An automobile is a self-propelled motor vehicle intended for passenger transportation on land. It usually has four wheels and an internal combustion engine fueled most often by gasoline, a liquid petroleum product. Known more commonly as a car, formerly as a motorcar, it is one of the most universal of modern technologies, manufactured by one of the world’s largest industries. More than 73 million new automobiles were produced worldwide in the year 2017.

The scientific and technical building blocks of the automobile go back several hundred years. For example, in the late 1600s, Dutch scientist Christiaan Huygens invented a type of internal combustion engine sparked by gunpowder. The “horseless carriage” in its modern form had been developed by the end of the 19th century. At that time, it was not clear which of three fuel sources would become most commercially successful: steam, electric power, or gasoline. Cars run by steam engines could go at high speeds but had a short range and were inconvenient to start. Battery-powered electric cars had a 38 percent share of the United States automobile market in 1900, but they also had a limited range and recharging stations were hard to find.

The gasoline-powered automobile won the competition. By 1920, it had overtaken the streets and byways of Europe and the United States. The manufacturing methods introduced by U.S. carmaker Henry Ford revolutionized industrial manufacturing. Ford was the first to install assembly lines in his factory to speed up production. Such techniques reduced the price of Ford’s Model T until it became affordable for most middle-class families. As the 20th century progressed, modern life came to seem increasingly inconceivable, or at least highly inconvenient, without access to a car. Nowadays, the U.S. population drives more than 4.8 trillion kilometers (three trillion miles) every year on average.

But this fundamental component of industrial and consumer society has played a major role in destabilizing Earth’s atmosphere, on which all living things depend. The average automobile emits between four and nine tons (3,629 to 8,165 kilograms; 8,000 to 18,000 pounds) of carbon dioxide and other greenhouse gases per year. Every gallon of gasoline burned to operate a car emits just under 9.1 kilograms (20 pounds) of carbon dioxide. The transportation sector as a whole, including cars, trucks, trains, and aircraft, became the largest source of U.S. greenhouse gas emissions in 2017. Air pollution from automobile exhaust is also a major problem, as are car accidents, which killed more than 100 people per day in the United States in 2016, according to the National Highway Traffic Safety Administration.