Life may have emerged 4.5 billion years ago,been destroyeyed by late heavy bombardmen

[dr.syntax]

Ever heard of the: Late Heavy Bombarment ? Part of what I read there suggests that the earliest life forms may have existed as much as 4.5 billion years ago. Some scientists believe the resultinng boiling off of the oceans would have destroyed all of these earliest life forms. Many if not most believe that some of these earliest life forms must have managed to survive somehow to explain the relatively short interval in time when up until this still controversial event occurred [from 4.1 to 3.8 billion years ago] and the widely accepted 3.8 billion year history of when life began. The source of this information is Absolute Astronomy and they give a pretty good argument that this event did occur and state that there is growing evidence and it is becoming more widely accepted. It was all new to me. If you wish to read about it go to : http://www.absoluteastronomy.com/topics/Late_Heavy_Bombardment . You can link up throughout the site for different information about all this that may interest you. It`s all new to me. ...Dr.Syntax

Edited September 24, 2009 by dr.syntax

[Mokele]

All the link provides is evidence of a massive bombardment.

 

There's no evidence that life preceded this bombardment except for "organic chemicals", which have turned up all sorts of places, including meteorites, and are therefore a poor indicator of the presence of life.

[dr.syntax]

All the link provides is evidence of a massive bombardment.

 

There's no evidence that life preceded this bombardment except for "organic chemicals", which have turned up all sorts of places, including meteorites, and are therefore a poor indicator of the presence of life.

REPLY:To find this information go to: http://www.absoluteastronomy.com/topics/Late_Heavy_Bombardment and scroll down

near to the end of scrolling down there is that bit by Thursten Giesler about about traces of carbon 12 to carbon 13 ratios being unusually high normally indicating a sign of procssesing life. This study of " Jack Hills Rocks" consisting of some specimens he found there dating to 4.25 billion years ago. The rocks containing the life indicators. Also the time line at : http://www.absoluteastronomy.com/topics/Timeline_of_Evolution places the developement of the earliest lifeforms between 4.5 billion and 2.5 billion years ago. You have to scroll down to THE DETAILED TIMELINE for this information. ...DS

Edited September 26, 2009 by dr.syntax

[Mokele]

Firstly, the dates listed in the first link are close to the commonly accepted value of 3.8 bya for life, so they aren't exactly special.

 

Your second link proves nothing. Can you link to an actual scientific journal article presenting evidence of life prior to 3.8 bya?

[dr.syntax]

Firstly, the dates listed in the first link are close to the commonly accepted value of 3.8 bya for life, so they aren't exactly special.

 

Your second link proves nothing. Can you link to an actual scientific journal article presenting evidence of life prior to 3.8 bya?

 

as some intestings findings some scientists are looking into. No one has made any definative claims about this. Only that there is growing evidence for the bombardment itself and that life may have existed prior to this Late Heavy Bombardment. I am not claiming anything so I have nothing to prove to you. ...Dr.Syntax

[Mokele]

Then where is that "growing evidence"?

[dr.syntax]

Then where is that "growing evidence"?

 

It`s there in the article if you care to read about it. Its not something I came up with. I you think the whole idea is a bunch of non-sense I do not care one little bit. ...Dr.Syntax

---

Merged post follows:

Consecutive posts merged

Then where is that "growing evidence"?

 

Appollo missions 15,16, and 17. Scroll down to " Evidence for a Cataclysm".

Edited September 26, 2009 by dr.syntax
Consecutive posts merged.

[Mokele]

...

 

The article contained excellent evidence of a phase of Earth's history characterized by massive bolide bombardment.

 

It does not, however, contain any even remotely convincing evidence that life had already appeared by this point. There's an oddity in isotopes, but that's hardly a fossilized stromatolite.

 

I don't dispute the bombardment, I dispute the origin of life as prior to it.

[Mythranil]

Even if life on Earth existed before the bombardment, I personally find it unlikely that these early life forms would have been decimated by it. Based in part on my own research and field observations, it seems more likely that some of these early forms of life were chemotrophs feeding off deep-sea thermal vents and were not affected by an increase in global temperature. If anything, the bombardment could have aggravated the earth's degassing processes and made food supply even more readily available.

 

The scientific community is reaching the point of its research into the origins of life where we have to distinguish between what exactly constitutes life and what does not... Perhaps similar to the human embryo debate, only on a simpler scale. Looking into the fossil and geochemical record of earth, we'll have to decide which isotopes are truly only unique to life forms, and which are just random agglomerates. I've seen several of these early 3.8 bya stromatolites and the evidence is pretty thin; I've also seen one of the supposedly 4.5 bya "organic dots", for lack of a better term, and I have a hard time accepting that it is truly life. It's more likely a geological oddity - a speck on the geological camera lens, if you will. Just like how ghost hunters see a speck of light on their film and call it an orb, or point out facial features in their photographs, so do we as scientists tend to employ that wishful thinking at times. Sometimes a speck is just a speck.

[dr.syntax]

Even if life on Earth existed before the bombardment, I personally find it unlikely that these early life forms would have been decimated by it. Based in part on my own research and field observations, it seems more likely that some of these early forms of life were chemotrophs feeding off deep-sea thermal vents and were not affected by an increase in global temperature. If anything, the bombardment could have aggravated the earth's degassing processes and made food supply even more readily available.

 

The scientific community is reaching the point of its research into the origins of life where we have to distinguish between what exactly constitutes life and what does not... Perhaps similar to the human embryo debate, only on a simpler scale. Looking into the fossil and geochemical record of earth, we'll have to decide which isotopes are truly only unique to life forms, and which are just random agglomerates. I've seen several of these early 3.8 bya stromatolites and the evidence is pretty thin; I've also seen one of the supposedly 4.5 bya "organic dots", for lack of a better term, and I have a hard time accepting that it is truly life. It's more likely a geological oddity - a speck on the geological camera lens, if you will. Just like how ghost hunters see a speck of light on their film and call it an orb, or point out facial features in their photographs, so do we as scientists tend to employ that wishful thinking at times. Sometimes a speck is just a speck.

 

REPLY:.......Dear Mythranil , Is there any likelyhood of discovering new areas where the surface of the Earth survived,did not melt during this: Late Heavy Bombardment. Also would there be any reason to suppose some such areas may exist under the oceans. Is there any reason to assume they do not exist under the oceans. Just curious as it would seem if they could locate some large areas that survived this event they may find some more definitive answers as to whether life pedates this event or not. ...Dr.Syntax

Edited September 27, 2009 by dr.syntax
edit

[Mythranil]

REPLY:.......Dear Mythranil , Is there any likelyhood of discovering new areas where the surface of the Earth survived,did not melt during this: Late Heavy Bombardment. Also would there be any reason to suppose some such areas may exist under the oceans. Is there any reason to assume they do not exist under the oceans. Just curious as it would seem if they could locate some large areas that survived this event they may find some more definitive answers as to whether life pedates this event or not. ...Dr.Syntax

 

Dear Dr. Syntax,

 

There is always the possibility that we will find older, more definitive proof that life existed that long ago. It will, however, be confined to terrestrial settings (and potentially some coastal submerged formations). The reason behind this is that, because of plate tectonics and the processes of subduction and continental drift, the ocean floor - worldwide - is no more than about 200 million years old, at most. You can basically divide the earth's tectonic plates into two varieties: oceanic and terrestrial; these correspond to heavy and light rocks, respectively. Because the ocean floors are made up of the more dense rocks, they always subduct and return to the mantle when they reach the edge of a continent. You can think of the oceanic plates as large conveyor belts - it will always be recycled, and the new rock being formed at plate seams has lost all former structure because it's been melted down and reconstituted into the earth's molten core.

 

That being said, there are some very old sedimentary rocks in northern Canada and Australia that hint at the evidence of life; unfortunately, due once again to plate tectonics and specifically the process of metamorphism - wherein rock is subjected to and deformed by a variety of pressures, temperatures, and hydrothermal fluids - the older the rock, the more deformed it has become. Some of the really old chlorophyll fossils (my aforementioned 'blobs') have been so deformed and stretched out that they have almost no semblance of anything living. Thus, it's quite a stretch that we'll find any evidence of life around 4.5 bya simply because the geological conditions of the earth, by themselves, probably won't allow for it. Of course, this is all before the forces of bombardment and erosion have their say in the matter.

 

Don't be discouraged by the thought, though - we find stuff all the time we previously said could not exist. We just have to know where to look. During my time as a palaeontologist, I worked extensively on the Burgess Shale deposits, which is a fossilized lottery ticket in itself - it should not exist, but because of some highly unusual circumstances, not only were the fossils preserved, but they were preserved with skin and all. Unbelievable stuff. I studied some of the fossilized deep-sea vents in the same area as the Burgess Shale, and my team and I found enormous communities of animals living beside the vents. My feeling on the subject is that if we're going to find convincing evidence of life on earth older than 3.8 bya, it's going to be around these deep-sea vents.

 

My memory is a little sketchy about my 4.5 bya geology - but I do recall that evidence of glaciation exists from at least that long ago, in the form of striation marks in Australia from where the glaciers scraped against solid rock. Consider for a moment that, in order for a relatively small set of scratches from such a glaciation to exist before, during, and after a global bombardment, it does not seem likely that the bombardment caused the surface of the earth to melt - otherwise, the striations would no longer exist.

 

My overall opinion of the global bombardment has been that it has been sensationalized and was likely not as major of an event as some claim it to be. I will admit, however, that I am not well read on the most recent literature regarding it, so if there is new evidence in the contrary, I'm pleased to be wrong.

[dr.syntax]

Dear Mythranil, You are an exellent writer. One of the very best. I thoroughly enjoyed your desertation regarding my questions. I am truly impressed. Thank you for taking your time to answer my questions. Regards, ...Dr.Syntax

[Ophiolite]

My memory is a little sketchy about my 4.5 bya geology - but I do recall that evidence of glaciation exists from at least that long ago, in the form of striation marks in Australia from where the glaciers scraped against solid rock.

I think you are confusing yourself here. Currently the oldest known rocks are found in the Nuvvuagittuq greenstone belt on the shores of Hudson Bay. They have recently been dated at 4.28 billion years.

 

Neodymium-142 Evidence for Hadean Mafic Crust

Jonathan O'Neil, Richard W. Carlson, Don Francis, and Ross K. Stevenson

Science 26 September 2008 321: 1828-1831

 

Prior to that I think the oldest rocks known were the Acasta Gneiss, also in Canada. They were right on the 4.0 billion year age.

 

Reworked zircons have been recovered from Jack Hills in Australia that are close to 4.44, o4 4.35 billion years old, but these do not represent whole rock.

[dr.syntax]

I think you are confusing yourself here. Currently the oldest known rocks are found in the Nuvvuagittuq greenstone belt on the shores of Hudson Bay. They have recently been dated at 4.28 billion years.

 

Neodymium-142 Evidence for Hadean Mafic Crust

Jonathan O'Neil, Richard W. Carlson, Don Francis, and Ross K. Stevenson

Science 26 September 2008 321: 1828-1831

 

Prior to that I think the oldest rocks known were the Acasta Gneiss, also in Canada. They were right on the 4.0 billion year age.

 

Reworked zircons have been recovered from Jack Hills in Australia that are close to 4.44, o4 4.35 billion years old, but these do not represent whole rock.

 

REPLY: Those zircons from the Jack Hills are the oldest rocks known dating to 4.4 billion years ago. read all about it at http://minerals.suite101.com/article.cfm/the_oldest_rock_on_earth . Those zircones were not reworked. the sedimentary rocks surounding them were. You want to parse words to make some contrived point for what purpose ? ...Dr.Syntax

---

Merged post follows:

Consecutive posts merged

I think you are confusing yourself here. Currently the oldest known rocks are found in the Nuvvuagittuq greenstone belt on the shores of Hudson Bay. They have recently been dated at 4.28 billion years.

 

Neodymium-142 Evidence for Hadean Mafic Crust

Jonathan O'Neil, Richard W. Carlson, Don Francis, and Ross K. Stevenson

Science 26 September 2008 321: 1828-1831

 

Prior to that I think the oldest rocks known were the Acasta Gneiss, also in Canada. They were right on the 4.0 billion year age.

 

Reworked zircons have been recovered from Jack Hills in Australia that are close to 4.44, o4 4.35 billion years old, but these do not represent whole rock.

 

REPLY: Those zircons from the Jack Hills are the oldest rocks known dating to 4.4 billion years ago. read all about it at http://minerals.suite101.com/article.cfm/the_oldest_rock_on_earth . Those zircones were not reworked. the sedimentary rocks surounding them were. You want to parse words to make some contrived point for what purpose ? Mythranil himself stated the rocks had been streched and deformed so if that is what you are referring to he had already stated that himself. Also he stated they were found in sedimentary rock.He never said they represent "whole rock". They are still the oldest rocks anyone has ever found. ...Dr.Syntax

Edited September 30, 2009 by dr.syntax
Consecutive posts merged.

[Ophiolite]

My apologies Dr.Syntax for not noticing your reply earlier. Regretfully I must correct you. Minerals, which zircons are, are not rocks. Rocks are made up of a variety of minerals (although there are some mono-mineralic examples).

 

The age of a rock is the age at which the whole rock was formed, not the age of its constituent minerals. For example there are quartz grains in the Old Red Sandstone in Scotland derived from Lower Palaeozoic rocks of the Dalradian sequence. We don't declare that the ORS rocks are Lower Palaeozoic because some of their minerals derive from rocks of that age. Some of those quartz crystals were recylced and can be found in neighbouring Carboniferous sandstones. Zircons are even more durable than quartz and can go through many such cycles of erosion, deposition, diagenesis, possibly metamorphosis, and then more erosion.

 

In the same way it is wholly incorrect to describe the Jack Hills rocks as the oldest on the planet simply because some of the minerals in them are that old. That is not the way geological terminology works.

 

Your own quoted article confirms this. For example in the opening paragraph the author notes "However, recent discoveries suggest that rock materials exist today that are older than 3.9 billion years."

 

This is followed by these observations:

"The oldest terrestrial material on Earth can be found in rock formations of the Jack Hills in Western Australia."

 

For terrestrial material read minerals of terrestrial origin. Note that this material is in the rock, it is not the rock. i.e. it is a component of the rock.

 

And then there is this nice description: "Zircon crystals are extremely durable and can therefore survive billions of years’ worth of weathering and erosion, as they have in the Jack Hills. Even after they are recycled through multiple periods of sedimentary and metamorphic rock-forming processes, they are able to tell geologists about the physical and chemical conditions under which they formed."

 

The Jack Hills rocks are themselves 'only' about three billion years old. Rather than being an attempt to 'parse words for a contrived point', this really is a fundamental issue. If those rocks were the same age as the zircons they contain we could gain an amazing insight into early crustal processes far beyond the remarkable understanding we have gained from the zircons alone.

 

If you remain in doubt I quote you this line from the relevant primary research.

"The Jack Hills zircons are therefore remnants of igneous rock-forming events that pre-date the rock record by up to 400 Ma......The variable age distributions within different rock units in the Jack Hills demonstrate that Early Archean zircons were derived from multiple source rocks;..."

 

Cavosiea, A.J., et al "Internal zoning and U–Th–Pb chemistry of Jack Hills detrital zircons: a mineral record of early Archean to Mesoproterozoic (4348–1576 Ma) magmatism" Precambrian Research 135 (2004) 251–279

 

The full paper is available here.