Step 1: Recall the total surface area of the earth.
The earth's total surface area is approximately \(510\) million \(\text{km}^2\).
Step 2: Recall the area covered by oceans and seas.
Standard oceanographic data put the combined area of the world's oceans and seas at approximately \(361\) million \(\text{km}^2\), with the remaining area being land.
Step 3: Compute the percentage.
The fraction of the earth covered by ocean is \(\dfrac{361}{510} \times 100 \approx 70.8\%\), which rounds to the commonly quoted figure of about 71 percent.
\[ \boxed{71 %} \]