APOD: Oklo: Ancient African Nuclear Reactors (2010 Sep 12)

[APOD Robot]

Oklo: Ancient African Nuclear Reactors

Explanation: The remnants of nuclear reactors nearly two billion years old were found in the 1970s in Africa. These reactors are thought to have occurred naturally. No natural reactors exist today, as the relative density of fissile uranium has now decayed below that needed for a sustainable reaction. Pictured above is Fossil Reactor 15, located in Oklo, Gabon. Uranium oxide remains are visible as the yellowish rock. Oklo by-products are being used today to probe the stability of the fundamental constants over cosmological time and distance scales and to develop more effective means for disposing of human-manufactured nuclear waste.

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[alter-ego]

1970?? The quality looks familiar, but with color added

[neufer]

Oklo: Ancient African Nuclear Reactors

[color=#0000FF]C[/color][color=#FF0000]AGN[/color]ey [color=#FF0000]BO[/color][color=#0000FF]G[/color]art : [color=#FF0000]GABON[/color] [color=#0000FF]G[/color]rey [color=#0000FF]C[/color]at

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Yellow crystals of francevillite on matrix

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<<Francevillite is a uranyl-group vanadate mineral in the tyuyamunite series. Its chemical formula is (Ba,Pb)(UO₂)₂V₂O₈·5(H₂O). Francevillite is a strongly radioactive mineral. It is typically orange, yellow or brownish yellow. Francevillite occurs in the oxidized zone of a lead-bearing uranium–vanadium deposits.>>

<<Franceville is one of the four largest cities in Gabon, with a population of around 22,000 people. It lies on the River Mpassa and at the end of the Trans-Gabon Railway. It grew from a village named Masuku when Pierre Savorgnan de Brazza chose it to resettle former slaves and renamed it "Francheville" (meaning "city of the freed" in French) in 1880. The city later came to be called Franceville.>>

<<From the 14th century until the present time Bantu groups immigrated into Gabon from several directions to escape enemies or to find new land. Little is known of tribal life before European contact but tribal art suggests a rich cultural heritage. Heinar Schilling stated "The high point of Nordic seafaring was reached around the year 1000, at which time the Vikings penetrated as far south as the Congo estuary". Gabon's first confirmed European visitors were Portuguese traders who arrived in the 15th century and named the country after the Portuguese word gabão — a coat with sleeve and hood resembling the shape of the Komo river estuary. The coast became a center of the slave trade. Dutch, English, and French traders came in the 16th century. France assumed the status of protector by signing treaties with Gabonese coastal chiefs in 1839 and 1841. In 1849, the French captured a slave ship and released the passengers at the mouth of the Komo; The slaves named their settlement Libreville, French for "free town".>>

[Ann]

To me, these naturally occurring but now-dead natural nuclear reactors, nearly two billion years old, testify to the amazing habitability and life-friendliness of the Earth.

My impression of the caption of today's APOD is that the Oklo natural reactor stopped "working" nearly two billion years ago, but that it may have been active far earlier than two billion years ago. (Although I may be wrong about that.)

In any case, the point I want to make is that the Earth is more than four billion years old, and life has existed on this planet for more than three billion years, maybe for as much as about three and a half billion years. Yet three billion years ago the Sun was considerably fainter than today. It produced significantly less energy than it does today, so it would not have been able to warm the Earth as efficiently as it does today. Yet the Earth has had a relatively constant temperature and liquid water on its surface for at least three billion years. That 's amazing. (There may have been brief episodes of global glaciation, when the Earth's oceans all froze. But the ice crust covering the Earth may not have been that thick, certainly not at the equator, and there was liquid water and warm "wells" below that ice, and the ice crust melted soon enough.)

Why has the Earth remained suitably warm for life to exist here in abundance for billions of years? An important reason must be that while the Sun got brighter and more energetic, the Earth's interior cooled. The naturally occuring nuclear reactors must of course have contributed to the warming of the young Earth at a time when the Sun may not have been sufficiently able to do so. Today, when the Earth is more than warm enough, no natural nuclear reactors exist any more, because the the Earth's supply of fissile uranium has decayed below a critical level. A fantastic "temperature balance" has thus been upheld on the surface of the Earth for billions of years.

Wow.

Ann

[smitty]

I seem to recall reading somewhere in the dim past that low-level nuclear reactions continue to occur in the Earth's core, and that these reactions are part of what keeps the core warm. Is that not correct? The explanation which accompanies today's apod suggests that it is not correct.

[Beyond]

A fantastic "tempreture balance" has thus been upheld on the surface of the Earth for billions of years.

UH-OH, that was all well and good in the past to make sure that that the Earth did not become an ice-ball, but what about now when the sun is getting warmer? Where's the cooling system to keep an even tempreture comeing from?? Can you spell - slow-cook?

[rstevenson]

... but what about now when the sun is getting warmer?

I think you must have misunderstood something along the way. I can't recall seeing any articles about the sun getting warmer. Planet Earth is warming, yes. But not the sun -- at least not in anything shorter than geologic time scales.

Rob

[neufer]

... but what about now when the sun is getting warmer?

I think you must have misunderstood something along the way. I can't recall seeing any articles about the sun getting warmer. Planet Earth is warming, yes. But not the sun -- at least not in anything shorter than geologic time scales.

<<Even during its current life in the main sequence, the Sun is gradually becoming more luminous (about 10% every 1 billion years), and its surface temperature is slowly rising. The Sun used to be fainter in the past, which is possibly the reason life on Earth has only existed for about 1 billion years on land. The increase in solar temperatures is such that already in about a billion years, the surface of the Earth will become too hot for liquid water to exist, ending all terrestrial life.>>

[Beyond]

... but what about now when the sun is getting warmer?

I think you must have misunderstood something along the way. I can't recall seeing any articles about the sun getting warmer. Planet Earth is warming, yes. But not the sun -- at least not in anything shorter than geologic time scales.

Rob

I should have said "brighter and more energetic" as Ann said in the fourth paragraph of her post. Somehow, it came out warmer. My bad

[Moonshadow]

I'll bet that cave would look cool lit by a shortwave UV lamp.

[Chris Peterson]

Why has the Earth remained suitably warm for life to exist here in abundance for billions of years? An important reason must be that while the Sun got brighter and more energetic, the Earth's interior cooled.

I don't think so. Escaping heat from the interior hasn't been a major factor in determining surface temperatures for billions of years. Earth has maintained its life-friendly temperature range because of feedback mechanisms driven by water. This has allowed for a relatively stable system despite significant variation in solar output.

[Chris Peterson]

I seem to recall reading somewhere in the dim past that low-level nuclear reactions continue to occur in the Earth's core, and that these reactions are part of what keeps the core warm. Is that not correct? The explanation which accompanies today's apod suggests that it is not correct.

The hot interior of the Earth is almost entirely due to radioactive decay. Without that, the residual heat of formation would have been insufficient to maintain a liquid core longer than a billion years or so. We would have long since lost our magnetic field, and in all likelihood would not have a planet suitable for life.

Radioactive decay was also responsible for maintaining the internal heat of planetesimals and asteroids long enough for them to become differentiated. Simple heat of formation would have been lost before they could end up with iron cores (and we wouldn't have any iron meteorites today).

[Ann]

The Earth is the largest of the terrestrial planets in the Solar System, but even in relation to its size it has the largest core and therefore the largest supply of radioactive elements which can keep its interior warm and uphold its magnetic field.

The Earth is the only terrestrial planet with ongoing plate tectonics. Plate tectonics recycle elements in the Earth's crust and is probably very beneficial for life, even though volcanic eruptions and earthquakes also kill life.

There are so many things about the Earth that makes it special. We will be so lucky if we ever detect a planet in another solar system which is remotely like the Earth.

Ann

[orin stepanek]

There are so many things about the Earth that makes it special. We will be so lucky if we ever detect a planet in another solar system which is remotely like the EArth.

Ann

We are looking; there's Kepler; SETI; and all the planet hunters. Maybe there are some terrestrial planets with oceans lurking out there. I don't think man wants to be alone in the universe. It seems unlikely that as vast as the universe is that that Earth is one of a kind. But what if it is?

[Ann]

Orin Stepanek wrote:

It seems unlikely that as vast as the universe is that that Earth is one of a kind. But what if it is?

Then, as Voltaire's hero Candide said, we'd better cultivate our garden.

Click to view full size image

This...

Click to view full size image

...not that.

Ann

[harry]

G'day

Two processes are at work one is the cyclic events within the Earth the other is the cyclic events within the Sun.

This link is quite interesting and to the point.
Heat in the Earth's Core
http://nov55.com/heat.html

It appears that the process of creating planets, by gravity drawing particles together, results in a lot of friction and collisions, which creates heat in the core. That heat dissipates out into space as infrared radiation. A crust then forms and holds the heat in. Heat moves slowly through the crust, but not fast enough to heat the air much. It's mostly the sun that heats the atmosphere. However, the earth's core does add significant heat to bodies of water including oceans and lakes.

Heat in the core of planets cannot be entirely due to nuclear reactions, because that source would require a gradual build-up rather than a gradual loss of heat. However, nuclear reactions could be occurring in the core, because heat and pressure should promote them. But then they must be producing heat at a lower rate than it is being lost through radiation into space. Otherwise, there would not be the observed cool-down.

It seems likely that ice ages on earth are caused by a nuclear hot spot in the core rotating toward the surface and heating the Pacific Ocean. The primary evidence for this is that the past ten ice ages have been cycling at 100 thousand year intervals. Environmental changes are not apt to be so cyclic, but a convectional oscillation in the earth's core could be.

There is new evidence that the entire core of the earth heats in a cyclic manner. The earth's magnetic field shows variations which correlate with global temperatures, and there is about a six year lag correlating with the amount of time required for the heat to conduct through the mantle. A summary article is here:

http://www.gsaaj.org/articles/TempPaperv1n22007.pdf

[Chris Peterson]

This link is quite interesting and to the point.
Heat in the Earth's Core
http://nov55.com/heat.html

Actually, this link demonstrates the sort of utter garbage that can be found on the Internet. In fact, "garbage" is too good a word for it. It is nothing but pseudoscientific nonsense. The site is instructive to people interested in where incompetent scientists sometimes end up, disgruntled, blaming their failures on peer review instead of their own lack of ability, sure that every major scientist past and present is wrong in their ideas.

Heat in the core of planets cannot be entirely due to nuclear reactions, because that source would require a gradual build-up rather than a gradual loss of heat...

The source of heat in the core of bodies in our own solar system is quite well understood, including the specific reactions involved, and how those reactions have changed over time. All bodies started with residual heat of formation, but that was largely replaced with heat from radioactive decay over time.

It seems likely that ice ages on earth are caused by a nuclear hot spot in the core rotating toward the surface and heating the Pacific Ocean.

Too stupid to even discuss. The general mechanisms and timing of glacial cycles is understood quite well in terms of the orbital dynamics of the Earth.

[neufer]

It seems likely that ice ages on earth are caused by a nuclear hot spot
in the core rotating toward the surface and heating the Pacific Ocean.

Too stupid to even discuss.
The general mechanisms and timing of glacial cycles is understood quite well in terms of the orbital dynamics of the Earth.

The general mechanisms and timing of glacial cycles is understood quite poorly just in terms of
the orbital dynamics of the Earth. But, at least it presents a reasonable & tractable scientific approach:

<<Milankovitch Theory describes the collective effects of changes in the Earth's movements upon its climate, named after Serbian civil engineer and mathematician Milutin Milanković, who worked on it during First World War internment. Milanković mathematically theorised that variations in eccentricity, axial tilt, and precession of the Earth's orbit determined climatic patterns on Earth.

Variations of Cyle Times, curves determined from ocean sediments

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Milankovic himself believed that reductions in summer insolation in northern high latitudes was the dominant factor leading to glaciation, which led to him (incorrectly) deducing an approximately 41 kyr period for ice ages. Subsequent research has shown that from 1-3 million years ago, the climate did have a dominant mode matching the 41 ka cycle in obliquity. However, after 1 million years ago, this changed to a 100 ka variation matching eccentricity. No reason for this change has been established.

41,000-year cycle

The angle between Earth's rotational axis and the normal to the plane of its orbit moves from 22.1 degrees to 24.5 degrees and back again on a 41,000-year cycle; currently, this angle is 23.44 degrees and is decreasing.

100,000-year cycle

The inclination of Earth's orbit drifts up and down relative to its present orbit with a cycle having a period of about 70,000 years. Milankovitch did not study this three-dimensional movement. This movement is known as "precession of the ecliptic" or "planetary precession". More recent researchers noted this drift and that the orbit also moves relative to the orbits of the other planets. The invariable plane, the plane that represents the angular momentum of the solar system, is approximately the orbital plane of Jupiter. The inclination of the Earth's orbit has a 100,000 year cycle relative to the invariable plane; by chance, this is very similar to the 100,000 year eccentricity period. This 100,000-year cycle closely matches the 100,000-year pattern of ice ages. It has been proposed that a disk of dust and other debris exists in the invariable plane, and this affects the Earth's climate through several possible means. The Earth presently moves through this plane around January 9 and July 9, when there is an increase in radar-detected meteors and meteor-related noctilucent clouds.>>

[Chris Peterson]

The general mechanisms and timing of glacial cycles is understood quite poorly just in terms of
the orbital dynamics of the Earth. But, at least it presents a reasonable & tractable scientific approach:

I'll stick by my original assessment, that glacial cycles are broadly understood in terms of orbital dynamics. But maybe we just have a difference of opinion on what constitutes broad or general understanding. Certainly, orbital dynamics provides little more than a mechanism for certain cyclical climate cycles, but it appears well supported by observation. Any detail can only come from complex climate models, of course.

[neufer]

The general mechanisms and timing of glacial cycles is understood quite poorly just in terms of
the orbital dynamics of the Earth. But, at least it presents a reasonable & tractable scientific approach:

I'll stick by my original assessment, that glacial cycles are broadly understood in terms of orbital dynamics. But maybe we just have a difference of opinion on what constitutes broad or general understanding. Certainly, orbital dynamics provides little more than a mechanism for certain cyclical climate cycles, but it appears well supported by observation. Any detail can only come from complex climate models, of course.

Variations of Cyle Times, curves determined from ocean sediments

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Milankovitch cycle climate theory is at about the same legitimacy level as sunspot climate theory IMO: the general mechanisms and periodicities are sort of in the right ball park but there is no real statistical significance to be found and theoretical causes & effects are probably be quite small in any event. The transition from a ~41kyr glacier cycle to a ~100kyr glacier cycle is actually quite consistent with the geomagnetic reversal from the Matuyama Age (2-1 Myrs before present) to the Brunhes/jaramillo Age (1-0 Myrs before present). I don't see why geophysical core changes (or possible solar output changes) can't be just as important orbital dynamic changes as regards to ice ages.

<<A geomagnetic reversal is a change in the orientation of Earth's magnetic field such that the positions of magnetic north and magnetic south become interchanged. These events often involve an extended decline in field strength followed by a rapid recovery after the new orientation has been established. These events occur on a scale of tens of thousands of years or longer.>>

[Chris Peterson]

Milankovitch cycle climate theory is at about the same legitimacy level as sunspot climate theory IMO: the general mechanisms and periodicities are sort of in the right ball park but there is no real statistical significance to be found and theoretical causes & effects are probably be quite small in any event.

I'm okay with saying they are in the same general ballpark. I think Milankovitch cycles are more accepted because they are statistically more robust- mainly because we are comparing well understood orbital theory with climate data of various degrees of uncertainty. Theories relating solar cycles and sunspots to climate are necessarily less statistically solid for the simple reason that the proxies for long term solar output are poor.

[neufer]

Milankovitch cycle climate theory is at about the same legitimacy level as sunspot climate theory IMO: the general mechanisms and periodicities are sort of in the right ball park but there is no real statistical significance to be found and theoretical causes & effects are probably be quite small in any event.

I'm okay with saying they are in the same general ballpark. I think Milankovitch cycles are more accepted because they are statistically more robust- mainly because we are comparing well understood orbital theory with climate data of various degrees of uncertainty. Theories relating solar cycles and sunspots to climate are necessarily less statistically solid for the simple reason that the proxies for long term solar output are poor.

If Milankovitch climate cycles are more statistically robust
(which is not at all clear based upon the chart below) then
that is ONLY because any forecast made will take FAR too long to disprove;
sunspot climate forecasts were never afforded that particular luxury.

Past and future Milankovitch cycles

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<<VSOP allows prediction of past and future orbital parameters with great accuracy. ε is obliquity (axial tilt). e is eccentricity. ϖ is longitude of perihelion. esin(ϖ) is the precession index, which together with obliquity, controls the seasonal cycle of insolation. Q is the calculated daily-averaged insolation at the top of the atmosphere, on the day of the summer solstice at 65º N latitude. Benthic forams and Vostok ice core show two distinct proxies for past global sealevel and temperature, from ocean sediment and Antarctic ice respectively. Vertical gray line is current conditions, at 2 ky A.D.>> ===>

<<There is still no absolute consensus on the mechanism responsible for the 100 ka periodicity. Orbital inclination has a 100 ka periodicity, whilst eccentricity's 95 and 125 ka periods combine to give a 100 ka effect. Whilst it is possible that the less significant, and originally overlooked, inclination variability has a profound effect on climate, the eccentricity only modifies insolation by a small amount: 1–2% of the change caused by the 21,000-year precession and 41,000-year obliquity cycles. Such a large impact would therefore be disproportionate in comparison to other cycles.>>

[harry]

G'day

Chris said

Actually, this link demonstrates the sort of utter garbage that can be found on the Internet. In fact, "garbage" is too good a word for it. It is nothing but pseudoscientific nonsense. The site is instructive to people interested in where incompetent scientists sometimes end up, disgruntled, blaming their failures on peer review instead of their own lack of ability, sure that every major scientist past and present is wrong in their ideas.

Mate with the very little science information that you do have it's amazing how yo can even write the above statement.

Re read the words

Cyclic Earth and Cyclic Sun very well understood terms and yet as a non scientist you have used words to gain what ever. This is one reason why I hardly come to this forum.

[neufer]

Click to play embedded YouTube video.

Mitochondrial DNA-based chart of large human migrations. (Numbers are millennia before present) http://en.wikipedia.org/wiki/Human_migration

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