SuperSmart Carbon: A Science Blog for Families

How Old is the Earth?

My daughter recently asked me, “How old is the Earth?” I thought for bit and guessed 2 billion years old. My rationale was that dinosaurs first roamed the Earth about 200 million years ago, so 2 billion years seemed sufficiently long. I was wrong. Scientists estimate that the Earth is about 4.5 billion years old.
 

To determine the age of the Earth, scientists study rocks and use a process called radiometric dating to determine the age of the rocks. Geologists have discovered rocks that are at least 3.5 billion years old on each of Earth’s continents. In north central Canada, scientists discovered a rock formation named the Acasta Gneiss that is 4.2 billion years old. These are the oldest known rocks from the Earth’s crust. Click here to go to the website for Dr. Yuichiro Ueno to see photos of the region of Canada and the rocks – item 3 includes photos from his research activities at the Acasta Gneiss complex.
 

Unfortunately, looking at the age of rocks formed on Earth is not sufficient to fully prove the age of the Earth. Scientists believe that most of Earth’s oldest rocks have been destroyed over time due to plate tectonics. All of the continents and oceans sit on plates that are constantly moving and over time, the plates collide into and cover each other. This process, over the history of the Earth, has destroyed most of the original rocks on the Earth’s crust. Thus, scientists have looked to space to determine the age of the Earth.
 

Scientists believe that Earth, the Moon, other planets and meteors in the Solar System all formed at about the same time. Using this premise, scientists have studied meteors and Moon rocks to determine the age of other items in the solar system. Scientists have used radioactive dating on Moon rocks and meteorites and have determined that those rocks formed between 4.53 and 4.58 billion years ago. Since the Earth is the same age as other objects in the Solar System, it must also be 4.5 billion years old.
 

Scientists estimate that the Milky Way Galaxy formed 11 to 13 billion years ago and the Universe formed 10 to 15 billion years ago.
For more information on the age of the Earth, please see this information from the US Geological Survey.