# Tag Info

## Hot answers tagged geochemistry

39 votes
Accepted

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

Some background: We are able to determine the age of certain rocks and minerals using measurements of radioactive and radiogenic isotopes of certain elements. The most common are U-Th-Pb, Rb-Sr and ...
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36 votes
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### How do we know the asteroids formed at the same time as earth?

what evidence do we have that the asteroids indeed formed at the same time as earth? It depends on what is your definition as "the same time". The formation of the solar system and Earth did not ...
• 22.2k
22 votes
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### What was the first rock in the rock cycle?

which came first That's actually a very hard question. The most simple answer would indeed be igneous. Here's why: Sedimentary rocks (in the sense of rock cycle) comes from pre-existing igneous or ...
• 22.2k
22 votes
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### Taking into account the decay products of transuranic elements, are the world's uranium reserves growing or shrinking?

Let's start with the easy question: given our current known reserves of transuranic elements and again taking into account their decay products, where will the greatest uranium reserves be in, say, ...
• 22.2k
21 votes
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### What is the origin of the dominant atmospheric nitrogen content in Earth's atmosphere?

According to the recent paper in Nature Geoscience: Nitrogen speciation in upper mantle fluids and the origin of Earth's nitrogen-rich atmosphere, $N_2$ originates from regions of the Earth where ...
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20 votes
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### Natural nuclear explosions

This hypothesis has been studied here as a possible explanation of selenogenesis (formation of the Moon). (Forming the Moon from terrestrial silicate-rich material. R.J. de Meijer, V.F. Anisichkin, W. ...
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19 votes
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### Why does phosphate rock contain uranium?

To understand why sedimentary phosphate rocks (hereafter referred to as phosphorites) have elevated uranium contents we first need to understand what are they made of and why do they form in the first ...
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18 votes
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### Which theory is stronger, that iron came from outside or was formed within earth?

The only elements that were formed on Earth are those produced by radioactive decay. There are four natural decay chains that start with transuranic elements and none terminate in iron; neither do the ...
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18 votes

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

The answers that have been provided are correct but they're omitting the fundamental issue that explains why they are correct: When you date a rock you get the point that it solidified, not the point ...
16 votes
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### What are the implications of the recent discovery that huge oceans exist close to the mantle of the Earth?

I am going to assume that you are referring to recent new stories with titles like "Rare Diamond Confirms That Earth's Mantle Holds an Ocean's Worth of Water" (Scientific America). These articles are ...
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16 votes
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### Why won't Yellowstone explode?

This is a complex question, and I cannot give you a complete answer I'd like to point out that there is a very important article published in February of this year on the subject: volcanoes are in an ...
• 6,386
16 votes

### Is the magma in one volcano different from the magma in every other volcano?

In keeping with your Lord of the Rings inspiration, the first reference is from New Zealand, where the Lord of the Rings movies were made. There are three main types of magma that volcanoes currently ...
• 21.8k
15 votes

### What was the first rock in the rock cycle?

The Earth existed long before there were crustal rocks or a "rock cycle." The idea of the "rock cycle" has prerequisites to even be meaningful. These include: The existence of a crust (both a ...
• 3,780
13 votes

### Do lead 206 and other daughter isotopes occur naturally?

While lead 206 does occur naturally, unless a zircon (a zirconium silicate crystal) is contaminated with lead or has been around a long time, it will contain no lead. Zirconium, uranium, and thorium ...
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12 votes

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

The formation of a T-Tauri star spells the beginning of the end of the protoplanetary disk from which planets and asteroids can form. The end is nigh when that star ignites. The large solar winds and ...
• 20.5k
12 votes

### Is oxygen the most abundant element on Earth?

Both of them. The composition of the atmosphere, crust, mantle, core and bulk earth are all notably different. The atmosphere is composed of ~78% nitrogen and ~21% oxygen, with small amounts of ...
• 2,211
12 votes

### Are fossil fuels really formed from fossils?

Let's look at this. A very large number of points for one question. First, the solar system. We do not see any hydrocarbons in the inner solar system (Mercury to Mars). This is because in this region ...
• 1,052
12 votes
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### Why don't iron meteorites on Mars rust or oxidize? Why are they shiny?

tl;dr: Compared to Earth, the atmosphere on Mars is very thin; in addition, it contains much less of oxygen and water (i.e., is very dry). It is much colder there. These conditions may slow down ...
• 596
11 votes

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

All the material that eventually formed our solar system is essentially recycled star dust. All iron on Earth was produced by large stars that existed before our Sun formed: the iron was created ...
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11 votes
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### Why do Volcanoes give out so much Sulphur Dioxide and Carbon Dioxide?

the mantle is in a highly reduced state This is not entirely correct. The core is in a highly reduced state, but the mantle is not necessarily reduced, and is quite oxidised in some places. The ...
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11 votes

### How do archaeologists address time dilation when analyzing carbon dating results?

For all intents and purposes, the Earth represents one frame of reference, as @kwinkunks states. Therefore no effect. Yes the gravitational field on top of a mountain is slightly less than at sea ...
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11 votes

### How do archaeologists address time dilation when analyzing carbon dating results?

How do archaeologists address time dilation when analyzing carbon dating results? They don't. There is NO point in doing so. Compare two hypothetical substances at the peak of Chimborazo (the highest ...
• 20.5k
11 votes
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### What are the high field strength and large ion lithophile (HFS or HFSE & LIL or LILE) elements?

First, a short introduction to incompatible elements The Earth's mantle is mostly composed of the minerals olivine, pyroxene, anorthite, spinel and garnet. These minerals are made from the elements ...
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11 votes
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### Age of fossils found in rocks

Yes, there is some amount of circular reasoning in the statement: "geologist date rocks by the fossils they contain and date fossils by the rocks in which they are found". However, that statement ...
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11 votes
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### Diamond at the core of Jupiter

I would think this is questionable, though we don't have a definitive answer yet. We usually think Jupiter has a roughly solar composition, which according to the solar abundance measurments of ...
11 votes
Accepted

### Non-invasive techniques to find rock composition

You are looking for a portable XRF. It does (almost) exactly what you said. It sends electromagnetic radiation to the rock (X-rays), which excites electrons in the atoms and when they bounce back ...
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