This is called a direct current > ———
Scientists can determine the age of the seafloor by watching the constant changing magnetic field of our planet. When it cools down, it records the magnetic field during its formation. The two parts of the oceanic plate are pulled apart, and magnetic stripes become older as they move away from the mid-ocean ridge. Hope that helps!
I believe both lands were targets for major powers such as Britain and France
frequency's unit is Hz which mean cycles per second
given frequency * wavelength = speed of wave
speed of light = 3x10^8 m/s
wavelength = 680nm = 680x10^-9 m
frequency * 680x10^-9 m = 3x10^8 m/s
frequency = 3x10^8 / 680x10^-9
= 4.41x10^14 Hz
= 441x10^12 Hz
= 441 THz
which is the frequency for red light