Observed from space, the United States is the brightest country on the brightest planet in the Solar System because Earth's water makes it the brightest planet and the United States is abundant in artificial lighting, especially at night. Russia is the largest country in the world, Vatican City is the smallest country, and 39 million Vatican Cities could fit inside Russia. In 2011, the global population topped 7 billion people and is expected to reach 10.5 billion by 2050.
Most biologists agree that all life on Earth descended from a common ancestor, and a recent study using computer modeling and statistical methods built around DNA evidence indicates that all life descended from a single-celled organism that lived 3.5 billion years ago. Researchers with the United Nations Environment Programme estimate that the total number of species in the world today numbers around 8.7 million.
The world travels through space at a speed of 66,700 miles per hour relative to the Sun, about 490,000 miles per hour relative to the center of the Milky Way galaxy and about 2.2 million miles per hour toward the Great Attractor, a region of space about 150 million light-years from Earth.
Despite being almost completely covered in ice most of the time, Antarctica is the driest continent on Earth.