Carbon Dating

How do scientists determine the ages of fossils, artifacts, and stones? When archeologists dig up fossils and artifacts they do not come with tag telling us the approximate time period they are from. There are multiple ways to do this, radio carbon dating is the most exact way to do this.
Carbon is a building block of life. All that was once living has carbon within it. Carbon has an isotope (or variation with a different amount of neutrons) number 14. That means it has 8 neutrons and 6 protons. The unstable carbon converts to nitrogen 14 through a process in which the extra neutron turns into a proton. Thus, they have 7 protons and 7 neutrons.

Carbon decays happens slowly over thousands of years. It has a half life of 5,500 years. That means that 5,500 years is the approximate time when half of the carbon has decayed into nitrogen. Carbon has an infinite number of half lives, each half of the half life before them. Using this system of half lives, scientists measure the amount of carbon and the amount of nitrogen in the fossil. From that data they are able to check how old the fossil is. For things like rocks without carbon in it, they look at the layer it was found in. Lower layers are older while layers higher up are newer. If they know the age of the fossil in the same layer as the rock they are able to determine the approximate age.
Source: http://phet.colorado.edu/

Becoming Human: Video on NOVA

Among  most scientists it is agreed that humanity’s closest link is to chimpanzees. In 1973, the Australopithecus Lucy was discovered in the Afar Triangle of Ethiopia. Her discovery was groundbreaking. Her skeleton was nearly complete. She is an important link between humans and chimpanzees. Another fossil from around the same time is Salam, the skull, shoulder blades, and spine of 3.3 million year old child. Paleoanthropologist Zeray Alemseged spent five years carefully excavating the sandstone-embedded fossil. It reveals clues about the brain development of our ancestors. For thousands of years our brain size pretty much remained the same, but beneath the surface, tiny, key changes  were happening.

Scientists are not quite sure why humans evolved from tree climbing chimps to animals that walk upright. One theory is that as the climate of lush Africa became drier, it became necessary to conserve more energy. Chimpanzees can walk but they need to exert more energy than a human to do so. They are mores suited towards walking for short periods of time. As the temperature increased, it was imperative to  walk further and further distances in order to obtain food. Chimpanzees  gradually evolved so that their walking became more energy efficient. The hips of humans and chimps are startlingly different. For chimpanzees the hip bones face forwards, they are in the same line as the spine. Meanwhile, in humans the hips are angled slightly. Salam may not have had comparable brain capacity to homo sapiens but the hip bones show we were starting to tilt.