Answers to last issue's Do You Know?
1. Why do many of us like to sleep under blankets, even on warm nights?
Answer: This is an experience many Indians have: a hot and humid summer night, rotating fans barely cooling the room, circulating hot air. Yet, many need some sort of covering, the barest edge of the lightest sheet, before they can fall asleep. Why is this so?
Blankets are a modern phenomenon. Historically, the effort involved in weaving large sheets made blankets too expensive for most to afford. From the linen bedsheets of Egypt around 3500 BCE to woollen sheets during the Roman empire through to cotton in India, bed coverings were for wealthy people.
According to historians, there has not been much research on bedding habits around the world. Anthropologists say that only the nomadic foragers (for food) regularly sleep without bed coverings. Everyone else uses some form of covering, whether it is plant matter or woven fabric, even in central Africa and Papua New Guinea, both tropical climates. Much more common than sheets or blankets are some form of padding.
The physiological explanation is as follows. About 60 to 90 minutes before usual bedtime, the body starts losing core temperature. This is because when the body is heated, we feel more alert. Conversely, when the body cools down, we tend to feel sleepier. Cooler internal body temperatures are correlated with a rise in melatonin, a hormone that induces sleepiness.
As the night progresses, things get complicated. In the first 4 hours and the hour before sleep, your body temperature falls a bit, from around 98 degrees Fahrenheit to around 96 or 97. In the second 4 hours, during REM sleep (Rapid Eye Movement), a host of changes takes place, including our ability to thermo-regulate.
Lizards have this problem: they cannot regulate their temperatures by sweating or shivering, and hence resort to the sun or cooler shades. During REM sleep, we all turn into lizards (in this sense)! This period coincides with the coolest parts of the night. The night is in fact coldest before dawn, just when we cannot thermoregulate. So, like lizards, we have to have some way to externally regulate our body temperatures. Hence the blanket.
You may think it unnecessary to use a blanket at 10 p.m., when it is still hot, but by 4 a.m., when it is colder and you are unable to shiver, you need help. Memory takes over, ensures that you at least keep a blanket nearby.
There is more. Another strange thing that happens in the REM periods of sleep is that our bodies drastically lower their levels of serotonin, the neurotransmitter most associated with feelings of calm, happiness and well-being. Guess what? Studies indicate that sleeping with a weighted blanket can trigger an increase in the brain's production of serotonin!
Psychologists say that use of blankets is due to "conditioning". This is what you had as a child, and your mind associates it with warmth and coziness, so you want it more.

2. What happens when we get flu? Why do we feel like lying in bed all the time?
Answer: Influenza is a virus, transmitted by touch contact but, more often, transmitted through the air. The virus infects the specialized epithelial tissue that lines your respiratory tract (like your nose, throat and airways). Once the virus enters your epithelial cells, it is able to "hijack" the machinery your cells usually use to create new proteins, and tricks them into creating more viral particles instead.
Then your cells release the newly created viruses; so they go on to infect more cells, and create even more viruses. Soon, that single virus turns into a major infection and, hey, you are sick.
Now your body fights back. Special immune cells, called T-cells, circulate through your body looking for infection. When they find infected cells or flu viruses they put your immune system on high alert. Other immune cells, called B-cells, rush in to start engulfing and destroying the viral particles, working to clear the infection from your system.
This has other effects. Once your immune system goes on alert, it releases chemicals called cytokines, that trigger inflammation. In fact, the most annoying symptoms like your stuffy nose or fever is due to the immune response. It can also make breathing difficult. All this takes a toll on you, makes you want to sleep for a whole week.

3. I can imagine that melting glaciers cause sea levels to rise. but I read that they can also cause ocean floor to sink. How is this possible?
Answer: Yes, we all know that the glaciers are melting. As the Earth's largest chunks of ice continue to get smaller and smaller, sea levels have risen. All that melting ice has to go somewhere, so as it seeps into the oceans, beaches and shorelines are feeling the pinch. However, a recent study on the effects of glacial melting has revealed another unexpected consequence of ice mass loss. As it turns out, the ever increasing mass of water is actually pushing the ocean floor down. The findings suggest that not only is the sea floor being pushed down and deformed, but also that its movement is going to make it even more difficult to predict and monitor the changes in sea level as climate change marches on.
That's all? All this fuss is about 2 millimeters?? It is natural for you to wonder, but remember that this is happening on a global scale. This is the entire ocean we are talking about here, all 340+ million square KM of it. A seemingly measly 2.1 millimeters is actually an incredible, potentially devastating change.
All this suggests that we may be facing a bigger problem before long. As the oceans get heavier and continue to push down on the sea floor, tracking and measuring changes in sea level as it relates to coastal communities could become increasingly difficult. We know very little about what the oceans will do under increasingly warm climates, and by the time we understand the issue in depth, it might be too late to act on it.

4. How does rain come down from the clouds?
Answer: We are used to saying that rain comes down from the clouds. We could equally well say that rain IS the clouds giving up on being water vapour and coming down to the earth, only to start the journey again. This is the precipitation cycle, the mechanism through which water moves from the Earth to the atmosphere and back again.
The amount of water available on Earth never changes. But its state (liquid or gas/vapour) does, and it is thanks to thermal energy from the sun. As liquid water is heated by the sun, it receives enough energy to break its molecules apart and transform into water vapour. The warmer the air, the more water vapour it can hold. That warm, moisture-saturated air rises, along with the water vapour it contains, and as it rises it cools. Once the air has cooled past the "dew point" it condenses around "condensation nuclei," which are usually tiny particles of dust, smoke or even salt that are suspended in the air. The tiny water droplets that initially form are what you see as clouds, and if you pay close attention to clouds in the sky, you see that they are constantly shrinking and growing in response to the warring forces of evaporation and condensation.
Water vapour that has condensed into tiny droplets and formed clouds is well on its way to becoming rain – but not yet. For now, the water droplets are so tiny that the air currents keep them up, just as swirling particles of dust can stay in the air. But as those droplets continue to rise, buoyed by rising bodies of warm air, they have two routes for making it back to Earth.
The first is when water droplets collide and coalesce with other droplets, eventually becoming heavier than the uplift of the air around them, at which point they fall down through the cloud. Or, through the ice process of precipitation (called the Bergeron process), the droplets rise high enough to freeze into ice crystals, attracting more water vapour to themselves and growing quickly until they are heavy enough to fall as snow or melt and fall as rain.
There are very interesting models of rain formation that help you not only understand this process, but also calculate how much of precipitation occurs.