Answers to last issue's Do You Know?
R. Ramanujam, The Institute of Mathematical Sciences, Chennai

1. I read that there will be more floods because of global warming. Why should this happen?
ANSWER: There have been many severe storms and cases of extensive flooding in the last few decades in many parts of the world. Researchers have looked at flooding activity they call "one in two-year" and "one in 30-year" events and projected the likelihood of floods occurring over the next 60 years. Their models predicted an increase in flooding in many parts of the world. For instance, in England, flooding could increase by an average of 15 to 35 per cent by the year 2080. 
These are data models, that only look at recorded data so far and predict trends based on data. They do not explain why flooding should increase.
There is no doubt that greenhouse gas emissions caused by human beings are changing our climate. This is resulting in a progressive rise in global average temperatures. Do all scientists agree on this? There is almost a scientific consensus on it, comparable to the consensus on the linkage between cigarette smoking and cancer.
What is climate? It is a very large intricate system of interlinking processes of temperature, pressure and air movement, so forecasting exactly how this temperature increase will impact countries across the globe is a complex task. Scientists base their predictions on powerful computer models that combine our understanding of climatic processes with past climate data.
Many large-scale trends can now be calculated with a high degree of certainty: for instance, warmer temperatures will cause sea water to expand and glaciers to melt, resulting in higher sea levels and flooding. It is much harder to make more localised predictions. 
Basically, because of global warming, when it rains, it pours more. Experts predict that rains will intensify, bringing as much as 50 percent more heavy rain by the end of this century. Of course, heavier rainfall does not automatically lead to floods, but it increases the potential for flooding, because our living spaces (especially crowded cities) cannot be reorganized to handle the increase in heavy rains.
Recently, on February 7, around 10 in the morning, a landslide, the trigger of which was unknown, crashed into a lake in the Nanda Devi Sanctuary in Uttarakhand. It resulted in a flash flood bearing mud and other debris that hurtled down the steep slopes. More than a hundred lives and two hydroelectric power projects were destroyed. This is sudden flooding, and perhaps also attributable to global warming. A scientist from Uttarakhand said that in a region with so many glaciers, it was natural that there would be avalanches too. Winter temperatures were on the rise and glaciers were very sensitive to temperature changes, he pointed out.
Thus temperature increase can lead to flooding of many kinds. 

2. Did other planets go through several Ice Ages like the Earth did?
ANSWER: Great question, and we do not know the answer to it! But scientists have found glaciers on Mars which reveal that the Red Planet did go through multiple ice ages.
Glaciers that have remained on the surface of Mars for hundreds of million years are now revealing secrets of the planet's unique geological past. By analysing the patterns and structures of rocks in 45 of the Red Planet's glaciers, researchers have found that Mars underwent between 6 and 20 separate ice ages over the last 300 to 800 million years.
Do you know how they got this valuable data? It comes from a series of high-resolution images collected by the Mars Reconnaissance Orbiter satellite and by measuring the size of around 60,000 rocks.
If there had been a single, long ice age they would found a steady progression of larger to smaller rocks as they gradually eroded over time. However, they found that rocks of different sizes were distributed at random. 
They also found that the rocks were distributed in clear bands of rocks across the glaciers' surfaces, with each marking the limit of separate and distinct flows of ice indicating that each formed during a separate ice age.
As we get and analyse more data, scientists expect to figure out how Mars' climate changed over time. They might even find microbes trapped inside the ice from many million years ago!

3. Can we make an artificial eye that behaves like the human eye?
ANSWER: "Behaving like" a human eye is a very big challenge, and we are very far from making any such thing. However, inspired by the workings of the human eye, scientists are developing an optical device that mimics the sensory input received by the eye. These optical sensors would at least make robotic components far more efficient.
The main challenge is to sense different intensities of light. The device does this by using ultra-thin layers of photosensitive material called perovskite. This material is normally employed in solar cells. It is a chemical composed of metal atoms carrying positive charges and oxygen or halide anions, carrying negative charges which are layered into an interesting lattice structure.
This charged lattice structure gives the material very interesting properties. Atomic level changes alter its electrical behaviour. The material can easily switch from insulating electricity to conducting it. It is called a "semi-conductor".
Unlike solar cells, the devices created do not store and use the light provided as energy, but instead respond to changes in illumination. In doing so, these new sensors send signals to process the image in front of them based on the changes in light. This is very similar to photo-receptors in our eyes, which are sensitive to changes in the light, but less responsive to constant illumination.
Such changes are often associated with motion, and our eyes perhaps evolved to detect motion. In any case, this motion sensitivity of these new devices make them very exciting for the field of artificial intelligence. It allows for these systems to prioritise the information they receive, so that it takes less time to process surroundings.
Thus, while we cannot replicate the human eye in technology, at least one important capability of the human eye may be within the reach of technology.

4. Can a venomous snake die from being bitten by another venomous snake?
ANSWER: Yes, this can happen, but there are many species of snakes which can survive bites that are deadly to others, even from their own species.
Snake venom is made by organs that evolved from salivary glands. Ordinary saliva contains enzymes to help digest food as you chew it and natural selection has favoured snakes that include far more toxic enzymes in their saliva. The toxins in its venom are slight variations of ordinary proteins. As prey gradually evolved immunity, so snakes have responded with a complex mix of 50-100 different proteins to alter blood pressure, prevent blood clotting and paralyse nerves.
Snake venom contains neurotoxins (nerve-attacking chemicals) that can kill small mammals in minutes – including other snakes. Then how do these snake species survive? Scientists have found that this is due to genetic changes in nerve cell receptors. These genetic mutations allow certain species, such as the Burmese pythons, mole snakes, and the southern stiletto snake, to repel a particular neurotoxin found in snake venom.
Researchers have identified the exact mutation and explained its protective powers. They found that due to these changes, receptor cells carry the same electrical charge as the venom. As a result, when the venom tries to attack the cells it is repelled, just like trying to bring two positive ends of magnets together.
A single gene mutation allows vulnerable snakes to develop resistance against these particular toxins, called alpha-neurotoxins. In fact, this mutation is seen in the predator snakes too, creating ‘autoresistance’ to protect them from their own deadly venom.
Snakes like cobras and kraits that prey on other snakes evolved their venom so that the alpha-neurotoxins have positively charged surface sites. Such sites enable the venom to bind with particular target nerves with negatively charged receptors, like bringing opposite sides of magnets together. This is an attractive interaction, and by this binding, the venom paralyses the snakes' prey.
What the Burmese python has done (through evolution) is to switch the amino acid of their target receptor from negatively to positively charged. As a result, the interaction with alpha-neurotoxins becomes repulsive, deterring the venom rather than binding.
Interesting as this is, scientists say that the predator's venom will probably adapt again, as they have been doing all along in evolutionary history.
Source: BBC Science Focus