Answer:
B and C
Explanation:
B. In a given rock sample, the amount of Silicon-32 isotopes gets divided in half about every 170yrs.
This is the concept of half-life. Half life is the time take for half of a radioactive isotope to disintegrate. The shorter the half life the faster the isotope disintegrates.
From the question, we were told that it would take 170yrs for half of the isotope of Silicon to disintegrate to Phosphorus. This is the half life.
C. The half life can be used to determine the amount of Si-32 that has decayed from the time closure temperature was reached.
The closure temperature is very important in radioactivity. It is the temperature at which a system has cooled and there is no resulting disintegration of parent and daughter isotopes.
From first order kinetics, we know that the rate at which radioactive elements decay at any time is directly proportional to the number of radioactive atoms present. A knowledge of the half life helps to figure out the number of atoms that has decayed in time.
Until the early Proterozic there were only negligible amounts of free oxygen in the atmosphere
Answer:
D. Kuwait trades oil for technology with the United States
Explanation:
This is the best answer since oil is a very useful commodity other countries will trade other resources like technology for it.
C. is incorrect because this isn't using oil as a strategic commodity. this is just using force to get what they want.
A. is incorrect because it clearly doesn't mention trading oil.
B. is incorrect because it's not using oil strategically. Trading oil for other resources that we need is strategic.
So that leaves D which is correct.
(have a great day!)
A stationary front is depicted in the picture at L. A stationary from is a narrow zone separating two air masses in which neither air mass is displacing the other. When this occurs there is a stall in the motion of the front. The blue triangles point away from the cold air and the red semicircles point away from the warm air.
The full moon cycle (from one phase to the same phase again), from start to finish, is generally 28 days. That being said, from one phase to its opposite, or one half-cycle, would be approximately 14 days.
