One study looked at Indian Ocean bottlenose dolphins in Shark Bay in Western Australia. Bottlenose dolphins show their aggression towards each other by their movements, postures and sounds—and they can intensify the aggressive behaviour by slamming their body against another dolphin, or ramming or even biting them.
More than 83% of the dolphins in Shark Bay over the years of this study had tooth-rake marks on their bodies. Male dolphins were often aggressive towards each other. There was also male-against-female aggression, especially when the females were in breeding condition.
Scientists looked at photographs of the dolphins over the years, and counted the tooth-rake marks on their flesh. They also directly observed the dolphins, and saw females being aggressive towards other females every 500 hours. But when there were males involved, this increased to one aggressive act every 61 hours. In about 85% of cases, it was an aggressive male attacking a female.
Rose-Tinted Glasses
The popular media portrays dolphins as cute, happy, playful and friendly. However, this widespread and inaccurate portrayal makes it difficult for the average person to see dolphins as they really are—wild animals. We need to stop seeing them through rose-tinted glasses.
Sharks and Dolphins
Because both dolphins and sharks compete for the same food sources, there must be some hostility between them.
In Moreton Bay near Brisbane in Queensland, about one-third of the dolphins in the area carry scars from sharks, usually Great White Sharks. In Southern Natal in South Africa, sharks are responsible for about 2.2% of bottlenose dolphin deaths. And dolphin flesh has been found in the stomachs of about 1.3% of tiger sharks.
Dolphin or Whale?
There are two major families of dolphins, ranging in size from 1.2 m and 40 kg right up to 9.5 m and 10 tonnes. The most common species is the bottlenose dolphin. There are about five species of river dolphins and about 32 species of ocean dolphins—including about six species commonly, but wrongly, called whales. These ‘whales’ include the pilot whale and the Killer Whale.
That’s right! The Orca, the so-called Killer Whale, is actually a member of the dolphin family. Many of us have seen the impressive footage of an Orca coming up onto a beach to savage a seal. Orcas are not exactly cute and friendly.
Dolphins must have a great PR agency on their team. After all, if they can disown Orca the Dolphin, and turn him into Orca the Killer Whale—well, the agency deserves at least as much applause as a performing dolphin can generate.
The Bottom Drawer Effect
In the Land of Science, the Bottom Drawer Effect relates to what you do with experiments that didn’t work, or results that didn’t prove anything. You can’t bear to throw them away, because they took so much time and effort. So you just shove them into the bottom drawer of your filing cabinet, and leave them there—and nobody else ever knows about them.
A variation on this Bottom Drawer Effect involves results that don’t even get recorded, e.g. when the dolphins kill people. They might ram them, bite them to death or just herd them out to sea until they drown. These people will never be able to report the dolphin’s aggression towards them—because the dolphins killed them.
The only people who can report back are the ones who lived—and they will tell you how wonderful dolphins are, because they saved their lives.
References
Fraser, John, et al., ‘Dolphins in popular literature and media’, Society & Animals, September 2006, Vol 14, No 4, pp 321–349.
Lloyd, John and Mitchinson, John, QI: The Book of Animal Ignorance, London: Faber and Faber, 2007, pp 102, 103.
Mann, J. and Barnett, H., ‘Lethal tiger shark (Galeocerdo cuvier) attack on bottlenose dolphin (Tursiops sp.) calf: Defense and reactions by the mother’, Marine Mammal Science, April 1999, pp 568–575.
Marino, Lori, et al., ‘Dolphin-assisted therapy: More flawed data and more flawed conclusions’, Anthrozoos: A Multidisciplinary Journal of the Interactions of People & Animals, September 2007, Vol 20, No 3, pp 239–249.
Samuels, Amy, et al., ‘A Review of the Literature Pertaining to Swimming with Wild Dolphins’, prepared for the Marine Mammal Commission, Maryland, USA, April 2000.
Samuels, Amy, et al., ‘Swimming with wild cetaceans, with a special focus on the Southern Hemisphere’, Chapter 14 in Marine Mammals: Fisheries, Tourism and Management Issues, edited by Nick Gales, et al., Collingwood, Victoria: CSIRO Publishing, 2003.
Scott, Erin M., ‘Aggression in bottlenose dolphins: Evidence for sexual coercion, male-male competition, and female tolerance through analysis of tooth-rake marks and behaviour’, Behaviour, 2005, Vol 142, Issue 1, pp 21–44.
Spradlin, Trevor R., et al., ‘Interactions between the public and wild dolphins in the United States: Biological concerns and the Marine Mammal Protection Act’, Presented at the ‘Wild Dolphin Swim Program Workshop’ held in conjunction with the 13th Biennial Conference on the Biology of Marine Mammals, 28 November 1999.
Webb, N.G., ‘Women and children abducted by a wild but sociable adult male bottlenose dolphin’, Carnivore, 1978, Vol 1, No 2, pp 89–94.
Dig Those Shooting Stars
One morning when I was about eight years of age, my father took me out to a coconut palm in our front yard. After showing me a hole in the ground (about the size of a golf ball), we started digging down into the hole. The hole continued through one of the roots of the tree and then stopped at a small, round rock. Then he told me that the previous night he had been staring out of the window, waiting for inspiration for another story (he was a writer) when he saw a shooting star zip past—and the golf ball–sized rock that I held in my hand was that shooting star.
At that moment, a myth crumbled, as I realised that a shooting star was not really a star falling out of the sky.
Meteoroid, Meteor, Meteorite?
‘Stars’ are huge objects, typically a million or more kilometres in diameter, burning with nuclear fires—and very far away from the Earth. Many of them have planets orbiting around them.
On the other hand, so-called ‘shooting stars’ are quite different—they are small rocks burning up in our atmosphere.
The naming of these rocks is a bit confusing. The word ‘meteor’ comes from the Greek word meteora, which means ‘things in the air’, or ‘high up in the atmosphere’. This ancient Greek word has given us the English words ‘meteorology’, the study of the weather, and ‘meteoritics’, the study of meteorites.
When these rocks are zipping through Space, they are called ‘meteoroids’. They range in size from millionths of a metre to metres in diameter. Once the meteoroids enter the atmosphere, leaving a visible, bright streak in the air, they are called ‘meteors’. And after they have landed, the lump of rock that you see on the ground is called a ‘meteorite’.
How to make a crater in 4 easy steps
Meteoroid to Meteor…
Let’s look at a meteoroid zipping through Space.
Speed has to be measured relative to some object, so let’s measure it relative to the Earth. Typically, the object can be moving through the solar system at speeds of between zero and 60 km/sec (216,000 kph). As it gets closer to the Earth, it gradually speeds up thanks to the Earth’s gravitational field, picking up another 11 km/sec of speed. So the meteoroid will hit the upper reaches of our atmosphere with a minimum speed of 11 km/sec (39,600 kph) and possibly a maximum speed of approximately 71 km/sec.
The Kinetic Energy increases enormously as the speed of the object increases. So even the relatively ‘slow’ speed of 11 km/sec gives the meteoroid ten times as much energy as the same weight of a high explosive such as TNT. Once it hits the thin atmosphere about 100 km above the ground, this energy appears in a few forms.
Most of the energy appears as heat. It vaporises the surface of the meteor, turning it into a liquid and then a gas. (The rock is in the Earth’s atmosphere, so it’s now called a ‘meteor’.)
The molten surface of the meteor is whisked away behind t
he meteor by its speed, and appears as a tail of ionised atoms. About 0.1–1% of the energy of the incoming meteor is turned into visible light, which we see as the tail of the meteor. Strictly speaking, the name ‘meteor’ refers to both the moving rock and the tail behind it.
Some of the energy of the meteor turns into a shock wave. This can sometimes be heard as a sonic boom. The shock wave can be so strong that it can register on seismometers down on the ground.
The shock wave also acts upon the meteor itself. The structural integrity of the meteor can vary enormously—from as weak as a clod of dirt, to as strong as a ball of iron. In some cases, the shock wave can break up, or fragment, the meteor.
As it falls deeper into the thicker atmosphere, the rock slows down and gets cooler. So the tail usually peters out at about 80 km above the ground, but it sometimes survives to an altitude of 50 km. The so-called visible flight takes only a few seconds.
So while a meteor is real, most of it is as intangible as a rainbow.
Atom Bombs from Space
About seven to eight times each year, US military satellites see a big lump of rock explode in the upper atmosphere with the energy of a small atom bomb. These lumps are too big to vaporise harmlessly in the atmosphere, but are too small to punch through the atmosphere and make it all the way to the ground. So, on average, they explode about 30 km above the ground.
We only found out about this in the mid-1990s, after the data had been first declassified by the US Defense Department. The military satellites saw some 136 atombombsize explosions between 1975 and 1992. According to scientists, the satellites probably see only 10% of all these explosions.
In 1994, President Bill Clinton was woken in the middle of the night because one such explosion was thought to be a human-made atomic explosion.
Brightest Meteor Ever
It seems that the brightest meteor ever recorded was the one that impacted the Tunguska region of central Siberia around 7.14 am, on 30 June 1908. The rock, probably about 40–50 m in diameter, created an airburst explosion at an altitude of about 5–10 km above the ground.
According to eyewitness accounts, it was as bright as the Sun. The incoming meteor was so big and moving so fast, that it flattened an estimated 80 million trees over about 2,000 km2 of countryside. It delivered the energy equivalent to a 10-megaton nuclear weapon.
Meteor to Meteorite
Most of the rocks do not make it down to the ground—they simply vaporise entirely or break up into smaller fragments that then vaporise.
The ones that do survive need a fairly low entry speed (say under 25 km/sec), so there is less energy available to destroy them. They also need to start off with a fairly large mass (say, at least 100–1,000 g) and be strong enough to resist the crushing effect of the shock wave.
These rocks will usually have lost all of their supersonic velocity at an altitude of between 5 and 25 km. They will then fall at a ‘terminal velocity’ of between 150 and 300 kph. This terminal velocity is a result of the balance between two forces—the ‘suck’ of gravity and the resistance of the wind.
The ‘dark flight’ of the meteor down to the ground can take a few minutes.
If the landing is noticed, it is usually only as a whistle and a dull thud. However, there have been a few rare cases where a meteor(ite) has smashed into the back end of a stationary car, landed just in front of the head of a sunbather on a beach, or even come through a roof and grazed the abdomen of an inhabitant of a house.
Where Do Meteors Come From?
We are not exactly sure where meteors come from.
Certainly, quite a lot of them come from the so-called Asteroid Belt between Mars and Jupiter. It is almost entirely empty Space—nothing at all like you see in the movies, where the spacecraft has to swerve frantically to avoid hitting an asteroid or being hit by one. But given enough time, asteroids do occasionally collide, creating rubble. Sometimes this rubble eventually makes it to Earth. We have discovered this by matching the colour of meteorites with the colour of various asteroids.
Some meteors are associated with comets. On one hand, we now think of comets as dirty iceballs of rubble and dust. But let’s think of a comet as a truck with a dirty exhaust, looping around the Sun in an elliptical orbit that might take up to several hundred years to complete. The comet is continually shedding material—huge amounts when it is close to the heat of the Sun and hardly any when it is in the depths of cold Space. Eventually, after many many orbits of the Sun, the entire path that the comet takes on its elliptical orbit is filled with rubble and ice from the comet. Typically, the Earth will cross this orbit at around the same time each year, and there will be a meteor shower. There are a dozen or so known meteor showers. Leonid meteor showers occur annually in mid-November, but every 33–34 years, they really light up the sky. The Leonids are associated with the Comet Tempel-Tuttle.
Surprisingly, a very tiny number of meteorites appear to come from the Moon or Mars. It seems that meteors have, in the distant past, smashed into the surface of the Moon or Mars with such force that they have splashed bits of rock from the Moon and Mars into Space. After thousands or millions of years of floating in Space, these rocks were captured by the Earth’s gravitational field, making it down to the ground for us to find.
Close Encounters
The most recent rock that came closest to actually hitting the Earth probably zipped past on 31 March 2004. On that day, the meteoroid known as 2004 FU162 missed the Earth by about the radius of the Earth—about 6,500 km. Measuring only about 10 m in diameter, it would almost certainly have exploded in the upper atmosphere—and caused no damage.
However, on 19 May 1996, the rock JA1 missed us by about 450,000 km—roughly the distance from the Earth to the Moon. As it was a lot bigger—about 500 m in diameter—it would have caused a lot of damage if it had hit the Earth.
In most cases, we find out about these objects only after they have missed hitting Earth, when astronomers are examining old photographs. Even though these rocks could end civilisation as we know it if they hit our planet, less money is actually spent looking for them than is spent making movies about them—e.g. movies like Armageddon and Deep Impact.
Even Closer Encounter
On 19 September 2007, a meteorite crashed to earth near the farming village of Carancas, in southeastern Peru, not far from Lake Titicaca. The impact knocked over a villager, Romulo Quispe, throwing him back 3 m. It also created a 20 m wide x 5 m deep crater that quickly filled with water. The impacting meteorite was about 1 m in diameter and produced a seismic shock equivalent to a 1.5 magnitude earthquake.
Many people visited the impact site, about 200 of them reporting that they had suffered headaches, nausea and breathing complaints. Some people suspected intergalactic attack, for example, biological or germ warfare. However, investigation showed that the illnesses were the result of breathing arsenic fumes from the underground water that was tainted with arsenic. (Before the meteor punched the 5 m deep crater into the ground, the water was safely away from human access.)
Ah well, a finding far more prosaic than the Killer Bugs from Outer Space…
What Are Meteors Made Of?
Most of the meteorites, about 82%, are predominantly stony. Inside these meteorites are small spheres of silicate called ‘chondrules’. So the stony meteorites that are made of these chondrules are called ‘chondrites’. Another 8% of meteorites are stony, but do not contain chondrules. These are called ‘stony achondrites’.
About 5% of meteorites are predominantly iron. Predictably, they are called ‘iron’ meteorites.
Of course, those that have a mix of iron and chondrules are called ‘stony iron’ meteorites.
Surprisingly, about 90% of meteorites have enough iron to be attracted by a magnet.
Meteor Shower/Storm
On a dark, moonless and cloudless night, according to the experts you should probably be able to see about five to ten meteors per hour. Every time that my family and I have been i
n the Outback, we usually see about 25 per hour. However, this is with a team of three or four of us checking out the entire sky.
But you can get rates much higher than this. Back in November 1966, the Leonid Meteor Storm showered North America with shooting stars at rates of up to 100 per second.
God’s TV
My family and I have spent a total of about two years travelling through the Australian Outback. Our evening routine is always the same.
We have an early dinner and then cuddle up on a big ground sheet in our swags. And then, armed only with our eyes and a laser, we spend the first hour and a half after sunset looking for satellites. Typically, we will see about 25. We use the laser to point out the very faint ones. We then spend the next hour and a half looking for falling stars—and again, we usually see about 25.
But in all this time, we have never been lucky enough to have one land near us. (And we have never been unlucky enough to have one thump into us.)
I still have the falling star that my father and I dug up—and yes, it is an iron-type meteorite, and no, it is not a star.
Cosmic Dust per Year
Meteors and other cosmic dust have been falling into our atmosphere ever since our planet sprung into existence.
A recent study looked at various isotopes of helium in Antarctic ice. It revealed that the Earth is getting heavier by about 40,000 tonnes each year—and that this weight gain has been relatively constant for the past 30,000 years.
Science is Golden Page 11