Questions tagged [earth-history]

Questions relating to Historical Geology.

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34
votes
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 ...
12
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3answers
6k views

Why is Earth's Core Iron?

The two major constituents of the Earth's core are iron and nickel. In documentaries and scientific conversations, iron gets more attention than nickel, probably because it makes up a bigger ...
4
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1answer
887 views

Causes of fluctuations in atmospheric oxygen in past 300 Mya

I have two questions based on the history of atmospheric oxygen levels depicted below. Source: https://commons.wikimedia.org/wiki/File:Sauerstoffgehalt-1000mj2.png. The notes below the chart explain ...
36
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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 ...
19
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4answers
16k views

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 ...
26
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4answers
12k views

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 ...
17
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3answers
3k views

How did Earth's plate tectonics start?

Plate tectonics is a theory which describes Earth's lithosphere as being composed of distinct plates which are able to move atop of the underlying asthenosphere. At plate boundaries, this movement ...
18
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2answers
809 views

Why are minerals found in “large” quantities and not scattered throughout the earth as individual atoms?

Heavier elements are created in stars. After stars die they scatter these heavier elements throughout the universe. These elements eventually gather to form planets. But why do we find "chunks" of ...
12
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2answers
470 views

Determining the paleoelevation of mountain ranges

In New Delhi, a lot of people say that the Aravali range used to be as tall as the Himalayas. How do scientists know that some mountain range used to be a lot taller millions of years ago, and what ...
11
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2answers
170 views

Water on Mars and Earth

If water on Earth came from meteorites, why doesn't Mars have substantial water? What made it more highly probable on Earth than on Mars?
11
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2answers
323 views

Change in earth mass since the time of the dinosaurs

Is there a significant difference in the mass of the Earth between now and the time of the dinosaurs (250 - 75 million years ago)? I was just wondering if the force of gravity on dinosaurs would have ...
9
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1answer
1k views

Was volcanic activity more prevalent when the dinosaurs roamed?

Popular film culture often depicts much volcanic activity during the time of the dinosaurs. Assuming "time of the dinosaurs" as the Jurassic (200 million years ago) until the end of the Cretaceous (...
6
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2answers
670 views

What was the likely composition of Earth's early crust (how did crustal composition evolve)?

Was the first crust entirely mafic (oceanic) crust which was later distilled via volcanic arcs along subduction zones to make felsic rocks or did the earth start with bits of felsic crust? Are the ...
5
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3answers
12k views

Why silicon is abundant in earth surface?

What is the reason for having silicon in so large quantity on earth surface?
25
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3answers
36k views

Why is Earth's inner core made of an iron-nickel alloy?

This question has puzzled me for a while. I know that earth's mantle is made of different minerals, metals and rocks etc. and that has always made complete sense to me. But why is the inner core made ...
18
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3answers
29k views

Why does the earth spin clockwise?

Why does earth rotate in a clockwise direction? Did a large meteor collide with earth causing earth to rotate? If that is what happened, could another, larger meteor cause earth to reverse its ...
11
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1answer
244 views

What caused a fall in atmospheric oxygen about 1.9 billion years ago?

Using chromium isotopes geochemistry, Frei et al. 2009, describe in the article Fluctuations in Precambrian atmospheric oxygenation recorded by chromium isotopes that after the Great Oxidation Event (...
18
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3answers
2k views

Why deep ocean didn't freeze during snowball Earth?

I know that at least twice in its history Earth was totally frozen. I also know that the last time it happened there were already life on Earth, and it survived. In deep water, under the ice, which ...
9
votes
1answer
308 views

Where did the atmosphere's nitrogen come from? [duplicate]

According to Wikipedia's article Atmosphere of Earth: Outgassing from volcanism, supplemented by gases produced during the late heavy bombardment of Earth by huge asteroids, produced [Earth's ...
8
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2answers
1k views

Why is earth's axis tilted?

Why is the axis of earth tilted? It can't possibly be that the Northern hemisphere is larger causing it to be pulled toward the sun, because then it would always be summer in the N hemisphere and ...
5
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2answers
636 views

Were all of Earth's minerals created before Earth's formation, during, or after?

I've heard that during the accretion of proto-planets that formed the earth, 60 minerals were created through the reactions of atoms and molecules in the nebula. Do these first minerals still make up ...
18
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2answers
1k views

Historically, how has the fraction of Earth covered by water changed?

Today, 70.8% of the Earth is covered in water (± a few tenths of a percent depending on how you account for lakes).1 How has this figure changed over the history of the Earth, and why? Of course, if ...
11
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1answer
264 views

Is there conclusive evidence for the Antarctic Circumpolar Current developing after the glaciation of Antarctica?

The Antarctic Circumpolar Current (ACC) is the continuous oceanic current that encircles the Antarctic continent, as is often explained in the literature as being the cause of the onset of glaciation ...
11
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1answer
2k views

What is the fastest the Earth has ever spun?

How fast can the Earth rotate and support life? In prehistoric times, dinosaurs were so massive that archeologists wonder how they were not crushed under their own weight. Could a faster spinning ...
9
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1answer
221 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, ...
7
votes
1answer
189 views

Where did the continents come from?

In animations that show the location / drift of the continents over the aeons, it seems that the continents (or cratons?) are just floating / drifting around, sometimes fusing or splitting, but having ...
6
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0answers
103 views

Did an impact crater cause the formation of the gas fields in north eastern South Australia

In the paper High Impact Reservoirs, the authors claim that impact craters have lead to both the creation and destruction of petroleum source rocks, reservoirs and traps. Recently it was announced ...
6
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1answer
511 views

How was the Earth formed?

What events took place in our Solar System which led to formation of the Earth? I have heard from sources that a big giant star exploded and the Earth was formed. Is this true ?
5
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2answers
6k views

Are there more earthquakes near the equator or poles?

When comparing the average distance of the all known earthquake epicenters to the nearest pole, is the longitudinal distance to the equator or the poles the smallest of the two? Please note that any ...
3
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1answer
227 views

Why is Great Oxidation Event associated with Iron oxidation but not Aluminum or Silicon?

Just to build up on my previous success with oxygen origin in the atmosphere, I want to expand the question as was advised in the answers. The official heresy, despite denied in the comments and ...
2
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2answers
589 views

Was the Earth's sea-level significantly lower in ancient times?

A lot of times, ancient artifacts or even whole ancient civilizations are found buried very deep into the ground surface of the earth. Entire civilizations that had high buildings have been found ...
1
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1answer
75 views

How can radiometric dating of meteorites determine the age of the earth? Wouldn't this only determine the age of the decaying nuclide in each rock? [duplicate]

How can the radiometric dating of different meteorites determine the age of the earth? Wouldn't radioactive decay have already been occurring in all of those meteorites long before they hit earth? ...