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A rare rhino's death means there's just 3 left on Earth — but there's hope.

Time is ticking on the fate of the northern white rhino.

On Saturday, Nov. 21, 2015, there were a total of four northern white rhinos on our planet.

On Sunday, Nov. 22, that number dropped to three.


RIP Nola. All images from San Diego Zoo Safari Park/YouTube.

Nola, a very rare and beloved rhino, died of an infection at the San Diego Zoo on Sunday.

The zoo had been her home since 1989.

"It is with heavy hearts that we announce the death of Nola, a critically endangered northern white rhino who lived at the San Diego Zoo Safari Park," the zoo wrote on its Facebook page.

"This is a very difficult loss for the animal care staff who worked with her, our volunteers, guests, and to her species worldwide."

Nola's death puts her species in a very precarious situation — one that, sadly, could have been prevented.

As recently as the 1960s, there were more than 2,000 northern white rhinos living in the wild. But poaching and civil wars in their native habitat have led to the species' rapid decline. Today, the three surviving northern white rhinos are living in captivity at the Ol Pejeta Conservancy in Kenya.

The last male rhino, Sudan, is guarded by armed rangers 24 hours a day, seven days a week for protection.

That's how serious the threat against him is.

Scientists and conservationists are racing against time to prevent the northern white rhino from going extinct.

The chances of 42-year-old Sudan successfully mating are slim to none, which means scientists are getting extra science-y in considering assisted reproductive techniques.

The San Diego Zoo, where Nola lived, has a "Frozen Zoo" that has been preserving cell samples of these rare white rhinos. And Ol Pejeta in Kenya hopes to explore in vitro fertilization and an embryo transfer to help with reproduction. They've started a GoFundMe campaign to raise funds for it.

"The future of the species now depends on the success of assisted methods of reproductions as the surviving rhinos are not capable of mating," Ol Pejeta Conservancy said on Facebook.

Is it worth all this effort just to bring the northern white rhino population back up to four?

"We wish we could give you the ultimate answer," Ol Pejeta says. "But beyond sheer, inspirational beauty, the maintenance of global biodiversity and the chance to see wild rhinos roaming free in central Africa at some stage in the future, we can't."

Nola's death sparked the hashtag #Nola4ever, which reflects a similar sentiment.

"We all love Nola so much, and she will be missed immensely," said one Facebook commenter. "Thank you to those who took such great care of her and to those who continue to fight to end extinction."

Fighting to end extinction can have positive results — rhino species have bounced back from near-extinction extinction before. Southern white rhinos were once thought to be goners, but thanks to successful protection and management, over 20,000 of them exist today, according to the World Wildlife Fund. That's nothing to sneeze at.

Let's hope the northern white rhino will bounce back too. If you want to show support for the San Diego Zoo and help keep these special rhinos on our planet, you can get involved here.