Answer:
After three half-lives, it is 7:1
Explanation:
- The rate at which the decay of the radioactive isotope is said to be half-life and is represented as the half-life of the atoms and the matter to disintegrate itself.
- The two radioactive isotopes are K 40 and Ar 40. After the K-Ar dating, they contain minerals such as the clay mica and the temphra minerals and Half-life of the K 40 is 1.3 more than 100,000 years i.e 10x9 years for Ar 40.
- <u>Thus the K 40 has to divide as three half-lives have passed if the ratio of argon to potassium atoms is 7:1. At the end of one half-life, the ratio of the number of argon to potassium atoms is 1:1. and two half lives its 3:1 thus after the third half-life it becomes as 7:1.</u>
Answer:
A. and is likely the basis for the Epic of Gilgamesh and the biblical epic of Noah's Ark.
Explanation:
These are two common stories about the great flood. They were also similar circumstances.
Mediterranean water flowed into the Black Sea through its single connection: the Bosporus Strait.
The Mediterranean water that does inflow mixes with fresher Black Sea water, and as its salinity and density decreases, the Mediterranean water forms plume-shaped features. These plumes flow away from the mouth of the strait and descend until their density matches that of surrounding waters, usually at depths of 100 to 600 meters.
This creates some sort of stormy environment, which is reminiscent of the two religious stories.
Answer: 
Explanation:
The Tropic of Cancer is one of the parallels (imaginary line around the Earth parallel to the equator) located in the northern hemisphere (currently its latitude is
).
It is called "Cancer" because a long time ago, when the summer solstice occurred in the northern hemisphere (on June 20th or 21st), the Sun was in the constellation Cancer (the crab).
Now, if we were just in the North Pole, Polaris would by exactly over our heads (
over the horizon), but as we go south and find the Tropic of Cancer parallel, Polaris altitude will be approximately at an angle of
over the horizon.
Hence, the altitude of Polaris measured by an observer at the Tropic of Cancer is
.
The apparent brightness is defined by how much light we get pretty much. The formula is:

This takes into account that the light is spreading out to a sphere that has the surface given by 4πd^2.
We have that d=20 ly and 1 ly is 9.46*10^12 km or 9.46*10^15m.
Hence, d=20*9.46*10^15=189.2 *10^15 m
Now, we can substitute the d value and calculate that L=<span>8.45184*

W/m^2</span>