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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 Sm-Nd. Simply put, the resulting date is the time that has passed from the crystallisation of that mineral. Obviously there are complexities, but there are not ...


35

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 happen at a particular second in time but was rather a continuous process. It also depends on what you define as "asteroids". I'll try to put some things in order. ...


24

Your assumption that there is not a lot of water elsewhere in the solar system is incorrect. According the this article on NASA's website; Missions in recent years have overturned our view of a dry solar system, returning mounting evidence of ample water from a vast array of locations. Comets from the remote corners of our solar system are made of ...


20

The water was already present when the Earth assembled itself out of the accretionary disk. Continued outgassing of volcanoes transferred the water into the atmosphere which was saturated with water. And rain transferred the water onto the surface. Compared to other planets and smaller solar system object Earth has a big advantage. It is large enough to ...


20

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. van Westrenen. 2013.) The only place cited as suitable for spontaneous criticality is the Core-Mantle Boundary (CMB). The calculations above show that ...


19

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 metamorphic rocks, so you need to have had them first. Metamorphic rocks, by definition, are rocks that form from other kinds of rocks (be it igneous or ...


17

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 decay chains that are artificial or those that result from cosmic radiation. So all of our iron is from the Earth's formation or meteor impacts since then.


17

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 plates are converging. Venus and Mars lack plate tectonics and therefore lack $N_2$ in their atmospheres. In other regions of Earth upper mantle, and in Venus and ...


17

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 the material came into being. Most rocks on Earth have melted time and again and thus are useless for figuring out how old the Earth is.


16

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 eruptable state very very short periods of time in the geologic timescale; the mobilization of magma is very rapid but its storage is kept near, but under the ...


16

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 referring to research published in Nature: Pearson, D. G. et al. (2014). The researchers found an inclusion of ringwoodite inside a diamond. Here is a quote ...


15

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 place. Phosphorites are rocks that are made of apatite, a mineral with the formula $\ce{Ca5(PO4)3(F,Cl,OH)}$. This mineral (especially the OH variant) is one ...


14

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 produce: basalt, andesite and rhyolite. Basalt magma has a high temperature, around 1200ºC, it is poor in silica, has a low viscosity and a low gas content. ...


12

It is bond strength, not hardness, that determines how easily oxygen can attack and burn a material, allowing me to burn a diamond in a pool of liquid oxygen resting in a block of graphite. Diamond is hard because its bonds form an inflexible, three-dimensional lattice. However, the strength of these bonds themselves is not even as strong as graphite, ...


12

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 solar radiation pressure sweep the disk clean of all small objects. Some spirals inward, some outward. There's no dust and no gas from which new planets and ...


11

According to wikipedia, there are around 5.5 million tonnes of uranium in ore deposits that are commercially viable at current prices, and perhaps 35 million tonnes that are potentially viable if prices increase. Also according to wikipedia, the Earth's crust (to 25 km depth) contains an estimated 10^14 tonnes (100 trillion tonnes), while the oceans may ...


11

"Rare earth" metals consist of Scandium, Yttrium, and 15 other metals of the so-called "Lanthanide" series toward the bottom of the Periodic Table of elements. Basically, these are the chemicals that we didn't study in chemistry class at school. Like other metals, they have two electrons in the outer shell, but unlike "metallic" chemicals such as sodium or ...


11

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 during nuclear fusion and later released when the parent star(s) exploded, presumably supernova. After our solar nebula had formed and material had been ...


11

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 mantle is heterogeneous. 2. however I justify it's emission because carbon dioxide is continually being fed into the mantle by the subduction of carbonate ...


11

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 level. This is very small though. Variations in gravity over the Earth's surface typically vary at most by a few hundred milligals (ie. "one part in 10,000" order ...


11

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 peak in the world with respect to distance from the center of the Earth). Suppose one of those substances spent all of the last 4.5 billion years at several ...


11

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 continental and oceanic crust actually.) Plate tectonics The existence of an atmosphere and ocean. Without all of these, the concept of the rock cycle (as ...


11

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 does not fully describe how geologists date rocks or fossils. Dating rocks by fossils is a branch of geology called "biostratigraphy". This is a non-absolute and a ...


11

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 other gases. The bulk composition of the earth by weight is mostly, iron, oxygen, silicon and magnesium, in that order, with all the other elements making up only ...


11

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 of the solar system, dissociation by solar UV rapidly destroys primordial hydrocarbons. This effect is much weaker further out. Oil well 'replenishment' will ...


10

Uranium is primarily lithophilic (it readily combines chemically with oxygen), but also is chalcophilic (it readily combines chemically with sulfur). It definitely is not siderophilic (it does not readily dissolve in molten iron). The first two means that uranium compounds are easily formed, which are of course much less dense than is pure uranium. That ...


10

This is a very good question Inkenbrandt. It is quite common for even some graduate students to think that the majority of partial-melting comes from the slab: when it is the the mantle above the fore-arc, in the volcanic region, where most of the partial melting occurs. Lets think about this mathematically: you say yourself that you realize that subduction ...


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