# Question: 1 the average height above sea level of all the...

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1) The average height above sea level of all the continents is 840 m and the average rate of lowering (or “denudation”) by erosion is 6 cm per thousand years. If this rate of denudation remains the same even as the land is lowered by erosion, and if no new mountains are formed, how long will it take to bring all the continents to sea level by erosion?

2) The gravitational attraction (Newton's Law of Universal Gravitational attraction) between the Earth and the Moon is equal to the centripetal force associated with the Moon’s orbit around the Earth. The orbital period of the Moon around the Earth is 27.26 days, and the gravitational constant (G) is 6.67x10-11 m3 s-2 kg-1 . Assume the orbit of the Moon around the Earth is circular and that the Earth is a perfect sphere. Using this information, calculate the density of the entire Earth in kg/m3 . Compare the density you calculate for the planet to the typical density of continental crust, and the solid core (see class notes or textbook). What does this tell you about the structure of the Earth?

The following formulas and values may be useful: Newton's Law of Universal Gravitational attraction = (G*Mmoon*MEarth)/d2

Centripetal Force = MmoonV2 /d where V is the orbital velocity (i.e. the orbital speed)

Effective distance from Earth to Moon = d = 382,751,000 m Radius of the Earth = 6,367,440 m

3) Cooling of oceanic crust causes contraction, leading to the subsidence of the seafloor away from the axis of spreading (i.e. the mid-ocean ridge). As a result, the depth of the ocean floor increases with age according to the following formula which is valid for seafloor < 80 million years old: d = 2500 + (350 x √� ) Where: d = depth of ocean floor in meters t = age in millions of years Graph a cross section of a mid-ocean ridge (x-axis = distance from ridge vs. y-axis = depth of ocean floor) that is spreading symmetrically in both directions at a rate of 1 cm/yr (10 km/million years). The age of the oldest seafloor shown should be 80 million years, and you should include values for every 5 million years from 0-80 million years. Using a spreadsheet might make this a little easier.