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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.

Formation of 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.

About one in every thousand potassium atoms is radioactive.”

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.

What will happen with the Earth cools?

When the Earth’s core finally does cool – billions of years from now – then Earth will solidify and there will be no more plate tectonics. Therefore there will be

  1. No more earthquakes

  2. No more volcanic eruptions

  3. no more island building

  4. No more mountain building

The Earth’s surface will eventually be eroded down to a flatter surface, marred only by new impact craters. Earth will then be a geologically dead planet, like the Moon.

Some scientists estimate that “The planet is now cooling about 100°C every 1 billion years, so eventually, maybe several billions of years from now, the waning rays of a dying sun will shine down on a tectonically dead planet whose continents are frozen in place.”

 

How do we know what lies at the Earth’s core?

How we know what lies at the Earth’s core. BBC

Addressing misconceptions

If the Earth’s core is radioactive why is there no radiation at the surface?

Click the link to read the article, but short version, there indeed is radioactivity here on the Earth’s surface!

External resources and discussions

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

Claim: Radioactive decay accounts for half of Earth’s heat, and related, What Keeps the Earth Cooking? Berkeley Lab scientists join their KamLAND colleagues to measure the radioactive sources of Earth’s heat flow

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)

Tidal water level changes in the Merrimack River

I knew about significant water level changes, due to the tides, out at the mouth of the Merrimack River, Massachusetts, but didn’t realize that they were so effective when miles inland. So when I heard that the water levels in Haverhill would be low, I had to take a drive out to the river to see what it would be like.

Haverhill River low tide 10 7 2019

So here I am, after I walked out into the middle of the river! GPS clearly shows how far I walked out.

Haverhill River on GPS low tide

I just looked at the NOAA (National Oceanic and Atmospheric Administration) Tides and Current pages for Newburyport, MA, Merrimack River, Station ID: 8440466

tidesandcurrents.noaa.gov, 8440466

This graph shows the significant differences between the river level at high and low tide, where the Merrimack meets the Atlantic Ocean, in Newburyport.

Merrimack River Entrance Massachusetts Tide Chart

So now I am looking here, likely close to where I was standing in Haverhill, Riverside, Merrimack River, – Station ID: 8440889

tidesandcurrents.noaa.gov, 8440889

This graph shows the differences between the river level at high and low tide, further upriver, in Haverhill, MA.

Merrimacport, Merrimack River, Haverhill MA Tides

This brings up the question, how are the tides created? Check out our resource, the origin of tides.

GIF Tides lighthouse

Beach in the UK

 

Origin of the oceans

Intro

“How the Oceans Came to Be” packet: How the ocean came to be

Ancient dry earth

and

Comets bombard ancient dry Earth

The oceans of water molecules trapped under the oceans, deep within the earth’s crust

Ancient Earth Globe

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Comet outgassing water

 

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related articles

The Guardian, Earth-may-have-underground-ocean-three-times-that-on-surface

Extremetech.com, An ocean-400-miles-beneath-our-feet-that-could-fill-our-oceans-three-times-over

Water-rich gem points to vast ‘oceans’ beneath Earth’s surface, study suggests

 

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The water cycle and atmospheric rivers

From NOAA, National Oceanic and Atmospheric Administration

The water cycle is often taught as a simple circular cycle of evaporation, condensation, and precipitation.

Although this can be a useful model, the reality is much more complicated. The paths and influences of water through Earth’s ecosystems are extremely complex and not completely understood.

watercycle

Image from NOAA, National Oceanic and Atmospheric Administration

Liquid water evaporates into water vapor, condenses to form clouds, and precipitates back to earth in the form of rain and snow.

Water in different phases moves through the atmosphere (transportation).

Liquid water flows across land (runoff), into the ground (infiltration and percolation), and through the ground (groundwater).

Groundwater moves into plants (plant uptake) and evaporates from plants into the atmosphere (transpiration).

Solid ice and snow can turn directly into gas (sublimation).

The opposite can also take place when water vapor becomes solid (deposition).

Atmospheric river

from the NOAA website

Atmospheric rivers are relatively long, narrow regions in the atmosphere – like rivers in the sky – that transport most of the water vapor outside of the tropics.

Atmospheric River GIF

These columns of vapor move with the weather, carrying an amount of water vapor roughly equivalent to the average flow of water at the mouth of the Mississippi River. When the atmospheric rivers make landfall, they often release this water vapor in the form of rain or snow.

North America from space

Although atmospheric rivers come in many shapes and sizes, those that contain the largest amounts of water vapor and the strongest winds can create extreme rainfall and floods, often by stalling over watersheds vulnerable to flooding.

These events can disrupt travel, induce mudslides and cause catastrophic damage to life and property.

A well-known example is the “Pineapple Express,” a strong atmospheric river that is capable of bringing moisture from the tropics near Hawaii over to the U.S. West Coast.

Not all atmospheric rivers cause damage; most are weak systems that often provide beneficial rain or snow that is crucial to the water supply. Atmospheric rivers are a key feature in the global water cycle and are closely tied to both water supply and flood risks — particularly in the western United States.

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Protecting New Orleans from rising water levels

New Orleans, Louisiana

This is a placeholder blogpost. The article is to be written

New Orleans canal gates flood control

Map: Google Maps. Photos by Mary Grace McKernan; infographic: by Marc Fusco.

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New Orleans Lake Pontchartrain Elevation map to Mississippi River

Image by Midnightcomm for Wikipedia, public domain.

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Apps & Interactive graphics

Louisiana’s Sea Level Is Rising: SeaLevelRise.org

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Articles

Fortified But Still In Peril, New Orleans Braces for Its Future: In the years after Hurricane Katrina, over 350 miles of levees, flood walls, gates and pumps came to encircle greater New Orleans. Experts say that is not enough.

By John Schwartz and Mark Schleifstein, 2/24/2018

Fortified But Still In Peril, New Orleans Braces for Its Future

After a $14-Billion Upgrade, New Orleans’ Levees Are Sinking. Sea level rise and ground subsidence will render the flood barriers inadequate in just four years. By Thomas Frank, E&E News, Scientific American, 4/11,/2019

After a $14-Billion Upgrade, New Orleans’ Levees Are Sinking. Scientific American

Rising Sea Levels May Limit New Orleans Adaptation Efforts. New Orleans sees that even modern engineering cannot eliminate flooding risk. By Emily Holden, ClimateWire on September 10, 2015. Scientific American.

Rising Sea Levels May Limit New Orleans Adaptation Efforts. Scientific American

Fortified but still in peril, New Orleans braces for its future: Our Drowning Coast. By Mark Schleifstein | Posted February 24, 2018.

Fortified but still in peril, New Orleans braces for its future

Rising sea to displace 500,000 New Orleans area residents, study says; see where they might go. By Tristan Baurick, NOLA.com | The Times-Picayune. 4/20/2017.

A study published this week (April 2017) predicts that sea level rise will push hundreds of thousands of people out of U.S. coastal cities such as New Orleans. It says the population will boom in nearby inland cities such as Austin. The University of Georgia study is considered the first detailed look at how inland cities might be affected by sea level rise. It estimates more than than 500,000 people will flee the seven-parish New Orleans area by 2100 due to sea level rise and the problems that come with it, including frequent flooding and greater exposure to storm surges. That’s more than one third of metro New Orleans’s current population…. Across the United States, the study estimates, 13 million people will be displaced by sea level rise under a scenario in which some efforts are taken to mitigate the impacts of sea level rise. The biggest draw, it predicts, will be Austin, gaining 600,00 to 800,000 people on top of the metro area’s current estimated population of 2.1 million. Other inland cities likely to grow substantially include Orlando, Fla., Atlanta and Phoenix.

Rising sea to displace 500,000 New Orleans area residents, study says. NOLA.com

Migration induced by sea-level rise could reshape the US population landscape
Mathew E. Hauer. Nature Climate Change volume 7, pages 321–325 (2017)

Many sea-level rise (SLR) assessments focus on populations presently inhabiting vulnerable coastal communities, but to date no studies have attempted to model the destinations of these potentially displaced persons. With millions of potential future migrants in heavily populated coastal communities, SLR scholarship focusing solely on coastal communities characterizes SLR as primarily a coastal issue, obscuring the potential impacts in landlocked communities created by SLR-induced displacement. Here I address this issue by merging projected populations at risk of SLR with migration systems simulations to project future destinations of SLR migrants in the United States. I find that unmitigated SLR is expected to reshape the US population distribution, potentially stressing landlocked areas unprepared to accommodate this wave of coastal migrants—even after accounting for potential adaptation. These results provide the first glimpse of how climate change will reshape future population distributions and establish a new foundation for modelling potential migration destinations from climate stressors in an era of global environmental change.

Migration induced by sea-level rise could reshape the US population landscape (Nature, science journal)

 

What did Earth look like millions of years ago?

Ever wonder what the Earth looked like before humans came along?

Ancient Earth Globe

The 3D interactive website called Ancient Earth Globe lets you glimpse the world from space during the age of the dinosaurs — and more. Seeing the Earth at various points in geological history, from 750 million years ago to today, is an eye-opening activity to say the least. The website allows you to see the entire globe as it slowly rotates, or zoom in to see closer details of land and oceans. There’s also an option to remove clouds for an even better look.

(Text by Bonnie Burton, Cnet, 8/7/18, See what Earth looked like from space when it was ruled by dinosaurs)

Sea level rise

Should we be worried about surging Antarctic ice melt and sea level rise?

Dana Nuccitelli, The Guardian, 18 Jun 2018

There’s recently been a spate of sea level rise denial in the conservative media, but in reality, sea level rise is accelerating and melting ice is playing an increasingly large role. In the first half of the 20th Century, average global sea level rose by about 1.4 millimeters per year (mm/yr). Since 1993, that rate has more than doubled to 3.2 mm/yr. And since 2012, it’s jumped to 4.5 mm/yr.

Global Average sea level

Global mean sea level data from the Colorado University Sea Level Research Group, with 4-to-5-year linear trends shown in black and red. Illustration: Dana Nuccitelli

Thermal expansion (ocean water expanding as it warms) continues to play the biggest role in sea level rise, but its contribution of about 1.3 mm/yr is now responsible for a smaller proportion of total sea level rise (30% in recent years) than its contribution since the 1990s (40% of the total). That’s because of the acceleration in melting ice.

Glacier melt is accelerating, recently contributing about 0.75 mm/yr to sea level rise, up from 0.65 mm/yr since the 1990s. But the biggest jumps have come from ice in Greenland and Antarctica. Greenland had been responsible for about 0.48 mm/yr sea level rise since 1990, but in recent years is up to 0.78 mm/yr. A recent study in Nature Climate Change found that Greenland contributed about 5% to sea level rise in 1993 and 25% in 2014.

Antarctica is a huge question mark with warning signs

A new study published in Nature using data from a range of satellites found that Antarctica’s contribution has tripled from about 0.2 mm/yr since the 1990s to 0.6 mm/yr since 2012, during which time global sea level rise also spiked. Accelerated ice melt from Antarctica, Greenland, and glaciers have all played a role in the faster recent sea level rise. The question is whether it’s a temporary jump, or if we need to worry about a continued acceleration in Antarctic ice loss.

Another recent paper published in Earth’s Future found that rapid losses from Antarctic ice are plausible. The study found that in moderate to high carbon-emission scenarios, an average expected sea level rise of 2 to 2.5 feet by 2100 could actually become 3 to 5 feet once Antarctic ice sheet dynamics are taken into account.

The vast majority of Antarctica’s current ice loss is coming from West Antarctica, where about 75% of the glaciers are located below sea level. In East Antarctica, which has so far remained stable, only about 35% of the glaciers are below sea level. Warming ocean waters are melting the Antarctic ice from below, which is particularly problematic for that low-lying ice in West Antarctica. Research suggests that the collapse of the Western Antarctic ice sheet is already unstoppable.

amount of ice loss across Antarctica

The amount of ice loss across Antarctica in total (purple), and in West Antarctica (green), East Antarctica (yellow) and the Antarctic Peninsula (red). Illustration: Shepherd et al. (2018), Nature

Should we be worried?

Short term variations in sea level rise do happen. Sea level actually briefly fell in 2010 due to a strong La Niña cycle, which typically results in an increase of rain and snow falling over land. This resulted in a number of epic deluges and flooding across the globe; more water on land temporarily meant less in the ocean.

However, Antarctica and Greenland could potentially cause rapid sea level rise. As James Hansen explains in the video below, there have been periods in the not-so-distant past when sea levels rose at an average rate of 1 meter every 20 years.

In past eras when temperatures and atmospheric carbon dioxide levels were similar to those today and to the Paris climate targets, like in the last interglaciation and the Pliocene, sea levels were about 20 to 80 feet higher. Unless we manage to actually cool global temperatures, we’re certainly due for significantly more sea level rise. The large ice sheets on Greenland and Antarctica will continue to melt for as long as 1,000 years. That’s why sea levels were so much higher in past eras whose climates remained at hot temperatures like today’s for thousands of years.

It takes time for ice to melt. The question is, how fast will it happen? Sea level rise unquestionably poses a long-term threat, but how much of a short-term threat largely depends on just how stable the Antarctic ice sheet turns out to be. The recent acceleration of Antarctic ice loss, while not yet definitive, is certainly cause for concern.

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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)