5 'facts' you learned in school that are no longer true

1. THEN: AMERICA WON ITS INDEPENDENCE ON JULY 4, 1776

• NOW: AMERICA WAS NOT OFFICIALLY INDEPENDENT UNTIL SEVEN YEARS LATER, IN 1783.

Every year on July 4th, Americans celebrate Independence Day with parades, barbecues, and fireworks.

But while the Declaration of Independence was adopted by 12 colonies on July 4, 1776 and signed by 13 colonies in August, America was not yet free from Great Britain's rule.

The American Revolution waged on for years. Finally, the Treaty of Paris was signed on September 3, 1783, and America became free.

     

  2.   THEN: GEORGE WASHINGTON'S TEETH WERE MADE OF WOOD

NOW: Washington's teeth were human teeth from his slaves and also made from ivory.

A set of dentures that George Washington wore are kept at the Mount Vernon plantation house museum. The dentures are fashioned out of ivory and human teeth.

While historians note the "limitations of history" when sourcing Washington's human teeth back to the individuals they were taken from, written evidence shows Washington purchased teeth from slaves and made note of it in one of his ledgers.

Slaves during the 18th century sometimes sold their teeth to dentists to make money. In 1784, Washington "paid several unnamed 'Negroes' ... 122 shillings for nine teeth, slightly less than one-third the going rate advertised in the papers," according to PBS.

Washington likely then had the teeth implanted into his jaw in a surgical procedure common at the time.

3. THEN: PLUTO IS A PLANET

NOW: PLUTO ISN'T A PLANET

We've known since the late 1800s that a ninth planet, after Uranus, potentially existed. In 1906, Percival Lowell, the founder of the Lowell Observatory in Flagstaff, Arizona, even began a research project intended to locate the mysterious "Planet X."

Then in 1930, a 23-year-old newbie at the facility found it. The discoverer, Clyde Tombaugh, had been tasked with systematically comparing photographs of the sky taken weeks apart to search for any moving objects. He eventually saw one and submitted his finding to the Harvard College Observatory. After an 11-year-old English girl named the new planet (for the Roman god of the underworld), we started including Pluto as a planet in our solar system.

But in 2003, an astronomer found a larger object beyond Pluto - which he named Eris, according to NASA. The new information caused a bunch of other astronomers to question what really makes a planet a planet, and they decided, based on size and location, that Pluto just didn't make the cut. Neither did Eris, actually. Pluto was demoted to a dwarf planet.

Needless to say, elementary schools kids were pretty bummed.

But there may be hope. Researchers have recently been debating whether to make Pluto a planet again.

                 4. THEN: DIAMOND IS THE HARDEST SUBSTANCE

NOW: Ultrahard nanotwinned cubic boron nitride is the hardest substance

We've known about two substances harder than a diamond since 2009: wurtzite boron nitride and lonsdaleite, according to Scientific American. The first resists indentation with 18% more fortitude than a diamond, and the second - a whopping 58%.

Unfortunately, both substances are rather unusual and unstable in nature. In fact, the study's authors, published in the journal "Physical Review Letters," only calculated the new substances' hardness, instead of actually testing it using a tangible specimen. That makes the discovery a bit theoretical.

But another contender was published in the January 2013 issue of the journal Nature. In the simplest terms, researchers compressed boron nitride particles to form "ultrahard nanotwinned cubic boron nitride." They simply re-organized the particles like an onion, or a flaky rose, or those little Russian dolls that fit inside one another, as the team explained to Wired.

As a result, expect women everywhere to start asking for ultrahard nanotwinned cubic boron nitride engagement rings. Because those really are forever.

5. THEN: DIAMOND IS THE HARDEST SUBSTANCE

NOW: ULTRAHARD NANOTWINNED CUBIC BORON NITRIDE IS THE HARDEST SUBSTANCE

We've known about two substances harder than a diamond since 2009: wurtzite boron nitride and lonsdaleite, according to Scientific American. The first resists indentation with 18% more fortitude than a diamond, and the second - a whopping 58%.

Unfortunately, both substances are rather unusual and unstable in nature. In fact, the study's authors, published in the journal "Physical Review Letters," only calculated the new substances' hardness, instead of actually testing it using a tangible specimen. That makes the discovery a bit theoretical.

But another contender was published in the January 2013 issue of the journal Nature. In the simplest terms, researchers compressed boron nitride particles to form "ultrahard nanotwinned cubic boron nitride." They simply re-organized the particles like an onion, or a flaky rose, or those little Russian dolls that fit inside one another, as the team explained to Wired.

As a result, expect women everywhere to start asking for ultrahard nanotwinned cubic boron nitride engagement rings. Because those really are forever.