To measure the passage of long periods of time, scientists take advantage of a regularity in certain unstable atoms.
In radioactive atoms the nucleus will spontaneously change into another type of nucleus.
Recall that an isotope is a particular form of an element.
Many independent measurements have established that the Earth and the universe are billions of years old.
Researchers studying bits of a meteorite discovered that the space rock was 4.5682 billion years old, predating previous estimates of the solar system's age by up to 1.9 million years.
This adjustment, though ever so slight, should help astronomers better understand how the Inclusions are minerals that get trapped inside meteorites as the space rocks are forming.
Geologists have found annual layers in ice that are easily counted to multiple tens of thousands of years, and when combined with radio isotope dating, we find hundreds of thousands of years of ice layers.
Using the known rate of change in radio-active elements (radiometric dating), some Earth rocks have been shown to be billions of years old, while the oldest solar system rocks are dated at 4.6 billion years.
We also determined the Al was homogeneously distributed in the nebular disc surrounding the proto-Sun.
From the consistently old ages in the studied inclusion, we conclude that the proto-Sun and the nebular disc formed earlier than previously thought.
There are several ways to figure out relative ages, that is, if one thing is older than another.
For example, looking at a series of layers in the side of a cliff, the younger layers will be on top of the older layers.
Or you can tell that certain parts of the Moon's surface are older than other parts by counting the number of craters per unit area.
The age of the Solar System can be defined as the time of formation of the first solid grains in the nebular disc surrounding the proto-Sun.