winwaed
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Why are oceanic plates denser than continental plates?
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23 votes

Ocean lithosphere (geophysical definition of crust + upper mantle that acts as a 'plate') is primarily of basaltic composition - the upper levels are basalt and the lower levels are gabbro. The top ...

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Can pyroclastic flows cross water?
16 votes

In answer to the title question, "yes"! Here are some videos from Montserrat Soufriere Hills where the phenomenon has been extensively studied (probably more than anywhere else): http://www.geo.mtu....

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During the "Ice Ages" or "Snowball Earth" times, where was all the energy?
15 votes

Of course it isn't "absurd", and looking at the ball-park energy budget figures you'll see why: First, I don't think anyone is claiming the Earth is completely frozen. More of a "slushy at the ...

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How deep could the surface of the Earth's crust get?
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15 votes

Challenger Deep (10.99km) in the Mariana's Trench is the deepest part of the ocean floor. This is probably close to the deepest theoretically possible ocean floor with the current thermal regime. ...

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How does one measure what causes earthquakes?
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14 votes

There are a number of causes (this list is probably not complete): Elastic Rebound of tectonic faults. This is the most common and well known. Here the energy is elastic energy stored as two blocks ...

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What happens to global temperature when we stop all the vehicles for a year?
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13 votes

There are two factors to be aware of: First, cars (and all road vehicles) account for only a fraction of human CO2 output. Off-hand I've a feeling it is about a quarter or a third although I don't ...

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How is the mass of the Earth determined?
13 votes

Cavendish may have used a more direct approach, but Neville Maskelyn did it earlier in the Schiehallion Experiment - publishing in 1778. Very much an Enlightenment story involving money left over from ...

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Does vegetation contribute to long-term carbon sequestration?
13 votes

Unlikely but theoretically possible. As the bits of tree work their way down to the sea, they are going to oxidise and release CO2. This would appear to our eyes as "rotting" and breaking down. Leaves ...

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Why does the "Ring of Fire" pretty much define "Pacific Rim"
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12 votes

There isn't a concentration of tectonic plates - rather the opposite! The "Ring of Fire" is a pattern really. It is marked by subduction zones. So the question becomes, "Why is the Pacific Ocean ...

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

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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Why does the so called "tornado alley" exist?
10 votes

In addition to @casey's answer regarding the conditions (which undoubtedly is the main answer), don't forget the issues of size and sampling. In the US, the tornadoes can be large and destructive. ...

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Sediment layer chronology
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9 votes

In simple big picture terms, Sediments were deposited first from the bottom upwards (as you understand). Then the area was uplifted and the river eroded from the top down. Most erosion is from the ...

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Is it feasible to use depleted oil wells for geothermal production?
8 votes

In most cases, probably not. Oil could be considered a metamorphic mineral, formed by "gentle" heating. That is gently on a geological scale - still enough to burn your hands! Geothermal systems ...

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Why is the Ring of Fire there?
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8 votes

This question is very similar to: Why does the "Ring of Fire" pretty much define "Pacific Rim" The high levels of volcanoes and earthquakes are primarily due to subduction. So why ...

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Formation of limestone without living organisms?
7 votes

Oolites are limestones that are usually considered as in-organic, although they may have bits of shell/etc in them. These form by the precipitation of calcium carbonate around particles (sand, broken ...

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What is a fault?
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7 votes

A fault is a crack in the rock that shows movement over time. The movement may have stopped (eg. small faults seen in the field in the UK) or be essentially dead even though the crack still represents ...

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Why are there no crystals with 5-fold symmetry?
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7 votes

All unit cells are parallel-sided hexahedra. These are six sided shapes with parallel opposite sides. Their three principle angles may or may not be 90 degrees. And the three side lengths may or may ...

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What causes bottom water to rise?
7 votes

Some areas may well be relatively isolated. However water will come up when it is pushed from behind! E.g. there are strong sinks in the Norwegian Sea and Weddell Sea. This water must go somewhere ...

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How, exactly, do scientists know location of earliest continents?
6 votes

Well, the really earliest continents, the answer is we don't. As you go further back the uncertainties get larger and larger. It has been speculated that there have been around 4-5 super continents ...

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Checking the bedrock with radiowaves - how does it work?
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6 votes

Do you mean Ground Penetrating Radar? This is typically limited to very shallow depths though - eg. archaeological investigations, police forensics (finding graves), and civil engineering site ...

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Is Challenger Deep really the deepest place in the ocean?
5 votes

Short answer : yes Challenger Deep was discovered by (and named after) HMS Challenger in 1875. This was the world's first true oceanic scientific voyage. They took a LOT of soundings but compared to ...

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Why are there no subduction trenches on continental land?
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5 votes

Continental crust is thick and relatively buoyant. Ocean crust is much thinner, and relatively dense. Hence ocean crust "goes down" more easily, and the density can even help pull the ocean ...

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Is heavier bodies fall faster than lighter ones
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5 votes

The two stones will accelerate at the same rate due to gravity. This is usually attributed to Galileo although it was known before that - eg. John Dee was aware of it and didn't think it a new ...

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How do I derive the formula for lithostatic (overburden) pressure?
5 votes

The SI unit for force is the Newton, not the kilogram. This is defined from Newton's Second Law: $F = ma$. Hence, dimensionally, force (Newton) is 1 kg·m·s-2 Pressure is force per distance squared (...

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Do river fluxes help contribute to long-term carbon sequestration?
5 votes

Rivers generally include dissolved oxygen. Therefore any organic content in suspension will tend to dissolve. The movement of water (open to the atmosphere, etc) will tend to entrain some oxygen from ...

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How does Vertical Electrical Sounding Work?
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4 votes

The diagram is perhaps a little mis-leading. Think of the ground/rock between the electrodes as a big resistor. The surrounding rock can be modeled as a set of parallel resistors. Most of the ...

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

The age of 4.55Ga for the Earth is actually a date of "hard stuff" based on Iron-Nickel meteorites, dated using radio-isotope dating. If you had enough meteorite samples it should be possible to ...

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Does anyone know of a DBMS with global geospatial search?
4 votes

I agree with Speissburger that PostGIS (an extension of Postgre) has excellent Geospatial support. In the open source world, this would also be my recommendation. (MySQL claims to have some geospatial ...

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is there any technique developed that can estimate depth of bedrock?
3 votes

A small scale seismic survey as well. I remember as students we found the water table using a 100m refraction line and a sledge hammer sound source. Scale that up from ~5m to 100m you're going to ...

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Is there a correlation between hot springs and earthquakes?
3 votes

As a counter to @stali's answer, it is possible to have hot springs without volcanism or normal faulting - although these two scenarios do cover the most well known examples. Hot Springs, Arkansas ...

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