A Whale's earwax is like its diary, leaving a record of the every year the giant marine mammal lived and what chemicals it was exposed to. The large "earplug" can also give humans an idea of their impact on wildlife and the environment.

Whales have a buildup of wax in their protected inner ear called an "earplug." The gradual buildup of wax forms layers which can be used similarly to tree rings, a Proceedings of the National Academy of Sciences press release reported.

The researchers studied an ear plug taken from a 12-year-old deceased blue whale and were able to create a profile of the animal's hormone levels and exposure to man-made chemicals throughout its life.  

"It might be the only life history of any free-ranging animal," Stephen Trumble, a marine biologist at Baylor University, told NBC News.

The 10-inch-long earplug taken from the whale was said to "]look] like a piece of striped bark but [feel] firm, like a candle."

"Oh my gosh, I can't even explain it, they smell terrible," Trumble told NBC,

Twenty-four bands each representing a six-month period told the story of the whale's life. Biologists have estimated a blue whale hits puberty between the ages of five and 15 years of age. With the tell-all earwax they were able to determine the whale hit puberty at around 10 years of age.

Right around the time of puberty the team noticed a spike in a hormone called cortisol, which is released in times of stress.

"I saw that and I just chuckled," Trumble said. "It was mixing with the big guys trying to mate, and probably getting a rough time from the other males."

The researchers also noticed that the whale had been exposed to "an unusual amount of toxins" while in the womb, which confirmed mother whales can pass pollutants to their young, NBC reported.

High levels of mercury in one layer of earwax suggest the whale resided in an exceptionally polluted area of the ocean at one point.

Whale's swim across thousands of miles of ocean during their lives, which is more than researchers, could ever hope to see in one study. The team is already making plans for the future.

"We have a female earplug from 1964 we're really excited about," Trumble told NBC. There are hundreds of other earplugs sitting in museums, waiting to tell their secrets.