1. In the twentieth century, electron microscopes have provided direct views of viruses and minuscule surface structures.

2. Unlike conventional electron microscopy, x-ray microscopy enablesspecimens to be kept in air and in water,

3. Because of the wavelength of the x-rays used, soft x-ray microscopes will never match the highest resolution possible with electron microscopes. Rather, their special properties will make possible investigations that will complement those performed with light- and electron-based instruments.

4. A useful definition of an air pollutant is a compound added directly or indirectly by humans to  the atmosphere in such quantities as to affect humans, animals vegetations, or materials adversely.

5. As the Earth developed, the concentrations of these pollutants were altered by various chemical reactions.

7. The result is an increased concentration of noxious chemicals in the air.

8. Sulfur dioxide has detectable health effects at 0.08 parts per million (ppm), which is about 400 times its natural level

9. Many ants forage across the countryside in large numbers and undertake mass migrations

9. As a worker ant returns home after finding a source of food, it marks the route by intermittently touching its stinger to the ground and depositing a tiny amount of trail pheromone.

10. A trail pheromone will evaporate to furnish the highest concentration of vapor right over the trail, in what is called a vapor space

11. In following the trail, the ant moves to the right and left, oscillating from side to side across the line of the trail itself

12. Europa was transformed-in our perception, at least-into one of the solar system’s most intriguing worlds.

13. The tides on Europa pull and relax in an endless cycle.

14. When the putrefied material is examined microscopically, it is found to be teeming with bacteria.

15. Pasteur showed that structures present in air closely resemble the. microorganisms seen in putrefying materials

16. He postulated that these bodies are constantly being deposited on all objects.

17. The origins of nest-building remain obscure, but current observation of nest-building activities provide evidence of their evolution.

18. Birds also display remarkable behavior in collecting building materials.

19. It is only relative to their size and most birds are able to carry an extra load of just over twenty percent of their body weight.

20. Other species may become better adapted to an Environment, resulting in competition and, ultimately, in the death of a species.

21. One of the best-known examples of mass extinction occurred 65 million years ago with the demise of dinosaurs and many other forms of life.

22. One interesting, and controversial, finding is that extinctions during the past 250 Million years have tended to be more intense every 26 million years.

23. One researcher observed babies and their mothers in six diverse cultures and found that, in all six languages, the mothers used simplified syntax, short utterances and nonsense sounds

24. Other investigators have noted that when mothers talk to babies who are only a few months old, they exaggerate the pitch, loudness, and intensity of their words.

25. They also exaggerate their facial expressions, hold vowels longer, and emphasize certain words.