Answers to last issue's Do You Know?

1. I read that the earth’s core is almost as hot as the sun. Why does it not melt the planet?
Ans: The Earth that we live on is actually a thin crust floating on the mantle of the Earth. This in turn is actually resting on top of a liquid outer core which surrounds a solid inner core (see figure). This inner core mostly composed of iron is nearly at the same temperature as the Sun. How come it does not melt?
The reason was found out only recently. The iron atoms in the core are arranged in a periodic crystal structure, just like the sodium and chloride atoms in salt (whose chemical composition is Sodium Chloride). These crsytal structures look different, depending on temperature and pressure.
At the temperature and pressures we feel on the Earth's surface`, iron takes on what's known as a body-centered cubic (BCC) structure. Think of a cube: it has eight corners and one centre. Now, fill in each of the corners and the centre with an iron atom — that will form a BCC structure. The phrase "body-centred" means that, apart from the corners, there is an iron atom in the centre of the cube.
When the temperature and pressure increases, the iron changes its structure into what is called a hexagonal close-packed (HCP) structure; see the figure. There are six atoms arranged around a central atom in the top and bottom layers (hexa means six). The in-between layer contains 3 atoms arranged in the "holes" left by the hexagonal arrangement above and below. You can see that, compared to the BCC structure, the hexagonal arrangement allows more atoms to be packed into the volume. This is necessary because of the high pressure that is compressing the iron.
Earth's core experiences a pressure of about 3.5 million times higher than the pressure on the surface. So scientists expected that the iron in the core will be arranged hexagonally rather than cubically. Surprisingly, some recent calculations found that this is not true.
The researchers used a massive supercomputer to analyze a large amount of data. They found that the core is indeed in a cube structure, in fact, because of the extreme temperature. At normal temperatures, that cube structure is unstable, and its atomic "planes" easily slide out of the structure into a liquid state. But in the extremes of the core, atoms are moving so quickly, so close together, that they don't have anywhere to go. Like passengers on a packed subway car, they just switch positions but maintain their original shape.
The sliding of these planes is a bit like shuffling a deck of cards. Even though the cards are put in different positions, the deck is still a deck. Likewise, the BCC iron retains its cubic structure. This explains why Earth's core is solid.

2. Where would a compass point to if I were at the North Pole?
Ans: Here is an answer that may confuse you twice! The first fact is that the Earth has an iron core (as we saw in the previous answer) and so acts like a magnet. But the South pole of this magnet is close to the geographical north pole (in the northern hemisphere) and the North pole is near the geographical south pole! A compass points to the magnetic north poles, so it should have pointed towards the southern hemisphere, but it doesn't. That is because of an old convention:
In olden days, when compass was invented, the end of the needle that pointed to Earth's north magnetic pole was called the "north pole" (or "north-seeking pole"). The other end was called the "south pole". Because opposite poles attract, this definition means that Earth's north magnetic pole is actually a magnetic south pole and Earth's south magnetic pole is a magnetic north pole! In short, although we call it the north pole, it is actually the south pole of the Earth's magnetic field that is close to the geographical north pole (near the Arctic Ocean).
Now let us answer the actual question. If you are standing at the (geographical) north pole, the compass will point to the magnetic north pole. In fact, where ever you are on the Earth, the compass will point here. This is somewhere near Alaska in the Arctic ocean. Don't we know exactly where the magnetic north pole is? It turns out that the mechanism that causes Earth to be a giant magnet is not well-understood. So there are two strange things about Earth's magnetic field. One is that the poles are not exactly 180 degrees apart (a straight line between them will not go through the centre of the Earth) and the second is that the poles actually wander about and are not fixed.
The figure shows how the north magnetic pole has moved over the last few hundred years and is in fact now rather close to the geographical north pole. Also, the Earth's magnetic field is known to flip (change direction) every few thousand years. This is the reason why the pole that is close to the geographical north pole is always called a north magnetic pole, whether it is actually the north or south magnetic pole.
Finally, what happens if you stand at the current north magnetic pole? Which way will your compass point? If you think about it for a moment, the answer is simple: it will point in the direction of the south magnetic pole. Of course, if the compass is being held horizontally, it can point in any random direction. But once you hold it vertically, it will point downwards, towards the magnetic south pole.

3. Is groundwater always clean?
Ans: Water in a well was once usually rain water. It seeps into the ground over time, through cracks in the rock. As it flows through, the sand, stones, leaves and other large particles are filtered away, leaving it looking clean.
But groundwater can contain other items that you can't see. Some are naturally occurring and some are human-made substances. Groundwater can contain hydrogen sulfide (makes the water smell like rotten eggs) or other naturally occurring chemicals. Groundwater also may contain petroleum, organic compounds, or other chemicals introduced by human activities.
The substances that can pollute ground water depends on the neighbourhood. Is it farm land, are there industries or chemical factories nearby? Pesticides an fertilisers can seep into the water. Even leakage from a septic tank can contaminate groundwater with bacteria.
Open wells are more prone to be contaminated. Ground water from bore wells come from deeper underground. Here, the water has trickled down into the Earth until it reaches a rock that cannot be passed through. Such a rock is called impermeable. Even clay soil is hard for water to flow through. But in hard rock, the water simply collects and either forms a small aquifer (like underground lake) or else flows like an underground river. This makes the nearby rocks (which are porous and can hold water) saturated with water. If a bore is dug into such rock, water can be tapped from it. Typically bore water from deep underground has cleaner water compared to wells which are not very deep.

4. Are red worms also earthworms?
Ans: Generally, "earthworm" is a term used to refer to any worm whose body is segmented, burrows into the soil and belong to the class Oligochaeta. "Red wigglers" are a group of earthworms mostly useful for composting. The usual earthworms are often called night crawlers.
An earthworm's body is usually segmented and reddish brown in color. The different earthworm species range in size from a half a centimetre to 15 cm. Night crawlers can be tens of feet long, while red wiggler worms are only about 5 cm. They are slightly reddish-purple in color, with yellowish marks at the tips of their tails. Stripes are evident in some red wiggler worm species.
What is the difference between them? Redworms ingest food scraps and other organic waste rapidly. After these have passed through the worm’s gut, the end product is a biologically active material called castings, commonly called worm poop. They contain significant amounts of beneficial micro-organisms, enzymes, humus, and plant stimulants compared to regular compost. Also, these castings are water soluble and can be easily absorbed by the plant.
(What is compost? Composting is the natural process of recycling organic leaves and food scraps into a valuable fertilizer called compost).
Nightcrawlers do produce castings as they eat, but don’t eat nearly as much as the red wrigglers! However, they’re extremely important to soil. As they burrow into the soil, they take organic material along with them much into the subsoils of the earth; where the red wigglers don’t travel. Earthworms do a lot of mixing and aerating.
While earthworms live in open gardens and like moist soil, red wrigglers like warm environments like compost bins. Even though earthworms are burrowers, they may kill themselves as they attempt to burrow to the bottoms of bins. This means the gardener would have to continuously turn the compost, since the earthworms won't be bringing material to the surface. For this reason, earthworms are unsuitable for compost bins.

5. Will all our jobs be taken by robots in the future?
Ans: We keep on hearing things like “robots will replace 40% of jobs in the next 15 years”. Progress in artificianl intelligence (AI) means that indeed there are many things robots are now doing than ever before. There are robots to clean houses, robots to make dosa, flying robots (drones) that can deliver food and medicines to remote places or during emergencies. They can also improve your life by making music, reading to you, or even help train you exercise to get fit. Some robots even help operate on patients. So, will robots take over all our jobs? Or will robots help us live simpler and more efficient lives? What do you think? Is it the most frightening thing to happen, or are we living in exciting times? Write back to Jantar Mantar and let us know what you think.
Sources: Discovery Science News, Wikipedia, USGS, and other Internet sources