Meteorite impacts leave behind time capsules of ecosystems

Meteorite impacts can be very destructive. One that fell in Mexico around 66m years ago created a 180km crater and caused the extinction of dinosaurs while spewing debris and molten rock into the air. Now, in what is a fascinating tale of serendipity, researchers have found that these events don’t entirely destroy all traces of life at the site of impact. Molten rocks can capture and preserve organic matter as they cool down to form glass beads.

When a meteor enters Earth’s atmosphere, the air around the meteor gets very quickly compressed causing it to heat up, scorching everything in its path. Most of the time that is where the story ends, as the meteor burns up in the sky as a “shooting star”. But sometimes it is big enough to reach all the way to the surface and transfer its remaining energy to the ground.

This energy is dissipated, as mild earthquakes, sound shockwaves – but mostly as heat. The heat energy can be so great that it melts rocks on the surface and hurls them up in the atmosphere. Anything that comes in contact with this molten rock would presumably get burnt, leaving nothing but rocky material that cools down in the atmosphere, forming glass beads and tektites (gravel-sized natural glass). This is what City University of New York researcher Kieren Howard assumed, but he was able to show that his assumptions were wrong.

For his PhD, Howard was studying the glass beads and tektites found near the Darwin crater in Tasmania. The 1.2km wide crater was created by a meteorite impact about 800,000 years ago.

The natural glass formed during cooling is (as implied by the term glass) not crystalline. Instead of a regular arrangement of atoms, the atoms inside it are randomly arranged. Howard’s analysis, however, kept showing the presence of crystals. At first, he dismissed this as a problem with the machine or with his method of analysis. But when it kept showing up, as a good scientist, he thought he should ask an expert to look at his data.

“This is unusual,” says Chris Jeynes, a physicist at the University of Surrey. “If there were indeed crystals, then it was the result of uneven cooling, which can occur when something gets trapped inside these glass beads.”

Jeynes used proton-beam analysis, a method to peer inside the glass to reveal its elemental make-up. Inside he found carbon. “Howard had no idea what his samples were, and he was very surprised when I told him,” Jeynes says.

The natural glass formed should contain only silicon, titanium, oxygen and other metallic elements in trace amounts. Detection of carbon meant that there was some organic matter inside. The only hypothesis was that, somehow during the formation of these glass beads, they captured organic matter that was floating in the atmosphere. That organic matter might have already been in the air, but it might also include material thrown up by the impact.

Howard then went to another expert to break open these glass beads and reveal what the carbon-rich matter was. It turned out that it included were cellulose, lignin and other biopolymers. This meant that somehow this matter, which originated from plants, had survived the temperature of more than 500°C, which is what the molten rock would have reached before cooling into a glass bead. Usually these temperatures will break down the organic matter, but clearly it didn’t in this case.

Mark Sephton, a geochemist at Imperial College London, was surprised and pleased: “What the results show is that these glass beads can capture an aliquot of the atmosphere of the planet at impact. It is like a time capsule of that ecosystem.” These results are published in Nature Geoscience.

The implications are enormous. It shows that other meteorite impacts, like the one that wiped out the dinosaurs, could have created such time capsules too. Sephton is now working on finding glass beads from other impact sites to reveal information about Earth’s ancient atmosphere.

This method of analysis means that we could also go looking for similar beads on other planets, like Mars, where meteorite impacts are common. They could also reveal vital information about the past atmosphere of those planets. Maybe they captured organic matter – if it ever existed there.

“We would not know any of this if it wasn’t for Howard,” Jeynes says, adding that Howard’s persistence to find out what “the wrong results” were led the researchers to a phenomenon that nobody knew existed.The Conversation

First published on The Conversation.

Image credit: rickmach

Indonesia’s Samalas volcano may have kickstarted the Little Ice Age

A volcano in Indonesia may be the location of a massive “mystery eruption” that has perplexed volcanologists for decades, according to a new study. The eruption occurred in 1257, and it could also be one of the volcanoes that started a 600-year cold period called the Little Ice Age.

Volcanic eruptions release sulfur into the atmosphere, which eventually falls back on Earth and gets deposited on ice sheets. These sulfur samples can be identified in ice cores obtained from polar regions. From the records, Clive Oppenheimer, a volcanologist at the University of Cambridge, found that an eruption in 1257 may may have been the largest release of sulfur in the past 7,000 years.

But where did the eruption happen? “Not being able to find the volcano can be discomforting,” said Thomas Crowley, a geoscientist at the University of Edinburgh. “If the sulfur wasn’t released by a volcano, it means something very strange is going on that we don’t know about.”

But locating the volcanic source can be tricky. For the 1257 eruption, there were many candidates: Okataina in New Zealand, El Chichón in Mexico, Quilotoa in Ecuador and Samalas in Indonesia (next to Mount Rinjani).

To narrow down their choice, Franck Lavigne at the Pantheon-Sorbonne University and his colleagues had to consider many types of data, just published in the Proceedings of the National Academy of Sciences. “They do a great job of combining historical data, geochemistry evidence, carbon dating, and physical data to arrive at the conclusion,” said Erik Klemetti, a geoscientist at Denison University and author of the popular Eruptions blog. “Their case for it to be Samalas is compelling.”

The historical data comes from Babad Lombok, which are records written down on palm leaves in Old Javanese. They describe a horseshoe-shaped collapse, which can occur when empty space is created under a mountain on ejection of large amount of magma.

Carbon dating is a commonly used technique, but its estimates are not accurate enough. Lavigne had to rely on comparing geochemical fingerprints, which gives a unique ratio of chemicals present in the ash from every volcano. The two sets of these geochemical fingerprints come from volcanic ash in ice core samples and the possible site of a volcano.

“In this study, the error margins for the chemical analysis are quite large,” said Rebecca Williams, a volcanologist at the University of Hull. “But I appreciate that matching the ice core data with volcanic samples is very difficult.” This is because the ice core samples often yield only one or two grains of the ash, which need to be subjected to many tests.

Volcanic eruptions, especially those containing a lot of sulfur, can have a large impact on the climate, which then have social, economic and environmental knock-on effects. An 1815 eruption in Tambora, Indonesia is infamous for producing the “year without summer”, one of the chilliest summers in Europe’s history, which was followed by mass shortage of food.

Lavigne speculates that the Samalas volcano could have similar impacts. One such speculation is about the thousands of bodies recovered from Spitalfields in London. Many of these were found to have been shoved in a single grave, indicating some sort of crisis. According to Lavigne, they’ve been recently dated to 1258, only one year after the Samalas eruption.

The Babad Lombok also notes that the volcanic eruption destroyed Pamatan, then capital of the Lombok kingdom. “There is a good possibility that an ancient city lies beneath the ash and pumice deposits of the Samalas volcano,” said Oppenheimer, also a co-author of the study. “Ruins under such deposits are not so uncommon,” added Williams, but finding a whole city might be.

More important, though, could be Samalas volcano’s role in triggering the Little Ice Age. In a 2012 study in the journal Geophysical Research Letters, scientists used climate models to show that a series of eruptions may have triggered the onset of the Little Ice Age. Although the precise timing varies somewhat, this period is typically considered to have occurred between 1250 and 1850.

“A single eruption could not have caused such long-term climate change,” said Klemetti. “Instead, it had to be a sequence of large eruptions, one of which might be the Samalas volcano.”The Conversation

First published on The Conversation.

Image credit: asgeirkroyer