Meteorite impacts leave behind time-capsules of ecosystems

Glass beads that form inside hot meteors as they fall to Earth capture particles from the atmosphere, creating a kind of permanent record of historic climates.

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” led the researchers to a phenomenon that nobody knew existed.

This article was originally published at The Conversation. Read the original article.

The Conversation

Meteor Crater in Arizona. (Photo: Angle Schatz/Flickr)
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Twitter is rolling out (slightly) longer tweets

Plus the demise of the dot-at. 

We've heard rumblings for a while that Twitter plans to move away from its simple USP (140 characters per tweet, a list of chronological tweets on your timeline) in favour of a more curated, less restrictive model. 

Today, the site announced changes that will reduce the limits on tweet length, but not in an extreme way – rumours that the site planned to kill off the character limit entirely seem unfounded, at least for now. Instead, usernames and media attachments like links, polls or images will no longer be included in the limit, which will come as a relief to anyone with a long handle or media brands (naming no names) which often tweet links. The company says the changes will roll out over the "next several months".  

This probably doesn't mean you'll be able to have a poll, a picture and a Periscope livestream in a single tweet, but it does mean you could potentially @ in unlimited numbers of people. For anyone who has been harassed on the site, this isn't great news - at least in the past trolls' audiences were limited by tweet length.  

The site is also killing off ".@": the method used by users who want replies or direct addressals to be seen by all their followers. At the moment, any tweet starting with an "@" doesn't feed onto the main timeline, and can only be seen by selecting "tweets and replies" on a specific user's profile.

In future, Twitter will recognise which tweets are actually replies and hide them, but non-replies which start with an "@" will still display in feeds. You'll also be able to retweet yourself, or quote your own tweets, so you can make replies appear on your followers' feeds if desired. The press release also toe-curlingly suggests that you could use this function for when you "feel like a really good one went unnoticed". 

The move suggests Twitter wants users to post media-filled tweets, and doesn't want to punish those that do with decreased space for a message. The social media site recently brought live-streaming app Periscope, which will also beneift from the change.

The company explains in the press release that the original 140 character limit, based on the length of a text message, is a little out of date. Now, apparently, tweets have become a "rich canvas for creative expression". You heard them - go forth and Periscope. 

Barbara Speed is a technology and digital culture writer at the New Statesman and a staff writer at CityMetric.