The layer of electrically charged molecules and atoms which spans 40-250 miles above ground called ionosphere causes the display of the aurora and the reflection of radio waves back to earth.
In practice, something that follows a very predictable pattern can be used as a time standard. This include things like radioactive decay, planetary orbit, and the speed of light, among others.
The answer is calcium. I just did it and it was correct
The east bound train travels at a speed of 95 mile per hour and the west bound train at 75 miles per hour.
Assuming eastbound train will cover distance x then the west bound train will cover distance 272-x .
Therefore, since time taken will be the same then; x/95 = (272-x)/75
= 75x = 95 (272-x)
= 75x = 25840 - 95x
= 170 x= 25840
x = 152 miles
Thus time taken will either be x/95 or (272-x)/75
= 152/95
= 1.6 hours or 1 hour 36 minutes