Humans simply can ask for directions. One type of bacterium has an internal compass. It uses the earth s geomagnetic field to navigate. These bacteria are called magnetotactic bacteria, because they make chains of tiny, iron-containing magnets. This magnet chain is their compass, and it tells them which way is north.
Magnetotactic bacteria dislike oxygen.
In water, the oxygen level decreases as one moves deeper. So, magnetotactic bacteria use their magnetic compass to tell them which way is down. It has to do with the direction of the earth s geomagnetic field. In the Northern Hemisphere, the geomagnetic north actually points down at an angle. So, if bacterium uses its compass to point north, it also is pointing down at an angle.