Applications are now open for PAs in Astronomy 101.  Once you have done all the non-essay assignments and the first three essays and had them graded, you can apply by filling in your answers to all the questions in the application form, which can be accessed through the following link:


Your application will be judged based on your grades for the assignments, your answers to the questions in the applications form, and your command of the English language.  If you have any questions, please send me, your Astronomy Professor, a message.

Lesson 4) A Somewhat Solid Foundation

Professor Gagarina stands at the head of the class as the students enter.  On her desk is a large globe of the Earth with a sizeable chunk missing and a cracked and broken lunascope.  On the walls are posters showing strange diagrams, volcanic eruptions, and a damaged city.

Hell on Earth

Let us turn our focus more firmly onto planet Earth.  Heat and pressure generated by the mass of accreted rock and dust were joined by heat created from heavy asteroid impacts.  Instead of solid ground, the surface of the Earth was a comparatively thin, cooled sheet of rock broken everywhere by volcanos.  This volcanic activity belched noxious elements into the atmosphere.  This atmosphere, too, resembles nothing we see today.  There was plenty of water vapor; the stuff that clouds are made of, but the air was mostly carbon dioxide and hydrogen.  This period in Earth’s history is known as the Hadean Eon after Hades, the Greek god of the Underworld.  It is an appropriate name; there are no signs of life.



       Artist's concept of early Earth


Earth is Like an Ogre, It has Layers

The lack of life does not mean that nothing is moving, growing, or changing.  The interior of the newly formed Earth is hot and molten, allowing elements and magic to move freely within the planet.  Heavier elements, mostly iron with some nickel, are pulled into the center of the planet by gravity in a process called differentiation; lighter elements like carbon and oxygen remain closer to the surface.  The high pressure at the center of the Earth means that even though the iron core is hot enough to be a liquid, it is compressed into a solid instead.  This solid mass is the innermost layer of the Earth, known as the inner core.

The second layer is also made up of the same heavy elements.  In fact, about a third of Earth’s mass and all but one percent of the total iron in the planet are contained within the first two layers.  However, the outer core, this second layer, is not subjected to the same pressure as the inner core so this layer is liquid, rather than solid.  Many believe that the innermost layers contain vast amounts of untapped magical energy, though no one has been able to create an instrument that can survive long enough to prove this.

                                                                                        The Earth and its layers Source

The largest layer by far is the mantle.  This third layer makes up more than eighty percent of the planet and contains about half its mass.  This layer is generally a solid, however over very long periods of time it can be seen to move and change.  This is also the only interior layer that we can ever see.  Material from this layer is the molten rock that comes to the surface around volcanos.  While the rocky material in this layer moves incredibly slowly, energy is still able to move through it bringing heat and magic from the core closer to the surface of the Earth.  In places where the surface layer of the Earth is thinner, people have begun to harvest this heat as geothermal energy.  High volcanic activity is also the cause of greater concentrations of more “wild” magic.  Here there is a greater concentration of raw power coming from the center of the earth, as opposed to the magic from the sun which is filtered by the atmosphere.

The final, fourth, layer of the Earth is smallest, but also the most important from a human perspective.  The thin shell of the planet is the crust.  Here is where we live, work, and play, and also what keeps the hot inner layers from instantly vaporizing the seas.  There are cracks, places where the mantle can come through, but the crust protects us all from the other hotter and more unpredictable layers.  It is not one solid piece but rather many pieces interacting with each other and floating on the mantle beneath them.

Set Adrift

The map of Earth we know today is far different from the Earth that came into being so many millions of years ago.  In fact, the continental plates that exist today are far younger than Earth itself, owing to tectonic movement, the motion of crust plates floating on the mantle; meteor impacts; and extreme volcanic activity that characterized the early Earth.  Supercontinents, the term used to refer to early, massive continental structures, have come and gone throughout the history of Earth.  Our current continents are fragments of the most recent supercontinent: Pangea.

One of the first supercontinents known to exist on Earth is called Vaalbara, named for the men who discovered evidence of its existence.  While most of Vaalbara has been completely destroyed by geological processes, evidence has been found in Africa and Australia.  Cratons, stable pieces of continents, discovered at sites on both modern continents, date back to about three and a half billion years ago.  Fossils discovered here have revealed some of the earliest known fossils as well as evidence of photosynthesis, the process by which plants produce oxygen.

Kenorland is another supercontinent that formed about 2.7 billion years ago.  This continent is thought to have formed by accretion, similar to the formation of the Earth, except that in this case cratons came together on Earth’s surface to create a very large land mass.  Intense volcanic activity across this continent caused it to break up.

Several other supercontinents came together and fell apart over the millennia including Columbia, Rodinia, and Pannotia.  Some of these lasted longer than others.  However, many of these continents were made up of cratons that form the basis of continents today.  Parts of Africa, Antarctica, and Russia have existed for far longer than the continents of which they are a part.

                                                                          Scientific reconstruction of Rodinia Source

Siberia, an ancient craton located in the Russian heartland today, is actually about two and a half billion years old.  For some time it was a continent alone, though it also became part of several other continents through accretion.  It formed a major part of the supercontinent Rodinia, a name that comes from the Russian родина (“rodina”) which means Motherland.  Siberia also became an integral part of the most recent supercontinent, Pangea.  Though it is mainly tundra and forest, today, geologists predict that another 250 million years from now Siberia may have a subtropical climate and be part of a new supercontinent altogether.

                                                    Scientific reconstruction of Pangea's continental drift Source

Pangea is the youngest supercontinent.  It formed only about three hundred million years ago, but is also the first supercontinent to be reconstructed because of its relative youth.  Pangea was made up of all the continental plates on Earth today, though it was located mainly in the Southern Hemisphere or the southern half of the planet.  The name comes from the Greek word pan meaning whole and the Greek word for Mother Earth, Gaia.  Approximately 175 million years ago Pangea began to break up.  Continental drift and volcanic activity pushed the various tectonic plates apart.  Over millions of years the continents moved into place as we know them today.  However, these plates are still moving and the face of our Earth is changing because of them.

Shake and Bake

The plates that make up the Earth’s crust are constantly moving, growing, and shrinking.  Heat from the core makes them drift apart and clash together, and in doing so they have shaped the world we live in; this is plate tectonics.  

There are two types of plates: continental which are thick, less dense plates that have continents on them; and oceanic which are thinner, denser plates located under the oceans.  Boundaries form where plates interact with each other.  These come in three types: converging, diverging, and transform.  

Converging boundaries come in three types that create their own physical features.  When two oceanic plates come together, the older, denser plate goes through subduction – the plate is forced down and into the mantle beneath the less dense plate.  As the subducting plate begins to melt, molten rock known as magma begins to rise.  Where this magma is forced to the surface, volcanos form.  Subduction also occurs when an oceanic plate and a continental plate converge.  The continental plate forces the dense oceanic plate downwards.  This type of plate boundary is seen best in the Ring of Fire, the boundary of the Pacific Plate which created a large number of volcanos.  Finally, when two continental plates converge they push up against each other, causing the plate material to fold up into ridges, creating mountains.

                                      Map of the Ring of Fire Source

                                                  Diagram of converging boundaries Source

Diverging boundaries are where plates are moving away from each other.  Heat from the mantle below pushes upwards, pushing the plates apart.  Molten rock from beneath the plates is forced up into the gap, where it cools and becomes part of the new plate boundary.  When continental plates diverge they create large rift valleys and are often filled with water making long, skinny lakes.  When oceanic plates diverge magma is cooled more rapidly by the water, forming a large ridge of new rock like the Mid-Atlantic Ridge, which also resulted in the formation of Iceland, a relatively small island with a lot of volcanic activity.


Finally, transform boundaries occur when plates are moving up against and past each other.  Since tectonic plates rarely have smooth edges, they do not slide easily.  Sometimes they get locked together which stores up a tremendous amount of energy.  Heat and pressure within locked up plates also cause a buildup of magical energy stored within the crust from the Earth’s formation.  Once energy builds up past the resistance of the rock, the plates release suddenly, sliding past each other, creating shockwaves called earthquakes.

                                                 Diagram of a transform boundary Source

Earthquakes generate seismic waves, waves of energy and magic that travel through the Earth’s crust from the point at which the earthquake was generated, the epicenter, outwards to the surrounding area like ripples in a pond.  This can cause massive amounts of damage to buildings, roads, and other infrastructure located on top of the shaking ground.  There are several scales for measuring the strength of earthquakes but the most common is the Richter magnitude scale.  Created in 1979 by the Muggle physicist and seismologist Charles Francis Richter, this scale is used to demonstrate the strength of an earthquake.  This scale is measured in factors of ten: this means that an earthquake that measures 7 on the Richter scale is ten times as powerful as an earthquake that is measured at a 6 on the Richter scale.

The release of magical energy during an earthquake can also have very damaging effects on nearby objects and enchantments.  The rippling shockwaves of magic can disrupt nearby spells and charms, causing them to fail or backfire.  In 1938, Hubert Keiser, a magical physicist and inventor in Los Angeles, California, noticed that enchanted clocks often stopped during earthquakes, a common occurrence in that area.  When the shaking was more noticeable, the clocks were behind for a longer amount of time.  Keiser then set many magical clocks throughout the city in an attempt to measure the strength of the disturbance, which led to the development of the Keiser disturbance magnitude scale.  The Keiser scale measures magical disturbance in factors of seven.  An earthquake that is a 5 on the Keiser scale is seven times more powerful than one that is only a 4 on the Keiser scale.  

The cracked lunascope you see before me was sent to me by a friend from my time at Durmstrang.  He now lives in Christchurch, New Zealand, which suffered an earthquake in 2011 measured at 6.3 on the Richter scale and at 7.5 on the Keiser scale.  As you can see it has been broken beyond use or repair as a result of the magical shockwave that went through the city, as well as the rather heavy bookcase that fell on top of it.

                                                           Christchurch Earthquake: February 22, 2011 Source

That will be all for this week.  Do remember to look over your notes before our next class, as you will also be taking your midterms next week.  In addition to the information we have already covered, we will also be looking at the various ways that we are protected from interstellar dangers by the Earth.

Our Big Blue Marble - Earth is the only planet we call home; it is what gives us life and security even as we look to the heavens all around us. In order to study the heavens, however, it is first necessary to understand ourselves. What makes the Earth so special and why are we the only planet in our whole Solar System known to contain life? This year is intended to give Astronomy students a foundation in our Earth even as we seek to compare ourselves to others. Students will leave this class with a better understanding of their own place in the universe, the ability to compare Earth with other planets, knowledge of the origins of magic in our near universe, and an appreciation for the uniqueness of the planet we call home.

If you are interested in being a PA for Astronomy, apply here:
Course Prerequisites:
  • ASTR-201

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