Cumberland Times-News

Bob Doyle - Astronomy

November 24, 2012

Learn about our planet’s key features

Recently, I had a MRI of my spine and a battery of X-rays of my back. These procedures confirmed my family doctor’s diagnosis as to why I had pains in my legs when walking my dog.

There’s a parallel between these procedures that reveal the shifts of the vertebrae deep in one’s back and procedures used by Earth scientists to learn the interior structure of the Earth.

“Planet Earth: One Million Things” is a marvelous book for all ages that beautifully describes the wonders of Earth’s surface and interior. “Planet Earth” is a Dorling Kindersley book by John Woodward, published in 2009 with ISBN 978-07566-5235-7.

As with other Dorling Kindersley books, the author works with an expert consultant (Kim Bryan for this book). These two individuals work with a team of superb graphic designers to produce a visually stunning book.

You can open any of the five sections of this book and quickly learn about the key features and processes that shape our planet. The five sections are: Planet Earth, Rocks and Minerals, Water and Weather, Life Zones and Human Influence.

Planet Earth, the first section starts with the location of our sun and Earth within our galaxy. Our sun lies near a spiral arm, whose gas clouds are lit up by the light of newly born stars.

Following is a review of our sun’s eight regular planets.

The smaller bodies that orbit our sun (comets and asteroids) shed small fragments that burn up in our atmosphere (meteors).

The early Earth was semi-molten, seething with many active volcanoes and hostile to life. The interior of the present Earth is revealed by shock waves from Earth quakes.

The S waves (S for transverse, with vibrations perpendicular to wave motion) are absorbed by liquids. The S wave shadow zone opposite the Earthquake location tells us that deep inside the Earth is a shell of liquid iron (88 percent) and sulfur (12 percent).

Earth models reveal that its core temperature is 7200 F or about 4,000 K, the temperature of orange giant stars (such as Aldebaran, the bright star to the right of bright Jupiter in the eastern evening sky). This liquid shell is about 1400 miles thick. It begins about 1800 miles beneath the Earth’s crust.

At the center of the Earth, the pressures and temperatures are so high that the inner core is solid (about 1,500 miles across). The inner core is 80 percent iron and 20 percent nickel.

Both regions of the core (solid and liquid) are at the same temperature as the metals there are great conductors of heat. (The easy flow of heat prevents any difference in temperature.)

The mantle of the Earth, which comprises 83 percent of the Earth’s volume is mostly made of peridotite, a dark, heavy rock. As one descends through the mantle, the temperature rises from 1800 F to 6300 F.

The crust has about a dozen major plates that are driven by currents in the mantle. In the upper part of the mantle, the material can flow very slowly (inches per year) pushing the crustal plates around.

We live on the North American plate that long ago collided with the African plate, causing the Appalachian Mountains. The west side of the Pacific Plate is diving under (subducting) the Asian plate. This caused the deadly Earth quakes that have recently struck Japan and Indonesia.

In the book’s treatment of Continental Drift, the southern continents were joined together in a supercontinent called Gondwanaland about 170 million years.

This allowed the dinosaurs to spread across Australia, Antarctica, South America and Africa. 95 million years ago, South America and Africa separated with North America drifting away from Europe.  

After the demise of the dinosaurs (65 million years ago), the Saudi Arabian peninsula split off from Africa and India drifted northward towards southern Asia. This collision would create the Himalayan Mountains, still rising today.

Three and a half million years ago, volcanic islands in the Caribbean formed a land bridge between North and South America.

SKY SIGHTS AHEAD:  Tomorrow and Tuesday, the brilliant planet Venus will line up with the distant planet Saturn. On both of these mornings (look about 6 a.m.), the two planets will be about two moon widths (one degree apart).

Venus is nearly 100 times brighter than Saturn due to its highly reflective clouds and Venus’ closeness both to the sun and Earth. On the night of Nov. 28-29, our moon will be full, rising as the sun sets and setting as the sun rises.

The Wednesday evening moon will appear just south of the bright planet Jupiter, a little more than one moon width away.

 Bob Doyle invites any readers comments and questions. E-mail him at rdoyle@frostburg.edu. He is available as a speaker on his column topics.

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Bob Doyle - Astronomy
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