Hi there! I’m Doug, and I want to share a cool story with you. Behind my house, there’s a patch of dirt. One day, after it rained, I found something interesting on the ground. It was a round object, and when I picked it up and cleaned it, I realized it was a nickel from 1927. That’s almost 100 years old! It made me think about how long people have been around in different places.
Someone named Anthony asked a great question: “How old is the Earth?” To answer that, let’s first think about how we know our own age. We celebrate our birthdays and use calendars to count each year. But calendars haven’t always been around, so we can’t use them to figure out the Earth’s age.
Instead, we can look at nature for clues. Have you ever heard about tree rings? Each ring inside a tree represents one year of growth. By counting the rings, we can tell how old a tree is. The oldest trees, called bristlecone pines, have about 4,000 rings. So, the Earth must be at least 4,000 years old, right?
But what if the Earth is even older than the oldest trees? Scientists have found another way to tell the Earth’s age by looking at rocks. Rocks form in layers, just like tree rings. For example, sandstone is made from sand that settles in layers over time. By studying these layers, scientists can estimate how long it took for them to form.
If a one-inch layer of sandstone takes 100 years to form, and there’s 100 feet of it, scientists can calculate that it took over 100,000 years for that rock to form. By adding up all the rock layers on Earth, scientists realized the Earth is much older than just a few thousand years.
Recently, scientists found an even better way to figure out the Earth’s age using something called radioactivity. By studying tiny particles in rocks, they discovered that the Earth is not just millions of years old, but billions! Today, scientists believe the Earth is about 4.5 billion years old.
So, the Earth has been around for a really long time—4.5 billion years! We know this because of the clues we find in rocks. Thanks to Anthony for asking such an interesting question! Remember, there are mysteries all around us, so stay curious and keep exploring!
Tree Ring Exploration: Find a small branch or log with visible rings. With the help of an adult, carefully count the rings to determine the age of the tree. Discuss how each ring represents a year of growth. Imagine if the tree could talk, what stories might it tell about its life and the changes it has seen over the years?
Rock Layer Experiment: Create your own “rock layers” using different colored sand or soil in a clear jar. Each layer represents a different period of time. Discuss how scientists use real rock layers to understand the Earth’s history. How many layers can you create, and what do you think each layer might represent in the Earth’s past?
Time Travel Imagination: Imagine you have a time machine that can take you back to when the Earth was just forming. Draw a picture or write a short story about what you might see and experience. How different do you think the Earth looked back then compared to now?
Here’s a sanitized version of the transcript:
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Hi, it’s Doug. Behind where I live is a patch of dirt. I came out here recently after it had rained and noticed something lying on the ground. Right on top of the dirt was this round object. I bent over and picked it up, then cleaned it off, and that’s when I realized it was a nickel from the year 1927. It’s almost 100 years old. While it may not be worth much money, it made me think about the fact that someone must have been standing in this exact spot nearly a hundred years ago. Every place around us has been a place long before we were born.
Someone named Anthony has a question related to this. Let’s give him a call now.
Hi, Doug. Hi, Anthony. I have a question for you: How old is the Earth? That’s a great question! Before we tackle the challenge of figuring out how old our entire planet is, think of something more familiar first. How do you know how old you are? Well, you know your birthday and you use a calendar to count each year as it goes by. The problem is this doesn’t work for counting how many years old the Earth is because the idea of counting years on a calendar isn’t something we’ve always done. The calendar is something we invented, and we only started counting years once we invented it. In fact, looking at our calendar, you can see almost exactly how long we’ve been counting years—about 2,000 years. That means there were lots of years before the invention of the calendar, years that nobody kept track of.
But what if I told you that you don’t need a calendar to keep track of years? There are other things in nature that can help us keep track of years. You probably already know about one of these things. Can you think of anything in nature that keeps track of years? Now would be a good time to pause the video and discuss.
Okay, you ready? Something like this: the rings inside a tree. Maybe you’ve heard about this before. Each ring inside a tree equals one year. You can count the rings inside a tree and find out how old that tree is. This works because as a tree grows, it creates a dark layer during late summer every year. Unfortunately, trees only create rings as long as they’re alive. The oldest living trees, called bristlecone pines, have around 4,000 rings. So that means the Earth is at least 4,000 years old.
But what if the Earth is older than the oldest tree? And surely it is, right? Is there anything besides trees that leaves behind some kind of layer every year, something we could count? There is—in rock. It’s not quite as obvious as tree rings, but scientists have realized that the solid ground under our feet contains layers. Rock, like this big section of sandstone, started out as sand that got carried by a stream and laid down in layers, slowly, one layer at a time. It doesn’t always make nice, neat light and dark layers the way a tree does, but by figuring out how long it takes for a layer of sandstone to form, scientists can measure how thick this rock is and then get a sense of how long ago this section of rock started to form.
For example, say that it takes 100 years for this little one-inch section of sandstone to get laid down by a river. If there’s 100 feet of rock here, then scientists can do some simple math and realize it took over 100,000 years just for this section of rock to form. By adding up all the different layers of rock on Earth, scientists started to realize that the Earth is much, much older than just thousands of years old. Just by looking at layers of rock, scientists became convinced that the Earth must be at least millions of years old.
More recently, scientists have discovered an even better way of figuring out how old the Earth might be. Using microscopes and advanced knowledge of something called radioactivity, scientists can break open rocks and find evidence that the Earth is even older than millions of years—it’s thousands of millions of years old, or in other words, billions. If you ask a scientist today, their current best estimate for the age of the Earth is 4,500 million years old, or 4.5 billion years.
In summary, we think that the Earth has been around for at least 4,500 million years. We base this on evidence or clues we get from rocks. That’s all for this week’s question. Thanks, Anthony, for asking it! Now for the next episode, I reached into my question jar and picked out three questions submitted to me that I’m thinking about answering. When this video is done playing, you’ll get to vote on one. You can choose from: How do you make cardboard? Do all plants grow from seeds? Or why do we have eyebrows? So submit your vote when the video is over. I want to hear from all of you watching. There are mysteries all around us. Stay curious, and see you next week!
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