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  • If you grew up in a place where it snowed,

  • you might have appreciated snow days.

  • On a cold winter's morning,

  • you may have found yourself staring longingly at a dark cloud in the distance,

  • wishing it would just dump all its snow so you could skip school and play.

  • Well now, imagine that all of a sudden,

  • you saw a pair of airplanes fly over those clouds

  • and release a powdery looking substance on top of them.

  • A few minutes later, it starts snowing.

  • This kind of weather manipulation may sound far-fetched,

  • but it's a real thing that's been around for decades.

  • It's called cloud seeding

  • though, it's not a get-out-of-school-free card.

  • It's been used to encourage precipitation in dry parts of the world.

  • The only problem is, scientists haven't been sure how well it

  • actually does that.

  • But a new study published this week in the journal PNAS

  • details a way to figure that out.

  • Cloud seeding involves finding a supercooled cloud of liquid

  • one where the water in the air is /already/ below freezing,

  • but it hasn't yet formed large enough ice crystals to precipitate as snow.

  • You then inject a fine mist of nucleating materials into that cloud

  • particles that all that ready-to-freeze water vapor can coalesce around.

  • And, if all goes well,

  • enough super-chilled water freezes onto those molecules

  • that they fall to the ground as snow.

  • Butresearchers have had basically no clue

  • how well this works in practice.

  • Some reports say seeding does nothing,

  • while others say it increases snowfall by 50%.

  • That's because, up until now,

  • researchers have had to rely on

  • comparing the volumes of snowfall from regular clouds

  • to the snowfall from seeded clouds.

  • And that's not all that reliable,

  • since you don't know what the difference between those clouds

  • would have been /without/ seeding.

  • You have to rely on statistics

  • and weather is hard to predict, y'know?

  • So this time around,

  • a team of U.S. researchers focused on separating out seeded snow from natural snow.

  • They set up snow gauges in strategic spots underneath the planes' flight path.

  • Then, they tracked the cloud

  • from the moment they seeded it with silver iodide

  • all the way until its snow fell on the ground using radar devices on nearby mountains.

  • Those let them detect when and where snow was bunching up around those nucleating molecules.

  • And if snow fell in a gauge right after the cloud above it was hit with silver iodide,

  • it was considered to be seeded snow.

  • In the end, they calculated that 20 minutes of seeding

  • resulted in 67 minutes of snowfall which covered about 900 square miles

  • in about a tenth of a millimeter of snow.

  • Now, I know that doesn't sound like much.

  • But it is enough water that, when melted,

  • it would fill almost 50 Olympic sized swimming pools.

  • And over three attempts,

  • the team managed to produce 282 Olympic pools' worth of precipitation from seeding.

  • That's not nothing in an area thirsty for water.

  • Most importantly, though,

  • it demonstrated you can measure the effect.

  • Before cloud seeding can become a common solution for water scarcity,

  • we have to figure out how well it works.

  • And now that researchers have shown they more reliably measure that,

  • they can hopefully improve on the technique.

  • And if nothing else,

  • they'll be able to accurately crunch the numbers to decide whether or not it's worth

  • the effort.

  • In other news,

  • researchers in China have found over a thousand tiny green algae fossils

  • that are /a billion years old/,

  • pushing the origin of these plants back by some 200 million years.

  • The advent of photosynthesis was kind of a big deal on Earth,

  • since it fundamentally changed the atmosphere

  • and made it possible for oxygen-breathing organisms like us to thrive.

  • So, evolutionary biologists are eager to understand

  • how different photosynthesizers came to be.

  • Of particular interest

  • are the origins of the group Viridiplantae

  • which literally means /green plants/.

  • As in, well, /all the green plants/ you can think of.

  • Trouble is, when and where different lineages of plants began isn't entirely clear.

  • Using genetic differences and fossils,

  • researchers have estimated that they diverged from their closest cousins

  • the red algae

  • sometime between 1.6 billion

  • and 720 million years ago.

  • But those estimates have a ton of uncertainty built into them,

  • and scientists haven't been able to validate them

  • since fossil evidence from that era is so rare.

  • Not only are there debates about timing,

  • some think /green/ plants began as /marine/ plants,

  • while others say they got their start in freshwater lakes, rivers, or streams instead.

  • So older fossils could really help nail down when and /where/ this group evolved.

  • The oldest fossils to date came from a research mission

  • to an island in the Arctic Ocean in the early 1990.

  • Among the finds were fossils of what appeared to be

  • a new green plant they called Proterocladus.

  • At about 700 million years old,

  • it was potentially the world's most ancient seaweed.

  • But, these fossils weren't in amazing shape,

  • so some questioned whether the seaweed really /was/ a seaweed.

  • [naan-fehn] In this new study,

  • published this week in Nature Ecology and Evolution,

  • researchers from universities in Virginia and China

  • went to the Nanfen Formation in northern China

  • and found /loads/ of Proterocladus fossils.

  • /Over a thousand specimens/, in fact.

  • Though each was /tiny/ — only 2 millimeters long!

  • And since these fossils were much older than the ones described in the 90s,

  • they called them Proterocladus antiquus.

  • The great part about finding so many of these little fossils was that,

  • with the help of high-powered microscopes,

  • the team was able to get a really solid sense of this ancient algae's features.

  • Like, that they had complex branches

  • and root-like structures similar to the green algae around today.

  • And since they were found in /ocean/-derived rocks,

  • the findings help bolster the argument that these plants arose in the sea.

  • Plus, they provide firmer support to the notion

  • that green plants had already split from their redder cousins a billion years ago

  • much earlier than some of the estimates to date.

  • That also means we have probably been underestimating their importance in marine ecosystems.

  • But, the more fossils we find,

  • the clearer our picture of ancient life becomes.

  • Thanks for watching this episode of SciShow News!

  • We put out news episodes every week,

  • so if you want to learn about more awesome breakthroughs,

  • be sure to check YouTube.com/SciShow every Friday!

  • Or, you know, just hit that subscribe button and ring the notification bell.

  • That way, you'll hear about /every/ episode we put out

  • and you won't miss any of the incredible science we talk about.

  • [ outro ]

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Let it Snow! The First Direct Measure of Cloud Seeding | SciShow News

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    林宜悉 posted on 2020/03/30
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