The correct answer is - D) covered by warm shallow seas.
The fact that the crinoids are have an abundance in the fossil records in Pennsylvania in the Mississippian Period, tells us that this area was covered with shallow and warm seas. The reason why we can get that conclusion is that the crinoids live only in that kind of environment, so it simply a logical conclusion.
The geological data is also confirming this, as it is easily noticeable in the layers that during this period of the geologic past, what is now Pennsylvania, was covered with shallow sea waters. Also, this waters were warm too, as the climate was warm and humid and that period, so it was a perfect environment for the crinoids to flourish.
Answer:
After 48 hours amount left = 6.25 g
Explanation:
Given data:
Half life of potassium = 12 hours
Total mass = 100 g
Mass left after 48 hours = ?
Solution:
Number of half lives passed:
Number of half lives = Time elapsed / half life
Number of half lives = 48 hours/ 12 hours
Number of half lives = 4
At time zero = 100 g
At first half life = 100 g/ 2 = 50 g
At 2nd half life = 50 g/2 = 25 g
At 3rd half life = 25 g/2 = 12.5g
At 4th half life = 12.5 g/2 = 6.25 g
The answer would be 36, you just fill in what you know and solve the problem.
Have cones as reproductive structures.
Have vascular tissue.
D. All of the above are true.
