Calculate the residence time of sodium in millions of years if the total amount of sodium in the oceans is 1.5 x 10 to the 22 grams, and is supplied to the ocean at a rate of 2.2 x 10 to the 14 grams per year.

To calculate the residence time of sodium in millions of years, we need to divide the total amount of sodium in the oceans by the rate at which sodium is supplied to the ocean per year. Here's how you can do that:

Step 1: Convert the total amount of sodium in the oceans to kilograms since the rate of supply is in grams per year.
1.5 x 10^22 grams = 1.5 x 10^19 kilograms

Step 2: Convert the rate at which sodium is supplied to the ocean to kilograms per year.
2.2 x 10^14 grams = 2.2 x 10^11 kilograms

Step 3: Divide the total amount of sodium in the oceans by the rate at which sodium is supplied to the ocean per year to get the residence time in years.
Residence Time = Total amount of sodium / Sodium supply rate per year
Residence Time = (1.5 x 10^19 kilograms) / (2.2 x 10^11 kilograms per year)
Residence Time = 6.82 x 10^7 years

Step 4: To convert years to millions of years, divide the residence time in years by 1 million.
Residence Time in millions of years = (Residence Time in years) / 1 million
Residence Time in millions of years = (6.82 x 10^7 years) / (1 million)
Residence Time in millions of years = 68.2 years

Therefore, the residence time of sodium in millions of years is 68.2 years.