1.   On the ground, teams of scientists will measure the amount of radiation reaching the earth.

2.   As the sun moves inexorably higher in the February sky, solar radiation reaching the earth is slowly becoming more intense.

3.   A major factor in determining whether biologically significant amounts reach the earth, Lubin said, is the natural variability of cloudiness in a given area.

4.   But from an airplane six miles high, cell phone signals reach the earth in a wide cone that covers a big chunk of geography.

5.   During fall, as less energy from the sun reaches the earth, the lower atmosphere cools, causing the snow level to drift downward.

6.   It is not absorbed by ozone and reaches the earth at a relatively constant intensity all year.

7.   It is not uncommon for twisters to form in thunderstorms and then fizzle out before reaching the earth or before doing any damage.

8.   The ozone layer prevents harmful ultraviolet rays from reaching the earth.

9.   They have proposed that life might have reached the earth in the form of spores sent out from some distant planet.

10.   Organizers say that ozone depletion has reached unprecedented levels, allowing more harmful UV-B radiation to reach the earth.