[ intro ].

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. But… researchers 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 ].