Cosmic Fossils: What Meteorites Reveal About Our Solar System
Humans have seen rocks falling from the sky for thousands of years. One of the earliest potential recorded accounts dates back to 1478 BC. AD, when, according to the Chronicle of Parian, a “lightning stone” fell on the island of Crete. In 465 BC. BC, the Greek poet Pindar saw a meteorite land not far from the hill where he was sitting. And in 1492, a stone fell from the sky just outside the town of Ensisheim, France, becoming a wonder in Europe for centuries. It was widely believed that these stones formed in the clouds and, when heavy enough, simply fell to Earth. Where could these ordinary-looking rocks come from?
But at the beginning of the 19th century, a number of events occurred that changed the way people understood and studied these objects. On April 26, 1803, the villagers of L’Aigle, France saw and heard an astonishing fall. Over 3,000 stones were recovered, making the event impossible to ignore. Just two years earlier, astronomer Giuseppe Piazzi had discovered the asteroid Ceres, clearly showing that there were other objects than planets circling the Sun. Geologists and chemists were also making great strides in understanding Earth’s rocks and developing techniques to reveal their structure.
Around the year 1800, British chemist Edward Charles Howard acquired several suspected meteorites, including examples of each of the three main types of meteorites recognized today: stony, ferrous, and ferrous. Howard was the first to dissect and subject these alien stones to chemical analysis. In 1802 he reported that all three types of meteorites had a high level of nickel, a composition unprecedented in Earth rocks.
Two years later, a British mineralogist, William Thomson, tried to polish an iron meteorite with nitric acid, revealing a striking crystalline pattern. These became known as the Widmanstätten lines after Count Alois von Beckh Widmanstätten, who made a similar discovery in 1808. No such pattern is seen in mined iron on Earth. These two men had discovered the ancient frozen crystal structure of iron meteorites, unchanged for billions of years.
Leapfrogging into the 20th and 21st centuries, meteorite research has advanced thanks to new techniques and equipment used to study these cosmic visitors. These investigations included, unexpectedly, an archaeological mystery. In 1911, British archaeologist Gerald Avery Wainwright discovered iron necklace beads in a 5,500-year-old Egyptian cemetery at Gerzeh, about 70 km south of modern Cairo. And when British archaeologist Howard Carter opened the tomb of Pharaoh Tutankhamun in 1922, he found – among many fine artifacts – a magnificent ceremonial dagger with a gold hilt and an iron blade.
The presence of these iron artifacts was obvious, because during Tutankhamun’s lifetime 3,300 years earlier, the Egyptians had not yet mastered the art of iron smelting and were still using bronze for their weapons. Chemical tests indicated a high level of nickel in the beads of Gerzeh and the blade of Tutankhamun, indicating an extraterrestrial origin. However, in the 1980s, some archaeo-metallurgists suggested that nickel-rich iron ores found on Earth may have been the source of these artifacts.
Finally, in 2016, researchers reported in Meteoritics and Planetary Science a non-invasive examination of King Tutankhamun’s iron dagger that confirmed its meteoritic origins. The team used a portable X-ray fluorescence spectrometer, which examines the wavelengths of fluorescent elements to determine their abundance. The researchers found that the dagger contained almost 11% nickel and around 0.6% cobalt, whereas earth iron produced before the 19th century rarely exceeds 4% nickel. They then compared this to iron meteorites found within a 1,200 mile (1,930 km) radius of Tutankhamun’s tomb and found a possible match – the Kharga meteorite, discovered in 2000 near the city of Marsa Matruh, in Egypt. Using similar tests, the Gerzeh pearls were shown in 2013 to have originated from an iron meteorite.