Part 5: Get to Know Earth Like You Never Have Before

Humans, together with animals and other living things, form what is called the biosphere, the living part of the world. Since modern humans first appeared in Africa about 200,000 years ago, we have colonized virtually the entire world, even hot deserts and the ice-cold Arctic. As we have done so, our impact on the biosphere has been far-reaching. The human footprint on planet Earth is deep and broad. We have transformed the landscape, clearing forests to produce food, digging minerals and ores from the ground and channeling and storing water to meet our own needs. Our living space is concentrated into larger and larger cities, but these cities are hungry for food and energy taken from surrounding land. In 1700 CE, about 7% of the Earth's land area was used for growing crops and raising farm animals. Today, that figure has risen to around 40%. Part of the success of humans is down to our ability to use the materials around us to give us protection and shelter. This ability opens up nearly every part of the globe for human living space. No matter how harsh the environment. Even thousands of years ago, the Inuit of the North American Arctic made coats from the fur of caribou and waterproof boots from seal skin. They found a way to live on the meager resources of the high Arctic. For most of humanity's existence though, the human population grew relatively slowly. For example, in 10,000 BCE, there were only between 1 million and 5 million people on Earth. By 1000 BCE, after farming was invented, the population has increased to about 50 million. Since reaching the 1 billion mark in 1804 during the early industrial revolution, the population has expanded much more quickly than ever before. Since 1965, the world's population has doubled, but its wealth has multiplied by 7. To sustain this growth of human existence on Earth, new ways of harnessing the energy of sunlight and wind are reducing our use of fossil fuels. Unlike fossil fuels, these energy sources will never run out. Buried beneath the Earth's crust, there are limited supplies of minerals, metal ores, and fossil fuels, coals, oil, and gas. Once these reserves are exhausted, we will not be able to replace them. Recycling materials and renewable energy will become ever more important. The world's 7 billion people are not spread evenly across the globe. Most live where there are natural resources and fertile land for farming. Some places are too hostile for humans to thrive in. More than half of the world's people now live in towns and cities, rather than in the countryside. Many cities have grown quickly, and there are now more than 25 continuously built-up areas of more than 20 million people. Tokyo, Japan, was the largest city in the world since the 1960s. Delhi, India, sits in the densely populated Ganges River Basin, home to 400 million people packed in at nearly 1,000 per square mile. And New York City has the largest population in the Americas. Over half of the U.S. 313 million people live in the eastern states. Sao Paulo, Brazil, is the largest city in South America, home to 11.2 million people. In Manila, the Philippines, on average 215 people live in an area the size of a football field. In 1800, the world's population was less than 1 billion people. The United Nations estimates that by 2100, it will be 10 billion. Besides people living in cities and towns, there are also up to 40 million nomads around the world. Nomads move every year to find fresh pasture or hunting grounds. Some are herders. Some are hunter-gatherers, and others are wandering traders. Their nomadic lifestyle is quickly dying out because many of them are settling in villages and towns. Most nomads live in desert, steppe, or tundra-dry places that don't provide enough food for people to stay all year round. In Canada, for 4,000 years, the Inuit have roamed the region they call Nunavut, meaning our land. In Europe, the semi-caribou herders and fur trappers have existed for over 5,000 years. There are also 8 to 10 million Roma worldwide, mostly in Europe. And every year, the Nenets move huge herds of caribou up to 600 miles. In Australia, groups of aboriginals have lived all over the land for about 60,000 years. Poorer, developing nations tend to have younger and faster-growing populations than wealthier, developed countries, whose populations are aging and sometimes even declining. By 2050, the world's median age is expected to be 38 years. By 2100, about 22% of the world's population will be age 65 or over, compared with 7.6% in 2010. The U.S. population's median age is 36.9 years. About 20% of its population are age 0 to 14. The population grows by 0.9% each year. In Mexico, where 28.8% of the population is 0 to 14 years old, the median age is 26.7 years, while Guatemala is the youngest population in Central America, with a median age of about 19.7 years. Guyana's median age of 23.6 years is the lowest in South America. About 32% of Guyanese are age 0 to 14, and Uruguay is the country with the highest median age in South America at 33.7 years. Africa is the continent with the youngest population, with a median age of only 19.7 years, while in Japan the median age is 44.6 years. Only in the tiny principality of Monaco is it higher at 48.9. Nearly 23% of Japan's population are older than 64 years. The most important factors that influence people's health are where they are born and the conditions in which they grow up and live. People who live in richer, more developed countries, who have enough food to eat and access to clean water and professional healthcare, can expect to live much longer than those who do not. A child born in Swaziland is nearly 30 times more likely to die before the age of 5 than a child born in Sweden. Monaco has only 151 patients for every doctor, the lowest patient-doctor ratio in the world. Most healthcare is funded by private health insurers. In South Sudan, a long-term shortage of food means that one-third of all its children are underweight, while Japan's healthcare system has been ranked by the World Health Organization as the best in the world. In Afghanistan, about 1 in 23 mothers die in childbirth or from pregnancy-related causes, the highest rate in the world. The world as a whole had a life expectancy of 30 years in 1900, today it's at 67 years. Infectious diseases are illnesses that pass between people and that can spread rapidly. Many people become sick, causing a local disaster called an epidemic. When this effect becomes global, we call it a pandemic. This map shows the spread of three of history's most lethal pandemics in ancient times, the Middle Ages, and modern times. The plague of Justinian, the Black Death, and the Spanish Flu. At its height during the rule of the Emperor Justinian, the ruler of the Eastern Roman Empire, this disease killed at least 25 million people. It may have started in Ethiopia, then spread along trade routes through northern Egypt and modern-day Istanbul into Europe. In the 14th century, an outbreak of bubonic plague spread from Asia across Europe, causing devastation along the way. In just four years, the disease killed 45-50% of Europe's population. The bubonic plague passed along sea trade routes, since the bacteria that caused the disease lived in fleas, which live on ships' rats. Around 3,000 people still die today from bubonic plague each year. The Spanish Flu actually began at a training camp for American soldiers in the US. The disease spread quickly when infected soldiers traveled to Europe to fight in World War I. Troops returning home from Asia after the end of World War I brought Spanish Flu back with them. In August of 1918, a second wave of Spanish Flu crossed the Atlantic and hit the port city of Freetown, Sierra Leone. In the same year, the Spanish Flu was brought to New Zealand by soldiers returning home from fighting in World War I in Europe as well. The Spanish Flu may have killed up to 100 million people, that's more than the total number of deaths during World War I. Global poverty is lower than it has ever been, but 1 in 4 people in the developing world still lives on less than $1.25 a day. Sub-Saharan Africa has by far the most cases of extreme poverty. Almost half of the people cannot afford basic necessities. Over 3 billion people live on less than $2.5 a day, and 4 out of every 5 people live on less than $10 a day. Although between 1981 and 2005, 5 million people came out of extreme poverty, more still needs to be done. Liberia has the highest proportion of poor people in the world. A shocking 83.7% of the country live below the $1.25 a day line. Even in the US, the poorest 40% of Americans own 0.3%, a tiny fraction of the country's wealth, while the top 20% own about 85% of the total wealth of the nation. In India, despite the country is generally becoming wealthier, over 40% of the population, about 500 million people, live below the international extreme poverty line. In Vietnam, about 1 third of the people have lifted themselves out of poverty since the 1980s. The average income went from $100 a year in 1986 to $1,130 by the end of 2010. In 1981, 85% of the population that lived in China are living on less than $1.25 a day. In 2005, that figure was 16%, and it's still falling. Over 660 million people have come out of poverty in China since the 1980s. Beautiful, rare, and highly prized, gold has been mined since the ancient Egyptian times. Sometimes a discovery of gold led to a gold rush, with thousands of people flocking to the site in hope of making their own fortune. China is the world's largest gold producer, extracting 376 tons in 2010. With 276 tons mined in 2010, Australia is the second largest gold producing nation. Found in Australia in 1869, Welcome Stranger was the biggest gold nugget ever found. It contained 156 pounds of gold. The U.S. is the world's third largest gold producer, mining 250 tons annually. Of the 182,000 tons of gold now above ground, more than half is now jewelry. One-fifth is stored as reserves in central banks. Some of the rest exist as parts in engineering, such as electric cables and protective coatings on spacecraft. Still more is in the hands of investors waiting for the right time to sell. All the gold that has ever been mined would make a cube of 67 feet along each side. Some billionaires inherit wealth, others get rich through banking, making or trading goods, or inventing new things. Not surprisingly, billionaires tend to be concentrated in more prosperous nations. This map shows the citizenship of the world's richest people and value of their fortunes in billions of U.S. dollars. The U.S. has the world's largest economy worth around $15.5 trillion and the world's third largest population. In 2011, Africa was the continent with the fewest billionaires, just 14 of them. Some examples of billionaires include Bill Gates, who founded Microsoft software firm in 1975 and now devotes himself to charity work. Since 1994, the Bill and Melinda Gates Foundation has given more than $23.5 billion to charitable causes. Another example would be Lillian Betancourt, who is a principal shareholder in the cosmetics and beauty company L'Oreal. Jeff Bezos, who founded Amazon in 1994, is also a billionaire. And Amazon is now the world's largest online store. And Facebook's Mark Zuckerberg was a billionaire by the age of 23. He co-founded Facebook, the social networking site, in 2004 while at Harvard. And Carlos Salim Heylou is a telecommunications tycoon and is the richest person in the world.