# Are we experiencing lower level of gravity now compared to past?

Whole civilizations have been buried underground and we have built new landscapes over them.

The fact that tall buildings and houses are being excavated from under the ground means that we are living very much away from earth's core than the past.

Does this mean that we are experiencing less gravity compared to past Since we are further from the earth's core that causes the pull?

Note: Parent question Was the Earth's sea-level significantly lower in ancient times?

asking as separate question as per community suggestion

• It might amuse you to know that the science fiction novel End of an Era by Robert J. Sawyer plays around with the idea that tens of millions of years ago the surface gravity of Planet Earth was much less than it is now, and that this was why some of the species of dinosaurs could grow to be so incredibly large. Nov 19 '19 at 4:27
• Not a real issue if you add in that the earth collects "space dust" (meteorites and so on) of around 45 metric tons per year ("today") - which used to be much more in earlier time due to higher dust-density in the early solar system Nov 19 '19 at 10:55
• No. To the contrary, I keep getting heavier. Nov 19 '19 at 13:50
• I don't think that we're digging up tall buildings. I wasn't aware that our ancestors could build much higher than the pyrimids (which aren't really tall buildings wrt the scales that would affect the pull of gravity and also aren't buried). Nov 19 '19 at 16:47
• It depends which level of precision you're asking about. Sure, when I just move a pencil on my desk, I've changed the gravitational forces around me. When a gust of air comes from some direction, I'm experiencing varying gravitational forces on me. I just can't measure them, because they're buried in many, many digits into $g$. Nov 20 '19 at 12:25

Earth's radius is about 6400 kilometres. That's 6400000 metres. Let's say that you have a mound 20 metres high, burying an older settlement. Your new "radius" is now 6400020 metres.

Let's say that $$g = 9.8\ \rm m/s^2$$ at 6400, your new gravity will be $$g = 9.799939\ \rm m/s^2$$.

Clearly, this is hardly "lower level of gravity".

To make this even less significant, the 20 metres of extra dirt underneath you have their own contribution to the gravity. Even though the overall mass of the Earth is the same, local mass variations cause gravity anomalies. Not much, but $$g$$ changes by a bit. So adding more dirt directly underneath you will increase $$g$$, counteracting the fact that you're 20 metres farther away from the centre.

• Also, the dirt came from some other place on earth, so the overall gravity hasn't changed.
– Erik
Nov 18 '19 at 13:07
• To highlight this answer even more, even going all the way up to the International Space Station only reduces gravity by about 11%. Nov 18 '19 at 23:51
• @Erik Moving farther away from the center of Earth does reduce the gravitational force experienced, even if the overall mass of Earth is unchanged. If the mass of Earth and some object remain equal, the gravitational force between them as the object rises from the surface will be proportional to 1/r^2, where r is the distance from Earth's center of gravity to the object's center of gravity. Nov 18 '19 at 23:53

To address your original concern, no, the fact that there are buildings underground does NOT mean that the surface of the earth is higher than in the past. What is actually happening is that these buildings are subsiding into the ground. How? Believe it or not, earthworms. Worms were once constantly tunneling through the soil underneath ancient buildings, 'eating' the organic material in the soil, compacting the residue in their digestive tracts, and leaving behind tunnels, i.e open space. When enough space opened up under the buildings, the soil was no longer strong enough to hold them up, and so they sank, maybe a few millimeters a year. This got repeated steadily over many millennia, so the buildings sank and were buried.

Additional causes of burial: Many buildings were built next to rivers, i.e near the bottom of flood plains, and repeated flooding built up cover; people often rebuild over existing sites, and their comings and goings track in new dirt; etc.

Correction: Actually, although the surface of the Earth -as a whole- hasn't risen appreciably, thanks to geologic forces there are some regions where the surface has risen relatively recently (while other regions have gotten lower). Example: Much of North America has risen in recent millenia due to the tectonic plates rebounding after shedding the weight of melted glaciers.

• "Worms were once constantly tunneling" Still are, no? Nov 18 '19 at 19:42
• "What is actually happening is that these buildings are subsiding into the ground." This is often not true at all. Nov 19 '19 at 0:12
• Some references to the worms would be nice... Nov 20 '19 at 13:51

The whole mass of the Earth, mantle, crust, atmosphere and sea, contributes to the Earth's gravitational field, not just the core. Unless you want to split hairs, the Earth's gravity is the same now as it always was. In case you do want to split hairs, the Earth collects a substantial amount of space dust, meteorites and cosmic debris every year, but no one knows exactly how much except that compared to the total mass of the Earth the amount is negligible.

Estimates of annual accumulation vary tremendously, and leave out the contribution of mega-meteorites and asteroid impacts because they are not annual events. Remember that for every major impact on land, two hit the sea and are therefore not recorded. This accumulation increases the mass of the Earth and therefore its gravitational field, but it is balanced by loss of gases, mostly hydrogen, from the upper atmosphere. It is controversial whether losses exceed gains, but it is my view that when you take into consideration the contribution of major impacts, gains marginally exceed losses. Therefore the gravitational field is gradually increasing by an infinitesimal and unmeasurable amount as time goes by.

As for whether sea level was lower in ancient times, yes it was, but it depends on which ancient time you are referring to. In warmer times melt water from glaciers raised sea level, while in ice ages evaporation and precipitation lowered sea level and increased the ice sheet on land.

• "The whole mass of the Earth, mantle, crust, atmosphere and sea, contributes to the Earth's gravitational field, not just the core." That's true, but gravitational force can be modeled to a pretty reasonable degree by modeling both objects as if all of their mass were concentrated at their center of mass. Moving to a higher altitude will indeed reduce the gravitational force you experience toward Earth. Though, in the case of a few meters (or tens of meters,) it won't change by enough to matter. If you go up to LEO, you reduce the gravitational force by approximately 10%. Nov 19 '19 at 0:17
• @reirab "[G]ravitational force can be modeled to a pretty reasonable degree by modeling both objects as if all of their mass were concentrated at their center of mass" - That's only true for homogenous spherically-symmetric objects, neither of which apply to the Earth. Inhomogeneities in the mantle produce significant (on the level of about 1 percent) variations in the strength of Earth's gravity even at equal altitudes. You weigh about 1 percent more in Oslo than you do in Singapore for this reason. Nov 19 '19 at 11:37
• @reirab In addition, the Earth itself is pretty far from being spherically-symmetric. For one, it's oblate, meaning sea level is further from the center of the Earth at the equator than at the poles. Second (this is admittedly a tiny correction), variations in topography on land can alter not only the magnitude, but also the direction, of gravity. This was first measured in 1774 by the Schiehallion Experiment, which was able to detect a horizontal component to gravity from a nearby mountain (en.wikipedia.org/wiki/Schiehallion_experiment). Nov 19 '19 at 11:39
• If you really want to get nitpicky, the Earth also loses an (infinitesimally small) amount of mass every time we launch a space probe. All of the satellites in orbit might even count, since they take a portion of the mass that was below you and move it above you. The effects of this are immeasurably small, however, so can be essentially ignored. Nov 19 '19 at 16:14
• @probably_someone The reason you weigh a bit more in Oslo than Singapore is mostly just because Earth isn't a perfect sphere (as you said, it's an oblate spheroid.) Modeling yourself and Earth as point masses still works. It's just that the two centers of mass are farther apart in Singapore than in Oslo. I'm aware that there are local variations due to topography and density, but these are pretty small compared to just the difference from being closer or farther from the center of mass. That's why I said "modeled to a reasonable degree," not "calculated exactly." Nov 19 '19 at 16:30