Chapter 12a/11a

 “The Dynamic Planet”

Geosystems, 4CE, pp. 346-355 (Note this is Chapter 12 in 4CE)

(Geosystems, 3CE, pp. 308-316 (Note this is Chapter 11 in 3CE))

**There is a video version of this lecture here:

**The exam is based on the content in these notes, so please print them off to study from.

In Proverbs 8:22-31 (NLT), God’s wisdom and power during the creation of the Earth is beautifully described …

“The LORD formed me (wisdom) from the beginning, before he created anything else. I was appointed in ages past, at the very first, before the earth began. I was born before the oceans were created, before the springs bubbled forth their waters. Before the mountains and the hills were formed, I was born– before he had made the earth and fields and the first handfuls of soil. “I was there when he established the heavens, when he drew the horizon on the oceans. I was there when he set the clouds above, when he established the deep fountains of the earth. I was there when he set the limits of the seas, so they would not spread beyond their boundaries. And when he marked off the earth’s foundations, I was the architect at his side. I was his constant delight, rejoicing always in his presence. And how happy I was with what he created–his wide world and all the human family!”

This chapter introduces the physical structure of the Earth.  It also introduces you to the geologic time scale (if this time scale is problematic for you, when we deal with Theological Issues later in the course we will discuss this further).  For the exam, you are NOT required to know “The Pace of Change” 4CE pp. 348-350 and 3CE pp. 310-312 (top).   But read them!

Two terms you DO need to know:

  • endogenic – energy and processes originating within the Earth.  The Earth’s interior is hot!  It contains a lot of energy!  This energy reveals itself in volcanoes, earthquakes, hot springs, geysers, etc.
  • exogenic – energy and processes originating outside the Earth.  The Sun is hot!  It provides a lot of energy.  This exogenic energy reveals itself by heating the Earth’s surface and atmosphere, evaporating moisture, powering weathering, erosion, etc.

   I.  The Structure of the Earth

12 earth cross sectionThe earth appears to be made up of several distinct layers (study Figures 12.2, 12.3, 4CE pp.351-352 (3CE 11.2, 11.3, pp. 313-4).  The three major layers (core/mantle/crust) are determined by distinct chemical/mineral composition.  Within each major layer, may be sub-layers (the core has two of these; the mantle has four), differentiated by density, temperature, and/or state (solid or liquid).  You should know how to define and locate:

A. the Crust

The crust is the outermost layer of the Earth, the Earth’s “surface,” The crust is “lighter,” cooler, and less dense compared to the mantle/core.  It is composed of igneous, sedimentary and metamorphic rock (below).  The crust is mostly composed of  elements and minerals that are “lighter” in weight (and in colour) than those in the mantle and core.  The crust contains much silicon, aluminum, potassium, calcium, and sodium.  These light-weight and light-coloured elements are not present to any degree in the mantle or core.

There are two major types of crust: oceanic and continental.  The oceanic crust tend to be mostly igneous rock and relatively thin.  The continental crust has all three major rock groups and tends to be much thicker.

  •  crust is thickest under the continents – up to 7h km thick – and is composed of the lightest elements and minerals:  mostly granite, which is made up of quartz (SiO2).
  • The crust is thinnest under the ocean basins – on average 5 km thick – and is composed of slightly heavier and darker elements and minerals:  mostly basalt, which is made of silicon, magnesium, and iron.

The boundary between the cooler, less (chemically) dense crust and the distinctly hotter and (chemically) denser mantle of the Earth, is the Mohorovicic Discontinuity.   This boundary, commonly called “the Moho,” was recognized in 1909 by Croatian seismologist Andrija Mohorovicic.

B. The Mantle

The mantle is the part of the Earth’s interior that lies between the outer core and the crust, with an average thickness of 2,886 kilometres. The mantle makes up about 84% of Earth’s volume.

The boundary between the mantle and the crust is known as the Moho (Mohorovicic Discontinuity).    The mantle is made up of olivine, iron, and magnesium, and other heavier elements (they are also usually dark in colour).  These often chemically combine with oxygen to form compounds such as iron oxides (FeO), and magnesium oxides (MgO).  These compounds are lighter than the (mostly) pure iron of the core.  The mantle is cooler and less dense than the core.

The mantle is subdivided into the:

  1. uppermost mantle – solid rock attached to the Earth’s crust.  With the Crust, the uppermost mantle is referred to as the lithosphere – the “rocky” sphere.  This is the outer, relatively rigid part of the Earth.  The lithosphere – the uppermost Mantle and Crust – consists of plates whose movements result in continental drift.  (The distinction between crust and mantle is based on chemistry, rock types, rheology and seismic characteristics. )
  2. The asthenospherethe “weak” sphere – is the soft, partially molten, upper portion of the Mantle that lies beneath the solid, rocky lithosphere (70 – 250 km below the surface).  The asthenosphere  is a soft layer in the upper mantle where rock is close to the boiling point (like the tip of a red hot iron rod).  Here the silicate rock behaves like a very thick plasticy liquide.  The lithosphere – the solid rocky upper part of the Earth – basically “floats” on the asthenosphere.    The asthenosphere appears to slowly move, almost plasticly, thus causing the lithosphere (the uppermost mantle + the crust) – floating upon it – to move as well.  This is believed to be mechanism behind continental drift (to come).
  3. The lower Mantle is still silicate minerals, but much hotter than the uppermost Mantle (over 4,000 °C at the boundary with the core).  Although the higher temperatures far exceed the melting points of the mantle rocks at the surface, the mantle is almost exclusively solid because of the enormous pressure on the rocks (the temperature at which melting begins increases with pressure).

The Mantle is separated from the Core by the Core-Mantle Boundary or Gutenberg Discontinuity (named after the person who identified it).  Gutenberg noticed that seismic waves that passed through the core travelled at different speeds and refracted differently than those that only passed through the mantle.  This implies a different composition and density of materials in the core than the mantle.  The core has heavier elements (pure iron) and higher densities..  At this point the Earth’s solid, mixed element mantle ends, and and its liquid iron-nickel outer core. This boundary is located at approximately 2880 km (1798 mi) depth beneath the Earth’s surface.

C. The Core

The core is the innermost layer.  It is divided into two zones, both with similar chemical compositions, but the inner core is believed to be solid, the outer core liquid.

The core is made up of:

  1. The outer core  is a liquid layer,  composed of iron and nickel that lies above Earth’s solid inner core and below its mantle.   The outer core (5150 km – 3000 km below surface)  is slightly cooler and less dense than the inner core.  It is still very hot and very dense by our standards!
    • The outer core is the layer that generates the Earth’s magnetic field.  The Earth acts like a huge bar magnet.  This is why compasses (with iron filings at one end of the moveable arrow), point north.  When molten rock containing iron cools, it also aligns with the Earth’s magnetic field, pointing north.  For no clear reason there appear to be periodic reversals in the magnetic field (N becomes S, and vice versa.  Some rock strata are aligned opposite from what we’d expect).
  2.  The inner core is the Earth’s layer, primarily a solid ball .  The inner core (6370 km to 5150 km below surface) is believed to be solid, mostly pure iron (Fe), under intense heat  and pressure.  Recent research suggests there may be more sublayers with in the core:  BBC News – Heart of Earth’s inner core revealed (this is all very interesting, but you don’t need to study it!  :)).  It is approximately the same temperature as the surface of the Sun: approximately 5400 °C.  That’s hot.  Very hot.  Ouch.

These layers have been determined by charting the paths of seismic waves.  Seismic waves occur when portions of the Earth’s crust move (earthquakes).  The speed and path of the waves generated by earth movements vary depending on the density, state (solid/liquid), and chemical composition of the materials through which they pass.  After a major earthquake, monitoring stations around the world record the speed and direction of the seismic waves generated.  Seismic waves, and the patterns created by them, allow scientists to determine the composition, density, and state of layers in the Earth’s interior

The U.S. Geological Survey has a great introduction to the earth’s structure.

Worth reflecting on …

Echoing the reading in the last lecture, New Zealand author, Dick Tripp, writes:

It is significant that the early pioneers in modern science were men of deep Christian faith. For Copernicus, the first astronomer of the scientific revolution, God was personally responsible for all the activity in the heavens. His radical ideas were contained in his book On the Revolutions of the Heavenly Spheres, which was published in 1543, the year of his death. The regularity he was discovering in the movements of the planets was, for him, a manifestation of the faithfulness of a loving Creator.

Galileo (d. 1642) invented the hydrostatic balance and discovered the laws of dynamics from observation of falling bodies. However, he is chiefly known for his achievements in astronomy. His discovery of the four satellites of Jupiter on January 7, 1610, with the aid of the newly invented telescope, revolutionised the study of astronomy. He has been called the first modern scientist and his work confirmed the observations of Copernicus. He regarded his science as illuminating the work of the Creator. For all his quarrelling with the church he remained a devout Christian until he died.

Kepler, the German astronomer, a contemporary of Galileo, was also a devout Christian. His discovery of the three laws of planetary motion laid the foundation for Newton’s theory of gravity. He regarded his study of the physical universe as “thinking God’s thoughts after him”. In The Secret of the Universe he wrote:

Here we are concerned with the book of nature, so greatly celebrated in sacred writings. It is in this that Paul proposes to the Gentiles that they should contemplate God like the Sun in water or in a mirror. Why then as Christians should we take any less delight in its contemplation, since it is for us with true worship to honor God, to venerate him, to wonder at him? The more rightly we understand the nature and scope of what our God has founded, the more devoted the spirit in which that is done.

The baton of scientific leadership passed in the next generation to Newton, born in the year of Galileo’s death. Though he had problems with the Christian view of the Trinity, he was a strong believer. As a member of the Anglican Church he was involved in distribution of Bibles to the poor and the construction of new churches. He actually wrote more than a million words on the Bible and theological topics, more than he wrote on science. His well-worn Bible, with marginal notes in his own handwriting, is in the Wren Library of Trinity College, Cambridge. He became the foremost mathematician in Europe. He published Principia mathematica in 1667, “a book that transformed the course of western science”. His work gave new direction to optics, mechanics and celestial dynamics. His work on gravity established the Cambridge reputation for mathematics. His studies of light produced the first reflecting telescope. His invention of calculus gave science the mathematical tool it needed for further exploration of the trails he blazed.

Feel free to discuss this quote on the course discussion site (see the syllabus for details …)

You might also enjoy these biographical interviews with biologist, Darrel Falk

Feel free to comment on these in the online discussion
To Review …

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Scripture quotations marked (NLT) are taken from the Holy Bible, New Living Translation, copyright © 1996. Used by permission of Tyndale House Publishers, Inc., Wheaton, Illinois 60189. All rights reserved.