Under natural conditions, it takes approximately $1000\text{ years}$ to form a $2.5\text{ cm}$ thick layer…
Under natural conditions, it takes approximately $1000\text{ years}$ to form a $2.5\text{ cm}$ thick layer of mature soil. How many years, on average, are required for the natural formation of just $1\text{ mm}$ of mature soil?
$40\text{ years}$
$25\text{ years}$
$400\text{ years}$
$100\text{ years}$
Solution
$2.5\text{ cm}$ is equal to $25\text{ mm}$. Dividing $1000\text{ years}$ by $25\text{ mm}$ gives $40\text{ years}$ for $1\text{ mm}$ of soil formation.