(Intro)

From the universe of Tumblr comes this compelling question to SciShow Space: is the Earth getting heavier? And it's a good question, because the answer is kinda surprising and also complicated, which makes it interesting!

The question is most often asked in the context of Earth's burgeoning human population. After all, like rats, cockroaches, pigeons and dubstep DJs, humans have become a very prolific species. We're everywhere now! And at 7.2 billion humans and counting, you'd be forgiven for thinking that the Earth has a lot weighing on it.

But it's important to remember that Earth is a closed system. That means that pretty much all of the mass that's on our planet stays on. It doesn't go anywhere, it's just converted and re-converted into other forms. In this sense, you're up of stuff from Earth that's been converted into you. Basically you're just a bunch of repurposed nachos, salad greens, water, possibly some animals, and maybe the occasional latte. So, more people doesn't mean a heavier world. It just means that more of the material on our world is being converted into people. 

Still, fact is, Earth is getting more massive. But it's not coming from more people or pigeons or rats; it's coming from space! Astronomers estimate that Earth acquires about 40,000 metric tons of mass every year in the form of cosmic dust. 

Tiny bits of rock and metal and other debris from the very earliest days of the formation of our solar system. In a single month, Earth collects enough of this celestial rubble to fill an Olympic size swimming pool, and in a year, it gains the equivalent of two aircraft carriers.

So, yes, Earth is putting on the kilos for sure. But at the same time it turns out that it's losing even more mass in the form of gas. See, Earth lives in one of the hotter neighborhoods of the solar system. And I don't mean like Williamsburgh in Brooklyn. I mean it's closer to the sun and all of the heat that we experience excites the gases in our atmosphere, especially the lighter ones like hydrogen and helium, and they can get moving so fast that they escape Earth's gravity: this is sometimes called atmospheric escape.

As a result of this effect, every second our Earth loses about 3 kg of hydrogen. That's about 95,000 metric tons each year. And about another 1,600 tons of helium is lost to space too. In other words, Earth loses more mass in gas every year that is gains in space dust.

So you put it all together: 40,000 tons of dust gained per year minus 96,600 tons lost in gas, and Earth ends up losing a net 56,600 metric tons of mass every year. So, like I said, a complicated answer, but an interesting one. And whatever it is you're doing Earth, keep it up, 'cause you're looking good!

Thanks to the viewers who asked this great question and thank you for watching. If you want to help us keep exploring the universe together, just go to subbable.com/scishow and don't forget to go to youtube.com/scishowspace and subscribe.