Is the Earth getting heavier? It’s a good question, because the answer is kind of surprising, and also complicated, which makes it interesting. The question is most often asked in the context of Earth's ever-expanding human population. After all, 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 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. It doesn't go anywhere - it's just converted and reconverted into other forms.
In this sense, you are made up of stuff from Earth that's been converted into you. Basically, you're just a bunch of repurposed potatoes, 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, the fact is Earth is getting more massive, but it isn’t coming from people or animals or plants; it's coming from dust.
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-sized 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.
Earth lives in one of the hotter neighborhoods of the Solar System, and I don't mean like the hipster side of west LA. 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.
They can get moving so fast that they escape Earth's gravity; this is sometimes called atmospheric escape. As a result of this effect, our planet loses about three kilograms (seven pounds) of hydrogen every second - that's about 95,000 metric tons each year, and about another 1,600 tons of helium is lost to space.
In other words, Earth loses even more mass in gas every year than it gains in space dust.
So like I said: a complicated answer. But an interesting one, and whatever it is you're doing, Earth, keep it up! Because you're looking good.
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Sources: This story was originally published on SciShow Space. I am republishing a lightly edited version on SkyFeed in light of interest in the subject. Reimers, Reid. "Is Earth Getting Heavier?" SciShow Space, YouTube. 29 July 2014. Web video.