Wonders of Life. Andrew Cohen
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Название: Wonders of Life
Автор: Andrew Cohen
Издательство: HarperCollins
Жанр: Прочая образовательная литература
isbn: 9780007452682
isbn:
This poses a series of interesting questions: What are the factors that make Earth a home to such a bewilderingly rich and complex ecosystem? What is the minimal set of ingredients necessary for life to evolve, and how widespread are these ingredients in the Universe beyond Earth? Is the emergence of complex living things such as monarch butterflies, fir trees and human beings an inevitable consequence of the laws of physics, or does it rely on a home whose existence is so improbable that Earth and its living ecosystem is a rare, even unique, corner of the Milky Way galaxy, itself one of billions of galaxies in the observable Universe?
The behaviour and biochemistry of monarch butterflies cannot be understood in isolation either from their habitat or from the shifting seasons.
It is difficult to do justice in a few short paragraphs to Mexico – or, as it is more correctly known, the United Mexican States. An intense and colourful country of contradictions, it is both welcoming yet occasionally frightening, peaceful yet troubled. It has a striking veneer of colonial architecture and customs, but the magnificent architecture of its great indigenous civilisations is intact and imposing, and their ancient mythology makes a vibrant contribution to twenty-first-century global culture. What schoolchild isn’t fascinated by the Aztecs, and which New Age conspiracy theorist doesn’t read infinitely too much into the Mayans’ fascination with the creation of complex and far-reaching calendars?
Physically, Mexico covers almost 2 million sq km and is home to 112 million people. Bordering the United States of America to the north, the Pacific Ocean to the south and west, the Gulf of Mexico to the east, and Guatemala, Belize and the Caribbean Sea to the southeast, it is a land of tremendous geological and climatic variation – from lowland rainforests to pine savannahs; from fertile grasslands to high volcanic mountain ranges. Its position – straddling the Tropic of Cancer and bounded by two of the world’s great oceans – also makes it one of the most biodiverse countries on Earth. Even though it covers only 1 per cent of the land area of our planet, it is home to over 200,000 different species – at the last count, 10 per cent of Earth’s bank of life. There are 707 species of reptiles, 438 species of mammals, 290 species of amphibians and over 26,000 species of flora. This is why we chose Mexico to tell the story of the ingredients that make our world such a comfortable home for life.
HOT SPOTS OF HIGH ENDEMISM AND SIGNIFICANT THREAT OF IMMINENT EXTINCTION
Mexico is one of the most biodiverse countries on Earth. Even though it covers only 1 per cent of the land area of our planet, it is home to over 200,000 different species – 10 per cent of Earth’s bank of life.
Surface water is often scarce in the rainforests of the Yucatan peninsula, Mexico. Yet this region is one of the most biodiverse on Earth.
Cenotes (a type of sinkhole) mark the edge of a massive crater, formed 65 million years ago when an asteroid, measuring some 10 km in diameter, smashed into Earth.
The ocellated turkey (Meleagris ocellata) resides primarily in the rainforests of Mexico’s Yucatan peninsula. Only the male – shown here – has such striking plumage.
The Mexican beaded lizard (Heloderma horridum) is just one of the 707 species of reptile known to exist in Mexico.
The cenotes of the Yucatan peninsula contain remarkably clear water, which has been filtered through the porous limestone above over many thousands of years.
We began filming in the tropical rainforests of the Yucatan peninsula, where accessible water resources can be unexpectedly scarce. Large areas of the Yucatan are devoid of rivers and streams because the bedrock, composed mainly of limestone, is porous. There is a large subterranean source of fresh water, however, contained in a complex, stratified aquifer. Fortunately for the occupants of the peninsula, this underground water source is easily accessible through a series of sinkholes known as cenotes. The cenotes lead into vast networks of subterranean caverns dissolved out of the limestone over many thousands of years and flooded by the clean waters of the aquifer. The Mayans built their civilisation around cenotes, many of which lie in a strange, semicircular arc centred on a small village called Chicxulub. They mark out the edge of a giant crater, formed 65 million years ago when an asteroid 10 km in diameter smashed into Earth. Known as the Cretaceous-Paleogene extinction event (or the K-T extinction), this impact is the most widely accepted theory for the cause of the mass extinction of the dinosaurs.
The Mayans built their civilisation around cenotes, many of which lie in a strange, semicircular arc centred on a small village called Chicxulub.
The water in the cenotes is exceptionally clear because it is filtered slowly through the porous rocks of the Yucatan before emerging after thousands of years to flood this subterranean world. Diving into the clear darkness of these underground wells is a unique experience and a welcome respite from the heat and insects of the forest. As you journey deeper into the cave systems, the sunlight fades to darkness but an abundance of life can still be found. This is typical of what we find in even the most extreme conditions on the planet. Remove light, heat, soil, plants, insects, and even oxygen, and life still thrives. But one ingredient is, as far as we know, absolutely essential for life to exist.
Cenotes contain an abundance of life, and taking a dive into their crystal-clear, yet dark, world is a unique experience.
Water arguably exhibits the most complex behaviour of any known substance. This may come as a shock, because the ubiquitous familiarity of its chemical signature – H2O – is the stuff of the most basic of classroom chemistry lessons. Yet this familiarity hides a deep complexity that we are only now beginning to understand. The complexity doesn’t lie in the structure of water molecules themselves of course: each molecule is made of three atoms – two hydrogen atoms and one oxygen atom. From chemistry lessons gone by, you might recall that the two hydrogen atoms are covalently bonded to a single atom of oxygen. Oxygen has eight electrons around its nucleus, six of which are in the outer shell; these are known СКАЧАТЬ