Wikipedia:Reference desk/Archives/Science/2018 July 24

Science desk
< July 23	<< Jun | July | Aug >>	July 25 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

July 24

Removing water to connect all current land...

How much would the sea level have to drop to have all *current* above the water land to be connected by land? And what would be the last piece of current land to be connected?Naraht (talk) 15:14, 24 July 2018 (UTC)

Does that include middle-of-the-ocean features such as Hawaii? ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:31, 24 July 2018 (UTC)

Yes. And Pitcairn, Bermuda, Kerguelen, etc....Naraht (talk) 15:33, 24 July 2018 (UTC)

To connect Mauna Kea to mainland, you would have to drain several miles of water. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:47, 24 July 2018 (UTC)

Any idea how to get more accurate information? (A decent map of depths of the Pacific would probably help, but I haven't found a great one) For Hawaii, it is entirely possible that the land bridge that gets revealed connects Mauna Kea to Kamchatka along the Hawaiian–Emperor seamount chain, but I'm not sure on the depths of some of the gaps in the chain?Naraht (talk) 18:02, 24 July 2018 (UTC)

In Google Images, there are various topographic maps of the ocean floor. This NG item[1] allows you to look at portions of it. The Hawaiian Ridge is a series of volcanoes which go way down deep, as are many of the other Pacific islands. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:33, 24 July 2018 (UTC)

Agreed, but the question is whether there are gaps in the Hawaiian-Emperor that go all the way down to the general seafloor or whether it stays significantly above that level as is true between Hawaii and Oahu.Naraht (talk) 19:46, 24 July 2018 (UTC)

You can download a detailed (30 arc second) grid of global bathymetry from GEBCO here. With the appropriate software you could mess about with a colour bar until you found what you were looking for. Mikenorton (talk) 19:57, 24 July 2018 (UTC)

In case you didn't know: Puerto Rico is surrounded by water. 2600:8806:4802:C700:19EF:9053:95DC:1C0A (talk) 21:05, 24 July 2018 (UTC)

Thanks, Donald. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:15, 24 July 2018 (UTC)

A related question [2].--Wikimedes (talk) 05:48, 25 July 2018 (UTC)

How do weeds manage to grow without a drop of water in the soil?

Not a drop of rain in two months, and yet I have to remove weed in the garden. I need to water the plants to prevent them from drying out in these extremely dry conditions, yet the weeds germinate and grow. How do these plants get enough water? Count Iblis (talk) 15:48, 24 July 2018 (UTC)

It's at least partly a circular problem: plants are called weeds because they grow where they're not supposed to. Plants with higher tolerance for dehydration would have an advantage filling that niche, so it makes sense that many weeds would survive/thrive while other plants dried out and died - if they didn't, they wouldn't out-compete your tomatoes and dahlias. So what makes them dehydration tolerant? Well, there are many adaptations that will play a part (pore placement and density, gross morphology, waxy coatings, the use of taproots, and so on. Weeds rarely spend a lot of energy on fleshy fruit or showy blooms (though there are some exceptions), and that also reduces their need. Matt Deres (talk) 16:21, 24 July 2018 (UTC)

Are you sure they're not coming up from the roots of weeds you've previously tried to remove? Anyway I've heard weed is associated with Satanism so it must be able to cope well with the heat ;-) Dmcq (talk) 16:24, 24 July 2018 (UTC)

There are indeed plants with deeper roots, but I'm puzzled about new weeds that germinate and have tiny roots when I pull them out. Somehow these tiny roots were able to extract water from the bone dry soil. So, it must be what Matt Deres says about losing less water than other plants, but there must also be mechanisms that allow water to be extracted from the top layers of the soil. Perhaps some of the water at greater depths in the soil evaporates and at night when the top layers of the soil cool down, the water vapor makes it there via pores and condenses there? Count Iblis (talk) 17:17, 24 July 2018 (UTC)

I suppose some weeds are better at conserving water but I think most just are far better at extracting the water and leaving the soil too dry for other plants - it is a major way they outcompete other plants I believe. Dmcq (talk) 17:50, 24 July 2018 (UTC)

If actual data doesn't match your assumption, it is quite likely your assumption is wrong. You have assumed the soil has zero water. Plants are growing in it. Therefore, your assumption is wrong. To have assumptions impervious to contrary evidence is a problem... --Jayron32 18:02, 24 July 2018 (UTC)

One way to get water in the top of the soil is via dew or frost. Before sunrise the soil surface may be moist, but when you look in the afternoon all that moisture may have evaporated. Graeme Bartlett (talk) 03:11, 25 July 2018 (UTC)

Thanks everyone for their input in this thread! Count Iblis (talk) 19:26, 30 July 2018 (UTC)

Deploying Compost in Extreme Heat.

I know that in the UAE and Saudi Arabia when farmers plant they have little water retention in sandy soils. Why cant they just compost all the organics from the big cities or ship in organics from other places for composting and plant in that. Is there something specific that happens to high organics soils(IE. Compost) when it is exposed to dry heat? Is this sustainable. Looking for someone to prove sustainability or not. If you have questions on more info Please Ask. — Preceding unsigned comment added by Mason201 (talk • contribs) 17:10, 24 July 2018 (UTC)

[ http://hal.cirad.fr/docs/00/18/03/35/PDF/Bahri.pdf ]

Abstract:

Water reuse in Tunisia: Stakes and prospects. In the arid and semi-arid region, countries like Tunisia are facing increasingly serious water shortage problems. According to forecasts, increased domestic and industrial water consumption by the year 2020 may cause a decrease in the volume of fresh water available for Tunisian agriculture. It is therefore important to develop additional water resources as well as protect the existing ones. One way to cope with these problems is to reuse wastewater in agriculture. Therefore and before launching the water reuse policy, a research program was undertaken...

--Guy Macon (talk) 17:44, 24 July 2018 (UTC)

Composting requires the presence of air. Water is needed in the right amounts to maintain activity without causing anaerobic conditions; the air/water balance is critical to maintaining high temperatures (135°-160° F / 50° - 70° C) until organic solid wastes decompose. Urine, itself useful as a nitrogen-rich fertilizer, is a suitable additive to a compost pile. DroneB (talk) 17:46, 24 July 2018 (UTC)

In addition to that, an obvious question is, why compost in the desert anyway? I mean the idea of composting waste from their own cities may make some sense. But what's the purpose of shipping in organic waste from elsewhere? Maybe you've never composted but if you ever did you'd know that the volume of what you start with is a lot more than what you end up with. [3] So there are at least 2 and probably more (shipping organic waste around seems a good way to ensure lots of problems with pests etc) problems with shipping in the waste and composting it on site. If the idea made any sense, it would seem better to simply compost it somewhere else and ship in the compost. BTW perhaps Desert greening will be of some interest. You'd note that it doesn't really mention shipping in compost or soil at massive scale as part of the process. Nil Einne (talk) 23:05, 24 July 2018 (UTC)

Insect from eastern Quebec

Graceful insect

Hello. Can you identify this little fellow who landed on my front door this morning (or last night..). I live in Rimouski suburb, Quebec Canada, in an open landscape of bungalows, many trees and several patches of mixed forest, a few hundred meters of St-Lawrence estuary. Body length : 1cm, wings span 2,5 cm. Thank you. Dhatier (talk) 17:45, 24 July 2018 (UTC)

I'm pretty sure it's a type of paleoptera (i.e. mayfly, dragonfly, or damselfly), though a rather more ornate one than I have ever seen. Maybe that will lead you in the right direction, though there are thousands of different species. --Jayron32 18:12, 24 July 2018 (UTC)

Looks like a rose plume moth Cnaemidophorus rhododactyla. Mikenorton (talk) 18:19, 24 July 2018 (UTC)

Agreed. T shapes are usually some sort of plume moth (although our local ones are ghostly white). Andy Dingley (talk) 18:30, 24 July 2018 (UTC)

Cnaemidophorus rhododactyla confirmed by numerous images on Google. Thank you very much. Dhatier (talk) 18:45, 24 July 2018 (UTC)