The Earth's population of 7,090,000,000 in scientific notation is 7.09 x 10⁹.

Here's how to convert it:

1. Move the decimal point to the left until you have a number between 1 and 10. In this case, we move it nine places to the left, leaving us with 7.09.

2. Count the number of places you moved the decimal point. This number becomes the exponent of 10. Since we moved the decimal point nine places, the exponent is 9.

3. Combine the number and the power of 10 to get the scientific notation: 7.09 x 10⁹.