39 votes
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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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  • 22.2k
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 ...
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31 votes
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During the "Ice Ages" or "Snowball Earth" times, where was all the energy?

I'm not quite sure if the question is asking about glacial, ice ages, or snowball Earth, and whether it's about the onset or end of a glacial period. I'll try to hit all three. Ice Ages and ...
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  • 20.2k
27 votes
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How old is the Earth?

Yes, the age of the Earth is about 4.5 billion years (4,500 million years). Your linked articles describes well how it was formed and how we know about it. The uncertainty is less than 1% and depends ...
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  • 5,896
26 votes
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Does the Plate tectonics contradict the theory of continental drift?

The boundary between the African and South American plate is a 'divergent' boundary. The two continents were joined as part of the Pangean super-continent. In the Cretaceous period a rift opened up ...
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  • 1,606
24 votes
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What is the fastest the Earth has ever spun?

The speed of rotation of Earth is controlled by its angular momentum. And the conservation of angular momentum is a very serious law of physics (perhaps even stricter than conservation of mass). So in ...
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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 ...
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  • 22.2k
21 votes
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Why is Earth's inner core made of an iron-nickel alloy?

The first thing you should think about is how the accretionary disk cooled and the cosmochemical constraints this put on Earth (But I am not going into details here). From studying meteorites it is ...
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  • 3,876
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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  • 5,892
20 votes

Why deep ocean didn't freeze during snowball Earth?

At least four things combined to prevent solid freeze-up during Ice/Slush Ball Earth periods: It takes a lower temperature to freeze water under pressure. Deep sea pressures are enormous. Ice ...
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19 votes
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How did Earth's plate tectonics start?

Is there a theory on how the Earth's plates were initially formed? The answer to this is has roots in another question you asked about the differences between continental crust and oceanic crust. ...
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  • 306
19 votes
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How did helium deposits form?

Helium (He) is formed by radioactive decay of uranium (U) and thorium (Th) to lead (Pb). There's another name for the nucleus of a 4He atom: It's an alpha particle. Alpha decay is one of the pathways ...
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  • 20.2k
19 votes
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When did wildfires start to occur on earth?

A definitive statement comes from the abstract of Scott and Glasspool1, 2006: Charcoal, a proxy for fire, occurs in the fossil record from the Late Silurian (≈420 Myr) to the present. One of the ...
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  • 3,038
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 ...
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18 votes
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Change in earth mass since the time of the dinosaurs

I gather, but may be wrong, that the mass of earth at present increases by around 108kg/day. All else being equal, one would expect the earth to have gained a mass, since 75 million years ago, of: $$ ...
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  • 20.2k
17 votes

Does the Plate tectonics contradict the theory of continental drift?

Alfred Wegener developed his theory of continental drift in the early 20th century. His theory wasn't well accepted at that time. Geologists of that time had their own not quite scientific ideas ...
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15 votes
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Why does the earth spin clockwise?

Earth's Spin Earth rotating clockwise is the result of a chain reaction that started when Earth's star formed as the result gas clouds collapsing. During the collapse of the gas, one direction was ...
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  • 4,561
15 votes

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

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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15 votes
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Why is the concept of "mass extinction" a relatively recent development in geology?

The idea of mass extinction is not that recent actually: Cuvier (1798), Buckland (1823) and d'Orbigny (1851) for instance were already talking about global catastrophes in earth history, linked to ...
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  • 5,238
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 ...
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  • 3,780
15 votes

If we assume the mega impact hypothesis for the formation of Moon, where on Earth is the impact point?

I think you are confused about the timescales and the magnitude of the impact that is being talked about here. The collision between the early Earth and a roughly Mars sized body, Theia is thought to ...
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  • 2,211
15 votes

What significant factors influencing geological change are still occurring?

The effects of Earth's past climate variations on the landscape, especially glaciation, cannot be underestimated. The multiple glacial advances and retreats over the last 4 million years or so have ...
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  • 3,038
14 votes

Why does the earth spin clockwise?

If you ascribe to the giant impact hypothesis, which most scientists do, whatever rotation the Earth had prior to the formation of the Moon was lost thanks to that 'giant impact'. That was a massive ...
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  • 20.2k
14 votes
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Why deep ocean didn't freeze during snowball Earth?

What makes you think Geothermal energy and underwater volcanoes are too weak? The mid-oceanic ridge system alone is 50000 miles long. The mean heat flow at the surface (91.6 mW/m2) has to be ...
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  • 2,361
14 votes
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What would it be like to live in an ice age?

It depends where, the continental landmasses at higher latitudes would be covered by massive ice sheets. Therefore the life in the sections of the US and Europe that are close to the Ice sheets would ...
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14 votes

Could the earth be much older than the currently accepted number?

The age of the solar system is 4.6 billion years. We know that because almost all meteorites are 4.6 billion years old¹. Therefore, that puts a very solid upper boundary to the age of the Earth. ...
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13 votes

How much have global GPP and biomass changed over Earth's history?

To answer your question to the point: we don't know at all. For most of living organisms, the fossil record is either inexistent or very fragmentary. Even estimating the number of species (which is ...
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  • 5,238
12 votes

How have global sedimentation rates changed over the last billion years?

Sedimentation rate presently varies many orders of magnitude depending on the place you observe. The rate of sedimentation is also different. Some places have continual sedimentation, others have ...
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