Layers of the Earth: A Classroom Activity

Photo by NASA

Photo by NASA

From the core to the crust, the Earth is a pretty big deal. It has a diameter of about 6,400 km, and it is made of various layers that help change the surface of the earth. These layers are defined by either what they are made of or how they move. When we look at the chemical composition of each layer, we are defining them as compositional layers. The compositional layers are the crust, the mantle and the core. When we look at the mechanical properties of the layers, we are defining them as the mechanical layers. The five mechanical layers are the lithosphere, the asthenosphere, the mesosphere, the inner core and the outer core. Although we only see the outermost layer of the earth, we have learned a lot about the layers underneath by looking at seismic waves and various rocks at the surface. 

The three compositional layers of the earth are defined by significant changes in chemical composition. The outermost layer is the crust. It is the thinnest layer making up only about 1 percent of the earth. The crust is mostly made of elements like silicon (Si), aluminum (Al), potassium (K), calcium (Ca), oxygen (O), sodium (Na) and minerals made of these elements. The crust can be subdivided into two types – oceanic crust and continental crust. Oceanic crust tends to be thinner (approx. 5-10km thick) than continental crust and younger too! Continental crust is on average 30 km thick, and contains the oldest rocks and minerals. Both types of crust cover the entire outer portion of the earth. Below the crust lies the mantle (approximately 2,890 km thick.) The mantle is made of silicon (Si) and oxygen (O) like the crust, but it also contains large amounts of iron (Fe) and magnesium (Mg). The final compositional layer of the earth is the core (approx.3,480 km thick). The core is made of iron (Fe) and nickel (Ni). It is under intense pressure and high temperatures, and it is the densest layer of the earth. Although these layers may share common elements, the contents differ enough to create the distinct layers.

The five mechanical layers of the earth are defined by how the layers move. The layers can be described as rigid, plastic or liquid in consistency. The outermost mechanical layer is the lithosphere. The lithosphere is rigid, and it includes the crust and the uppermost part of the mantle. The lithosphere is divided into the tectonic plates, areas of continental crust and/or oceanic crust that move and shift over time. The tectonic plates of the lithosphere move and shift on the plastic layer called the asthenosphere. The asthenosphere is under more pressure than the lithosphere and has a higher temperature. It is considered plastic because the rock has the ability to flow more than a rigid layer, but not as easily as a liquid layer.  The rock in the asthenosphere could melt if exposed to the surface, but it is under extreme pressure causing it to flow like a plastic. The mesosphere is the layer below the asthenosphere. The mesosphere is hotter than the asthenosphere, but it is rigid because it is experiencing more pressure than the layers above. The last mechanical layers of the earth are found in the core. The core is split into the outer core and the inner core because the two layers differ in rigidity. The outer core is liquid iron (Fe) and nickel (Ni). The flow of the outer core creates and sustains the earth’s magnetic field. Unlike the outer core, the inner core is solid. The inner core is made from mostly iron (Fe), but it can also contain nickel (Ni) and traces of precious elements like gold (Au). It is extremely hot, and under extreme pressure from the layers of the earth and atmosphere around it. All of these layers work together to make our dynamic earth!

Create a foldable Earth with the activity below to teach students about the various layers of the earth. To learn how the asthenosphere moves tectonic plates or learn about the natural disasters caused by that movement, check out our new Earth Science on Wheels topic Dynamic Earth!

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This project models two different ways to understand the layers of the earth. It addresses the compositional layers of the earth, and the mechanical layers of the earth.

Materials:

all the supplies edit

Procedure:

  1. Pass out template to each student.
  2. Instruct students to cut out the Earth. Once they have cut the outside, tell them to cut along the dashed line that says “cut here.”
  3. Next, fold along the “Fold line.” Then, set the Earth aside.
  4. Now, tell students to cut out the quarter circle labeled A. This will represent the mechanical layers of the earth.
  5. Invite students to color each of the areas in the quarter circle a different color starting from the inside:
    1. Yellow – inner corre
    2. Orange – outer core
    3. Red – mesosphere
    4. Pink – asthenosphere
    5. Purple – lithospherecut and colored edit
  6. Have students set aside the mechanical layers (A.) for now
  7. Instruct students to cut out the second quarter circle (B.) from the template sheet. These will represent the compositional layers of the earth. Invite students to color each of the sections a different color:
    1. Yellow – core
    2. Red – mantle
    3. Brown – crust
  8. Have students set aside the compositional layers (B.) for now
  9. Instruct students to glue the earth, to the background paper. Remind them to not glue down the flap.
  10. Tell students to place the mechanical layers (A.) on the background paper underneath the flap and glue it to the paper.
  11. They should then take the quarter circle that represents the compositional layers (B.), and place it on the backside of the flap of the Earth. Then, carefully glue it to the back of the flap.
  12. Once completed, show students how to flip up the flap and see the mechanical layers on the background page and the compositional layers on the back of the flap. Students can add notes to the layers to help them learn what the layers do!

Seeing Stars with James Wooten: Exciting Rare Mercury Transit Next Monday!

May Starmap

Jupiter is now high in the south at dusk. It outshines all stars we ever see at night, so you can’t miss it.

Mars and Saturn become late evening objects this month. Tonight, May 2, Mars rises in the southeast at 9:48 p.m. while Saturn comes up soon afterwards, at 10:24 p.m. By May 15, though, both planets rise during twilight, and on Memorial Day both are in the southeastern sky as soon as it gets dark. Mars and Saturn are still above the distinctive pattern of Scorpius, the scorpion. As you watch them rise, Mars is to the upper right and is much brighter.

In fact, this month, Mars outshines all of the stars and even rivals Jupiter in brightness! That’s because on May 22, Earth passes between the Sun and Mars. That alignment is called ‘opposition’ because it puts Mars opposite the Sun in our sky, making Mars visible literally all night long. It also makes Mars much brighter than normal in the sky, since we’re as close to it as we’ll ever get until Earth overtakes Mars again in 2018. Saturn comes to opposition June 3.

Venus is lost in the Sun’s glare and out of sight all month.

A swath of brilliant winter stars sets in the west at dusk. Orion, the Hunter, is still visible in the west as May begins. His two dogs, represented by Sirius and Procyon, are to his left.  Gemini, the Twins, are above Orion. The Big Dipper is above the North Star, with its handle pointing to the right. From that handle, you can ‘arc to Arcturus’ and then ‘speed on to Spica’; those stars are high in the east and in the south, respectively, at dusk. Leo, the Lion, passes almost overhead at dusk.

As Orion and his dogs set, look for Antares, the brightest star in Scorpius, the Scorpion, to rise in the southeast. Saturn and Mars will rise with the Scorpion’s head, above Antares. At the same time, Vega, brightest star of the Summer Triangle, appears low in the northeast. These stars remind us that summer is on the way.

Moon Phases

Moon Phases in May 2016:

New: May 6, 2:30 p.m.

First Quarter: May 13, 12:02 p.m.

Full: May 21, 4:14 p.m.

Last Quarter: May 29, 7:12 a.m.

Mercury Transit:

On Monday, May 9, 2016, Mercury overtakes Earth on its much faster orbit. This time, though, when Mercury passes Earth, the alignment is almost exact, such that Mercury appears in silhouette against the sun’s disk. This event is known as a transit of Mercury. Keep in mind that the planets are almost, but not exactly, in the same plane. Indeed, Mercury’s orbit is the most inclined — tilted up to 7 degrees from Earth’s orbital plane. That’s why Mercury does not usually transit the sun when it overtakes Earth. Monday’s event is therefore rare and special, occurring only 14 times in the 21st century (the next one occurs Nov. 11, 2019).

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Thus, weather permitting, the Houston Museum of Natural Science has arranged for volunteers from local astronomy clubs to set up solar telescopes outside our museum’s main entrance, near the sundial, to show you the transit. Mercury, already in the sun’s disk by sunrise in Houston, takes until 1:42 p.m. to cross to the other side of the sun’s disk. If skies cooperate, we’ll observe the transit from 10 a.m. until 1:42 p.m. on Monday, May 9. If there are sunspots on the sun’s disk while Mercury is there, Mercury will stand out because its disk is fully round and because Mercury moves noticeably across the sun’s disk during the hours we’re watching.

We will observe the sun (and Mercury in silhouette) through telescopes with filters especially designed to filter the sun safely, and by projecting the sun’s image onto a screen. These are the only two ways to observe the Sun safely. Please do not try to observe the sun directly or through an unfiltered telescope, as this will lead to permanent eye damage or blindness. Our common sense tells us this because we always avert our eyes when we accidentally turn towards the Sun. When something cool happens on the sun, some of us try to override our common sense, and there is no reason to do so. Come observe safely with us.

On most clear Saturday nights at the George Observatory, you can hear me do live star tours on the observation deck with a green laser pointer. As of now, George is closed which Brazos Bend State Park dries out from last month’s floods, and is scheduled to reopen May 10. If you’re there, listen for my announcement. 

Seeing Stars with James Wooten: Last Chance for Winter Constellations in April

Starmap April

Jupiter is now high in the east-southeast at dusk. It outshines all stars we ever see at night, so you can’t miss it. 

Mercury is visible just after sunset this month. Face west at twilight, and look low in the sky over the point where the sun sets. Mercury isn’t as brilliant as Venus or Jupiter, but it easily outshines the stars near it in the sky, so it’s not too hard to find. 

Mars is in the south-southwest at dawn. Noticeably reddish in tint, Mars continues to brighten each day until its opposition in May. It has now surpassed nearby Saturn in brightness.

Saturn is in the south-southwest at dawn, above the distinctive pattern of Scorpius, the scorpion. Mars remains close to Saturn this month.

Venus is becoming lost in the sun’s glare. Already, it doesn’t rise until deep into morning twilight, and Venus continues to approach the sun all month.

April is the last month to see the set of brilliant winter stars which now fill the western evening sky. Dazzling Orion is in the southwest at dusk. His three-starred belt is halfway between reddish Betelgeuse and bluish Rigel. Orion’s belt points rightward to Aldebaran in Taurus the Bull. To Orion’s upper left are the twin stars Castor and Pollux, marking the heads of Gemini, the Twins. You can find Sirius, the brightest star we ever see at night, by drawing a line from Orion’s belt towards the left. Forming a triangle with Sirius and Betelgeuse is Procyon, the Little Dog Star. 

Joining the winter stars are stars of spring rising in the east. Look for Leo, the Lion at dusk. Ursa Major, the Great Bear, which includes the Big Dipper, is high above the North Star on spring evenings. Extend the Big Dipper’s handle to ‘Arc to Arcturus’ and then ‘speed on to Spica’. There are fewer bright stars in this direction because of where the plane of our galaxy is in the sky. The area of sky between Gemini and Taurus and over Orion’s head is the galactic anticenter, which means that we face directly away from the galactic center when we look in this direction. Those bright winter stars setting in the west are the stars in our galactic arm, right behind the sun. On the other hand, if you look at the sky between Ursa Major, Leo, Virgo, and Bootes, you’re looking straight up out of the galactic plane, towards the galactic pole. There are fewer stars in this direction.

Moon Phases

Moon Phases in April 2016:

New: April 7, 6:24 a.m.

First Quarter: April 13, 10:59 p.m.

Full: April 22, 12:24 a.m.

Last Quarter: April 29 10:29 p.m.

On most clear Saturday nights at the George Observatory, you can hear me do live star tours on the observation deck with a green laser pointer. If you’re there, listen for my announcement. 

Clear Skies!

Leap years: proof that Earth is always running late

Unless you’ve been living under a rock, you’re probably aware 2016 is a leap year. February will have 29 days as part of a four-year mathematical cycle that has been observed in the Gregorian calendar since 1582. The reason we do this? To make up for a slight discrepancy in the Earth’s orbit around the sun.

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As humans, we like to count things and measure our lives by predictable cycles, so Western cultures designed a calendar counting 365 days in a year. However, Earth’s true orbit is actually 365 days, five hours, 49 minutes and 16 seconds. That’s right; every New Year’s Eve, Earth is little under six hours late to the party. Talk about procrastination!

To make up for Earth’s tardiness, we add those six hours together every four years to make a full day. This keeps the calendar from drifting through the seasons over time. It might take a while, but if we didn’t add leap days, in 31 leap years (or 124 years), Jan. 1 would occur the first day in February. That means the Spring Equinox would happen Feb. 20 instead of in March!

But that’s not the end of the problem. In adding a day every four years, we overcompensate by 10 minutes and 44 seconds. (Remember Earth doesn’t really take another full six hours to complete its trip around the sun.) However, the Gregorian calendar accounts for this, as well.

epa04383191 A handout picture made available by NASA on 04 September 2014 shows a view of Earth taken by NASA astronaut Gregory Reid Wiseman of the US from the International Space Station (ISS) on space, 02 September 2014. The Expedition 40 crew has been busy on the ISS performing health checks and humanoid robot upgrades. A trio of orbital residents is packing up gear as they prepare to return home in less than two weeks. Commander Steve Swanson powered down and stowed Robonaut 2 after wrapping up its mobility upgrades this week. He installed new legs on the humanoid robot including external and internal gear as well as cables. This sets the stage for more upgrades in the fall before Robonaut takes its first steps as an assistant crew member. Robonaut was designed to enhance crew productivity and safety while also aiding people on Earth with physical disabilities.  EPA/NASA/REID WISEMAN  HANDOUT EDITORIAL USE ONLY

A view of Earth by NASA.

Over a period of 400 years, the true length of the leap cycle, this overcompensation amounts to a total of three days. So in every century that isn’t divisible by 400, we don’t add a leap day. The last one was back in 1900. The year 2000, divided by 400, equals five, so we did observe leap year the February after Y2K. But you’ll have to live until 2100 to notice the next time we skip it. Your kids and grandkids will probably still be around, though, likely talking about lazy Earth and the crazy math behind leap years!

When the renovated Burke Baker Planetarium opens March 11, you can see leap years in action with a full map of Earth’s orbit, as well as the rest of the planets in the Solar System. Speed up time to compare rates and see how Earth measures up. Travel to the edge of our neighborhood and meet up with Pluto and other dwarf planets, and see how astronomers found evidence of a new Planet Nine! (I wonder how long that calendar is…)