Scientists closely observe the planet in attempts to figure out its true age.
Observation is a scientist's main tool when attempting to date the Earth, the galaxy and the universe. By observing how chemicals break down here on Earth, scientists have uncovered methods for dating rocks and other materials. The Earth is ever-changing and by looking to the heavens, scientists are able to find solar bodies that are not affected by atmospheric changes. There are some assumptions that must be made in order to confidently use these methods of dating and, because of this fact, nothing has been proven.
Radiometric Dating
Radiometric dating provides a large leg on which scientists stand when dating the Earth and solar system. It involves isotopes of radioactive elements contained within rock. Over time, radioactive elements change into different elements at a fixed rate. By measuring how much of the original element versus how much of the new element is contained within a rock sample, scientists extrapolate how old the rock is. This is not the age of the rock's parent material, rather it is the age at which the rock was made in the Earths crust.
Oldest Rocks
The oldest rocks found on Earth so far have been found in northwestern Canada, western Greenland and northern Michigan, and date between three and four billion years old. In western Australia, scientists have discovered crystals dating to 4.2 billion years old. This does not significantly date the Earth, but it tells scientists at least how old it is. From these old rocks they are able to deduce that the Earth is at least 4.2 billion years old.
Space Rocks
By assuming that all of the solar bodies in the Milky Way solar system are roughly the same age, scientists get even more accurate dating techniques. Because plate tectonics do not destroy and recycle material on meteorites and the Moon, these stones have been of particular interest. It is unlikely that the Earth existed before the solar system, so if scientists date rocks from the solar system they are more accurately able to theorize the age of the Earth. It is through this method that scientists have come up with the 21st century estimated age of the Earth at 4.54 billion years.
Universe
By assuming that the big bang theory is correct, and deducing that at one time all of the elements in the universe were contained within a single point, scientists estimate the age of the universe. Since the time of the big bang, the universe has been expanding. Scientists search the furthest regions of space for objects like white dwarfs. After observing these items and becoming familiar with their life cycles, scientists can tell how old they are. The faintest, furthest objects in the universe are the oldest, giving scientists a frame of reference for dating the Universe. As of 2011, the universe is estimated to be 13 billion years old.
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