Other scientists have shown that sun spot activity can be measured in periods of time that last about eleven years.

VOA: special.2009.09.29

Charles Darwin developed the theory of how living things develop from simpler organisms over long periods of time.

VOA: special.2009.02.25

The next time you think about going without sleep, consider this: Laboratory animals that are kept awake for long periods of time ...die.

VOA: special.2009.08.26

Often the mother had to be treated in a hospital for long periods of time.

VOA: special.2009.12.06

Over long periods of time, these small changes result in the creation of new species.

VOA: special.2009.12.01

He thought that this was evidence that the bottom of the ocean had been lifted up by powerful geological forces over long periods of time.

VOA: special.2009.02.25

Astronauts worked for longer periods of time in the hostile environment of space.

VOA: special.2009.07.01

And to prepare himself, he went without sleep for long periods of time.

VOA: special.2009.03.18

He says even if people have a healthy body weight, sitting for long periods of time still has an unhealthy influence on blood sugar and blood fats.

VOA: special.2010.01.13

The interrogators were told they could put them in painful standing positions, deprive them of solid food, keep them awake for extended periods of time, lock them in cold rooms, and submit them to the technique of simulated drowning known as waterboarding.

VOA: standard.2009.04.17

Archeologists are able to estimate the age of these objects by dividing layers of dirt into time periods.

VOA: special.2009.08.18

And we started seeing these big,giant periods of drought that took place around that time.

VOA: standard.2010.04.05