Low-head dams are dangerous structures that basically extend from one side of a riverbank to the other. Low-head dams block the water way partially and the water moving over the dam produces a strong circular current at the lower part of the dam. Low-head dams are dangerous to small boats and paddle craft because the strong circular current below the dam can trap small boats and paddle craft and pull them under the dam.
Answer:
A. Ancient bacteria
Explanation:
From the salt of the earth, researchers have isolated and revived a Bacillus strain, which they believe is >250 million years old. If correct, Russell Vreeland and his colleagues from West Chester University, Pennsylvania, have discovered the oldest living organism in the world.
B. Scientists used radioactive dating to study the age of material from the moon and Earth
Explanation:
All organic compounds contain <u>carbon</u>
All organic compounds contain carbon, as well as hydrogen unless it has been replaced by another element
All galaxies have a dense core of stars. Spiral galaxies, however, have arms that are often visible. There are two kinds of spiral galaxies: barred, where there appears to be a line running from arm to arm through the core, and <span>ordinary, where there is no bar. @Badbunnyhunny</span>
