Coral reefs evolved 240 million years ago and today's reefs may be 5,000 to 10,000 years old.

But now scientists say coral reefs could be gone before the end of this century. The biggest threat, say the scientists, is the warming ocean water.

Three major institutions in Chicago, Northwestern University, the Shedd Aquarium and the Field Museum are now actively engaged in the fight to save the coral reefs. Elizabeth Brackett reports.

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Great Barrier Reef (Lock the Gate Alliance / Flickr)

Elizabeth Brackett: The survey results are in, and they are devastating: 93 percent of Australia’s 1,400-mile long Great Barrier Reef is now dead or in danger of dying.

The news hit Shedd Aquarium’s George Parsons hard.

George Parsons: I was pretty horrified, we knew that it may be coming but to this extent and this long, it just seems pretty astronomical.

Brackett: The worst damage is seen on the northernmost pristine part of the reef, where 50 percent of the coral is already dead and nearly all the rest is bleached.

Luisa Marcelino, Northwestern University researcher: It’s coincides a lot with El Nino events that are bringing warm water into the Pacific. We now have about a quarter of coral reefs disappeared and they are estimating that another quarter to 30-plus percent of coral reefs in the whole world may disappear within the next few decades.

Luisa Marcelino

Brackett: Northwestern University researcher Luisa Marcelino says bleaching does not kill the coral, but makes it much more likely that the reef will die.

Marcelino: They're nurseries for more than a quarter of all marine species in the world. So they're incredible centers of biodiversity and their loss will be a loss that everybody in the planet will see and will notice.

Brackett: Both the Shedd and Northwestern are involved with institutions around the world to try and save the coral reefs.

Shedd is now one of the five aquariums in the world that is growing coral to rebuild the oceans’ disappearing reefs.

Parsons: We go out and we repopulate reefs in Curacao and Mexico with coral species that we've grown up from larvae.

One of the other remarkable things that corals do is that they spawn one night a year–its usually triggered by the full moon.