Earth ate a Mercury-like body early in its history, study finds

April 16, 2015 by Amina Khan, Los Angeles Times
A composite image of the Western hemisphere of the Earth. Credit: NASA

A Mercury-like body smashed into a young Earth and gave our planet's core the radioactive elements necessary to generate a magnetic field, two Oxford geochemists say.

Without that magnetic field, there would be no shield to protect us from the onslaught of radiation constantly bombarding Earth from space, making the existence of life as we know it impossible, scientists say.

The study, published in the journal Nature, offers insight into how Earth's magnetic field - and, perhaps, the moon - came to be.

Our planet is thought to have formed from small rocky bodies like the ones in the asteroid belt today, study co-author Bernard Wood, a geochemist at the University of Oxford, said in an interview. It's a theory that fits quite well with what's been studied on Earth, though it's not a perfect fit, he said.

"That sort of roughly works, but there are all kinds of little questions that don't quite work," Wood said, "and one of them is, what is the energy source that drives the Earth's magnetic field?"

Here's the problem. To drive Earth's magnetic field, you need radioactive elements like potassium, thorium or uranium - elements that give off heat as they decay - to also be in the planet's churning iron . Those elements love getting together with oxygen, making oxides - but oxides are really light and would float toward the planet's surface; they wouldn't be heavy enough to stay in the core. These elements also hate getting together with iron.

"They love oxygen so much and they hate being metals so much that they shouldn't go into the Earth's core," Wood said.

So there's no good way, under current models, to keep enough radioactive material in Earth's center to power our vital magnetic field - a conundrum for planetary scientists.

But Wood and Oxford colleague Anke Wohlers realized that if you had a source of reduced sulfides - sulfur compounds that don't have oxygen - into the iron core, it would make it easier for these iron-hating radioactive elements to hang with the metal.

"We said OK, we'll re-create those conditions in our high-pressure apparatus and we'll look and see whether the uranium and thorium, and also some of the so-called rare elements, would partition into the sulfur-rich metal under those conditions," Wood said. "And we found much to our pleasure and surprise that uranium very strongly partitions into sulfur-rich metal under those very oxygen-poor or -reducing conditions."

It would also explain why the ratio of two such , samarium to neodymium, is higher in the crust and mantle than it is in the rest of the solar system, he added. Because neodymium mixes with iron sulfides more easily than samarium, it more easily sinks into the core, leaving relatively more samarium behind in Earth's upper layers.

But how did Earth, which is full of oxides, get all these reduced sulfides in the first place? It probably came from a body that looked a lot like Mercury, which is rich in sulfur and very poor in oxygen.

The scientists think that, early in the planet's history, Earth gobbled up a Mercury-like body, and those sulfides allowed the uranium to stay in the core, which is what has allowed it to power our for an estimated 3.5 billion years.

"Before Wohlers and Wood's experiments, there was only limited (and controversial) experimental evidence that either uranium or potassium can be incorporated in iron metal at the high temperatures and pressures of core formation," Richard Carlson of the Carnegie Institution for Science in Washington, who was not involved in the study, wrote in a commentary on the paper.

However, he added, "a more stringent test" of whether uranium made it into the core in this way would be to study the radio of different isotopes of neodymium in Earth's crust and mantle.

This body, by the way, was Mercury-like in composition, but it was not Mercury-sized, Wood said. It was probably closer to the mass of Mars.

That's interesting, because scientists think that a Mars-sized body's dramatic collision with Earth is what gave birth to the moon. It's possible that this Mercury-like body was in fact that selfsame Earth-shattering missile.

"We think that that is quite conceivable," Wood said. "It's kind of exciting to think that this reduced body could actually be the thing which caused the moon."

Explore further: Is iron rain the reason why Earth and the moon are so different?

More information: A Mercury-like component of early Earth yields uranium in the core and high mantle 142Nd, Nature 520, 337–340 (16 April 2015) DOI: 10.1038/nature14350

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vlaaing peerd
4.7 / 5 (11) Apr 16, 2015
Would be interesting to know how relevant a magnetic core is to birth and evolution of life on planets. Keeping us from radiation exposure seems just as important as the availability of water.

Considering I don't expect such an event (collission of a mercury-like planet) would be common in any random star system, the chances of finding habitable planets would be slimmed down a lot.

antialias_physorg
5 / 5 (9) Apr 16, 2015
Would be interesting to know how relevant a magnetic core is to birth and evolution of life on planets. Keeping us from radiation exposure seems just as important as the availability of water.

High radiation levels are not an iussue if life forms in the oceans first (or even deep underground)

Lack of radiation protection may be a reason why life then doesn't make the jump onto land/into the air. However, evolution does seem to be able to produce species that have a fair bit of radiation tolerance (e.g. Deinococcus radiodurans...or in the insect world the common cockroach (or basically any other insect).)
Torbjorn_Larsson_OM
5 / 5 (7) Apr 16, 2015
The paper is very speculative.

- The amount of radioactive heating is known (from neutrino measurements) and it is ~ 40 % of the total heat flow today. Potassium, and now thorium, are the dominant radioactive sources. [ http://en.wikiped...t_budget ]

- The geodynamo is insufficiently known. For example, the reason why Venus shut down its dynamo is thought to be the runaway greenhouse that makes the temperature difference between core and mantle much smaller.

@vlaaing: What protects the surface from radiation is mainly the atmosphere.

- Cosmic radiation is ~ 90 % blocked by the heliosphere dynamo, the rest by the atmosphere.

- CMEs (and so solar vinds) can penetrate deep into the martian atmosphere [MAVEN], and remove much oxygen in the venusian atmosphere [Magellan, I think]. But it would mainly be upper atmosphere effects.

- UV is blocked by oxygen (ozone).

[tbctd]
Torbjorn_Larsson_OM
5 / 5 (4) Apr 16, 2015
[ctd]

Actually, while the jury is still out, it may be that the geodynamo field is mostly protecting water. (Which is hydrolyzed in the upper atmosphere by UV and then lost as hydrogen and, apparently to some degree, oxygen.)

@aa: It may be a bit of a chicken-and-egg situation re radiation protection. The latter is mostly, and specifically in radiodurans it looks like, a byproduct from desiccation tolerance functionality (such as stress proteins, or radiodurans DNA repair mechanism). [ http://en.wikiped...sistance ]

So while it looks to be a generic capability, re other biospheres, it is also dependent on access to dry, near surface, environments.
antialias_physorg
5 / 5 (5) Apr 16, 2015
So while it looks to be a generic capability, re other biospheres, it is also dependent on access to dry, near surface, environments.

D. Radiodurans has been found miles underground (where it's dry also). The jump from oceans to land does not have to go via the surface.
TheGhostofOtto1923
3.5 / 5 (11) Apr 16, 2015
Such a random collision where the smaller body would penetrate to the center of the larger one is mathematically very tiny. Almost zero. Very similar to all of the unique made-up happenings needed to keep the evolution theory alive. Put together it amounts to the most ridiculous lie that men have fallen for.
And here we have a good example of the destructive potential of the concept of a personal god.

Xians are encouraged to compose their personal god to suit their fancy. It gives them the idea that they can reorder the world in the same way.

"The world can't be a globe or we would obviously fall off it. God gave us common sense did he not? Only flat earths make sense." -This is how verkle does science.

This is one of the many ways in which religion threatens this world as never before.
viko_mx
1 / 5 (5) Apr 16, 2015
It is very cleaner from natural satellites in orbit around the Earth to be plausible such scenario. I wonder the people who offer such theories do you ever bother to think. If the impact between two planetary bodies is with low speed they will never achieve homogenization. If the impact is with high speed will get cloud of debris moving at high speed which never will consolidate. The idea for such clashes raises eyebrows, but apparently the basic work for some people is to support myths and legends.
Steve 200mph Cruiz
4.7 / 5 (13) Apr 16, 2015
Verkle,
You're out of your element because now you're talking evolution and you don't know what evolution is.
Life on earth as it exists today is a reflection of the past, from its biologic past, it's geologic past, and a chemical past that was dictated by conditions of our solar system as a whole.
It is impossible to say for certain what factors are needed because life evolved categorically to be perfect for our specific planet, because that's how evolution works. so until we find life or don't find life in a different solar system, it may very well be a biased illusion that our earth so perfect for life.
cjn
5 / 5 (5) Apr 16, 2015
@vlaaing
Considering I don't expect such an event (collission of a mercury-like planet) would be common in any random star system, the chances of finding habitable planets would be slimmed down a lot.


Our data set is also pretty small. We have four local terrestrial planets to study; even with the one on which we live, we only have highly-speculative theories on formation. Its going to be a while longer before we know if our condition is the norm or the outlier.
cjn
5 / 5 (4) Apr 16, 2015
@Steve

Agree 100%. We have a data set of "1" for the characteristics of life and contributing conditions. Until we have a broader data set, its a bit premature to declare anything regarding "life" to be absolute.
Steve 200mph Cruiz
4.5 / 5 (8) Apr 16, 2015
Also Verkle, you figured out it was mathematically very tiny, lemme see your math, I've been trying to learn more math and physics myself, I would love to see your calculations
thingumbobesquire
1 / 5 (4) Apr 16, 2015
I do think that it is the case that Earth's protective magnetic shield from harmful radiation is a necessary precondition for life and the same may be true for the radioactive core. Regardless of whether this particular scenario is correct, the preconditions for life may be constrained much much more stringently than the field of "astrobiology" assumes. Here is an excerpt from Cotton Mather, the mentor of Ben Franklin, on this: http://thingumbob...ogy.html
TheGhostofOtto1923
3.7 / 5 (9) Apr 16, 2015
If the impact between two planetary bodies is with low speed they will never achieve homogenization. If the impact is with high speed will get cloud of debris moving at high speed which never will consolidate. The idea for such clashes raises eyebrows, but apparently the basic work for some people is to support myths and legends
Ahaahaaa the unbridled audacity of religionists who think they can do computer models in their minds.

Here are a few real models by people who know they need computers to do this.
http://youtu.be/3JNNKQrfXzk
http://youtu.be/ibV4MdN5wo0
robweeve
5 / 5 (1) Apr 16, 2015
amazing
TheGhostofOtto1923
3.4 / 5 (8) Apr 17, 2015
I do think that it is the case that Earth's protective magnetic shield from harmful radiation is a necessary precondition for life
Why? Dirt and water also protect against radiation and we have found life miles underground here on earth.

And scientists expect to find life on Mars which has no magnetic field.
gkam
4.2 / 5 (5) Apr 17, 2015
Ren82, computer models are as imperfect and as usable as can be with Human designers. They are wonderful tools, which give us better ability to predict and prepare.

Just do not expect them to deliver us Absolute Truth.
Greenhorn
5 / 5 (4) Apr 17, 2015
Computer models continue to improve over time. For example weather modeling is much better now than 10+ years ago and 10 years from now it will be even better. The same concept applies to other computer modeling. As we move forward and learn things we put that knowledge into the models which makes them better. As to planetary science and modeling collisions we have a pretty good grasp on the basic physics which we can feed into a computer which will then do the number crunching and show us the result. Look at the graphics in current computer games. Compare what we have now vs what we had 20 years ago. The modeling is much improved and looks very life like.
TheGhostofOtto1923
3.3 / 5 (7) Apr 18, 2015
Since when computer models serve as evidence? I can write computer programs and can assure you that the program does not think but perform the algorithm set by the programmer. From him and theorists behind it depends result of computer simulations
The difference between your faith-based brain models and the models constructed by scientists is that theirs are derived from evidence, while yours depend on the disregard of evidence. IOW yours are wish-based.
If the obtained results from simulation causes confusion in their souls
Science does not consider a 'soul' part of the scientific method. But that artifice enables you to make up whatever science you want.
Math itself does not reflect reality
YES it does. Your denial does not change this fact.
You must observe the reality and to be honest with yourself
As I pointed out, religious reality looks in the books and finds out that the earth is flat and so any evidence that says otherwise is the devils work.
Mike_Massen
2.7 / 5 (7) Apr 19, 2015
Ren82 with hypocrisy offered
You must observe the reality and to be honest with yourself.
Then you must observe Nature, the work of your god of Moses' claim, is ALL about eat & be eaten and ALL the time, this competition and variance in reproduction offers change driven by mutation, ie Evolution.

All moses did was try to rationalise why it was so bad for ALL life, ie Suffering is implicit within Nature's struggle, obviously it cannot be any other way despite moses' claim there is a heaven or even a soul.

Just because a book claims it, especially without evidence, does not make it true ie god is silent !

Moses' book does nothing other than claim, it is a dream story, nothing can be tested !

bible only speaks; Authority, Status & Punishment. Moses obviously got a great deal of power for proclaiming he was a prophet of god. Thats what humans do, make claims, get status & power.

god has been silent for a long time since Moses, despite jesus, krishna & mohammed.
Returners
not rated yet Apr 19, 2015
early in the planet's history, Earth gobbled up a Mercury-like body, and those sulfides allowed the uranium to stay in the core


Where is all the mantle rock that should have been ejected by such a collision? Don't say the Moon, as there should have been volcanic bombs of every size ejected and recooled, with mantle rock signatures left in tact as some crystals and such would stay in their original form.

There is very, very little mantle rock on Earth's surface, much of it in Eastern Canada actually.

You're going to have to accept the fact you can't know everything about the planet's past. Also we've seen another article showing how the core has enormous iron crystals in a lattice, not something you'd expect to survive a planetary core merger.
TheGhostofOtto1923
3.3 / 5 (7) Apr 19, 2015
Not by the desire for a successful career which multiplies only people suitable to maintain system (not true researchers and inventors), but by love
Yes. Love as defined by the lovegod who sacrificed himself out of love for all peoples. But if you are so ungrateful as to spurn his advances, he will condemn you to eternal torture. But he will still love you every second that you writhe in agony.

Your lovegod is truly a beast. Which is why he so desperately wants you to ignore the overwhelming evidence which proves, among other things, that he doesnt exist.
TheGhostofOtto1923
3.4 / 5 (5) Apr 20, 2015
moses got a great deal of power
No, the people who invented Moses got a great deal of power. Evidence tells us that the Torah was written by at least 5 different people.

Further, there were never 2M Hebrew slaves in goshen who never travelled through a Sinai occupied by garrisoned Egyptian troops, nor did Joshua lead them on a genocidal rampage through a Palestine similarly occupied, nor were there ever great Solomonic/Davidic kingdoms.

These people never existed and these events never took place. And ascribing any sort of wisdom to a cartoon character is just silly.
Mike_Massen
2.3 / 5 (3) Apr 21, 2015
viko_mx claimed
It is very cleaner from natural satellites in orbit around the Earth to be plausible such scenario
What are you failing to articulate, many planets have moons ?

viko_mx hypocritically stated
I wonder the people who offer such theories do you ever bother to think
Do you think about the claims in the old testament, the flawed logic & admission by David god (only) spoke in a dream, are dreams ever definitive ?

Heard of Science ? viko_mx = "discipline of the acquisition of knowledge", religion has NONE !

viko_mx claims
If the impact between two planetary bodies is with low speed they will never achieve homogenization. If the impact is with high speed will get cloud of debris moving at high speed which never will consolidate
Your definition of low/high, & what happens between those speeds pls ?

viko_mx with more hypocrisy
..apparently the basic work for some people is to support myths and legends
ie. All religious books - lol !

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