Hank: Climate change may have been on your mind last week when you heard about that gigantic iceberg breaking off Antarctica. This piece of ice separated from a part of the continent called the Larsen C ice shelf. It weighs some 1 trillion metric tons, it's roughly equal to the size of the state of Delaware (about 5800 square kilometers) and now it is floating in the southern ocean. And now we're in the plot of an environmental disaster movie. Icebergs break off, they melt, and suddenly it's water world. But, there is no need to panic here. Because the iceberg was part of an ice shelf, it was already floating when it broke off. And, when ice floats, it already displaces the same amount of water it'll become when it melts, so this event won't be adding to rising sea levels.

Also, it wasn't a surprise to researchers, and it might not actually have had much to do with climate change. Human caused climate change is happening, of course, and it's already made an impact on Antarctica, but scientists say that, from what they can tell, this isn't a directly related event. Icebergs breaking off glaciers is a normal process. It's something scientists call calving, although different from when a cow has a baby cow. As glaciers extend out over water, they form floating ice shelves, and as these shelves continue to move, they reach a point where the edge of the ice can become unstable, and they shed an iceberg. In the case of Larsen C, scientists have been following a crack in the shelf for 7 years, so we've been expecting this to happen for a while. It's mostly making headlines because this 'berg is much bigger than usual. 12% of the entire Larsen C ice shelf.

There's some bad news too. Glaciologists, the scientists who study ice and glaciers, know that when icebergs calve, it can make the land ice more likely to collapse. More ice could dump into the ocean because less of the ice shelf is there to block it, which can raise sea levels. There's still a chance that Larsen C could rebuild itself instead of totally breaking down, but the track record isn't great. It's smaller neighbor, the Larsen B ice shelf, partially collapsed in 2002, seven years after calving its own iceberg.  Climate change is no joke, but thankfully this one iceberg
is not ushering in the end of the world.


Meanwhile, archaeologists this week reported that they’d found evidence humans arrived in Australia 65,000 years ago, which is about 5,000 years earlier than anyone expected.  A team from Queensland University dug up around 11,000 new artifacts from a rock shelter called
Madjedbebe, which had been excavated twice before in the 1970s and ‘80s.  In those first digs, archaeologists had found some stone tools and pieces of natural pigment called ochre that they thought were 50 to 60,000 years old, which suggested that humans might have shown up in Australia around then.  But this was before scientists had really perfected their dating techniques for things that old.

Radiocarbon dating, which uses the predictable, radioactive decay of certain carbon atoms as a clock, can only really go back around 50,000 years.  Other methods that could go back much further were only just getting started.  So those techniques might have skewed estimates by as much as 20,000 years, which is nothing to shake your spear at.
Besides all of that, many archaeologists thought that the layers of dirt and rock at the site had been disrupted enough that they couldn’t really trust the dates anyway.

So, in 2012 and 2015, researchers went back to the site to see what they could turn up with newer methods, and the third time was the charm!  The team found thousands of new objects: grinding stones, ochre crayons, and the oldest edge-ground hatchets in the world.
To date the new artifacts, the team used a technique called optically stimulated luminescence, or OSL, which reveals the last time a mineral was exposed to sunlight.

Basically, scientists can shine a light on quartz grains in rocks to release radioactive energy they've picked up from the environment over centuries, and measuring that energy can tell how old the rock artifacts are.  With OSL, the team was able to confirm the earlier dates.
And they pushed back the age of the oldest artifacts even further,
to around 65,000 years ago, with just a few thousand years of uncertainty.  This discovery helps us understand how early humans fit in
with other hominid and animal species.  The earlier time frame means humans making their way from Southeast Asia into Australia
maybe had longer to interbreed with other human-like hominins, like the Denisovans or Homo erectus, one of our closest relatives.  And these early humans likely spent more time with huge animals that used to live in Australia.

Because if you thought Australia had weird animals now,
it also used to have gigantic, two-ton wombats.  Scientists have debated for years whether giant creatures like those wombats and the
short-faced kangaroo died out because of humans, climate change, or some mix of the two.  The latest finding doesn’t fully resolve that issue.
But it does suggest that these big animals lived with humans for about 20,000 years before going extinct. So it wasn’t as quick a kill, as some scientists had proposed.

From the iceberg in Antarctica to early humans in Australia, there’s still a lot we’re figuring out about Earth’s past, present, and future, but we’re getting there!

Speaking of the future: the Great American Solar Eclipse is just a month away!  If you’re interested in learning more about it, you can check out our episode on that at the SciShow Space channel at youtube.com/scishowspace.  And if you’re looking for a safe way to see the eclipse, we’ve got you covered with our special SciShow pinhole projector card!  All you have to do is poke a hole in the middle, grab a piece of paper to project the image onto, and adjust the distance between the card and the paper until you see a clear image of the eclipse.  The tiny hole acts kind of like the lens in a camera, focusing the light that passes through it to make an image on the paper behind it.
You can get your SciShow pinhole projector at dftba.com/scishow!
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