The World

[Mexican18]

Yesterday in the pub a friend asked,quite innocently,'if we could weigh the earth ,would it weigh more less or the same as 5000 yrs. ago? It was unbelievable the argument that started! One bright spark said it must be heavier because of all the people,cars and buildings! Any thoughts?

[murraymints]

hmmmm..but all the materials used would be here already ? but more bodies ?? perplexing thought !

[jackthehat]

The accumulation of meteorite fragments, and the like, will probably have added some weight......but the materials sent out into space (satellites, etc) will have reduced it.

The weight of 7 billion people will be far more than the estimated 18 million of 5000 years ago, too.

Quite how much difference is unknowable, I suppose.

[albaqwerty]

it might weigh the same by the time you've deducted all the extinct stuff and added new stuff

[Old_Geezer]

Must be more. We are bombarded with space dust, meteors/asteroids/whatever continually: which will be massively more weight that a few space exploration things sent out recently. Plus centuries of sunlight energy being converted into biomass.
Anyway, where do all the top layers that cover the archilogical dig sites come from ? That must weigh something ;-)

[Mexican18]

The 7 billion people didn't drop from Mars! What about the pollution that is floating about? And planes flying around.

[albaqwerty]

If the earth weighed more, surely the moon would have commented?

'your bum's looking big'

[Islay]

I don't think it would weigh more!

[bhg481]

There would be an increase in weight due to the meteorites etc coming in from outer space.
There would be a decrease in weight due to satellites etc being sent away from the earth.
Any items such as cars, people, buildings etc are created by changing stuff already on the earth from one form into another, hence no change of mass from that.
Since the first two items above will have a trivial effect, the mass of the earth will be almost the same as it was 5000 years ago.

[goodgoalie]

OG, I've always wondered that too: why are, say, Roman floor mosaics found so far beneath current ground level? Where does all the several feet of earth come from - can't just be plants growing and dying. Several years ago I read about a Saxon pavement being discovered during building work in London, and it was about 40 feet below the current street level!

[albaqwerty]

I can understand a few feet of dirt/sand on top of ruins over a period of time, well, just about understand that.
I think the likes of Roman mosaics discovered in London may have been built on top of, once the Romans left, and then other people came and built on top of that and so on and so forth.
(Probably doesn't make any sense and is a load of rubbish)

[mccfluff]

i can just imagine the pub convo..... not something i have ever thought about before and now...

[SIRandyraven]

Humm interesting question and it seems to even stump the physics boffs.

It seems the Earth gains 40,000 tons per years via cosmic dust.
But also loses a huge amount each year due to the atmosphere simply escaping into space.


https://physics.stackexchange.com/questions/297622/is-the-earth-gaining-or-losing-mass-over-time

[albaqwerty]

don't forget the earth isn't round, it's more pear-shaped I believe (according to stuff I read as a youngster)

[goodgoalie]

It's an oblate spheroid, alba :)

[Old_Geezer]

Does one count the atmosphere surrounding the planet as part of the planet ? Debatable, but I suspect not. It's something covering the planet (thankfully).

[bhg481]

The atmosphere must count as part of the planet because the elements/compounds comprising it are converted into solids which form part of the planet. eg, plants take CO2, O2, N2 etc from the atmosphere and use the energy from sunlight to convert them into organic chemicals (cellulose?) from which they are built. When you burn carbon-based fuel you convert it into CO2, H2O etc; the water vapour in the atmosphere wll eventually fall as rain, the CO2 will be converted to organic material by plants.

[Old_Geezer]

Isn't that simply a process which adds to and subtracts from the actual planet's mass ?

[bhg481]

OG - No. Converting oxygen and hydrogen into water doesn't change any mass ie, the mass of water produced is equal to the sum of the mass of oxygen + the mass of hydrogen used to create it. The water is denser than the gasses but doesn't weigh any more. The same is true of all chemical reactions. Nuclear is different because mass is converted into energy when one element is converted to others.

[Old_Geezer]

Aye but as oxygen and hydrogen it is part of the atmosphere, as water it rains down and becomes part of, and adds mass to, the planet.