Answer: the main purpouse of physical maps usually show the most important political boundaries, such as state and country boundaries. So, this is true.
Explanation:
The troposphere because it has half of all air in the Atmosphere
The statement is correct.
When a flood is giving a time-bonding term, such as the 100-year flood, in this statement, it means that it has been noticed that the floods from the particular river occur on approximately that much of a time span.
If there has been a flood recently, than it most probably means that there isn't going to be a flooding caused by that river for the foreseeable future.
Now, there's always exceptions, as the climate patters are changing constantly, and there's always surprises, but in general, in lot of regions of the world, there has been noticed a certain consistency in some natural occurrences.
Fossils help scientists date rocks: True
Sometimes younger rock layers are found beneath older rock layers: True, because it happens with landslides and other causes.
No fossils from the Precambrian era have been found because there were no organisms at the time: False because there were organisims like algae and bacteria, and there are a very small amout of fossils from that era.
The map of Earth has changed over millions of years, but is now set: False
