Universe Today

Early earthquake picture posted on Twitter by @tapeks.

An earthquake is the spontaneous release of kinetic energy in the earth's crust that results in seismic tremors or waves. An earthquake can range anywhere from a mild tremor to a catastrophic and deadly event. Earthquakes are generated by the interaction of the tectonic plates that makes up the lithosphere of the Earth's crust.

These plates are just like a bunch of float rafts that are close together. The currents of the magma in the mantel cause them to move and bump into each other. When plates meet plate boundaries and fractures in the crust called faults are made.

However, not all faults cause earthquakes. This is because earthquakes are created by stress in the crust. Most faults and boundaries go by smoothly. The ones that cause earthquakes are irregular in shape and experience a lot of friction. This strike slip phenomena cause the opposite sides of a fault to catch and lock. This causes a build up in pressure and stress until the sides of the fault suddenly slip past each other. This is what causes the release of energy that creates an earth quake.

There are three major types of faults that can cause earthquakes. There is the normal fault, the reverse fault, and finally the strike slip fault. The first deals with one side of a fault actually sinking. The reverse fault occurs when one side of the fault actually rises over the other. The last type of fault is a strike slip or transform fault. This is when the sides of a fault slide past each other laterally.

Earthquakes vary in power. Scientist know from geological evidence that the early Earth underwent very powerful earthquakes. Even the ones in early recorded history dealt some serious damage. In the First Century, the Mediterranean experience an earthquake so powerful, it created a tsunami that devastated ancient Alexandria.

The measurement of an earthquake is done in magintudes. The systems of magnitudes universally used is the Richter Scale. The Richter ranges from 1 to 10 with 10 being the strongest Earthquake. The measurement has not to Moment magnitude. This number is derived from the moment energy released, the area of the epicenter, and how much the fault slipped.

If you enjoyed the article there are several others on Universe Today that you will enjoy. There is a great article about the Chilean Earthquake and how it may have shortened the length of a day. There is also an interesting piece on famous earthquakes.

There are also some great resources online if you want to learn more about earthquakes. You can check out USGS.gov. You can also check out National Geographic's earthquake web page.

You can also check out Astronomy Cast. There is a great show on plate tectonics.

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In the beginning of 2010 there has already been some significant seismic events. There was the Haiti Earthquake that flattened Port Au Prince and took over 200,000 lives. It was the deadliest disaster since the Christmas Tsunamis. Now Chile has just experienced a major earthquake that was 8.8 on the Richter Scale. This earthquake is the most powerful to hit Chile in 50 years. It is now likely spurring tsunamis all across the Pacific Ocean. However what causes these seismic events and other geological phenomena? The reason is plate tectonics.

To understand plate tectonics you need to understand the structure of the Earth. The Earth is like an onion with many layers. However, not all these layers are solid and neither are they all one piece. The part of the Earth where life resides and where most of the geological activity we observe occurs is called the crust. The Crust includes both the continents and the bottom of the Earth's seas. The interesting thing is that instead of being all one peace it is made of interlocking and interacting pieces that we call plates. This is where plate tectonics. The Earth's crust essentially floats on a layer of molten rock and magma called the mantle.

What causes plate activity is the convection currents in the magma. Like a raft on the ocean currents the plates are moved by the magma this is what causes the formation and separation of landmasses over periods of times. What cause earthquakes and other seismic activity is when the plates literally bump into each other.
One source of this interaction is sea floor spreading. The oceanic crust is much thinner than that of the Continents. So in certain areas of the ocean floor there are weak zones where magma from the mantle can escape. This hardens and create new rock to form the crust. This is one of the forces that help push the continents apart. Another phenomena is subduction when two plates where they are oceanic or continental meet one most "win." That is one will slide over the other forcing it down into the mantle. Normally the denser plate is the one that sinks.

The interaction of plates cause boundaries called plate boundaries and faults. These can either be convergent, divergent, or transforming boundaries. This can cause different things. For example, if the boundary is convergent like when two continental plates are colliding can cause the formation of volcanoes and young mountains. They also cause other events like earthquakes and tsunamis.

If you enjoyed this article there are several others that you will enjoy. There is a great article about Plate Boundaries. There is also an interesting article on tectonic plates which talks in detail about how the plate move and are formed.

You can also find some great resources online. You can check out the Plate Tectonics page on the University of California Berkley website. The USGS Dynamic Earth website is another excellent source of information.

You can also listen to Astronomy Cast. Episode 142 talks at length about Plate Tectonics.

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One of the oldest questions for mankind is how the Earth was formed. However, no one has an exact answer. First by the best estimates it occurred over 4 billion years ago before any life appeared. So there are no eyewitness accounts and other pieces of evidence. The best we can do is look at the geologic record and the stars to get our answers. While we may not have the entire picture we have a good idea and it all starts with how stars are born.

Just like the formation of the Earth and other planets stars take a long time to be be born. Stars are essentially formed from clouds of gas in space. We know these as nebulas. You can basically consider them to be star forges. Over time gravity causes the atoms of gases and space dust to start coming together and gathering. Over time this gather of gases gains more mass and with it stronger gravity. This is a process that can take millions of years. In time the gravity causes the gases, mainly hydrogen to fuse in a nuclear reaction and a star is formed.

The formation of the Earth occurred after this intial phase happened for our Sun. After the Sun was formed we know from observations and other indirect evidence that there were left over gases and heavier elements. The gravity of the Sun helped to flatten these left overs into a disk and start to fuse them together. This created the planetesimals and planetoids which would later make up the planets. Over time these planetesimals would collide creating even bigger masses. It was in this method that the Earth was eventually formed.

Now we need to know that fusion eventually creates heavier elements such as carbon and iron. These elements were to compose a significant part of young Earth. The pressure and heat from radioactive decay of elements and the aftershocks of massive collisions caused the Earth to be molten. Over time the surface of the Earth cooled and became the Crust. However the molten layers that remained became our mantle and the core. The currents of this massive underground ocean of magma cause volcanic activity that released gases. These would lead to the creation of the atmosphere and the oceans starting the water cycle.

The formation of the Earth was only the beginning and we still see the Earth changing year by years through erosion and plate tectonics. However in learning more about the formation of the Earth we are able to better understand what makes life possible on our planet.

If you enjoyed this article there are several others on Universe Today that you will enjoy. There is a great article on plate boundaries and an interesting piece on early Earth.

You can also find some great resources online. There is a great web page on the University of Oregon web site that goes into detail about the formation of the Earth. You can also look at the Hadean page on the Smithsonian website. It talks about the Hadean period the period of geologic time when the Earth was formed.

You can also listen to Astronomy Cast. Episode 108 is about the life of the Sun.

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Illustration of the Krakatoa eruption.

The region where the volcano resided in located on the ring a fire a region of volcanic and seismic activity that surrounds the Pacific Ocean. The cataclysmic eruption that happened did have some warning signs. For a couple of years before the final eruption, the region experienced intense earthquakes that were felt as far as Australia. The nearby volcanoes also become active emitting steam. However, no one was prepared for what would happen next.

The first eruptions started on Aug 12. The main event happend on later on 25 when the Krakatoa literally blew apart in four stupendous explosions. To explain how powerful it is, it had the force of the detonation of 200 megatons of TNT. The noise was so powerful that eardrums of nearby sailors in the region burst. It was also heard over 4800 km at one point. The eruptions also created a smoke plume of ash over 30 km tall and set of a series of tsunamis in the region. Ironically for such a powerful eruption, relatively few people were killed just over 1,000.

What makes the Krakatoa Volcano the deadliest in history was the after effects. These effects were the cause of officially 36,000 deaths but some accounts assert that over 100,000 died. These people died from tsunamis, hot ash, or pyroclastic flows. Even with this horrific damage, the trouble did not stop there.

Krakatoa's eruption emitted so much ash that it literally altered the world's climate in way not seen since the age of the dinosaurs. The Northern Continents of the North America, Europe,and Asia experienced a drastic drop in temperatures that created what was later called the "Year without Summer" numerous crops failed and the citizens of many unfortunate countries faced starvation.

The island of Krakatoa itself was devastated. The center of the island sank beneath the waves like fabled Atlantis. However, the area stayed active and a new volcano the Anak Krakatoa, the "Child of Krakatoa" grew up in its place.

Few volcanoes in modern history have exhibited the sheer power of Krakatoa or even had such a profound effect. To this day scientists are still researching the volcano to better understand the how and why of the eruption.

If you enjoyed this article there are several others on Universe Today that you will enjoy. There is a great article about active volcanoes. There is also a piece about the parts of a volcano.

There are also some great resources online if you want to learn more about the Krakatoa eruption. There is a great web page on Krakatoa by the Sand Diego State University. You can also check out a Daily Mail news article online that talks about the possibility of another major eruption from Krakatoa.

You can also listen to listen to Astronomy Cast. Episode 141 Volcanoes Hot and Cold is an informative episode.

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A Fault is basically a big crack in the earth's crust. They can be either shallow or deep but the deformation of the rock around them is something all faults have in common. Faults are the most visible evidence of seismic activity. That is why they are so useful in helping scientist determine plate boundaries and regions that experience geological activity.

Faults are caused when seismic activity causes stress on a layer of rock causing it to fracture then slip against itself. There are three main types of faults. The first type of fault is a dip slip fault. This is a fault that occurs where one side of a rock fracture is pushed over or beneath the other. These can be either reverse or normal. The next type of fault is the strike slip. This one is completely horizontal with little up or down movement. Instead to the two sides of the fault slip past each other horizontally. The third major type is the oblique slip fault. It is sort of a combination of both a strike slip and a dip slip fault. There are other less common types of faults such as ring faults and lispic faults. There are more circular in shape.

Major seismic activity such as earthquakes are result of energy being released when a fault slips. This is why cities like San Francisco are at risk for earthquakes. A more recent example would be Port Au Prince, Haiti. Though the Caribbean has not experience a major earthquake for 200 years before the events, of last month the fault was there with pressure steadily building. That is what determines the force of an earthquake. In general the longer it takes for the pressure between the two sides of the fault the strong the resulting earthquake.

Nevertheless whether a fault is a seismically active area like California or in a place that see's very few earthquakes like New Jersey a fault is still a location where pressure builds up. That is why one of the main jobs of geologists is to locate fault lines. By finding these locations along with observation and measurement scientist can find what regions are at risk and find ways to help communities prepare.

If you enjoyed this article there are others on Universe Today. There is a great article about famous earthquakes. There is also a great article about fault lines on Mars.

There are also some great resources online. There is the USGS web site which has a lot of information on seismic activity. The earthquake web page on the Cal tech website is another great source of information.

You can also check out Astronomy Cast. You should definitely try checking out Episode 142 which talks about plate tectonics.

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Interior of the Earth. Image credit: NASA

We know more about the interior of other planets than we know about the interior of our own planet. The way we learn about it is through seismography, thermal reading, and sound waves. The best we can identify is the composition and density of each layer of the interior.

The core is about 3,000 to 6,000 km below the surface of the earth. It is believed that it was formed when the earth was still molten. In this more liquid state it is hypothesized that the denser and heavier elements sank to the center of the planet while the lighter elements rose to the top aided by the rotation of the earth.

The core is more complex than you would immediately assume. For example, while it is entire made of iron, the Earths core has an outer layer of liquid iron and one of solid iron. The radius of the solid core is believed to be about 1200 km and the outer core a radius of 3000 km.

The core just does not exist for its own sake or just act as stuffing for the planet. The iron core is also what helps to create the Earth's magnetic field. This field has many important functions one of the most important being a radiation shield. It is really effective because it help to reflect a good portion of the charged particles that make up solar radiation.

There still a lot we don't know about the Earth's core. It was only confirmed that core had two components in 1936. Also some scientist are hypothesizing that to a certain extent that the core spins independently of the rest of the earth. Some estimate have rotating faster while others propose that the core spins once every 120 years. On top of that new data is suggesting that core is not as uniform as it was first assumed and might resemble something pitted sphere with pockets of molten iron interspersed.

If you enjoyed this article there are others on Universe Today that you will definitely enjoy. There is a great article about the discovery of the Earth's inner and outer core. There is another article about the layers of the earth.

There are also some great resources you can check out. The University of Nevada Reno has a great web page on the Earth's Core. You can also look at the United State Geological Survey web page on the interior of the Earth.

You should also listen to Astronomy Cast. There is a great show about the Earth.

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We know about the crust of the Earth than any other part of the Earth's structure. It is mainly because this the layer that we live on and it the region most easily within our reach. Thought it is only the "peel' of the earth we have been able to learn a lot about the Earth from investigating it. We know how old the earth is by dating the rocks and classifying the different kinds that rose to the surface from the interior of the earth. We know the fault lines and boundaries of tectonic plates and where and how the effect the formation of volcanoes and other geothermal activity.

Scientist believe that the crust was the last part of the earth to be formed. It is theorized that over 4 billion years ago the Earth was a molten ball. The denser elements sank to the center of the planet and became the core. The lighter elements rose and stratified forming the mantle. The last layer the crust was formed when the molten exterior of the Earth finally cooled.

The Earth's crust can be divided into two distinct categories. The first is the oceanic crust and the second is the continental crust. Each has a unique composition that is different from the other and the mantle below. The oceanic crust is most made up of basalt, diabase, gabbro. The continental crust is made mostly of granite. The thickness of the crust also varies depending on whether it is the continental or oceanic crust. The continental crust can be anywhere from 30 km to 50 km thick and the oceanic crust can be 5 to 10 km thick.

The crust of the Earth is not one single piece but is made up of interacting pieces called the tectonic plates. This is because the crust sort of floats on top of the lower layer of the earth made of rock and magma called the mantle. The convection of magma in the mantle create the current that causes plate tectonics forcing different plate to crash or pull away creating seismic activity.

The crust is also the source of many of the minerals and other substances that we use in industry and other fields. The continental crust is especially known for the wide variety of minerals in its its composition.

If you enjoyed this article there are others on Universe Today that you will like. There is a great article about the history of iron in the Earth's crust. There is another article that talks about the continental crust.

You can also look at resources online. You can check out the USGS web pages on the Earth's crust. There is also the Earthforce web page on the Franklin Institute web site.

You should also listen to Astronomy Cast. Episode 142 talks about plate tectonics.

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An earthquake can be a deadly and powerful phenomenon that can occur with almost no warning. So it is important for anyone who lives in an area that is prone to them to know what to do when one strikes. While there is no way to completely protect yourself, there are still ways to increase your chances of survival and reduce the likelihood of injury. Many of the steps are common sense but should be all the more remembered.

The first important thing to do is to make sure that you earthquake proof your home. This means that you try to remove or secure objects and rooms that may become dangerous when an earthquake happens. For example you should make sure all shelves are securely fastened. You should also make sure that all heavy objects are placed at ground level to prevent accidents. You should also designate specific locations in your home as safe zones. These will be areas that are away from windows and near inside walls that support the house.

The next important thing you need to do is to prepare an emergency kit. This will be what you will rely on in case an earthquake happens. Your emergency kit should have a flashlight, water, a radio, and some emergency rations. This should help sustain in case you are trapped or have any wounded. You should also contrive to have a cell phone to call for help.

While these preparations are needed you also need to know what to do during an earthquake. The two most important things to know is that you should stay where you are and get as low as possible. These two steps will be likely what saves your life. Studies and anecdotal evidence show that more people are hurt when try to move to a different location in the home during an earthquake. The other thing is that by staying on the ground in an area free of hazards is the safest place to be. So if where you are is not safe only then should you go for the nearest safe zone.

The last thing to remember is that if you are trapped, don't shout unless you are sure rescuers are near. This will prevent you from breathing in too much dust or dangerous chemicals or gases. Try instead to use a cell phone, or tap on the walls or exposed pipes.

If you enjoyed this article there are others on the Universe Today website that you will enjoy. There is a great article about Famous Earthquakes. There is also another about how earthquakes happen.

There are also some great resources online. There is a great article on the FEMA web site. You can also check out the tips on the earthquake page on the California government website.

Astronomy Cast is something else that you can look into. Episode 142 Plate Tectonic is very relevant to earthquakes.

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Cut away of planet Earth

In the past scientists have defined the center of the Earth’s mass in two ways: either as the mass center of Earth as a single object or as the mass-center of Earth’s system, including ice sheets, oceans and our atmosphere in the equation. The reason that there are two definitions of the core is that the Earth is ever changing. "By its very nature, Earth's reference frame is moderately uncertain no matter how it is defined," said Donald Argus of NASA’s Jet Propulsion Laboratory in California. “The problem is very much akin to measuring the center of mass of a glob of Jell-O, because Earth is constantly changing shape due to tectonic and climatic forces." If Earth were a completely solid, perfectly round object, finding its center of mass would be sweet and simple. However, our planet is not perfectly round. Couple that with the fact that the Earth's mass doesn’t stay put, but instead changes over time as glaciers melt, tectonic plates move and volcanoes empty out to lay massive lava on Earth’s surface. These changes in mass atop and beneath Earth’s surface cause the center of mass to shift slightly over time.

Donald Argus has proposed a new way to measure the center of the Earth. The new center-finding technique can estimate Earth’s center of mass to within 0.04 inches a year. The center of mass is calculated as a relative measurement, and so the measurement is given as a velocity. The Earth-only reference frame will improve estimates of sea-level rise made by satellite altimeters, which rely on measurements of the location and motion of the center of mass of Earth’s system. Sea-level rise is a gauge of global warming, and so the results will boost scientists’ understanding of the increase in our planet’s average temperature.

The center of the Earth is thought to be in two parts: a solid iron inner core and a molten core surrounding that. The core was discovered in 1936 by monitoring the internal rumbles of earthquakes, which send seismic waves rippling through the planet. The waves, which are much like sound waves, are bent when they pass through layers of differing densities, just as light is bent as it enters water. By noting a wave's travel time, much can be inferred about the Earth's insides.

The Integrated Ocean Drilling Program (IODP) seeks the elusive "Moho," a boundary formally known as the Mohorovicic discontinuity. It marks the division between Earth's brittle outer crust and the hotter, softer mantle. This is one step in a series to reach the center of the Earth. The new hole, which took nearly eight weeks to drill, is the third deepest ever made into the floor of the sea, according to the National Science Foundation (NSF). The rock collection brought back to the surface is providing new information about the planet's composition. If we are gleaning new information from the upper mantle, what might we learn when we reach the center of the Earth?

There are a couple of good articles about the quest to reach the center of the Earth here and here. We have a great article about how far it is to the center of the Earth here on Universe Today. Astronomy Cast offers a good article about the plate tectonics that make measuring the Earth's core so difficult.

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Earthquake near Chengdu, China

Many earthquakes occur every year; however, most of them are not powerful enough to cause any serious damage. In fact, many earthquakes are too slight to even be felt. Major earthquakes do occur however and cause terrible damage. Because most earthquakes are not major, many people do not realize exactly how frequently earthquakes occur. More than 3 million earthquakes occur each year, which means approximately 8,000 earthquakes each day.

Most earthquakes occur in specific regions. This is because they usually happen along the borders of tectonic plates. That is why so many earthquakes happen in California – there is a major fault line near the coast of California.

Even though major earthquakes do not happen that often, they can cause substantial damage. One reason why earthquakes cause so much damage is that they can trigger other natural disasters, such as tsunamis and volcanoes, which are also linked to tectonic plates. Additionally, earthquakes can also trigger fires when gas or electrical lines are damaged and floods when dams break. Some famous earthquakes that resulted in terrible damage to property and life include the 1906 San Francisco Earthquake and the earthquake that destroyed Pompeii in 62 AD.

Scientists measure earthquakes using a seismometer, which is an instrument that has been around for centuries. There is also a method of measuring the intensity of an earthquake. It is known as the Richter scale. The scale starts at one and goes up in intensity. Although there is no upper limit to the scale, most people set ten as the upper limit because no earthquakes greater than ten have been recorded.

Universe Today has articles on famous earthquakes and the Richter scale.

For more information, you should check out earthquakes and how earthquakes work.

Astronomy Cast has an episode on Earth  you will definitely enjoy.

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Olympus Mons. Image credit: NASA/JPL

There are many tall mountains around the world as well as on other worlds. Mount Everest is the highest mountain in the world at 8,848 meters. Mauna Kea is the tallest mountain in the world. The tallest mountain is measured from base to top while the highest mountain is measured from sea level to the top.  Everest is located in the Himalayan mountain range in Nepal and near Tibet. Mauna Kea is located in Hawaii and is 10,200 meters from base to tip. From sea level though, it is only about 4,205 meters tall.  Mauna Kea is an extinct shield volcano.

These are not the only tall mountains though. K2 is in the Karakoram mountain range on the border of Pakistan and China. It is 8,612 meters tall and is generally considered the second tallest mountain in the world. The Himalayans are home to many tall mountains besides Mount Everest. This includes Mount Kangchenjunga at 8,586 meters and Mount Lhotse I at 8,501 meters.

Most of the world’s tallest mountains are located in Asia; however, there are a number of tall mountains that are located on other continents. The seven tallest mountains in different continents are known as the Seven Summits. Climbing all seven mountains is a mountaineering challenge that was started in the 1980’s.The first of these is Mount Everest. Another summit is Aconcagua, which is a mountain in Argentina in South America. At approximately 6,962 meters, it is the tallest mountain in the Americas. North America’s tallest mountain is Mount McKinley at 6,194 meters. Mount Kilimanjaro can be found in Tanzania in the continent of Africa and is 5,895 meters tall. The large summit of Mount Kilimanjaro is covered with an ice cap that is receding and according to scientists will eventually be gone. Mount Elbrus, the tallest mountain in Europe at 5,642 meters, can be found in Russia. Vinson Massif is Antarctica’s tallest mountain at 4,897 meters. It is also very large being 21 kilometers long and 13 kilometers wide.  Australia-Oceania’s largest mountain can be found in Indonesia. At 4,884 meters, it is Puncak Jaya, which is also known as the Carstensz Pyramid.

The tallest mountain that we know of is not even on Earth. It is located on Mars and is known as Olympus Mon.  A shield volcano, Olympus Mon is 27,000 meters tall. Mars is not the only other planet with tall mountains though. Venus’ Maxwell Montes is 11,000 meters tall. Satellites also have tall mountains including our Moon, which has Mons Huygens at 4,700 meters tall. The moon Io has a mountain, Boösaule Montes, which is approximately 17,000 meters tall.

Universe Today has articles on tallest mountain and tallest mountain in the Solar System.

For more information, you should take a look at what are the world's tallest mountains and highest mountains.

Astronomy Cast has an episode on Earth you will find interesting.

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A'a lava

How are igneous rocks formed?

Igneous rocks are formed when melted rock cools and solidifies. Melted rock may come in the form of magma, when it is found underneath the Earth's surface. It can also come in the form of lava, when it is released unto the Earth's surface during a volcanic eruption.

Some examples of igneous rocks are granite, scoria, pumice, and obsidian.

Pumice, for instance, is formed when lava made up of melted rock, water, and trapped gas is ejected from a volcano during a violent eruption. As the ejected material undergoes very rapid cooling and depressurization, some of the trapped gas escape, leaving holes and gas bubbles on the solidified material.

How are sedimentary rocks formed?

Sedimentary rocks start forming when soil and other materials on the Earth's surface are eroded and finally settle down, forming one layer of sediments. As time passes, more and more materials get eroded and settle on the older layers. Thus, layer upon layer is formed. The lower layers undergo intense pressure due to the weight of the upper layers, eventually evolving into rocks.

Some examples of sedimentary rocks are sandstone, limestone, shale, conglomerate, and gypsum.

Sandstone, for instance, is a result of depositions of sand from beaches and rivers. You can find them mostly in deltas, since this is where the rivers flow into the ocean.

How are metamorphic rocks formed?

To metamorphose or simply to morph means 'to change in form'. Metamorphic rocks are actually products of rocks that have undergone changes. Thus, a metamorphic rock may have originally been an igneous, sedimentary, or even another metamorphic rock.

The changes occur when the original rocks are subjected to extreme heat and pressure beneath the Earth's surface. They may also occur when the the original rocks are caught in the middle of two colliding tectonic boundaries.

Some examples of metamorphic rocks are marble, slate, schist and gneiss.

Marble, for instance is the result of the metamorphism of limestone and dolostone. When limestone metamorphoses, its calcite grains grow and interlock with one another. As such, marble is denser and harder compared to limestone.

We've got lots of articles about rocks here in Universe Today. For variety, we recommend these two:
Volcanic Rock
Moon Rocks

If you want to read more about Fray's device that extracts oxygen from Moon rocks, we've got exactly what you need here in Universe Today. Just click on that link. We also have an article featuring secrets that may be revealed from moon rocks even 40 years since the Apollo missions brought them to Earth.

Here's an article from NASA that debunks the hoax theory using the Moon rock arguments. Another article about Moon rocks from the same site.
Episodes about the moon from Astronomy Cast. Lend us your ears!
Shooting Lasers at the Moon and Losing Contact with Rovers
The Moon Part I

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If you've wanted to take a swim in a lake on Titan, don't: they're not lakes like we have here on Earth, composed of methane and ethane instead of water. If you have somehow evolved lungs to breathe and swim in these chemicals, you should take your beach vacation in the northern hemisphere of Titan, where you'll find many more lakes. Data taken by the Cassini mission has shown that there are more of these methane lakes concentrated in the northern hemisphere of Saturn's moon than in the southern hemisphere. A recent analysis of the Cassini findings by a team at Caltech has shown that the cause of this asymmetry of lakes is due to the orbit of Saturn. Read more…

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Beichuan Region of China, before and after Earthquake. Image credit: Formosat 2

Richter magnitude scale is used to measure the size of earthquakes.  It is also known as the local magnitude scale and was created in 1935 by Charles Richter and Beno Gutenberg both from the California Institute of Technology. Originally, the scale was created in order to differentiate between the smaller and larger earthquakes observed in California.  At first, the scale only worked on one type of seismograph. That changed however, and now any calibrated seismograph can use the Richter scale. When Richter first designed the system, the size of the earthquakes was reported using quarter units. However, the system later changed to using decimals.

The Richter scale measures the amplitude of waves created by the earthquake then uses a logarithm to determine the numeric value of the earthquake. For every whole number increase in the scale, the amplitude of the quake is ten times greater. The Richter scale goes from zero with stronger earthquakes in higher numbers. The Richter scale does not have a higher limit. Generally, earthquakes below 2.0 on the Richter scale cannot even be felt; these are known as microearthquakes. Earthquakes between 2.0 and 3.9 almost never cause damage. Earthquakes between 4.0 and 5.9 can begin to cause damage while those 6.0 and above can start causing severe damage to the surroundings. An earthquake 10.0 or above on the Richter has never been recorded. The intensity of an earthquake and the damage it causes also depend on other factors, such as geological conditions and the distance to the origin of the earthquake.

As the quakes increase in magnitude on the Richter scale, they decrease in frequency. For example, around 8,000 microearthquakes are believed to occur each day. However, earthquakes that are between 8.0 and 8.9 on the Richter scale only happen about once a year. Some of these great earthquakes include the Sumatra earthquake in Indonesia in 2007, the 1960 Valvida earthquake in Chile, and the Mexico City earthquake in 1985.

A newer scale to measure earthquakes is the moment magnitude scale (MMS). This method, developed in the 1970’s, measures the earthquakes by how much energy they release. It uses the same values for the quakes that the Richter scale does; the new method is used by the United States Geological Survey to measure all new large earthquakes. For small earthquakes, however, the Richter scale is still generally used. Neither of these scales actually measure the intensity of the earthquake, meaning movement and damage caused by the earthquakes.

Universe Today has articles on the Torino scale and the biggest earthquake.

For more information, check out the Richter magnitude scale and the Richter scale.

Astronomy Cast has an episode on Earth.

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Orbicular granitoid near Caldera Chile

Granite rock can be pink to dark gray or even black, depending on its chemistry and mineralogy. Outcrops of granite tend to form tors, and rounded massifs. Granites sometimes occur in circular depressions surrounded by a range of hills, formed by the metamorphic aureole or hornfels. Granite is nearly always massive (lacking internal structures), hard and tough, and therefore it has gained widespread use as a construction stone.

Granite rock is classified according to the QAPF diagram for coarse grained plutonic rocks and is named by the percentage of quartz, alkali feldspar and plagioclase feldspar on the A-Q-P half of the diagram. True granite contains both plagioclase and alkali feldspars. When a granitoid is devoid or nearly devoid of plagioclase the rock is referred to as alkali granite. When a granitoid contains less than 10% orthoclase it is called tonalite. A granite containing both muscovite and biotite mica is called a binary or two-mica granite. Two-mica granites are typically high in potassium and low in plagioclase, and are usually S-type granites or A-type granites. The volcanic equivalent of plutonic granite is rhyolite. Granite has poor primary permeability.

Granite rock is currently known only on Earth where it forms a major part of continental crust. Granite has been intruded into the crust of the Earth during all geological periods, although much of it is of Precambrian age. Granitic rock is widely distributed throughout the continental crust of the Earth and is the most abundant basement rock that underlies the relatively thin sedimentary veneer of the continents.

This is just an introduction to granite rock. Here is a great in depth article on the subject. Here on Universe Today there is a great article on the types of igneous rock. Astronomy Cast has a wonderful episode on the Earth itself. The best way to understand rock is to understand the planet you live on.

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