Oldest Rock Speck Zeros In On Earth's Cooling Date

The oldest remaining grain of early Earth's original solid rock crust has now been confirmed to be a 4.374-billion-year-old old zircon crystal from Jack Hills, Australia.

That age should settle a scientific debate over the accuracy of that mineral's internal clock, and cuts the time from when Earth was hit by a Mars-sized body (which led to the formation of the Moon) and the cooling and creation of Earth's first solid crust from 600 million years to 100 million years.

"This, I believe, is the oldest zircon that's ever been dated on Earth," said John Valley, of the University of Wisconsin in Madison. He and his colleagues have published their findings in the Feb. 23 issue of the journal Nature Geoscience.

Previous dating of the ancient Jack Hills zircons about ten years ago had arrived at ages of about 4.4 billion years, Valley explained. But there were doubts about whether some of the atomic elements used for the dating had moved about in the crystals and thrown off the age by a few hundred million years.

"Whether a grain is 4.3 or 4.4 billion years old, and whether this reflects a primary age, is not a trivial matter," explained Sam Bowring of the Massachusetts Institute of Technology.

"In the context of the 4.4- to 4.5-billion-year age of the Earth, a difference in age of 0.1 or 0.2 billion years (100 or 200 million years) is enormous in terms of modeling the geochemical evolution of Earth and the formation and recycling of the first continental crust."

The element in question is an isotope of lead, which is created by the radioactive decay of uranium in zircons.

The age of a grain is figured by measuring the amounts of the parent uranium isotopes compared to the daughter lead isotopes. This is only accurate if no uranium or lead gets into or escapes the zircon.

Researchers were concerned that the very process of uranium decaying -- which fires out a high-speed alpha particle -- might have kicked around lead atoms in the zircons and messed things up.

"If the lead leaves, it can be concentrated somewhere else," said Valley. "The apparent age where it goes will appear older and where it has left will appear younger. What we've done is solve the lead mobility problem."

They did it by laboriously counting and mapping clusters of lead atoms in the zircon using what's called atom-probe tomography.

"It's astonishing to be able to do this," said Valley, "literally counting atoms with an atomic probe."

Valley and his colleagues found that the lead was indeed getting kicked around, but it wasn't going far enough to throw off the age of the zircon.

"I think it settles it, as far as it's possible," said Valley.

It also points the way for techniques that can be used to better study zircons from beyond Earth, said Valley. There are, for instance, zircons from meteorites that are older than the Earth -- up to perhaps 4.6 billion years old.

And Moon rocks have zircons that are dated to 4.44 billion years old (this fits with the idea that the Moon solidified more quickly because it is smaller than Earth).

In fact the Valley's research is funded, in part, by NASA's Astrobiology program in anticipation of the day when a sample-return mission to Mars brings back aspirin-sized rock samples for analysis.

"We're now establishing the tools for examining those samples," Valley said.

The researchers used a new technique to count individual atoms in the grain of rock.

All gemstones are rare; some are just harder to find than others.

In fact, there is no consensus on what is the rarest mineral or the rarest gemstone because there is no consensus on the definition of "rarity," according to the Gemological Institute of America. However, many of the stones in this series come from only one or two localities in the entire world, so in that sense, they are scarce.

Pink Star Diamond

In the image above, model Annabeth Murphy-Thomas poses with the Pink Star diamond at Sotheby's auction house in central London. The diamond was put up for auction in Geneva on Nov. 13, 2013, at $60 million, an already record price for a gemstone, and sold for $83 million. Diamond cutter Isaac Wolf of New York purchased the Pink Star diamond ring, and renamed it the Pink Dream. The diamond measures 1.06 inches by 0.81 inches (2.69cm by 2.06cm).

This Blue Moon diamond, discovered in South Africa in January, 2014, weighs in at 12.03 carats, and is the largest cushion-shaped stone in that category to ever appear at auction. The Gemological Institute of America declared the Blue Moon to be “internally flawless.” It was purchased in November, 2015, by Hong Kong businessman Joseph Lau, who spent $48 million on it for his seven-year-old daughter, Josephine.

This giant rock is said to be the biggest diamond unearthed in more than century. Second in size only to the 3,106-carat Cullinan diamond found in South Africa in 1905, this chunk was found in Botswana.

Opal is Australia’s national gemstone, and black opal is the rarest and most valuable of its kind, at times selling at prices that rival the best diamonds. The stone must have a rich, black background, but base colors come in all shades of gray, which is why opinions vary on what is a "true" black opal. Found in the Lightning Ridge area in northwestern New South Wales, black opals are natural, solid stones that absorb scattered white light, giving it brilliant spectral colors.

The Gemological Institute of America (GIA) calls musgravite "a rarity among the rare... a particular gem on our research examination 'want list.'" A very close relative of another hard-to-find gemstone, taaffeite (and often misidentified as such), musgravite was first discovered in 1967 in the Musgrave Range of South Australia. Facet grade -- the baseline measurement of how clean cut a sellable stone must be -- for musgravite was not reported until 1993. As of 2005, there were only eight musgravite specimens in the world.

Discovered in 1951 in Mogok, Burma, painite was once considered the rarest mineral on Earth. For decades, only two crystals were known to exist. It didn't obtain official gemstone status until 1957 when the British Museum conducted X-ray analysis on a sample. In 1979, a third crystal was recovered by the GIA. Today, more than a thousand crystals and crystal fragments have been found. However, only a small percentage of the rough are suitable for sale. Painite is made up of aluminium, calcium, boron, zirconium and oxygen. It gets its orange-red to brownish-red color from trace amounts of iron.

Jeremejevite is an extremely rare, aluminium borate mineral. It was discovered in the late 19th century and named after Pavel V. Jeremejev, a Russian mineralogist and engineer. Until recently, the only two known localities for jeremejevite were Mt. Soktuj in the Transbaikal region of Russia and Cape Cross, Swakopmund, Namibia. Not much is known about jeremejevite. The color is typically aquamarine, but other records show the mineral can also be dark blue, pale yellow-brown or colorless.

Red diamonds, just like any other diamonds, are made of compressed carbon. However, the brilliant red color in these diamonds is formed from a structural defect in the crystal lattice structure, which is why they are the rarest of the colored diamond collection. Only a handful have ever received the grade of "Fancy Red," meaning that they are pure red with no modifying color. Most are sold at market for millions of dollars. The Argyle mine in Australia is the primary producer of pink and sometimes red diamonds.

This transparent, blue gem first turned up in 1962 and has been found scattered throughout northern Tanzania in Africa. Ranging in color from light blue to pure blue to dark violet-blue, the deepest hues are valued most. Made popular by jewerly giant Tiffany & Co. in 1968, Tanzanite has seen wild price fluctuations over the years. Tanzania's violent political, social and economic conditions have made it difficult at times to mine the mineral. However, the nation remains the gem's only known source.

Although "red emerald” is its snazzy marketing name, and it was originally called "bixbite," this mineral goes by the name "red beryl" today. The brilliant red-purple color is not a trick of the light. The stone's actual chemistry is distinctive and separate from other beryls. It is found along fractures in topaz rhyolites. The gem crystallizes when rhyolite-derived gases, vapors from heated groundwater, and preexisting minerals and volcanic glass in the rhyolite react all at once. There is only one known commercial production of gem-quality red beryl in the world: the Ruby Violet (or Red Beryl) mine in the Wah Wah Mountains of Beaver County, Utah.

Still one of the rarest gems known today, this pinkish mineral was named after the Poudrette family, owners and operators of a quarry near Mont Saint-Hilaire, Quebec, Canada, where poudretteite was first found. It was discovered as a few tiny crystals during the mid-1960s, but wasn't recognized as a new mineral until 1986. The first documented gem-quality specimen of poudretteite wasn't discovered until 2000, when it was found in Mogok, Burma. This remarkable, flawless 9.41 carat poudretteite gem from Burma is truly one-of-a-kind. It is considered to be one of the largest -- if not the largest -- faceted poudretteite in existence.