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Millions of Years Ago, the Caribbean Flooded the Amazon Rain Forest—Twice

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Long before the trees of today’s Amazon reached for the sky, scientists say, sharks weaved through salty waters there, and mantis shrimp rattled across the flooded forest floor. The researchers published their findings in the journal Science Advances.

Scientists have known for some time now that an area of the western Amazon basin was underwater millions of years ago. The exact source of that water has been the subject of some dispute. Some researchers have envisioned a wide river sweeping down from the Andes, while others say the inundation must have washed inland from the sea. But neither side had compelling evidence to support their ideas—until now.

The researchers studied two nearly-2000-foot-long sediment cores, one taken by an oil company in eastern Colombia, and the other taken across the border in northwestern Brazil by Brazilian Geological Survey. Each was packed with the natural detritus of millions of years of local life.

The bulk of each core told the story of a world on dry land, but within two thin slices—one from about 18 million years ago, another from about 12 million years ago—a glimmer of the sea appeared. The complete cores contained a total of 933 different types of pollen grains. The thin slices included types of pollen only found in salt water.

Bigger clues were yet to come: The researchers also found a fossilized shark tooth and the remains of a mantis shrimp. “It’s a lost ecosystem,” lead author Carlos Jaramillo, of the Smithsonian Tropical Research Institute, told Lizzie Wade in Science.


Carcharhiniformes indet. tooth from the Saltarin core, Carbonera C2 Formation, early Miocene flooding.
Jorge Carillo


A modern Carcharhinus shark, similar to the fossil shark found in the early Miocene flooding.

Lasting a few hundred thousand to a few million years, each flood period was relatively brief from a geological perspective, Jaramillo says. But they weren't so brief that they didn’t completely alter the landscape.

“The life span of a single Amazonia canopy tree is about 200-400 years,” he tells Mental Floss. “Therefore, for thousands of generations, not a single tree could occupy Amazonia. In other words, the immense forest we see today is geologically young.”

The findings came as a surprise even to Jaramillo and his colleagues. He added, “I was of the opinion that there were no floodings, but it turned out I was mistaken!”

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Can You 'Hear' These Silent GIFs?
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GIFs are silent—otherwise they wouldn't be GIFs. But some people claim to hear distinct noises accompanying certain clips. Check out the GIF below as an example: Do you hear a boom every time the structure hits the ground? If so, you may belong to the 20 to 30 percent of people who experience "visual-evoked auditory response," also known as vEAR.

Researchers from City University London recently published a paper online on the phenomenon in the journal Cortex, the British Psychological Society's Research Digest reports. For their study, they recruited more than 4000 volunteers and 126 paid participants and showed them 24 five-second video clips. Each clip lacked audio, but when asked how they rated the auditory sensation for each video on a scale of 0 to 5, 20 percent of the paid participants rated at least half the videos a 3 or more. The percentage was even higher for the volunteer group.

You can try out the researchers' survey yourself. It takes about 10 minutes.

The likelihood of visual-evoked auditory response, according to the researchers, directly relates to what the subject is looking at. "Some people hear what they see: Car indicator lights, flashing neon shop signs, and people's movements as they walk may all trigger an auditory sensation," they write in the study.

Images packed with meaning, like two cars colliding, are more likely to trigger the auditory illusion. But even more abstract images can produce the effect if they have high levels of something called "motion energy." Motion energy is what you see in the video above when the structure bounces and the camera shakes. It's why a video of a race car driving straight down a road might have less of an auditory impact than a clip of a flickering abstract pattern.

The researchers categorize vEAR as a type of synesthesia, a brain condition in which people's senses are combined. Those with synesthesia might "see" patterns when music plays or "taste" certain colors. Most synesthesia is rare, affecting just 4 percent of the population, but this new study suggests that "hearing motion synesthesia" is much more prevalent.

[h/t BPS Research Digest]

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The Surprising Link Between Language and Depression
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Skim through the poems of Sylvia Plath, the lyrics of Kurt Cobain, or posts on an internet forum dedicated to depression, and you'll probably start to see some commonalities. That's because there's a particular way that people with clinical depression communicate, whether they're speaking or writing, and psychologists believe they now understand the link between the two.

According to a recent study published in Clinical Psychological Science, there are certain "markers" in a person's parlance that may point to symptoms of clinical depression. Researchers used automated text analysis methods to comb through large quantities of posts in 63 internet forums with more than 6400 members, searching for certain words and phrases. They also noted average sentence length, grammatical patterns, and other factors.

What researchers found was that a person's use (or overuse) of first-person pronouns can provide some insight into the state of their mental health. People with clinical depression tend to use more first-person singular pronouns, such as "I" and "me," and fewer third-person pronouns, like "they," "he," or "she." As Mohammed Al-Mosaiwi, a Ph.D. candidate in psychology at the University of Reading and the head of the study, writes in a post for IFL Science:

"This pattern of pronoun use suggests people with depression are more focused on themselves, and less connected with others. Researchers have reported that pronouns are actually more reliable in identifying depression than negative emotion words."

What remains unclear, though, is whether people who are more focused on themselves tend to depression, or if depression turns a person's focus on themselves. Perhaps unsurprisingly, people with depression also use more negative descriptors, like "lonely" and "miserable."

But, Al-Mosaiwi notes, it's hardly the most important clue when using language to assess clinical depression. Far better indicators, he says, are the presence of "absolutist words" in a person's speech or writing, such as "always," "constantly," and "completely." When overused, they tend to indicate that someone has a "black-and-white view of the world," Al-Mosaiwi says. An analysis of posts on different internet forums found that absolutist words were 50 percent more prevalent on anxiety and depression forums, and 80 percent more prevalent on suicidal ideation forums.

Researchers hope these types of classifications, supported by computerized methods, will prove more and more beneficial in a clinical setting.

[h/t IFL Science]

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