Wikipedia:Reference desk/Archives/Science/2018 July 14

= July 14 =

Mass of earth over time
This article discussing a meteorite impact 3 Ga ago claims that "when this asteroid hit, Earth was only a third its current size". I've interpreted that as meaning that the earth was 1/3 of it's current mass at that time, which I find very, very hard to believe. An alternative interpretation is not occurring to me either. I've been trying to find something like a graph of the mass of earth over time, but I can't find such a thing. I imagine it's because the mass of the earth only substantially changed in the period up to and during the formation of the moon (4.5 Ga ago), and that since then changes to the earth's total mass have been negligible. The late heavy bombardment (4.1 to 3.8 Ga ago) consisted of around 22,000 objects large enough to leave craters at least 20km in diameter on earth. Even if we assume all 22,000 of them were the size of 5 Astraea (which would leave a crater far larger than only 20km in diameter) and no ejecta escapes the earth's gravity, the event only would have increased the earth's mass by around 1%. Since the LHB, I don't think there have been any major sources of additional mass, and the slow accretion of additional mass which is negligible anyway has been opposed by the gradual loss of hydrogen and helium. Is there any possibility that the claim in this article is correct? Also, does anyone know if a graph of the estimated mass of the earth over time, even if it just covers the accretion and moon formation stages exists anywhere? 2A0D:5600:3:9:201:200:0:10B3 (talk) 08:26, 14 July 2018 (UTC)


 * Yeah, that's nonsense. I suspect what someone intended to say was that at 3 Ga, the earth was 1/3 it's present age, but somehow that got miscommunicated as "size".  Dragons flight (talk) 08:34, 14 July 2018 (UTC)


 * (EC) Several of the comments under the article say that this should read "a third its current age". That is numerically correct, and presumably also what the author intended to write. If Earth had indeed tripled in size by whatever process, there would be no way that any traces of this crater would be detectable now. --Wrongfilter (talk) 08:36, 14 July 2018 (UTC)


 * (ECx2) Yeah I was right about to post the same, after "lulwhat?" I did check the the original paper to make sure, and no, it doesn't make this statement anywhere. Someguy1221 (talk) 08:36, 14 July 2018 (UTC)


 * Pfft. This is clearly a clever set-up for a geologically based "Yo mama..." joke. Matt Deres (talk) 02:49, 15 July 2018 (UTC)
 * See, they just admitted expanding Earth is true! Wake up sheeple! --47.146.63.87 (talk) 07:52, 15 July 2018 (UTC)


 * Note that Earth gains mass from meteors and loses mass from gasses stripped by solar wind and by radioactive decay -- at nearly identical rates  (estimates vary). —2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 18:04, 15 July 2018 (UTC)