Nothing is sure but death and taxes, and of course that north is north and…
2024
Nothing is sure but death and taxes, and of course that north is north and south is south, and thus it has always been, so they say. But they’d be wrong. You can perhaps be sure about death and taxes, but you might want to reconsider the rest of it. In fact, at many times in our planet’s history, north has become south and south has become north, in a process called magnetic reversal.
Paleogeologists have discovered the existence of these mysterious phenomena (in a field study known as paleomagnetism) by investigating rocks. When rocks are being formed from magmas, atoms within their crystals respond to the earth’s magnetic field by “pointing” towards the magnetic alignment, scientists can determine where on earth the north pole was located at that time because as the rocks solidified, they trapped that information within them. The study of ancient lava flows has revealed that at certain periods in the earth’s history magnetic north was directly opposite to its present location. In fact, it has been determined that the north/south reversal has occurred on average every 500,000 years and that the last reversal took place about 700,000 years ago. Scientists call those periods of “normal” polarity (the magnetic orientation of our modern er(1) and “reversed” polarity (the magnetic orientation of reverse situation) by the name “magnetic chrons.”
Although the fad : of such reversals is clear, why and how they happen and their effects on the planet are subjects of considerable debate. Because no one knows precisely how the earth’s magnetic field is produced, it becomes difficult so say how it might be reversed. Among explanations proposed are a reversal of the direction of convection currents in the liquid outer core of the earth and a collision between the earth and a meteorite or comet. And while the precise effects of a reversal are not known, there can be little doubt that the earth would receive during the process a great deal more damaging ultraviolet radiation than it now does and that such occurrences have been correlated with the extinction of certain species in the geologic past.
‘Magnetic reversal’ refers to :
- A.
the reversal of direction in ancient lava flows
- B.
a reversal of the direction of convection currents in the outer core of the earth
- C.
north becoming south and south becoming north
- D.
the atoms in rock crystal pointing towards the magnetic north pole
Attempted by 11 students.
Show answer & explanation
Correct answer: C
Answer: north becoming south and south becoming north.
Explanation: A magnetic reversal is the swapping of the Earth’s magnetic polarity so that the magnetic north pole becomes the magnetic south pole and vice versa.
How we know: Magnetic minerals in cooling lava and other rocks align with the prevailing magnetic field and lock in that orientation, so geologists can read past field directions from rock records.
Possible causes: Changes in convection in the liquid outer core or large impacts have been proposed as mechanisms that could trigger a reversal, but these are explanations, not the definition.
Recorded evidence: Reversed orientations found in sequences of ancient lava flows are an indicator that a reversal occurred at that time.
Why the other choices are not correct: The statements about atoms in rock crystals and about lava flow directions describe how reversals are detected, and the statement about convection currents describes a proposed cause. None of those statements define the phenomenon itself.