Talk:Geothermal gradient

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I removed a description from the graph at top because it seemed to apply to a different picture. Lollipop (talk) 03:49, 17 May 2018 (UTC)[reply]

Sorry, but I find the top schematic figure (https://en.wikipedia.org/wiki/File:Temperature_schematic_of_inner_Earth.jpg) very confusing. What is on the horizontal axis ? There is no scale, no label other than "Temperature". — Preceding unsigned comment added by 2001:1458:202:55:0:0:101:EBB1 (talk) 14:28, 2 March 2022 (UTC)[reply]

In the first paragraph of this article, the geothermal gradient is given as "about 25–30 °C/km (72-87 °F/mi)".

The Template:Convert seems to be unable to cope with simultaneous conversion (1) from a °C range to a °F range and (2) from km to mi. Therefore, the calculation has been done manually. Here is the calculation: 25-30 °C per km. Convert °C per km range from km to mi by dividing °C per km range by 0.6214 (the km to mi conversion factor); so 25 to 30 °C per km divided by 0.6214 equals 40.2 to 48.3 °C per mi. Multiplying both of the °C per mi values by 1.8 (the °C range to °F range conversion factor) gives 72.4 to 86.9 °F per mi. Rounding up or down to whole numbers gives 72 to 87 °F per mi. GeoWriter (talk) 12:37, 14 March 2020 (UTC)[reply]

Another way to calculate the conversion is "°C per metre x 54.86 = °F per 100 feet". (See source reference: Lovering, TS and Goode, HD (1963) "Measuring Geothermal Gradients in Drill Holes Less Than 60 Feet Deep East Tintic District, Utah", United States Geological Survey Bulletin 1172, page 2 at https://pubs.usgs.gov/bul/1172/report.pdf ). Thus: 25 °C per km = 0.025 °C per m. Multiply by 54.86 = 1.3715 °F per 100 ft. 52.80 x 100 ft = 1 mile. 1.3715 x 52.8 = 72.4 °F/mi. 30 °C per km = 0.030 °C per m. Multiply by 54.86 = 1.6458 °F per 100 ft. 52.80 x 100 ft = 1 mile. 1.6458 x 52.8 = 86.9 °F/mi. Rounding up or down to whole numbers gives 72 to 87 °F per mi.

The geothermal gradient is a temperature change per unit distance; adding or subtracting 32 is not applicable to calculations of temperature changes. (Conversion of individual specific temperatures, however, does add or subtract 32). GeoWriter (talk) 22:51, 10 June 2023 (UTC)[reply]

This article refers to our planet as "Earth"', "the Earth" and "the earth". This inconsistency seems unencyclopedic to me. I suggest that a single variant should be used throughout for consistency. Any preferences or comments? GeoWriter (talk) 18:11, 8 August 2021 (UTC)[reply]

I changed all occurrences (except "earth tides") to "Earth" on 2 March 2022. —GeoWriter (talk) 00:30, 17 November 2022 (UTC)[reply]

Hey all, I don't know how to change it myself but the depths on the first image are completely wrong (https://commons.wikimedia.org/wiki/File:Temperature_schematic_of_inner_Earth.jpg?uselang=de) The lithosphere is not 410 km thick, at 410 km there is a phase transition which marks the boundary between upper and lower mantle (see, e.g. here https://en.wikipedia.org/wiki/Upper_mantle_(Earth)). — Preceding unsigned comment added by Linesbijan (talk • contribs) 13:04, 7 November 2022 (UTC)[reply]

Agreed. The graph itself seems okay; the 410 label looks wrong, and should be replaced with a more reasonable value for the base of the lithosphere (say, 280 km, the maximum continental thickness). I suggest copying this criticism to the Commons page for the graph, as its originator is in the best position to correct the graoh. Kent G. Budge (talk) 14:42, 7 November 2022 (UTC)[reply]

I have added some text to the image caption in the article: "410 refers to the top of a "transition zone" in the upper mantle. The lithosphere is less than 300 km thick.". I hope this clarifies the graph, at least until the actual image can be improved. GeoWriter (talk) 20:55, 11 November 2022 (UTC)[reply]

The depth of the surface of the outer mantle is also inconsistent between the first figure and the text: 5100km vs 3500km. (I don't know which is correct) PhysicistQuery (talk) 11:26, 29 October 2025 (UTC)[reply]

Thanks for reporting a depth discrepancy. It is actually the inner core/outer core boundary. I have corrected the depth and added a source reference citation. GeoWriter (talk) 20:27, 29 October 2025 (UTC)[reply]

The article lead currently quotes an IPCC document on " "The possible role and contribution of geothermal energy to the mitigation of climate change" as its source for a 25–30°C/km gradient. The focus on geothermal energy generation limits the scope of that document to accessible continental crust.

The magnitude of the geothermal gradient depends on the rate of heat production at depth, the dynamics of the system, and the conductivity of rocks. The highest gradients, 40–80 K km−1, are measured at oceanic spreading centers (mid-ocean ridges) or at island arcs where magma is close to the surface. The lowest gradients occur at subduction zones where cold lithosphere descends into the mantle. The gradient in old stable continental crust is ~30 K km−1 and is somewhat lower in cratons.

The source quoted above may be too detailed for the article lead and does not directly address the much higher average thermal gradient in oceanic crust which is typically thinner, covers more than half of the Earth's surface and is where most of the heat flow occurs.

It seems strange that an entry titled "Geothermal gradient" provides more information about Heat Flow while the only numerical information about the thermal gradient is partial and misleading. Annette Maon (talk) 23:38, 29 February 2024 (UTC)[reply]