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How did one comet kill all the dinosaurs? If crocodiles, snakes and birds came from dinosaurs, did it actually kill all of them? — Mya, 11.4, Virginia

Dear Mya,

It’s hard to imagine that one space rock wiped out the dinosaurs. But it did more than that. It killed 75% of the plants and animals on Earth. Me-OW.

I talked about that with my friend Barry Walker. He teaches geology classes about Earth’s history at Washington State University.

Walker told me that we call a space rock that hits Earth a meteorite. The meteorite that took out the dinosaurs set off changes on Earth. Those changes lasted for thousands of years. That’s how it killed so many things.

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How did our planet get to be the one with breathable air? – Jacob, 11, Idaho

Dear Jacob,

When I wake up from a cat nap, I stretch and take a deep breath. It feels good to fill my lungs with oxygen.

But that wasn’t always possible on Earth.

I talked about this with my friend Sean Long. He’s a geologist at Washington State University.

“The cool thing is the answer has to do with life,” Long said. “Early life forms on Earth gave us all the oxygen. They were single-celled bacteria.”

Our planet is about 4.5 billion years old. There’s been life on Earth for 3.5 billion years. The first life forms were made of just one cell. They were bacteria and their cousins called archaea.

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What causes the oceans to rise? – Ash, 11, Kentucky

Dear Ash,

There are two ways to answer your question. One looks at why the ocean rises and falls every day. The other explores what’s causing sea level to rise over time.

I talked about both with my friend Jonathan Robinson. He’s the Beach Watchers coordinator at Washington State University Snohomish County Extension.

If you’re at the beach during high tide, the beach looks smaller because the water comes up higher onto the beach. The tides are what make that happen, Robinson told me.

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How do gems form underground? – Jett, 11, Kansas

Dear Jett,

When I was a kitten, I loved collecting rocks and gems. So, I was very excited to talk about your question with my friend Johannes Haemmerli. He studies minerals in the School of the Environment at Washington State University.

Minerals are solids that form from non-living elements in nature. They have a very specific structure for how those elements are arranged. Haemmerli told me that nearly all gems are minerals or sometimes mixtures of minerals.

You’re right that gems form underground. A diamond forms when the element carbon is buried nearly 100 miles deep inside the Earth. It’s super-hot and there’s tons of pressure down there. Eventually the pressure pushes the carbon atoms together to form the mineral we call diamond. Above ground, where there is much less pressure, the same carbon can come together and form a mineral we call graphite. That’s the “lead” of your pencil.

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How did life begin? Kelsey, 10, Texas

Dear Kelsey,

The universe is a big place. Thinking about how we fit into it is part of what makes humans (and cats like me) special.

I talked about your question with my friend Afshin Khan who studied astrobiology and environmental science at Washington State University. Astrobiologists explore how life began. They also look for signs of life outside Earth.

Khan told me your question is a huge mystery.

“We have very good ideas about what could have happened,” she said. “In different labs around the world, we’ve gotten very close to simulating some of those conditions. But simulations can only get so … » More …

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Dr. Universe: How come some rocks are easy to break and some are hard? - Natalie, 10, Russellville, Kentucky

Dear Natalie,

If you draw with a pencil, you can tell how soft the graphite inside is. Pieces of graphite break off to leave the pencil mark. But can you imagine drawing with a diamond? Diamonds and graphite are both what you might call rocks. How come they’re so different?

To find out, I talked to my friend Katie Cooper, a geologist and associate professor in the Washington State University School of the Environment. Geologists often study how different types of rocks and minerals form—and that’s the secret to whether they’re easy or hard to break.

Rocks are made of minerals, and minerals are made of elements, which are substances made of a single type of atom. You can get to know the Earth’s elements by looking at a Periodic Table.

Some minerals are made of a single element, like diamond and graphite, which are both made of carbon. Others are a mix, like limestone, which is made of calcium and carbon.

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What is a sinkhole? What causes one? - Kathrine, 12, Calgary, Canada

Dear Kathrine,

Sinkholes can be scary to think about. They don’t happen too often, but when they do, they can take people by surprise. The solid ground disappears, and a hole suddenly appears.

It might seem like sinkholes appear out of nowhere. But they actually need specific conditions to form.

To have a sinkhole, you first must have a cave.

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Dr. Universe: How do earthquakes happen? -Aescli E., 10, Utah

We’ve had a lot of earthquakes on our planet this year. Maybe you’ve learned about them from the news or felt one shaking up your own neighborhood. First, it is important to know a bit about the Earth’s outer layer, or crust. The crust is made of seven big pieces called “plates.” They are about 60 miles thick and sort of float on the molten rock beneath them. That’s what I found out from my friend Sean Long, a geology professor at Washington State University who knows a lot about earthquakes. Read More ...