Wednesday, 20 August 2014

Mass Movement

Mass Movement


Mass wasting does not rely on a carrier material like water, ice or wind. It is due to the force of gravity on an object at rest.
An object at rest stays at rest unless acted upon by a force. Once it is acted upon it will stay in motion until some equal and opposite force stops it.
When an object is placed on a flat surface, the only force acting on it is gravity. As the ground plane is inclined, the force of gravity can be shown to act in two directions. The force which keeps the object from moving is friction. Friction acts like a force opposing any movement.
As the incline increases the force parallel (book calls it tangential) with the surface grows and eventually becomes greater then the frictional force. This force is called the sheer stress. When this happens the object begins to move.
The perpendicular force component acts to keep the body in place. This force decreases as the slope increases. Another force that aids in keeping the body in place is called sheer strength. As long as the sheer strength remains higher than the sheer stress the body will remain motionless.

Capillary Action

Water in small quantities can act like a gluing agent. Through a force called surface tension, water can form a temporary bond between surfaces. If to much water is added the bond is weakened and disappears, and the water then acts more like a lubricant.
When a slope saturated with water receives more water, the added pressure may cause a catastrophic failure.

Tuesday, 19 August 2014

Metamorphic Rocks

Metamorphic Rocks

Greek: "meta" = change , "morph" = form

Metamorphic rocks by definition are formed by a change in another rock. Metamorphism can only occur inside the earth and not at the earth's crust. The changes are caused by heat, and pressure on an already existing rock.
Metamorphic rocks must change without melting, they are solid state transformations. Why? Because if they melted and recrystallized they would be igneous!
Since the changes are done in the solid state, the textures and components in the rock often store historical information about the processes they have undergone. By cataloguing metamorphic rock types and determining the conditions under which they were formed, geologist are attempting to find ancient continental boundaries.

Boundaries Of Metamorphism

Metamorphic changes are defined as changes that happen with temperature over 100 C and over a few 100 Mpa. The upper limit is easily defined as the melting point of the rock. Within the range of possible metamorphic activity are two types of metamorphic change.As we learned in the section on igneous rocks, melt temperature is directly relate to the amount of water (H2O) in the rock. If there is limited water in a rock, then initial melting will be limited to isolated areas in the rock. If a metamorphic rock is found with small areas of partial melting, then it is called a migmatite.
If more material melts, the loss in density and the migration of the melt can produce a basolith or other igneous intrusion. If the original material was metamorphic, then this combination is indicative of a subduction zone or a collision margin. When we find a large intrusive body with surrounding metamorphic rock we know the area was sometime in its history along a plate boundary.

Things that effect the metamorphic process

TemperaturePressureInitial compositionPresence fluidsTime

Sunday, 17 August 2014

Sedimentary Rocks

Sedimentary Rocks

Gravity Rules!The most important thing to know about sedimentation is that "it's a down hill process." Sedimentation" is the deposition of materials in an orderly fashion.Stratification is the arrangement of sediment in distinct layers. As with most things studied in geology they are further subdivided by physical or chemical characteristics.
Multiple layers are referred to as bedding, a single layer is a bed, and the contact points are the bedding planes.

Clastic Sediments                                                

Starting MaterialSedimentary Rock
Loose fragments of rock or mineral that are broken down by mechanical (physical) processes are called detritus. It is also known as clastic sediment. Each individual particle is known as a clast.
These materials may be of any size. From boulders to microscopic clay particles. The table above shows the starting material and the resultant type of sedimentary rock they form.
The first two images to the left show classic sandstones. The close-up image reveals small rounded stones that appear to be glued together. The majority of the stones are transparent to translucent and are likely quartz. Quartz being very resistant to weathering. There may also be some feldspar in the material.
There is a natural process in which the various size grains are classified (separated) into similar size pieces. These then define some of the types of sediment and sedimentary rocks.
Sorting is the measure of the size RANGE of particles in sediment. If the range is narrow the sediment is termed "well sorted."
Sorting is a function of the speed of the transport medium. A fast moving river tends to move larger particles as well as smaller. There are natural places where additional sorting may happen, like a sharp bend in the river. Centrifugal force within fans the debris outward around the corner, and increase the separation by size.
Weight also plays a role in separation. Heavy materials like gold or platinum will sink rapidly and move less. Materials with similar specific gravity will be sorted by size rather than by weight, and hence quartz and feldspars are sorted in this manner.
Enrichment of one mineral over all others is a function of the minerals characteristics and strength. Basically is resistance to weathering. Since quartz is very high on this scale it is often the final survivor. It is "durable".
Particle shape can also be used to help identify some types of strata. There are two similar but different features. First there is "roundness", which describes the wear at a particles corners. If the particle has no sharp corners or crystal structure reaming it is said to be rounded. The overall shape may be thin and long, or it may be roughly equi-dimensional. Rounding is related to the fine structure of the particle and not the overall shape.
If a particle has become more spherical in shape, more equi-dimensional, then you are viewing its sphericity. Sphericity is the measure of the overall shape of the particle.
The farther a particle travels, the more rounded it will become.



The chemical or physical alteration of rock by water, air, or organic matter. Weathering is the process by which rock is converted to regolith. (The irregular blanket of lose material cover the earth.)
Physical weathering is the breaking down of rock by physical means, there is no chemical change, rather there is size reduction while maintaining the same original chemistry.
Chemical weathering, is the reaction of the mineral material and its conversion from one composition to another. The rocks most susceptible to chemical weathering are those that were farthest from the conditions present on the earths surface. (What does that mean? - Rocks formed at high temperature and under high pressure are more susceptible to chemical weathering than rocks formed near or at the surface.)

Physical Weathering .. causes of:
1.) Water (freeze thaw cycle)2.) Salt growth3.) Fire4.) Plant Growth
Water has a rather unique property, when it freezes to a solid it increases in volume rather than decreases. Ice takes up about 9% more volume than the same amount of liquid water.
It's a cyclic process, water enters a crack or joint, freezes and causes the joint to expand. More water can enter the expanded joint, freezing again, and causing further joint expansion.
Enough expansion in a joint will cause the rock to crack, and this is the main process for creating rock debris on higher mountains.

Volcanoes and Magma

Volcanoes And Magma

Magma is molten rock and the other materials contained within: gases, liquids, solids. Magma reaching the earth's surface is expelled through a volcano. It is a vent from lower regions of the earth.
Lava is a river of molten magma. Magma may also be explosively expelled and be in the form of super heated gases and tiny hot particles.
As with most things in geology, magma too can be characterized and compartmentalized. Three distinct types of magma are more common than all others and are described by the following:
Composition and in particular percentage silica.
Dissolved gases in magma are very important in determining the physical characteristics of the magma. Even at low concentrations 0.2 - 3% they have tremendous effect.
The main gases are H2O, and CO2 (98%)gases that sometimes achieve 1% are SO2, HCl, N2 and Ar.

Temperature of magma is hard to measure, first it is not easy to get near molten magma, secondly the magma cools quickly when removed from its heat source, and thirdly the sensor must survive the measurement.
Magmas tend to be in the range of 1000 C - 1400 C
Viscosity is the measure of flow of a magma, most magmas do not flow very fast, but a few have been clocked at speeds in excess of about 10-15 mph. The more viscous a magma is the slower it flows.
A good model for magma coming upward is a bottle of soda pop shaken well then quickly opened. The sudden release of pressure and extra energy placed into the liquid from shaking causes some of the gas in the liquid to come out of solution. This gas being many times less dense than the surrounding liquid rushes to get out of the bottle carrying with it a good deal of the liquid.
We talked about convection in an earlier chapter, and it is convection set up by the heated magma which makes it begin to rise. As a magma gets hotter, it becomes less dense than surrounding cooler rock and begins to rise. If it maintains its heat, it becomes lighter and lighter the further it rises, and as it rises the external pressure also decreases. This makes the escaping gas form bubbles and then the gas expands or builds pressure even faster.

Basaltic magmas tend to move more slowly and have less gas dissolved, so their eruptions tend to be less violent. At the beginning of an eruption there is fast out pouring of gas and fountains are often created for a time. Eventually the magma reaches more of a steady state and issues forth smoothly and without a great deal of energy.

Since it is extremely hot, yet only slightly above the crystallization point of the minerals present within it, it will "skin" rapidly. The outside cools quickly and forms a rock coating. This coating acts like a thermos bottle and maintains the heat inside. This may create a lava tube, a conduit for hot molten lava to travel great distances while maintaining much of its heat.
As it continues to cool and loses more gas, it forms thin tube like structures called "pahoehoe", and eventually slows almost to a halt, it forms rough aa (pronounced ah-ah) flows that barely move. They look a little like black popcorn falling down a very slow moving embankment.

Crust Of The Earth

Crust Of the Earth

Igeology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle. The crusts of Earth, the MoonMercuryVenusMarsIo, and other planetary bodies have been generated largely by igneous processes, and these crusts are richer in incompatible elements than their respective mantles.
The crust of the Earth is composed of a great variety of igneousmetamorphic, and sedimentary rocks. The crust is underlain by the mantle. The upper part of the mantle is composed mostly of peridotite, a rock denser than rocks common in the overlying crust. The boundary between the crust and mantle is conventionally placed at the Mohorovičić discontinuity, a boundary defined by a contrast in seismic velocity. The crust occupies less than 1% of Earth's volume. 
The oceanic crust of the sheet is different from its continental crust. The oceanic crust is 5 km (3 mi) to 10 km (6 mi) thick and is composed primarily of basaltdiabase, and gabbro. The continental crust is typically from 30 km (20 mi) to 50 km (30 mi) thick and is mostly composed of slightly less dense rocks than those of the oceanic crust. Some of these less dense rocks, such as granite, are common in the continental crust but rare to absent in the oceanic crust. Both the continental and oceanic crust "float" on the mantle. Because the continental crust is thicker, it extends both above and below the oceanic crust. The slightly lighter density of felsic continental rock compared to basaltic ocean rock contributes to the higher relative elevation of the top of the continental crust. Because the top of the continental crust is above that of the oceanic, water runs off the continents and collects above the oceanic crust. The continental crust and the oceanic crust are sometimes called sial and sima respectively. Because of the change in velocity of seismic waves it is believed that on continents at a certain depth sial becomes close in its physical properties to sima, and the dividing line is called the Conrad discontinuity.

Outer Core

Outer Core

The outer core of the Earth is a liquid layer about 2,260 km thick composed of iron and nickel which lies above the Earth's solid inner core and below its mantle. Its outer boundary lies approximately 2,890 km (1,800 mi) beneath the Earth's surface]. The transition between the inner core and outer core is located approximately 5,150 km beneath the Earth's surface.
The temperature of the outer core ranges from 4400 °C in the outer regions to 6100 °C near the inner core. Eddy currents in the nickel iron fluid of the outer core are believed to influence the Earth's magnetic field. The outer core is not under enough pressure to be solid, so it is liquid even though it has a composition similar to that of the inner core. Sulfur and oxygen could also be present in the outer core.
Without the outer core, life on Earth would be very different. Scientists believe that convection of liquid metals in the outer core create the Earth's magnetic field. This magnetic field extends outward from the Earth for several thousand kilometers, and creates a protective bubble around the Earth that deflects the Sun's solar wind. Without this field, the solar wind would have blasted away our atmosphere, and Earth would be lifeless like Mars.

Inner Core

Inner Core

What is the inner core and who discovered it?

The inner core is the very center of the planet and is the hottest part of a planet. The inner core was discovered by Inge Lehmann in 1929. Inge Lehmann was studying a large New Zealand earthquake. An earthquake makes vibrations which move across the inside of the Earth. The vibrations that Inge Lehmann was studying seemed to be moving across something solid in the center of the planet. She wrote about this inner core for many years but it was not proved to exist until 1970, when studies were much more exact.

Where is it, how big is it, and what is it made of?

The inner core is between 300 and 400 kilometers wide and more than 12,000 kilometers below our feet. It is believed to be made of molten (melted) iron and nickel but the Earth is so heavy that the inner core does not move like a liquid. Scientists believe that the inner core may be hotter than the surface (edge) of the Sun at near 106,000 °C.

What other ideas are there about the inner core?

The inner core was thought to be a type of huge diamond because diamonds are made by huge weight but studying the way the Earth vibrates shows that the inner core is not as solid as a diamond. There may be smaller diamonds but it is not possible to know because of the huge heat and weight of the world.



The lithosphere is the solid shell of a rocky planet called earth. That means the crust and the upper part of the mantle which is joined to the crust (see picture on the right).
Under the lithosphere there is the asthenosphere, the weaker, hotter, and deeper part of the upper mantle.
The lithosphere is the surface layer of the fluid parts of the Earth's convection system, therefore it thickens over time. It is broken up into pieces called plates (shown in picture on the left), which move independently relative to one another. This movement of lithospheric plates is described as plate tectonics.
The division of Earth's outer layers into lithosphere and asthenosphere should not be confused with the chemical subdivision of the outer Earth into mantle, and crust. All crust is in the lithosphere, but lithosphere generally contains more mantle than crust.

There are two types of lithosphere:
  • Oceanic lithosphere, which is associated with Oceanic crust
  • Continental lithosphere, which is associated with Continental crust
Oceanic lithosphere is typically about 50-100 km thick (but beneath the mid-ocean ridges is no thicker than the crust). Continental lithosphere is thicker (about 150 km). It consists of about 50 km of crust and 100 km or more of uppermost mantle.
Oceanic lithosphere consists mainly of mafic crust and ultramafic mantle and is denser than continental lithosphere, for which the mantle is associated with crust made of felsic rocks. The crust is distinguished from the upper mantle by the change in chemical composition that takes place at the Moho discontinuity. Oceanic lithosphere thickens as it ages and moves away from the mid-ocean ridge. This thickening occurs by conductive cooling, which converts hot asthenosphere into lithospheric mantle, and causes the oceanic lithosphere to become increasingly dense with age. Oceanic lithosphere is less dense than asthenosphere for a few tens of millions of years, but after this becomes increasingly denser than asthenosphere. The gravitational instability of mature oceanic lithosphere has the effect that at subduction zones the oceanic lithosphere invariably sinks underneath the overriding lithosphere, which can be oceanic or continental. New oceanic lithosphere is constantly being produced at mid-ocean ridges and is recycled back to the mantle at subduction zones. As a result, oceanic lithosphere is much younger than continental lithosphere: the oldest oceanic lithosphere is about 170 million years old, while parts of the continental lithosphere are billions of years old.
Another distinguishing characteristic of the lithosphere is its flow properties. Under the influence of the low-intensity, long-term stresses that drive plate tectonic motions, the lithosphere responds essentially as a rigid shell and thus deforms primarily through brittle failure, whereas the asthenosphere (the layer of the mantle below the lithosphere) is heat-softened and accommodates strain through plastic deformation.

Saturday, 16 August 2014

Dynamic Earth

The dynamic Earth

When an object spins it exerts centrifugal force. This is an outward force that is the strongest at the point farthest from the spinning center and perpendicular with the axis of spin.
In the case of a sphere, that force is maximized at the equator and can cause a bulge at that point. If the sphere is made out of a hard, non compressive material (steel) then the amount of deformation is very small. If it made out of something pliable (rubber like), then it increases with increasing speed of rotation and is easily visible.
The earth is just such a rotating sphere, and as it happens, it is about 21 km wider if measured at the equator . (vs. measurement through the two poles.)
If a conceptual earth is created from nothing but water, the degree of deformation almost exactly matches the actual deformation of the planet. Since we know the earth is not made up mostly of water, we are lead to the idea that the center material must be deformable in a similar way.
The interior of the earth is not rigid, and can undergo deformation under pressure or external force.
The exterior of the earth is made up of land and ocean. The ocean comprises about 71% of the earths surface and has been growing slowing for many years. The land is distributed over the remaining 29% but the majority of it is located in the Northern hemisphere.
Modern day shorelines do not match up well with the continental crust and the theoretical ocean boundaries. This is due to the sea level fluctuating.
If the earth is a closed system, where does the extra water come from?
The answer is the "polar glaciers". These enormous ice masses hold more than 24,000,000 km3 of water. More than enough water to raise the world oceans up to 66 m (~200 feet). As glaciers melt they push the ocean higher on to the continents.
This is a profile of a continent and its contact area with the ocean.
The "continental shelf" is the area of most recent contact, and there has been little time for the ocean to aid in the erosion of the continent.
Further out is the "continental slope". The bottom of this slope is actual the part of the continent that is in contact with the sea floor. (Oceanic crust.) The "continental rise" is the area of silt deposition than has settled from erosion of the continent.
If the outline of a continent were made at the edge of the slope, then there would be 40% land mass and 60% water mass covering the surface of the earth. This has been more nearly achieved in the past during times of glaciation (also known as "ice ages").
The oceans cover the longest mountain ranges on earth. They lie at the center of the deep oceans and divide the ocean basins into two "abyssal planes".

Principle of isostacy

If you look at a group of objects floating in a liquid, they will tend to float at different levels. One reason is their internal density. Rocks tend to float at a lower level than beach balls. (Remember density is weight per unit volume.) For any given density of material an object will displace as much water as its overall weight.
First, objects will only float if their density is less than the material they are floating in. Water has a density of 1 gm per cc. A piece of floating wood must then have a density less than 1 gm per cc or it would sink. Another way to look at this is that the wood has more volume for the same weight.
The piece of wood will displace its weight in water, and that which remains will be above the water line around the wood.

In each case this wood displaces 50% of its volume. Notice the amount showing (volume) above the water is the same, but the profiles are quite different.

Structure of the Earth

Structure of the Earth

The interior structure of the Earth is layered in spherical shells, like an onion. These layers can be defined by either their chemical or their rheological properties. Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core. Scientific understanding of Earth's internal structure is based on observations of topography and bathymetry, observations of rock in outcrop, samples brought to the surface from greater depths by volcanic activity, analysis of the seismic waves that pass through Earth, measurements of the gravity field of Earth, and experiments with crystalline solids at pressures and temperatures characteristic of Earth's deep interior.


0–600–37Lithosphere (locally varies between 5 and 200 km)
0–350–22… Crust (locally varies between 5 and 70 km)
35–6022–37… Uppermost part of mantle
100–200210-270… Upper mesosphere (upper mantle)
660–2,890410–1,790… Lower mesosphere (lower mantle)
2,890–5,1501,790–3,160Outer core
5,150–6,3603,160–3,954Inner core

What does a geologist do ?

What does a geologist do ?

Geologists work to understand the history of our planet. The better they can understand Earth’s history the better they can foresee how events and processes of the past might influence the future. Here are some examples: 

Geologists study earth processes:   Many processes such as landslidesearthquakesfloods and volcanic eruptions can be hazardous to people. Geologists work to understand these processes well enough to avoid building important structures where they might be damaged. If geologists can prepare maps of areas that have flooded in the past they can prepare maps of areas that might be flooded in the future. These maps can be used to guide the development of communities and determine where flood protection or flood insurance is needed. 

Geologists study earth materials:   People use earth materials every day. They use oil that is produced from wells, metals that are produced from mines, and water that has been drawn from streams or from underground. Geologists conduct studies that locate rocks that contain important metals, plan the mines that produce them and the methods used to remove the metals from the rocks. They do similar work to locate and produce oil, natural gas and ground water. 

Geologists study earth history:   Today we are concerned about climate change. Many geologists are working to learn about the past climates of earth and how they have changed across time. This historical geology news information is valuable to understand how our current climate is changing and what the results might be. 

Geology as a career :

Geology can be a very interesting and rewarding career. The minimum training required is a four-year college degree in geology. Pre-college students who are interested in becoming geologists should take a full curriculum of college preparatory courses, especially those in math, science, and writing. Courses related to computers, geography and communication are also valuable. 
Geologists work in a variety of settings. These include: natural resource companies, environmental consulting companies, government agencies, non-profit organizations, and universities. Many geologists do field work at least part of the time. Others spend their time in laboratories, classrooms or offices. All geologists prepare reports, do calculations and use computers. 

Although a bachelor's degree is required for entry level employment, many geologists earn master's and/or doctorate degrees. The advanced degrees provide a higher level of training, often in a geology specialty area such as paleontology, mineralogy, hydrology or volcanology. Advanced degrees will often qualify the geologist for supervisory positions, research assignments or teaching positions at the university level. These are some of the most sought after jobs in the field of geology. 
Employment opportunities for geologists are very good. Most geology graduates with a strong academic background and good grades have no trouble finding employment if they are willing to move to a location where work is available. 

Employment outlook :

Over the next several years the number of geology job openings is expected to exceed the number of students graduating from university geology programs. Starting salaries for geologists have recently ranged from $50,000 to $100,000 per year.

How can you become a geologist :

If you are a pre-college student can prepare to become a geologist by doing well in all of your courses. Science courses are especially important but math, writing, and other disciplines are used by every geologist during every working day. 

If you are considering college or graduate school there are many universities that offer courses or programs in geology. Visit the website of a school that offers a geology degree, get in touch with the geology department, let them know you are interested and make arrangements to visit the campus. Don't be hesitant. Good schools and professors want to be contacted by interested students. 




mineral is a naturally occurring substance that is solid and stable at room temperature, representable by a chemical formula, usually abiogenic, and has an ordered atomic structure. It is different from a rock, which can be an aggregate of minerals or non-minerals and does not have a specific chemical composition. The exact definition of a mineral is under debate, especially with respect to the requirement a valid species be abiogenic, and to a lesser extent with regard to it having an ordered atomic structure. The study of minerals is called mineralogy.
There are over 4,900 known mineral species; over 4,660 of these have been approved by the International Mineralogical Association(IMA). The silicate minerals compose over 90% of the Earth's crust. The diversity and abundance of mineral species is controlled by the Earth's chemistry. Silicon and oxygen constitute approximately 75% of the Earth's crust, which translates directly into the predominance of silicate minerals. Minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish various species, and these properties in turn are influenced by the mineral's geological environment of formation. Changes in the temperature, pressure, and bulk composition of a rock mass cause changes in its mineralogy; however, a rock can maintain its bulk composition, but as long as temperature and pressure change, its mineralogy can change as well.
Minerals can be described by various physical properties which relate to their chemical structure and composition. Common distinguishing characteristics include crystal structure and habithardnesslustrediaphaneity, colour, streak, tenacity, cleavage, fracture, parting, and specific gravity. More specific tests for minerals include reaction to acid, magnetism, taste or smell, and radioactivity.
Minerals are classified by key chemical constituents; the two dominant systems are the Dana classification and the Strunz classification. The silicate class of minerals is subdivided into six sub classes by the degree of polymerization in the chemical structure. All silicate minerals have a base unit of a [SiO4]4- silica tetrahedra—that is, a silicon cation coordinated by four oxygen anions, which gives the shape of a tetrahedron. These tetrahedra can be polymerized to give the subclasses: orthosilicates (no polymerization, thus single tetrahedra), disilicates (two tetrahedra bonded together), cyclosilicates (rings of tetrahedra), inosilicates (chains of tetrahedra), phyllosilicates (sheets of tetrahedra), and tectosilicates (three-dimensional network of tetrahedra). Other important mineral groups include the native elementssulfidesoxideshalidescarbonatessulfates, and phosphates.


Basic Geology

Geology (from Greek γη- (ge-, "the earth") and λογος ("logos", "word", "reason")) is the science and study of the solid matter of a celestial body, its composition, structure, physical properties, history and the processes that shape it. In this book, the term Geology will apply to the Earth in particular.
Geology can be split into two main branches: historical and physical. Historical geology attempts to understand the origins, composition, systems and changes of the Earth.


Geology is the study of the things that make up Earth. Geologists have used geology to find out many things about Earth, such as that it is about 4.6 billion years old.


According to the widely accepted Big Bang theory, the Universe began at some point in space and time around 13,700,000,000 years ago, as evidenced by the Doppler effectobserved in all stars and a 3 degree Kelvin background radiation observed elsewhere.
  • In about 10E-43 seconds, physics became defined and gravity separated from other forces. The Universe was 10E32 K in temperature.
  • At 10E-35 seconds, the Universe expanded to the size of a softball and the strong nuclear force separated. Energy turned into quarks and electrons and their anti-matter counterparts. The temperature was 1027 K.
  • At 10E-6 seconds, quarks began to bind into protons and neutrons; matter and antimatter destroyed each other and the balance turned out to be in favor of matter. The Universe was about the size of our solar system and 1013 K hot.
  • 1 second after its inception, the electromagnetic and weak nuclear forces appeared as the Universe cooled to 109 K.
  • 3 minutes later, protons and neutrons fused into nuclei.
  • After 100,000 years, the electrons and the nuclei came together to form atoms; photons separated from matter and there was light.
  • In the next 1,000,000,000 years the Universe became clumpy as galaxies began to take shape.
  • Ever since then, the Universe has cooled down to 3 K, galaxies have developed, generations of stars have passed, creating heavier elements, and life has appeared. Our galaxy, the Milky Way, contains about 200,000,000,000 stars and lies 1 million light years from its nearest neighbor.
  • The solar system was formed around 4,600,000,000 years ago as dust collapsed into the protostar that was to become the Sun, and into planetesimals orbiting it. The inner planets, from Mercury to Mars, are solid because the solar winds have driven gases away and have a core; the outer planets are larger and consist of gas.

Plate tectonics

Plate Tectonics is a theory that almost all of the world's scientists believe is true. It involves tectonic plates: puzzle-like formations under the Earth's crust that are floating on a layer of magma called the mantle. The mantle is a layer of the earth. The crust is another, it is what we live on. Tectonic plates are part of a layer called the lithosphere. The lithosphere floats on a section of the upper mantle called the asthenosphere. The asthenosphere is a place where hot magma swirls in a convection current. This current causes the movement of the tectonic plates.
Tectonic plates are constantly moving around, colliding, and drifting apart. Sometimes one plate slides under the other. This is called subduction. Divergence means that two plates are sliding apart, and convergence is the opposite. Transform is when the edges of two plates slide along each other. When plates collide, it can cause earthquakes and tsunamis. Volcanoes, however, are more commonly caused by subduction, because when two plates part it allows the magma in the mantle to burst forth.