Describe four important physical properties that can be used in the identification of hand samples. Include an example for each property.
1) Hardness describes the ease or difficulty with which a sample scratches. Hardness has been standardized along the Moh's Hardness Scale, which appoints a mineral as the standard for each number between one and ten. The mineral apatite, for example, has a hardness of five, while the more resistant quartz has a hardness of seven. 2) The color of a rock or mineral often is an important diagnostic tool. Quartz, for example, can be clear, yellow, purple, pink, etc. Because a given mineral often can occur in many colors, it is usually important to also consider other diagnostic properties. 3) Streak describes the color of a sample once it has been powderized, such as by rubbing across a white scratch plane. Because a mineral's streak color can be quite different from its in-situ sample color (such as in hematite, where streak is a deep red), it often is important 4) In many cases, optical microscopic characteristics are especially precise means of identifying rock and mineral samples. When a thin (and therefore transluscent) sample section is used in conjunction with a light-polarizing microscope, properties such as crystal shape and cleavage often can be reliably observed. The hexagonal mineralogical structure of quartz, for example, can often be seen in thin section.
Provide and detail three reasons why the following sentence is ineffective. Explain how the sentence could be improved upon. "When Nathan finalized his preparations, he was ready, he got up and left for the adventure ahead."
1) The sentence unnecessarily repeats an implicit idea, namely that Nathan was prepared: Because the word "ready" in the second clause suggested the same information at the words "finalized his preparations" in the first clause, it added nothing to the amount of information present in the sentence. 2) This is a run-on sentence. The word "ready" should be followed by a period, semicolon, or comma and appropriate conjunction. 3) The phrase "got up and left," which does not precisely explain the nature of Nathan's motion, fails to meaningfully develop the subject. The phrase could be replaced, for example, by the more descriptive "giddily threw himself out the apartment door."
Name and briefly describe three important variables of Earth's orbit that affect the planet's climate on millennia-length cycles. Include the approximate recurrence interval for each cycle.
Eccentricity describes change in the shape of Earth's orbit (circular vs elliptical). It cycles on a roughly 100 ky basis. Obliquity describes change in the tilt of the Earth's axis relative to the orbital plane (~41 ky cycle). Precession describes change in direction of the Earth's axis relative to distance reference points (~26 k.y. cycle).