Study Guide and Practice Questions for 1^st Midterm Exam

NOTE: Answers to Sample Questions posted at bottom of this page

Carefully review all of the handouts and activities – as well as the questions/study problems from Murphy & Nance. Virtually all of the questions and problems on the exam will be drawn from this material. You will need your calculator. You must be able to work with exponents.

Be able to:

explain the scientific method (e.g. explain to an 8-year old what scientists "do")

describe the internal layering of the earth: core, mantle, crust - you should be able to cite physical and chemical characteristics that distinguish these layers

calculate areas and volumes

calculate volumes of spherical objects as we did in Playdough Earth.

calculate percentages

define density - calculate mass, density & volumes using the equation d = m/v

explain why things sink or float

explain the source of instability in the earth that results in plate motions at the surface

distinguish between heat flow by conduction, convection, and radiation

relate variable (thermal conductivity, heat capacity, viscosity, and thermal expansion) to a systems tendency to transfer heat by convection versus conduction

explain the "main ideas" in plate tectonic theory

review the basic lines of evidence that were used to develop plate tectonic theory

define lithosphere and asthenosphere

determine the rate of sea floor spreading between two plates given appropriate data – calculate distances, time & rates using the equation r = d/t

answer questions about earthquakes – e.g. where they occur, why earthquakes are difficult or impossible to predict

determine the distance between points on a map using the map scale

solve simple scale problems using fractions

 

Sample Questions

1. The Atlantic Ocean is ~5000 km wide and has been opening at an average rate of ~20 mm/yr due to seafloor spreading at the mid-Atlantic ridge. Estimate the age of the Atlantic ocean basin – ie., the time it began to form.

2. Recall that the formula for the volume of a sphere is V = 4/3 pi r³ (pi = 3.14) and that the radius of the earth is ~6370 km. 99.9% of the mass of the earth’s atmosphere lies below a height of ~50 kilometers.

What is the volume of the atmosphere in cubic kilometers up to this height?

What percentage of the total earth volume is this?

The average density of the atmosphere is ~ 2.07 x 10^-4 gm/cm³ = 2.07 x 10¹¹ gm/km³

What is the total weight of the atmosphere?

 

Because gases are highly compressible – the density of the atmosphere varies strongly as a function of altitude above sealevel - ie., the atmosphere is density stratified (atmospheric density at sealevel is 1.23 kg/m3 = 1.23 x 10¹² gm/cm³ ). Nevertheless, despite its apparently stable density structure, the lower atmosphere is characterized by very strong vertical mixing – try to explain this mixing in terms of temperature and heat transfer mechanisms. (Hint: the temperature of air decreases with altitude)

SHORT ESSAY QUESTIONS

I) Draw a neat and accurate sketch of a spreading ridge, and an ocean-ocean subduction zone. Be sure and show the crust, lithosphere, asthenosphere, depth scale, any volcanic or seismic activity, and any other important details that come to mind.

II) Briefly explain and show with a diagram if necessary how elastic rebound works in generating the earthquake cycle. Be very specific and outline the various steps in the process, and please also describe the various types of stress and strain involved.

Solutions to the first two Sample Questions from above:

1) This is a rate problem r = d/t therefore t = d/r

units must be the same so first convert 5000 km to millimeters

5000 km x 1000 m/km x 100 cm/m x 10 mm/cm = 5 x 10⁹ mm

t = 5 x 10⁹ mm / 20 mm/yr = 2.5 x 10⁸ years = 250 million years

2) (Volume_{Earth+Atmosphere}) - Volume_Earth = Volume_Atmosphere

therefore V_atm = 4/3 pi (6370km + 50km)³ - 4/3 pi (6370km)³ = 2.57 x 10¹⁰ km³

Percentage of total Earth Volume = Vatm / Vearth x 100 = 2.37%

 

Why does lower atmosphere mix? Because warmer temperature at surface results in thermal expansion of air - this produces buoyant forces that cause surface air to rise convectively.