David Hubble, US asked:
Is the Earth getting heavier? As the human population grows, are we putting on weight as a planet?
Chris - Yes but perhaps not for the reason that he was suggesting. People often think that as we increase our population the weight of the people comes from nowhere. People just weigh more and the Earth therefore weighs more. That's not true. The Earth is an isolated system where all the of the mass that was on it to start with doesn't go anywhere. You don't make mass from nowhere, so people have got to gain weight by taking mass from elsewhere on the Earth: in other words, eating food that's come out of the Earth and into their bodies.
But the planet as a whole, does that get heavier over time? The answer is yes, it can. Every year, Earth gains about the weight of two aircraft carriers landing on it – two HMS Ark Royals, or about 40,000 tonnes-worth of debris, which lands on Earth from space. You can demonstrate this for yourself. If you put a big plastic sheet or a white sheet on your grass in the garden on a nice day, leave it for a few hours and then run a magnet over it. You can often find specks have just fallen down from outer space and landed on your magnet. Debris, dust and other stuff raining in from space contributes a huge amount of weight to the Earth every single year.
No. Matter can neither be created nor destroyed.
Don_1 is spot on but you could argue that if the loss of atmosphere to space has stopped then the Earth is getting imperceptibly heavier with the arrival of meteorites and other interstellar stuff that lands here. blakestyger, Thu, 2nd Oct 2008
Yes, you could take the weight of such interstellar bodies and subtract the weight of space probes sent out by man, never to return, to arrive at a figure. But as you say it would be so infinitesimal by comparison to the weight of the planet as to be as to be imperceivable. Don_1, Thu, 2nd Oct 2008