We learned a lot in 2017, but some circumstances remain a mystery.
From why octopus suddenly walked out of the ocean, to what's inside the mysterious void of an ancient Egyptian pyramid, these were some of 2017's most mysterious finds in our natural world.
Ancient's Egypt's Great Pyramid has inspired theories, both conspiratorial and historical, for centuries, and a new discovery of a mysterious void has added to the mystique. The void is 153 feet long and 26 feet tall, and it lies above the corridor leading to the burial chamber of Khufu, an Egyptian pharaoh.
Is the void one or several rooms? What's inside it? What purpose did it serve? These are questions that remain to be answered.
Archaeologists have yet to access the void in person. That's because it was found using muon radiography, a type of imaging that uses subatomic particles to peer through walls or solid structures.
"I've never seen anything that parallels it," said Philip de Jersey last October. He's the state archaeologist for the Guernsey Museum and Galleries, and he's referring to the skeletal remains of porpoise bones found on a small Guernsey island in the English Channel.
The bones were carefully arranged in a small, cleanly cut grave on grounds just outside a monastic retreat.
Two theories prevailed for why the bones were so neatly aligned: the porpoise was caught for food and leftover meat was buried, or the burial was a component of a religious ceremony. de Jersey kept a video diary of the excavations at the retreat.
In his last post on Oct. 2, he still did not know more about why the bones were buried. National Geographic reached out to de Jersey for more information but has not heard back yet. The next step was to try carbon dating on the remains, to see if that provides any more clues.
At the beginning of September, astronomers heard 15 blasts of radio waves hurling through space. Astronomers described the blasts as fleeting but extremely powerful.
The bursts are coming from a galaxy that's roughly three billion light-years away. Scientists still aren't sure what powers these energetic blasts, but they occasionally come from locations with strong magnetic fields.
It wasn't the first time these waves were detected in this galaxy. They were first identified in 2007 and about two dozen have been heard since.
It's not unusual to see an octopus hop out of one tide pool to jump into another. But in late October, more than two dozen of the invertebrates were spotted walking on land in Wales. According to one local who had lived in the sea-side town for his entire life, nothing comparable had ever happened before.
We reached out to several experts at the time, who provided three theories: The first was that the octopuses were going through what's called senescence—essentially, they had gone senile. Octopuses usually live for only a year and die soon after they lay eggs. Because October is around the time that they finish laying eggs, it's possible they were showing the cognitive decline associated with senescence.
Another theory was that two recent major storms, Hurricane Ophelia and storm Brian, had displaced the creatures from the water.
Other theories cited a 2016 study in Current Biology that found octopus populations were booming and possibly forcing the creatures to travel farther in search of food and shelter. In the weeks that followed, octopuses were still found walking on land, but reported sightings seem to have stopped by around mid-November.
From February to July, thousands of sharks and rays washed up dead in San Francisco Bay. Exactly why had been a mystery until scientists were able to analyze DNA from some of the dead sharks.
They found that a brain-eating parasite was crawling up their noses and eating their grey matter.
We may know what parasite was likely eating shark brains, but we still don't know why now or where exactly it came from. According to the researchers who examined the remains, it's the first case of this specific pathogen infecting wild sharks. Scientists have theorized that crowding in the bay has allowed the parasite to spread more efficiently. Higher than average rainfall could also be impacting the water's salinity, which might impact sharks' immune systems.
Blue dogs were first documented in India in mid-August. The domestic canines were seen roaming through a heavily industrialized neighborhood in Mumbai. Eventually, locals discovered that the dogs had waded through wastewater, which had turned their fur blue.
The dye was found to be non-toxic and easily washed out of their fur, but it sparked local outrage over who polluted the water and how dogs were able to access it.
India has some of the strictest animal rights laws in the world, and it's illegal to kill a healthy stray.
The Maharashtra Pollution Control Board was tasked with investigating the incident but never released the name of the company or the specific chemical causing the blue color.
In the reports from journalists on the ground that followed in the weeks after the dogs were found, they noted the dye may have been released by more than one factory. In this heavily industrialized zone, factories have been running since the 1960s and implementing pollution control laws remains difficult.
What happened to Amelia Earhart? The pioneering aviator mysteriously disappeared 80 years ago, and researchers, historians, and Earhart's fans have been searching for her remains ever since.
In July, four forensic dogs identified an area on Nikumaroro Island, Kiribati, where Earhart may have died. Kiribati is a small island nation in the central Pacific. A British official reported seeing human bones in one region in 1940, and searchers located possible remains of an American castaway in 2001.
Other alleged evidence has turned up in the past decades pointing to other fates, but most has been discredited, like this photograph. Scientists say something firmer like a bone or DNA could really help solve the case.
This summer, the dogs detected a lingering scent of human bones but no actual remains were found. In a last-ditch effort, researchers sent soil samples to a German lab to see if any DNA was present. No results are yet available
When this article was written in late June, six whales had been found dead and wildlife conservationists were scrambling to find out why. By August, the death toll was at 10. As the year comes to a close, a total of 17 North Atlantic right whales will have been found dead in or around the Gulf of St. Lawrence in Canada.
Before this year, North Atlantic right whales had already been considered one of the world's most endangered whale species. Only about 450 are left. The sudden, unexpected spike in deaths is now leading some experts to predict that the species could go extinct in 20 years.
So why are so many dying so suddenly?
To determine cause of death, scientists have been performing necropsies on the carcasses that aren't too decomposed. On some of the carcasses, they've found injuries consistent with ship strikes. Entanglement in fishing gear is also frequently cited as a cause of death. One investigation published in the journal Endangered Species Research looked at the feces of living and dead whales from the past 15 years. They found "sky-high hormone levels" indicating the whales were under extreme stress. Another study published in Nature Scientific Reports found that the population may be changing its distribution, meaning the whales are swimming outside of protected areas.