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# Category Archives: Earth Science

## Geodesy

### Geodesy combines applied mathematics and earth sciences to measure and represent the Earth (or any planet.)

NOAA National Geodetic Survey, from a PPT by Hawaii Geographic Information Coordinating Council

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from the  National Oceanic and Atmospheric Administration Ocean Service Education page on Geodesy:

### As positioning and navigation have become fundamental to the functions of society, geodesy has become increasingly important.

https://www.ngs.noaa.gov/INFO/WhatWeDo.shtml

https://oceanservice.noaa.gov/facts/geodesy.html

Precise Geodetic Infrastructure: National Requirements for a Shared Resource (2010) – Geodesy for the Benefit of Society

## Seismic waves

### P waves

Earth Science, Tarbuck & Lutgens, Chapter 8

### S waves

Earth Science, Tarbuck & Lutgens, Chapter 8

### Surface waves

Tarbuck & Lutgens

### Rayleigh surface waves

“The Rayleigh surface waves are the waves that cause the most damage during an earthquake. They travel with velocities slower than S waves, and arrive later, but with much greater amplitudes. These are also the waves that are most easily felt during an earthquake and involve both up-down and side-to-side motion.”

## How do we measure motions of the Earth?

### What is a seismograph?

Intro to be written

Earth Science, Tarbuck & Lutgens, Chapter 8

### This is a seismograph record.

Earth Science, Tarbuck & Lutgens, Chapter 8

## Mineral Identification

### All crystals are atoms in a three dimensional pattern. Here some examples.

Image from Molecular and Solid State Physics, http://lampx.tugraz.at

.

## Cleavage

### Mica has 1d cleavage

Lumen Geology, Identify and classify common rock forming minerals.

## Fracture

### Chrysotile has splintery fracture.

Quartz has conchodial fracture

## Further examples

GG101 Lab Minerals

## Terminology

### Fibrous – Fracture surface shows fibres or splinters.

This section from

Geololgy, Rocks and Minerals, Univ. of Auckland

## Why are some moons spherical while others are shaped like potatoes?

### Why are some moons spherical while others are shaped like potatoes?

This blog post was written by Physicist Dr. Matt Caplan, who used to run the QuarksAndCoffee blog. That blog no longer exists, but I’m showing this archived copy of one of his posts for my students.

### This works out to about 240 km [1], right in the middle of the 200-300 km range of the more rigorous calculation!

(1) How High Can A Mountain Be? P. A. G. Scheuer, Journal of Astrophysics and Astronomy, vol. 2, June 1981, p. 165-169.

Web.archive.org copy
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This website is educational. Materials within it are being used in accord with the Fair Use doctrine, as defined by United States law.
§107. Limitations on Exclusive Rights: Fair Use. Notwithstanding the provisions of section 106, the fair use of a copyrighted work, including such use by reproduction in copies or phone records or by any other means specified by that section, for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research, is not an infringement of copyright. In determining whether the use made of a work in any particular case is a fair use, the factors to be considered shall include: the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes; the nature of the copyrighted work; the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and the effect of the use upon the potential market for or value of the copyrighted work. (added pub. l 94-553, Title I, 101, Oct 19, 1976, 90 Stat 2546)

## What factors control the height of a mountain?

### Don’t believe me? Even rock has a maximum amount of strength. Here is a GIF of what happens to solid rock when you put enough pressure on it! 🙂

Source: Unconfined compressive strength test of rock

Roy Blitz

## What else makes mountains rise or grow?

### This causes delamination to occur. Depending on the amount of material removed, the rate of new material added, and erosion, scenarios with net increases or decreases in elevation are possible after a delamination event. This sets another limit on how thick a crustal root can get (and thus how high a mountain range grow on the long term).

Source, Reddit comment

## Why are there some special spots on Earth where mountains can grow twice as high?

### So the Himalayas have double the thickness of the average continental plate, thus double the mountain height that would be considered “normal”.

George W Hatcher, Planetary Scientist, Aerospace Engineer

## References

How high can a mountain possibly get? Earth Science StackExchange

How High can a mountain get? 2 Earth Science Stack Exchange

How tall can a mountain become on Earth? Quora

What is the theoretical limit to how tall mountains can get on Earth? Reddit

Glacial Buzz Saw Hypothesis: New Scientist article

## Examples with math details

Why are some moons spherical while others are shaped like potatoes? Quarks & Coffee

How High Can Mountains Be? Talking Physics

How High Could A Mountain Be? Physics World hk-phy.org

How tall can I make a column of stone? Rhett Allain, Wired magazine columnist

### Related lab ideas

Play Doh Modeling Folds: Block Diagrams and Structure Contours

Play-Doh Modeling Folds: Block Diagrams and Structure Contours

Play Doh Introduction to Igneous Intrusions

Play Doh Unconformities

## Reliable sources of information

CDC: Centers for Disease Control – Coronavirus Disease 2019 (COVID-19)

Massachusetts Department of Public Health

US FDA Food and Drug Administration Coronavirus Disease 2019

Coronavirus disease: Myth busters – WHO World Health Organization

## How much area would renewable energy require?

### As a 🇨🇦 let me hasten to clarify that I’m not advocating for removing maple syrup production but rather for co-production of energy on land that is also used for farming or pollinator ecosystems 😁 For example, @FreshEnergy runs this amazing clearinghouse, The Center for Pollinators in Energy

This graphic from Here’s How America Uses Its Land, By Dave Merrill and Lauren Leatherby, Bloomberg, 7/31/2018

“Land use classifications are based on data published in 2017 by the U.S. Department of Agriculture’s Economic Research Service in a report called the Major Uses of Land in the United States (MLU). Data from the report provide total land-use acreage estimates for each state across six broad categories. Those totals are displayed per 250,000 acres.”

### Ramez Naam has a similar analysis, How Much Land Would it Take to Power the US via Solar?

Guest writer Ben Heard [see above] complains that solar’s land footprint (specifically at the Ivanpah plant) is 92 times that of a small modular nuclear reactor… What Heard’s Breakthrough Institute article doesn’t tell you is how tiny that land footprint, in the grand scheme of things, actually is. Do the math on the numbers he presents: 1087 Gwh / yr, or 0.31 Gwh / acre / year.

At that output, to meet the US electricity demand of 3.7 million Gwh per year, you’d need about 48,000 square kilometers of solar sites. (That’s total area, not just area of panels.) That may sound like a stunningly large area, and in some sense, it is. But it’s less than half the size of the Mojave desert. And more importantly, the continental United States has a land area of 7.6 million square kilometers. That implies to that meet US electrical demand via this real world example of Ivanpah, would require just 0.6 percent of the land area of the continental US.

Asked about this on twitter, Heard replied that larger size nevertheless is a disadvantage. It threatens ecosystems and endangered species, for instance. And this is a legitimate point, in some specific areas. (Though certainly far less so than coal and natural gas.)

But, for context, agriculture uses roughly 30% of all land in the United States, or 50 times as much land as would be needed to meet US electricity needs via solar.

## Discovering lost continents under the Earth

Never mind those stories about a “lost continent of Atlantis.” True, there likely is a lost island that is the basis of the Atlantis tale. Yet we know for a fact that there is no sunken Atlantean continent on the bottom of the Atlantic ocean or Mediterranean Sea. We can now literally see the entire bottom of the Atlantic seafloor in high resolution, and there’s no missing continent.

But although those tales of Atlantis as a lost continent are incorrect that doesn’t mean that some kind of amazing lost continents don’t exist. In fact, several do and we’re going to learn about them today!

We normally think of the Earth’s interior as looking like this

But now we know there are details:

To review what a continent is, and how one is defined, see Continents and plate tectonics

## The Farallon Plate

Some text from Farallon plate, Karin Sigloch *08, Art of Science 2009

### and the Nazca Plate subducting under the South American Plate.

http://en.wikipedia.org/wiki/Farallon_Plate

‘Lost’ Tectonic Plate Found Beneath California
http://www.livescience.com/27994-lost-tectonic-plate-california.html

How do we see inside the Earth

## Continents of the Underworld

Large low-shear-velocity provinces, or LLSVPs

By Olena Shmahalo at Quanta Magazine, source data from Sanne Cottaar.

In Continents of the Underworld Come Into Focus, Quanta Magazine, Josjua Sokol writes

Decades ago, scientists first harnessed the echoes of earthquakes to make a map of Earth’s deep interior. They didn’t just find the onion layers you might remember from a grade school textbook — core and mantle covered by a cracked crust. Instead, they saw the vague outlines of two vast anomalies, unknown forms staring back from the abyss.

Over the years, better maps kept showing the same bloblike features. One huddles under Africa; the other is beneath the Pacific. They lurk where the planet’s molten iron core meets its rocky mantle, floating like mega-continents in the underworld. Their highest points may measure over 100 times the height of Everest. And if you somehow brought them to the surface, God forbid, they contain enough material to cover the entire globe in a lava lake roughly 100 kilometers deep.

In these regions, earthquake waves seem to slow down, suggesting that the blobs are hotter than the surrounding mantle. How do we know this? Rock expands when heated. That causes waves to travel sluggishly through warm regions, said Garnero, like the slower vibrations moving through a loose guitar string.

The slowing waves gave these features their formal name: large low-shear-velocity provinces, or LLSVPs — an unmagical abbreviation that may have contributed to the topic’s low profile. “We are also to blame,” said Sanne Cottaar, a seismologist at the University of Cambridge, “for misnaming this feature so badly.”

Learning Standards

tba

## Why is the Earth still hot?

I. The formation of the Earth created a huge amount of heat

The Earth is thought to have formed from the collision of many rocky asteroids, perhaps hundreds of kilometers in diameter, in the early solar system.

As the proto-Earth gradually bulked up, continuing asteroid collisions and gravitational collapse kept the planet molten.

Heavier elements – in particular iron – would have sunk to the core in 10 to 100 million years’ time, carrying with it other elements that bind to iron.

Radioactive potassium may be major heat source in Earth’s core,  Robert Sanders, UC Berkeley News, 12/13/2003

II. More heat generated when dense material sank down towards the center of Earth

When the Earth was first formed this material was not solid; some was hot enough to become viscous (like silly putty) or even liquid (like lava.)

The denser material was mostly iron and some radioactive metals.

This dense metal slowly sank towards the center, while less dense rock floated upwards.

This process itself created a lot of friction, which created a lot of heat.

“Gradually, however, the Earth would have cooled off and become a dead rocky globe with a cold iron ball at the core if not for the continued release of heat by the decay of radioactive elements like:

potassium-40, uranium-238 and thorium-232, which have half-lives of 1.25 billion, 4 billion and 14 billion years, respectively.

III. Heat from the decay of radioactive elements.

Most metals we know are stable. Think of Nickel, Iron, Copper and Gold. If you put them in a box so that they don’t get exposed to oxygen, then they don’t rust, and never change. Millions of years from now they will still be around.

What’s inside metal atoms? Electrons, protons and neutrons. In a metal atom, the number of these particles will normally never change.

Example: Iron-56 26 protons, 30 neutrons, 26 electrons.
But some very large atoms are special: they not stable – they do change, all by themselves. These are called radioactive elements.

Uranium-238 92 protons, 146 neutrons, 92 electrons

-> spontaneously will change into

Plutonium-239 94 protons, 145 neutrons, 94 electrons + heat
– – –

In sum, there was no shortage of heat in the early earth, and the planet’s inability to cool off quickly results in the continued high temperatures of the Earth’s interior. In effect, not only do the earth’s plates act as a blanket on the interior, but not even convective heat transport in the solid mantle provides a particularly efficient mechanism for heat loss.

The planet does lose some heat through the processes that drive plate tectonics, especially at mid-ocean ridges. For comparison, smaller bodies such as Mars and the Moon show little evidence for recent tectonic activity or volcanism.

We derive our primary estimate of the temperature of the deep earth from the melting behavior of iron at ultrahigh pressures.

We know that the earth’s core depths from 2,886 kilometers to the center at 6,371 kilometers (1,794 to 3,960 miles), is predominantly iron, with some contaminants.

How? The speed of sound through the core (as measured from the velocity at which seismic waves travel across it) and the density of the core are quite similar to those seen in of iron at high pressures and temperatures, as measured in the laboratory. Iron is the only element that closely matches the seismic properties of the earth’s core and is also sufficiently abundant present in sufficient abundance in the universe to make up the approximately 35 percent of the mass of the planet present in the core.

The earth’s core is divided into two separate regions: the liquid outer core and the solid inner core, with the transition between the two lying at a depth of 5,156 kilometers (3,204 miles).

Therefore, If we can measure the melting temperature of iron at the extreme pressure of the boundary between the inner and outer cores, then this lab temperature should reasonably closely approximate the real temperature at this liquid-solid interface. Scientists in mineral physics laboratories use lasers and high-pressure devices called diamond-anvil cells to re-create these hellish pressures and temperatures as closely as possible.

Those experiments provide a stiff challenge, but our estimates for the melting temperature of iron at these conditions range from about 4,500 to 7,500 kelvins (about 7,600 to 13,000 degrees F).

As the outer core is fluid and presumably convecting (and with an additional correction for the presence of impurities in the outer core), we can extrapolate this range of temperatures to a temperature at the base of Earth’s mantle (the top of the outer core) of roughly 3,500 to 5,500 kelvins (5,800 to 9,400 degrees F) at the base of the earth’s mantle.

The bottom line here is simply that a large part of the interior of the planet (the outer core) is composed of somewhat impure molten iron alloy. The melting temperature of iron under deep-earth conditions is high, thus providing prima facie evidence that the deep earth is quite hot.

Gregory Lyzenga is an associate professor of physics at Harvey Mudd College. He provided some additional details on estimating the temperature of the earth’s core:

How do we know the temperature? The answer is that we really don’t–at least not with great certainty or precision. The center of the earth lies 6,400 kilometers (4,000 miles) beneath our feet, but the deepest that it has ever been possible to drill to make direct measurements of temperature (or other physical quantities) is just about 10 kilometers (six miles).

Ironically, the core of the earth is by far less accessible more inaccessible to direct probing than would be the surface of Pluto. Not only do we not have the technology to “go to the core,” but it is not at all clear how it will ever be possible to do so.

As a result, scientists must infer the temperature in the earth’s deep interior indirectly. Observing the speed at which of passage of seismic waves pass through the earth allows geophysicists to determine the density and stiffness of rocks at depths inaccessible to direct examination.

If it is possible to match up those properties with the properties of known substances at elevated temperatures and pressures, it is possible (in principle) to infer what the environmental conditions must be deep in the earth.

The problem with this is that the conditions are so extreme at the earth’s center that it is very difficult to perform any kind of laboratory experiment that faithfully simulates conditions in the earth’s core.

Nevertheless, geophysicists are constantly trying these experiments and improving on them, so that their results can be extrapolated to the earth’s center, where the pressure is more than three million times atmospheric pressure.

The bottom line of these efforts is that there is a rather wide range of current estimates of the earth’s core temperature. The “popular” estimates range from about 4,000 kelvins up to over 7,000 kelvins (about 7,000 to 12,000 degrees F).

If we knew the melting temperature of iron very precisely at high pressure, we could pin down the temperature of the Earth’s core more precisely, because it is largely made up of molten iron. But until our experiments at high temperature and pressure become more precise, uncertainty in this fundamental property of our planet will persist.

## External resources and discussions

What percent of the Earth’s core is uranium? earthscience.stackexchange.com

A fascinating although somewhat controversial article, Andrault, Denis & Monteux, J. & Le Bars, Michael & Samuel, H.. (2016). The deep Earth may not be cooling down. Earth and Planetary Science Letters. 443. 10.1016/j.epsl.2016.03.020.

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This website is educational. Materials within it are being used in accord with the Fair Use doctrine, as defined by United States law.
§107. Limitations on Exclusive Rights: Fair Use. Notwithstanding the provisions of section 106, the fair use of a copyrighted work, including such use by reproduction in copies or phone records or by any other means specified by that section, for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research, is not an infringement of copyright. In determining whether the use made of a work in any particular case is a fair use, the factors to be considered shall include: the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes; the nature of the copyrighted work; the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and the effect of the use upon the potential market for or value of the copyrighted work. (added pub. l 94-553, Title I, 101, Oct 19, 1976, 90 Stat 2546)