EXERCISE 1.9 Name: Course: How Long Does It Take to Make an Ocean? To Erode a Mountain? Section: Date: (a) Rates of uplift and erosion. The following questions will give you a sense of the rates at which uplift and erosion take place. We will assume that uplift and erosion do not occur at the same time-that mountains are first uplifted, and only then does erosion begin-whereas the two processes actually operate simultaneously. If mountains rose by 1 mm/yr, how high would they be (in meters) after 1,000 years? 10,000,000 years?_ m 50 million years? m The Himalayas now reach an elevation of 8.8 km, and radiometric dating suggests that their uplift began about 45 million years ago. Assuming a constant rate of uplift, how fast did the Himalayas rise?. km/yr .mm/yr . m m/yr. Evidence shows that there were once Himalaya-scale mountains in northern Canada, in an area now eroded nearly flat. If the Earth were only 6,000 years old, as was once believed, how fast would the rate of erosion have had to be .mm/yr for these mountains to be eroded to sea level in 6,000 years?. m/yr. Observations of modern mountain ranges suggest that they erode at rates of 2 mm per 10 years. At this rate, how long would it take to erode the Himalayas down to sea level? years (b) Rates of seafloor spreading. Today the Atlantic Ocean is about 5,700 km wide at the latitude of Boston. At one time, however, there was no Atlantic Ocean because the east coast of the United States and the northwest coast of Africa were joined in a huge supercontinent. The Atlantic Ocean started to form "only" 185,000,000 years ago, as modern North America split from Africa and the two continents slowly drifted apart in a process called seafloor spreading. Assuming that the rate of seafloor spreading has been constant, at what rate has North America been moving away from Africa?. .mm/yr. km per million years