Questions tagged [geochemistry]

The science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems.

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35
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5answers
3k views

How do we know the asteroids formed at the same time as earth?

In continuation of the question Why is Earth's age given by dating meteorites rather than its own rocks?, what evidence do we have that the asteroids indeed formed at the same time as earth? Is there ...
33
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3answers
14k views

Why is Earth's age given by dating meteorites rather than its own rocks?

Reading a course on Precambrian, I read that: Earth Age (around 4.5 billion years) is dated thanks to the meteorites hitting Earth during its formation rather than the inner materials composing the ...
33
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5answers
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How and why did the oceans form on Earth but not on other planets?

Earth is the only planet in our solar system that has copious amounts of water on it. Where did this water come from and why is there so much water on Earth compared to every other planet in the ...
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What is the origin of the dominant atmospheric nitrogen content in Earth's atmosphere?

Comparing the atmospheric compositions of Earth with our nearest neighbours: As the table shows, the Earth's atmospheric nitrogen concentration is 78%, compared to 3.8% for Venus and 2.7% for Mars ...
24
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2answers
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Natural nuclear explosions

I'm aware of the Oklo reactor and other natural nuclear fission reactors, in which geological processes can lead to the formation of a sustained, self-regulating uranium fission reactor. Is it also ...
22
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2answers
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Peak phosphorus - what are the sinks?

The minable phosphorus reserves are limited. Where is the mined phosphoprus landing, what are the global phosphorus sinks? I would assume that most phosphorus is used for fertilizer and ultimately ...
21
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2answers
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Why does phosphate rock contain uranium?

I have been doing some research on the issue of phosphogypsum pollution. Phosphogypsum is a waste by-product formed with the "wet process" method of extraction of phosphoric acid out of phosphate ...
20
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3answers
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What are rare earths and why do they cluster near alkaline magmatism?

'Rare earths' play a vital role in the modern economy, and they are becoming more of a point of focus in geopolitical realms. What are 'rare earths' and why do they appear to cluster in association ...
20
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0answers
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How are Mauna Loa $\ce{CO2}$ monthly trends computed?

The problem I am trying to figure out how $\ce{CO2}$ concentration trends are computed in the data provided by the Earth Systems Research Laboratory Mauna Loa Observatory. The data contains monthly ...
19
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4answers
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What was the first rock in the rock cycle?

I am an undergraduate student but I am a tutor at a High School, and one student asked me. Attempting to explain the rock cycle "if one rock turns into the other then which came first" my gut is ...
19
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2answers
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What is the origin of the ocean's salt?

We know we cannot live without salt, but an investigation into the origins of ocean's salt leads one to believe that this issue is not fully resolved yet. What geological phenomenon caused the earth ...
19
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3answers
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Why does Earth have abundant oxygen in the atmosphere?

Because of photosynthesis, obviously. But then it's not actually that obvious after all, because photosynthesis is mostly balanced by respiration. We can summarise the processes of photosynthesis ...
18
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3answers
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Is the magma in one volcano different from the magma in every other volcano?

First off, a confession: I'm asking this question because of The Lord of the Rings. If you're not aware already, in the story, a magical ring can only be destroyed in a specific volcano. The reason ...
16
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1answer
477 views

Why won't Yellowstone explode?

From my understanding Yellowstone is a massive super-volcano, so why isn't it active? Where has its (correct me if I'm using the wrong term) hot-spot gone? Can it still erupt?
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How much Uranium is there in the Earth's Crust?

Are there any estimates of the amount of Uranium there is in Earth's Crust? From what I know, it's supposed that there are large amounts of Uranium in Earth's Core, the decay of which is responsible ...
16
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603 views

Why is there Uranium in Earth's Crust?

Uranium's density is greater than most elements, so you would expect it to settle to the bottom of a volume of fluid. In the case of the Earth, which was molten in the beginning, you might then expect ...
16
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2answers
865 views

What processes produced the basalt columns of the Giant's Causeway?

The Giant's Causeway is, according to the Wikipedia page was formed during during the Paleogene Period, Antrim was subject to intense volcanic activity, when highly fluid molten basalt intruded ...
15
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1answer
307 views

When a tectonic plate subducts, does any of the subducted material melt, or is it just the mantle above the subducted slab that melts?

I know that water released from oceanic crust causes melting of the mantle in subduction zones, but does any part of the subducted slab melt as well - such as the sediments on the slab or the basalt? ...
14
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Would oceans regenerate if removed?

On Earth, there is enough Hydrogen and Oxygen to make 13,88 million km$^3$ of water (calculation below). However, oceans contain only a tenth of that. Clearly, most of the hydrogen must be stored in ...
13
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3answers
491 views

What, if any, paleoclimate data can be derived from igneous rocks?

Paleoclimate data often derives from sedimentary rocks. Metamorphic rocks can also contribute to paleoclimate information in a wide variety of ways. What about igneous rocks? I guess that this can ...
13
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1answer
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What are the high field strength and large ion lithophile (HFS or HFSE & LIL or LILE) elements?

There are two groups of elements that are frequently mentioned when discussing incompatible trace elements. They are the high field strength elements (HFS or HFSE) and the large ion lithophile ...
13
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1answer
125 views

Does the heating of the oceans due to greenhouse effect negate the acidification due to increased CO2 levels?

As I understand, the dissolving of carbon dioxide leads to increased acidification of the oceans, and thus increased atmospheric CO2 levels would lead to more dissolution in the oceans and thus ...
13
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1answer
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What is it about ancient craton geology that results in associated kimberlite pipes containing economic diamond deposits?

According to the Australian Geological Survey Organisation paper Kimberlite and lamproite diamond pipes (Jaques, 1998), economic deposits of volcanically-formed diamonds are restricted to ancient ...
13
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1answer
228 views

Why does aragonite form in one case and an acetate in another?

If I add acetic acid to limestone, I can get calcium acetate crystals to grow but if I add acetic acid to dolomite, supposedly I can grow aragonite which is a form of calcium carbonate. Why would I ...
12
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395 views

Nuclear testing and the Anthropocene, a chemostratigraphic link?

The Anthropocene is described by Wikipedia as an informal geologic chronological term for the proposed epoch that began when human activities had a significant global impact on the Earth's ...
12
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2answers
384 views

What does groundwater consist of?

I heard that groundwater is rich in minerals and fluorides, but I have no clear thoughts on what else it contains and whether the ground water differs from area to area. Can someone please shed some ...
12
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1answer
71 views

Why are titanium oxides lumped in with magnetite for the purposes of analyzing water bubble nucleation?

I was reading a bit about the fluid mechanics of volcanoes to further understand some of the dynamics of "magma wagging" from my earlier question. From [2]: Heterogeneous nucleation, in which the ...
12
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1answer
349 views

How much silicon is in the Earth's core, and how did it get there?

With some informal conversation with a peer of mine, he had suggested that there is evidence (which he couldn't find,but had remembered reading) that there was Silicon in the Earth's core. I referred ...
12
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1answer
317 views

Are there significant amounts of rare earth elements on Iceland?

The rare earth elements form in magmatic rocks. The Iceland is very active vulcanic region, and it's, to my knowledge, entirely build from magmatic rocks. So it wouldn't be surprising if there were ...
12
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1answer
445 views

How is abundance of elements in the Earth's crust estimated?

In an quiz app I surprisingly learned that aluminium has a larger abundance then iron. When researching this on Wikipedia, I found this article, which also had the comment: Note that numbers are ...
11
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3answers
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Looking at ocean depth/latitude profiles of dissolved oxygen and nitrate. Why is dissolved oxygen low when nitrate is high?

I was looking at a depth profile of a segment of the Atlantic Ocean. What is the relationship between dissolved oxygen and nitrate? When nitrate is high, dissolved oxygen is low and vice versa. I've ...
11
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5answers
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Why is continental crust less dense than oceanic?

Why is it that continental crust is less dense than oceanic, where in fact continental crust is thicker than oceanic crust?
11
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2answers
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Why are alkali basalts found at rifting centres and on top of 'plumes', whereas MORBs are generally tholeiitic?

So I was essentially wondering why it was that the basalts on top of 'plumes' at 'hotspots' (sometimes called OIBs, ocean island basalts) and at continental rifting centres are enriched in alkaline ...
11
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1answer
1k views

Why do most opal deposits occur in Australia?

According to the Wikipedia page about opals, this hydrated amorphous silica based gemstone is most commonly found in Australia, with according to the page, over 90% from Australia. Opal from Coober ...
11
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1answer
144 views

Are there any metal anomalies other than iridium in the K-Pg boundary?

The iridium anomaly marks the elevated concentration of iridium in sedimentary deposits of the Cretaceous-Paleogene boundary. The iridium is said to come from the impactor, which is supposed to have ...
11
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1answer
118 views

Why would a suite of related rocks have one anomalous sample?

I have a suite of rocks that have nearly identical major element chemistry, but a single sample has quite different trace element concentrations. All the rocks are trachydacites. I know the analysis ...
11
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1answer
141 views

What is the mechanism behind changes in oxidation state (of iron, for example) as magma rises?

From this answer, I learned that rising magma may change oxidation state, which I wasn't aware of. In [#1], the authors state in the abstract The conventional view holds that the oxidation state ...
11
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1answer
256 views

Use of Neodymium in Paleoceanography

$\varepsilon_{Nd}$ (i. e. the relative deviation of $\frac{^{143}Nd}{^{144}Nd}$ from a standard) is often used as a proxy in paleoceanography to identify the basin of origin of oceanic currents. But ...
10
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5answers
26k views

Which theory is stronger, that iron came from outside or was formed within earth?

Where is the current body of science learning towards, that iron came from meteor or it was somehow formed on earth?
10
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1answer
263 views

Why would magma have high amounts of nickel and chromium?

I am doing a research project on Mount Lamington and through my research I have found that its magma has unusually high amounts of chronium and nickel. What would cause this to happen? Is there ...
10
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1answer
1k views

Why do Volcanoes give out so much Sulphur Dioxide and Carbon Dioxide?

From my understanding, the mantle is in a highly reduced state, so I can't understand why a volcano would give off a highly oxidised gas such as sulphur dioxide. Carbon dioxide is too an oxidised ...
10
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2answers
206 views

What is the geothermal potential of a volcano?

If there were lots of geothermal plants—even mobile ones—near a volcano, how much power could this provide? Could the sapping of some of the heat energy make the volcano less likely to erupt?
10
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1answer
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What is the Calcite Compensation Depth and what is its significance for carbonate deposits?

What is the Calcite Compensation Depth (CCD) and what is its significance for carbonate deposits?
10
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1answer
130 views

What does geochemical data tell us about Earth's earliest palaeoclimatic conditions?

Given that the age of the oldest zircon samples are about 4.4 billion years old, and meteorites and other extraterrestrial samples can also give us some indication about the Earth's composition into ...
10
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1answer
126 views

What's the partition coefficient (D) of Nb for apatite?

Was there any experimental study that determined $D$ for apatite and silicate liquid? The GERM Kd database only lists one study with carbonatite liquid, but that's not what I'm looking for.
10
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1answer
287 views

What is the geochemical origin of carbon dioxide with the 'white smokers' of the Champagne Vent?

Associated with the NW Eifuku volcano, a small submarine volcano in Japan's Volcano Island chain in the Pacific Ocean is a carbon dioxide rich hydrothermal vents called white smokers by NOAA (see ...
9
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1answer
366 views

How does the composition of volcanic rock change as it makes its ascent towards the surface?

A schematic for the fluid mechanics of a volcano is represented below. Graciously borrowed from Figure 1 of the reference cited below From the caption of that figure: During explosive eruptions, ...
9
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1answer
144 views

What makes the conditions at the core/mantle boundary ideal for aluminum to combine with other elements besides oxygen?

Recently, steinhardite was accepted as a new mineral by the International Mineralogical Association. It's quite an interesting story in its own right. There's an interesting article in New Scientist ...
9
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1answer
254 views

Simplest formula of a calcium phosphate mineral?

I had a homework question: Given the formula: $$\ce{Ca}_x\ce{(PO4)}_y\ce{OH}$$ Find the lowest possible values of $x,y$ and state (look up) the mineral name. Based on the anion charges ...
9
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1answer
216 views

Did an impact crater influence the formation of uranium deposits in South Australia?

As a supplementary question Did an impact crater cause the formation of the gas fields in north eastern South Australia . South Australia is a well documented uranium province. Could an impact crater, ...