkles -or mountains- would form, leading to the shapes we see today.

But how did we arrive at our modern theory of plate tectonics? Stay tuned for the next post in this series.
Interested in reading more? Try:
FRISCH, W. & BLAKEY, R. (2011): Plate Tectonics - Continental Drift and Mountain Building. Springer-Publisher: 212

MILLER, R. & ATWATER, T. (1983): Continents in Collision. Time-life books, Amsterdam: 176

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How Maps And Mountain Fossils Led To Plate Tectonics

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Last Sunday, May 24, marked the 109th birthday of geologist Harry Hammond Hess, who discovered the primary mechanism of plate tectonics. That's the process through that determined how the shape of continents came to be. But long before his birthday, people wondered how it was that the sea and the land were formed.

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Smithsonian - Dinosaurs in Our Backyard - Finding Fossils

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In addition to looking for rocks of the right age, it is important to identify rocks that formed in the right environments. Some Mesozoic rocks, such as those in the Great Plains, formed in ancient oceans and are unlikely to yield fossils of land-living animals such as dinosaurs.

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The Distribution of Fossils and Plate Tectonics Theory

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According to the theory of plate tectonics, the continents are not rigidly fixed to the surface of the Earth. These huge land masses, referred to as plates, gradually change position relative to each other as they slide over underlying material. In consequence, the map of the Earth's surface is constantly changing over geological timescales.

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It is also common to find tracks in sediments that were deposited along the shores, or in the shallow waters of lakes (called lacustrine sediments). Below right are tracks of a web-footed bird found in the Green River Formation of Utah, USA.

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Seven Continents Geography/Seven Continents Song for Kids

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A rift valley is a linear-shaped lowland between several highlands or mountain ranges created by the action of a geologic rift or fault. A rift valley is formed on a divergent plate boundary, a crustal extension, a spreading apart of the surface, which is subsequently further deepened by the forces of erosion.

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Tides: StudyJams! Science | Scholastic.com

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The ocean does not always stay the same depth. This activity will teach students about how tides are created and how they affect the depth of the ocean.