Have you ever wondered how scientists learn what a rock is made of, how it was formed, and when it was formed? In this activity, you’ll make your own “rock” and then use simple tools to explore inside!

Materials for this activity laid out on a wood table


Close-up image of a dark gray and black speckled rock

1. Learn about rocks on Earth and the Moon

Watch this video to learn about the three classes of Earth rocks – igneous, sedimentary, and metamorphic – and the three types of rocks found so far on the Moon: basalt and anorthosite, which are igneous rocks, and breccia, a type of sedimentary rock. We can tell what type of rock we're looking at, how it formed, and how old it is by studying its characteristics. These characteristics include the rock’s appearance (both inside and outside) and composition.

About the image: A Moon rock sample collected by the Apollo 14 mission. › Full image and caption
Side-by-side images of rounded rocks in an outcropping on Mars and Earth

2. Learn about rocks on Mars

Scientists are still learning about the igneous, sedimentary, and metamorphic rocks on Mars. Sedimentary rocks can give us a glimpse into the history of Mars if we are able to analyze the layers and the materials inside the rock. Because humans haven’t yet been to Mars, we rely on robots, like Mars rovers, to explore and report back on their findings.

Scientists are especially interested in a type of sedimentary rock called a conglomerate. These rocks are made up of small pebbles of other rock types cemented together. Conglomerates are interesting to scientists because the rounding of the pebbles indicates that water once eroded, or ate away at, these rocks. And where there was once water, there might have once been life. (Scientific evidence indicates that life forms, if they existed on Mars in the past, would likely have been microscopic.)

NASA’s Perseverance rover is specially designed to investigate rocks like conglomerates as part of its mission to seek signs of ancient microbial life and collect rock and soil samples for possible return to Earth.

About the image: The image above, captured by NASA's Curiosity rover on Mars, shows an outcropping – an area where ancient bedrock underneath the surface is exposed. Outcroppings on Earth are known to form as a result of running water and create gravel that's a similar size and shape. By comparing this image of Mars to similar features on Earth, geologists have been able to theorize that Mars might have also once had running water. › Full image and caption
Close-up image of two long cylindrical samples of grayish brown lunar rock and soil

3. Learn how scientists plan to study Mars rocks

The Martian atmosphere has weathered the exterior of rocks on Mars for billions of years, erasing much of the information we might gather from simply looking at a picture of a rock. To gather more information from a given rock sample, we need to drill into the rocks and retrieve samples from inside. Scientists call this process core sampling.

A core sample is a long narrow piece of rock obtained by drilling into a rock with a special tool that lifts out an intact part of the rock. In-depth study of core samples requires a science lab full of equipment – something we don’t yet have on Mars. So, we must return these samples to Earth for study.

NASA’s Perseverance rover will be taking core samples of Mars rocks that could be brought to Earth someday and studied in more detail. Mars rock core samples will be stored in special caching tubes that Perseverance will leave on the surface for a future mission to collect and bring to Earth.

About the image: This image shows core samples collected from the Moon. › Full image and caption

Collage of images showing a person starting with one color of play dough, adding chunks of various colors with pepper mixed in and covering everything with the base color

4. Make a conglomerate rock using play dough

  1. Choose one color of play dough that will make up most of your rock and cement your other rock pieces together.
  2. From the other colors of play dough, form pea-size and marble-size spheres of play dough to represent inclusions, or material trapped inside a rock during its formation.
  3. If you have cake sprinkles, ground pepper or sand, mix some into one or more colors of play dough. Mix a lot into one or more small spheres of play dough until it becomes stiff and grainy, then form it into a cube – this will represent harder rocks.
  4. Grab a chunk of your main color of play dough that will become the bottom of your rock. Flatten it onto the piece of paper. Add the spheres and cubes of other colors and chunks of the main color and press them all together to form a rock.
  5. Cover your rock with the main color of play dough so it looks like the rock is one color. This represents the weathering that can oxidize, or change the surface by chemically reacting with oxygen, rock surfaces on Mars.

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A person holds a completed play dough rock

5. Trade your rock

If possible, trade your rock with another person, so you can investigate one that is unknown! If you can't trade with anyone, find a family member who didn’t watch you make the rock and challenge them to do the next steps.

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Side-by-side images showing a person placing a straw into their play dough rock and the rock cores removed and sitting next to the rock.

6. Take a core sample

Cut a plastic straw into thirds or fourths or disassemble an old ballpoint pen and retain the straw-like cylinder.

Push an open end of the straw or cylinder straight down into the rock, all the way to the paper. Twist the straw or cylinder in place and lift out a sample.

This is a core sample of your rock. Use a toothpick, chopstick or short stick to push your core sample out of the cylinder for inspection.

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A person holds a magnifying glass over their play dough rock cores

7. Investigate your core sample

Examine your core sample. Can you see inclusions or layers underneath the surface of the rock?

Use your core sample to investigate how the rock formed over time and how many different materials it’s made of.

Compare the size and roundness of any inclusions in your core sample. The larger an inclusion, the closer to its source it is. Smaller inclusions will have traveled farther, perhaps in moving water or in a landslide or other geologic event. Rounder inclusions indicate a more active body of water that smoothed them during tumbling.

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A green play dough rock is shown with multiple cores taken out of it and sitting next to it on a table.

8. Take more core samples

Repeat steps 6 and 7 several times. Think about the best places to collect samples so that you can get as much information about your rock as possible.

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9. Draw conclusions

Use a magnifying glass to explore your core samples and a plastic knife or piece of thick paper to slice your cores into thin sections for study.

  • How many different types of rock inclusions are in the conglomerate?
  • Which color of rock makes up most of the rock? Which color makes up the least?
  • Are some inclusions or layers denser than others?
  • Do any inclusions indicate they formed in the presence of water?
  • Which inclusions are farthest from their source?

Animated image of the Perseverance rover drilling on Mars