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Building blocks for life on Earth arrived later than thought

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#1 BillP

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Posted 13 March 2020 - 01:02 AM

Recent paper published in Nature concludes that water, carbon and nitrogen were not on Earth initially but arrived from the outer Solar System during late accretion period, i.e., most likely in a late heavy bombardment.

 

https://phys.org/new...n-year-old.html


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#2 sg6

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Posted 13 March 2020 - 02:59 AM

That Late Heavy Bombardment gets the given the glory for just about everything. And I just don't see how.

 

Remember that image of "A little blue dot"?

The earth is small yet somehow just about everything hit us and left something behind. With the actual size of the earth by far the vast majority would miss us.

 

First it was the water we have, slight catch for that is that water from the bombardment is slightly different and the percentage we have of that on earth is less then 10%. In effect the other 90% came from elsewhere.

 

I believe that from sprectral analysis of M42 they can detect the building blocks of life as chemicals.

 

I do have the opinion that astronomers like the big sounding ideas. Not what I suggest is maybe the small sensible ones.

 

How about: Water existed in the nebula cloud we formed from, was therefore present in the planetary disk debris after the sun came to life and rather boringly and simply as we cleaned our orbit the earth collected it. Same for the building blocks of life, the earth bumped into and collected organic carbon compounds as it cleaned out its orbit.

 

I know it is not a grand sounding as a Late Heavy Bombardment, but it seems a much greater probability.


Edited by sg6, 13 March 2020 - 03:00 AM.


#3 goodricke1

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Posted 13 March 2020 - 05:27 AM

How about: Water existed in the nebula cloud we formed from, was therefore present in the planetary disk debris after the sun came to life and rather boringly and simply as we cleaned our orbit the earth collected it. Same for the building blocks of life, the earth bumped into and collected organic carbon compounds as it cleaned out its orbit.

 

Water cannot simply be 'collected' as the Earth ploughs through space; the speed of the collisions would just vaporise the water molecules and leave nothing like the quantities we ended up with. Water must be delivered by hitching a ride in some mode of transport, with comets and/or asteroids being the most likely option.



#4 jaraxx

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Posted 13 March 2020 - 06:51 AM

Looking at our closest neighbors it doesn't seem that collecting water sets us apart from them. Mars and Venus had water as did Earth from whatever source (astroids, comets, meteorites, icy Oort cloud objects) at whatever period (accretion, lunar collision, late heavy bombardment, late-late heavy bombardment). At some point, the inner solar system was seeded with water.

The cool thing about Earth-and what sets it apart from its neighbors - is the retention of that water.



#5 ColoHank

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Posted 13 March 2020 - 01:52 PM

Water cannot simply be 'collected' as the Earth ploughs through space; the speed of the collisions would just vaporise the water molecules and leave nothing like the quantities we ended up with. Water must be delivered by hitching a ride in some mode of transport, with comets and/or asteroids being the most likely option.

Quite the opposite, I'd imagine.  The nascent Earth was just a larger blob in our part of the accretion disk, circling the Sun at about the same velocity as all of the smaller "stuff" its gravity was sweeping up as the whole mass moved along.  Later, incoming asteroids and comets would be impacting Earth at escape velocity or even much faster, depending on the angle of incidence.  Which would be the higher energy events?  

 

Water might be vaporized in both circumstances, but so what?    



#6 Astrola72

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Posted 13 March 2020 - 02:23 PM

I'm no geologist, so this was all a little esoteric to me, but if you follow the "read more" links down two levels you come to an article by another team of geologists which seems to conclude that almost all of earth's water came from the collision with Theia, which lead to the formation of our moon. This left me completely unclear. I was interested in the original article as a biochemist, as I've always been curious why it took so long, with all the ingredients seemingly present, for life to evolve on earth. I thought the first article asserted that, since the essential elements were not here as early as previously thought, in fact it did not take nearly as long for life to evolve.

 

From puzzled to confused.

 

Joe



#7 russell23

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Posted 13 March 2020 - 10:40 PM

Ok, this (planetary formation and how the Earth got its water) is something I have been reading journal articles on and summarizing in a notebook for the last several months.    Observational research and models have reached a point where a picture of planetary formation processes is forming that provides a pretty solid understanding of exoplanetary systems and why the Solar System is "weird" as one paper put it.

 

For me one of the big takeaways from the research I have been reading is that there are quite a few possible planetary processes that can happen and some of those processes are most likely to have happened in our Solar System whereas others may explain the various architectures of exoplanetary systems. So here are some processes and other information that is important to understand how the Earth ended up with its water.

 

Proto-planetary gas disks only last a few million years. One of the primary ways planetary cores grow within the gas disk is through "pebble accretion" which involves the planetesimal sweeping up mm to a few cm sized "pebbles".  Within the gas disk this process can act very rapidly and is much more efficient than planetesimal collisions with other planetesimals.   In the outer disk, beyond the various "snow lines" ices can condense on dust grains to more rapidly grow pebbles so pebble accretion acts very fast to grow large cores in the outer disk.

 

The best models and observations indicate that Jupiter's core grew rapidly (within ~ 1 million years) at a distance of 26 - 40 Astronomical units from the Sun.   Jupiter's core migrated inward to its current distance.  As Jupiter collected its gas envelope runaway accretion began when the mass of the gas envelope was approximately the same as the solid core.   At this point Jupiter opened up a gap in the gas disk which effectively shut down the flow of pebbles into the terrestrial region. 

 

Now there are some things about the Solar System's structure that have to be explained.  One interesting challenge has been to develop models to explain the dichotomy in the composition of the asteroid belt and the segregation of meteorite types.  The inner asteroid belt is primarily rocky S-types whereas the outer asteroid belt is more hydrated C-types.  S-type asteroids are dry and match the composition of ordinary chondrites whereas the C-types are ~10% water by mass and match the composition of carbonaceous chondrites.   Earth's water is a good composition match for the carbonaceous chondrites.

 

Another oddity about the Solar System's terrestrial zone is the low mass of Mars and the narrow ring that has ~90% of the rocky material (Earth and Venus). 

 

In addition to pebble accretion and core migrations, researchers have figured out that migrating cores from the outer disks will set up resonant chains that become unstable when the disk dissipates.   So you can have numerous planetary embryos (~Mars sized or larger) that get ejected from the system due to instability once the gas disk dissipates.

 

It is believed that in our Solar System there were about 100 Mars sized planetary embryos that formed in the Venus/Earth region and the Mars region and asteroid belt had much less planetesimal mass. 

 

To cut to the main points.  The terrestrial region was dry and the water had to come from the outer system.  The best model is that Jupiter formed rapidly and as it migrated it scattered ice-rich planetesimals mostly outward, but some into terrestrial crossing paths and the outer asteroid belt.   This model is called the "external pollution" model.  There are other possible models (Earth migrated from outer system, pebble accretion, in-situ, comets) but the "external pollution" model seems to be the model that has the best ability to match the complete set of observations about the structure of the Solar System. 

 

When the gas disk dissipated Mars was done forming within about 10 million years whereas the Earth took 40-100 million years to finish forming as the numerous Mars sized embryos collided with the final massive collision forming the Moon.   Mixed in with all the planetesimals and embryos are the planetesimals scattered into high eccentricity orbits by Jupiter.  These bodies provided the Earth's water. 

 

Note that the "external pollution" model is not the same as the idea that comets provided the water.   The differences are that (1) the external pollution model takes into account and is consistent with the collection of models that explain the full architecture of the Solar System and (2) does not invoke comets but instead "polluting" bodies from the C-type asteroid reservoir that actually match the Earth's deuterium/hydrogen and N15/N14 isotope ratios.  Comets do not match the Nitrogen ratios. 

 

Another aspect is that the polluting bodies are delivered throughout the long period of formation after the disk dissipates whereas the comets model would deliver the water as a late veneer. 

 

I'm leaving a lot out.  For example, in exoplanetary systems the large cores can sometimes migrate all the way inward to the edge of the gas disk and this is thought to explain the existence of close in super-Earths.  In our Solar System Jupiter did not migrate into the terrestrial zone.  One idea is that Saturn and Jupiter shared the gap carved out by Jupiter and the torque caused by that situation resulted in outward migration after the initial inward migration. 

 

Another aspect of our Solar System is that Jupiter's rapid growth may have shut down the supply of pebbles to the terrestrial zone and thereby limited the growth of the terrestrial planets. 


Edited by russell23, 13 March 2020 - 10:43 PM.

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#8 scottk

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Posted 14 March 2020 - 09:42 AM

Yet this brings us no closer to understanding how life began regardless of when, where, or how the ingredients arrived.

 

How life began...


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#9 HouseBuilder328

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Posted 14 March 2020 - 10:35 AM

Yet this brings us no closer to understanding how life began regardless of when, where, or how the ingredients arrived.

 

How life began...

Yep, you're correct.  This is my reason for living as long as possible to maybe even get an ounce more of an answer.  Or  maybe the answer will come when I'm not alive anymore?



#10 russell23

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Posted 14 March 2020 - 10:40 AM

Yet this brings us no closer to understanding how life began regardless of when, where, or how the ingredients arrived.

 

How life began...

The research article this article was based on was not even about the origin of life.  It was about how volatiles (planetary ices) arrived on the Earth. 

 

Really the physics.org article title was somewhat misleading or sloppy. 



#11 BillP

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Posted 14 March 2020 - 11:28 AM

Ok, this (planetary formation and how the Earth got its water) is something I have been reading journal articles on and summarizing in a notebook for the last several months.    Observational research and models have reached a point where a picture of planetary formation processes is forming that provides a pretty solid understanding of exoplanetary systems and why the Solar System is "weird" as one paper put it.

 

...

Wow!  Fantastic response waytogo.gifwaytogo.gif  Thank you!



#12 llanitedave

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Posted 14 March 2020 - 11:38 AM

Yet this brings us no closer to understanding how life began regardless of when, where, or how the ingredients arrived.

 

How life began...

Sure it brings us closer, if only infinitesimally.  Understanding requires an aggregate of knowledge, and that knowledge is accumulated slowly, and in tiny bits.



#13 scottk

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Posted 14 March 2020 - 02:20 PM

From the article:

 

"If you combine this with the evidence for very ancient life on Earth, it reveals that life got started on our planet surprisingly quickly, within only a few hundred million years."

 

"Within" being the operative word. It could in fact have taken three and a quarter years.

 

Must tighten gap. twitch.gif



#14 davidpitre

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Posted 22 March 2020 - 01:49 PM

Thank you Dave for taking the time for your summary. Well done



#15 Dave Mitsky

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Posted 31 March 2020 - 02:31 PM

Thank you Dave for taking the time for your summary. Well done

It was entirely new information for me.  Thanks!




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