A child thought he saw trash in a creek. It was a mammoth’s tooth.

Jeremiah Longbrake was jumping on a trampoline outside of his grandmother’s house after school last month when he decided to hop down and explore the stream that runs through her property in Winston, Oregon.

As Jeremiah, 9, approached the stream, he saw what he thought was a dirty plastic container.

He used a stick to get the object out of the creek bed “because I didn’t want to leave pollution in the water,” he said. But when he picked up the dark brown lump, he realized that it appeared to be layered and wasn’t made of plastic.

“It felt like it was a medium-sized rock,” Jeremiah said.

He ran inside to show his grandmother and his mother what he’d found.

“He came running up the steps and shouted, ‘Hey, Mom, look at this!’” said his mother, Megan Johnson, noting that the object was about the size of her son’s two fists.

“I thought it looked like petrified wood,” she said. “But when I checked it out more closely, I could see it had an odd shape, and that it was plated.”

Johnson, 31, decided to snap some photos and post them on her Facebook page in the hope that someone might be able to identify what Jeremiah had fished out of the stream that afternoon on April 11.

“People started commenting, ‘Hey, that looks like a tooth,’” she said, adding that she was confused because it did not look like any tooth she’d seen before. “So I started calling around to find an expert who could tell us for sure whether it was a tooth or just an odd-shaped rock.”

Three days and several phone calls and emails later, her family had an answer: It was a large fragment from the tooth of a mammoth, the gigantic tusked mammal that roamed Earth more than 10,000 years ago.

Patrick O’Grady, an archaeologist at the University of Oregon Museum of Natural and Cultural History, was familiar with what mammoth teeth looked like and confirmed the finding. Upon seeing the photos, he said he knew instantly what it was. Identifying most parts of ancient animal fossils is difficult, but not mammoth teeth, he said. They’re quite distinct.

“We were all pretty shocked and excited,” Johnson said. “We’ve enjoyed rockhounding in our family for years, but nobody has ever found anything like this.”

“It’s definitely much cooler than the stuff I found as a kid,” she added.

O’Grady was also enthusiastic about Jeremiah’s backyard discovery. Johnson had emailed him photos of the grooved tooth after another archaeologist in Oregon referred her to his office.

“Finding anything like this that is over 10,000 years old is really unusual, especially in western Oregon where the landscape is covered with heavy layers of soil and lots of vegetation,” O’Grady said.

“And for [Jeremiah] to pluck this from a stream bed is even more incredible,” he added. “If it had tumbled downstream in the water, the energy impact would have torn the layers of enamel to pieces after bumping into other rocks.”

O’Grady said that Jeremiah was at the right place at the right time to retrieve the fossilized tooth “before it could be lost to the ages.”

“He’s living the dream of every adult who wanted to find something like that when they were his age,” he said. “It’s really uncommon.”

Mammoths roamed the planet from about 300,000 years ago until they became extinct about 10,000 years ago, O’Grady noted.

“They could stand nine feet at the shoulder, and they got up into the 12,000-pound range,” he said. “They were also pretty widespread around this part of the country.”

A 2015 study by researchers at the University of Adelaide in Australia concluded that abrupt climate change may have caused the enormous mammals - closely related to elephants - to become extinct.

Some scientists now hope to create something similar to a woolly mammoth, one species of mammoth, through cloning, using the same process that was used in 1997 to create Dolly the sheep.

Jeremiah acknowledged that it would be cool to see a live mammoth, but he said he’s happy with a tooth, even though his friends at school initially thought it was fake when he showed it to them.

“Now they know it’s true,” he said.

Jeremiah’s grandmother estimates that the tooth was found about 100 feet from her house.

“We’ve always rock-hunted - I used to take his mom rock and fossil hunting when she was young and we’d find arrowheads and fossils of leaves,” said Rhonda Johnson, 64. “But for Jeremiah to find something like this was way beyond what any of us could figure out.”

“I’m thankful to those who got involved and identified this as a mammoth tooth,” she added, noting that some people now wonder whether the rest of the mammoth might be buried somewhere on her property.

“They ask if we’ve found anything else, but so far, no,” Rhonda Johnson said. “You never know, though. There could be. I’m just happy Jeremiah found [the tooth]. It’s been a lot of fun for him.”

O’Grady said he’d love to eventually give the tooth a close examination and perhaps send a dime-sized sample to an archaeology lab for radiocarbon dating so a more precise time frame can be determined.

That would be fine with Jeremiah at some point. His mom said he hasn’t made a decision yet whether to donate the tooth to a museum.

“He wants to hang on to it for now, because it’s his incredible find,” she said. “I hope his experience will encourage other curious kiddos to get outside and look around. There is still a lot of stuff out there, yet to be discovered.”