Читать книгу The Double Dangerous Book for Boys - Conn Iggulden - Страница 13
ОглавлениеQUESTIONS ABOUT THE WORLD – PART ONE
The first Dangerous Book asked and answered a number of questions: Why is a summer day longer than a winter day? Why is it hotter at the Equator? What is a vacuum? What is latitude and longitude? How do you tell the age of a tree? How do we measure the earth’s circumference? Why does a day have twenty-four hours? How far away are the stars? Why is the sky blue? Why can’t we see the other side of the moon? What causes the tides? How do ships sail against the wind? Where does cork come from? What causes the wind? and What is chalk? Could there possibly be any questions left unanswered? Well, yes.
1. What is the tallest mountain on earth?
2. Why does the earth have a magnetic field?
3. Where are the hottest and the coldest places on earth?
6. What are the longest rivers?
1
WHAT IS THE TALLEST MOUNTAIN ON EARTH?
Hawaii. Mauna Kea on the island of Hawaii is the tip of a much larger mountain. From the sea floor to that mountaintop is over 33,000 feet (10,203m). In comparison, Mount Everest on the Nepal/Tibet border is just over 29,000 feet (8,848m). Of course, at the bottom of Mauna Kea, pressure is crushing, so the mountain may never be climbed.
If you measured all the peaks from the centre of the earth, the mountain known as Chimborazo in Ecuador is furthest out. It lies almost on the Equator. As an actual bottom-to-top measurement, though, Hawaii’s Mauna Kea is No. 1.
(The deepest spot on earth is the Mariana Trench. Everest could be dropped into it.)
2
WHY DOES THE EARTH HAVE A MAGNETIC FIELD?
The earth’s magnetic field deflects charged particles coming off the sun, known as the ‘solar wind’. We suspect it is a key requirement for life to exist, so it’s something we look for in the solar system and further out.
It is generated by the rotation of liquid metal at the earth’s core. The forces involved are almost beyond imagination, but that much molten iron/nickel moving at that speed produces a huge magnetic field. In comparison, Mars has a very weak magnetic field – and one problem of Mars colonisation would always be that lack of protection from solar particles.
By measuring the strength of gravity at the surface (scientists jumping up and down, mostly), we are able to estimate the mass of the earth – it’s around 5.9 sextillion tonnes. Nothing on the surface is heavy enough to produce the gravity we can observe, which means the centre has to be a dense metal able to produce a magnetic field. Iron and nickel are the best candidates – both dense enough to explain gravity and a magnetic field.
A number of planets in the solar system have magnetic fields. Yet when it comes to future exploration, our best bet might be the only moon that does – Ganymede, a moon of Jupiter. Dwarfed by the largest planet in the solar system, Ganymede is a respectable size – about two-thirds the size of Mars. Although its magnetic field is relatively weak, it should mean it has a liquid core, which suggests a source of heat to tap for future explorers.
3
WHERE ARE THE HOTTEST AND THE COLDEST PLACES ON EARTH?
The hottest air temperature ever recorded was in Death Valley, California, in June 1913, of 134°F (56°C). (There was actually a temperature of 136°F recorded in Libya in 1922, but that’s considered dubious due to problems with the instrumentation.) Either way, temperatures of over 110°F (43°C) are common in Death Valley each year from May to October, which makes it all the more extraordinary that long-distance races are run across it. The Badwater Ultramarathon is run across Death Valley in summer each year – 135 miles (217 km) from the lowest point in California to the foothills of Mount Whitney. The runners tend to use the white lines in the middle of the road. If they run on black tarmac, their shoes melt. Human beings can be extraordinary.
The coldest place on the earth is Antarctica. This measurement is complicated by wind chill, which can make a low temperature much, much lower. However, in still air, the coldest temperatures recorded in Antarctica are −135°F (−93°C). The Antarctic Ice Marathon has been run every December since 2006. It takes place at 80 degrees south latitude, at the foot of the Ellsworth Mountains. Although it is run during the Antarctic ‘summer’, temperatures of −20°C (−4°F) are common, with winds of 10–25 knots.
(Note: Centigrade/Celsius (C) is used almost universally in Britain, influenced by its wide adoption in European countries. Fahrenheit (F) used to be the British standard and is still more common in America. The best idea, it seems to us, is to use Fahrenheit for hot days (It’s 80 degrees!) and Centigrade for cold days (It’s −5!) There’s no particular reason to choose Fahrenheit (German/Polish/Dutch) over Celsius (Swedish), but using both underlines that they are utterly artificial and man-made.)
4
Alfred Wegener (1880–1930) was a German scientist and the first to notice that the continents of earth look as if they might fit together. Africa and South America share a suspiciously similar-looking coastline, for example.
Wegener’s theory was that continents drift on enormous plates – and if time could be wound back, they would creep towards one another. The original land mass would have been a single super-plate that slowly broke up to form modern continents. Later measurements of drifting plates and similarities in fossil records have borne out the theory. The name ‘Pangaea’ was coined to describe that single land mass of ‘all the earth’.
5
The short answer is yes. This is measurable by the length of the day, which is getting longer. That much is certain – 2017 was the fourth year in a row that we measured a decrease in the earth’s spin. The reasons for this are still a matter of conjecture, of course. One theory is that the moon exerts a braking effect on the earth. That is a good possibility. We know tides are created by the moon’s gravitational pull. It makes sense that this might exert a slowing effect.
However, the effect is incredibly small. It would take millions of years to get to the point of a 28-hour day, for example.
6
There are two possibilities. The Nile is usually given as the longest river system on earth, providing water to eleven countries and stretching 4,200 miles (6,700 km) across Africa. However, until every tributary and source has been mapped and measured, we can never know for certain.
The river rises in the great lakes of central Africa and flows north until it reaches Egypt and the Mediterranean Sea.
The Amazon in South America is the other candidate. Usually described as the second-longest river in the world, it too has its champions and it is true that more water passes through the Amazon than the Nile each day. It begins in Brazil – or Peru, depending whom you ask. Rivers can run underground, which is one of the reasons it’s not always easy to measure their length and pin down the exact source. Still, these are by far the two longest – the Amazon is just over 4,000 miles (6,400 km).
