29:52 Characteristics and Origins of the Solar System

February 9, 2004

. Addendum to Lecture 5

Note to students in EXW section: Check the material on the CD, under Lecture 8; see the demonstration entitled “Density”. It shows the “chocolate sampler” of minerals I discuss in the lecture notes.

For all students: Get on WebCT for this course and look under “Course Content”. The video clip under Lecture 8 shows a repeat of the discussion of minerals and the demo on density. This video clip also shows some examples of “primitive rocks” that I didn’t show in class.

Here are some additional points to make in association with the discussion of Earth as a planet.

(1) Continental Drift is not just a theory; it has been confirmed experimentally. We can measure the distance between radio telescopes to an amazing degree of precision, and it has been confirmed that the continents are moving apart at about 2-3 cm/year, and in the directions indicated in the textbook and the lecture notes.

(2) We can see the tectonic plate boundaries around the world. An excellent example is the Mid-Atlantic ridge shown in Figure 8.11. Figure 8.18 shows all the plate boundaries around the world, which usually are deep in the Ocean. If we drained all the water off the Earth, this is what the world would look like. This picture is worth remembering when we start comparing the Earth to other planets.

(3) The motion of the plates is due to convection currents, or an up-and-down boiling motion of the magma in the mantle. These currents transport heat from the center of the planet to the exterior. The “boiler” in the center of the Earth is radioactive decay of elements such as Uranium and Thorium that settled there at the time the Earth formed.

(4) The liquid metallic core of the Earth has electrical currents flowing there, which are responsible for generation of the magnetic field. Of the Earth. The existence of this magnetic field is probably very important for life on Earth; it shields the Earth from cosmic rays and the solar wind of material from the Sun. The region of space dominated by the Earth’s magnetic field is called the magnetosphere, and was discovered in the late 1950’s by Professor James Van Allen of the University of Iowa. A diagram of the magnetosphere is shown in Figure 8.28 of the textbook.