La Brea Tar Pits

[Moontanman]

What is the result of the La Brea type tar pits in the future? Will it eventually harden into something like coal and if covered and refound just be a coal deposit? What will the Tar Pit formations become? 

[Moontanman]

No one has a take on this? 

[DrP]

27 minutes ago, Moontanman said:

No one has a take on this? 

Sorry - I haven't a clue, never heard of the place.   Interesting looking it up though - some nice fossil finds around there  -  maybe I'll have to think about arranging a fossil hunting holiday there sometime.  

[StringJunky]

47 minutes ago, Moontanman said:

No one has a take on this? 

It seems coal came first and the coal, under heat and pressure, pyrolysed* into tars.

Quote

While tar is a major component produced in coal pyrolysis, there is little agreement on how to quantitatively describe the steps in its evolution (formation of tar molecules, transport, evaporation and repolymerization). Because coal is insoluble, heterogeneous and complex, it is very difficult to verify proposed models. In an attempt to overcome some of these difficulties, polymers with ethylene bridges between naphthalene rings have been used to model tar release in pyrolysis of softening coals. A theory has been developed that combines random cleavage of weak bonds in the polymer (to produce metaplast) with transport of depolymerization fragments by vaporization and diffusion. The theoretical predictions for various temperatures, heating rates and pressures compare favourably with tar yields measured in a heated grid apparatus and molecular weight distribution determined by field ionization mass spectrometry. The predicted trends agree with the results on coal tars produced under the same conditions.

* Pyrolysis -

Pyrolysis is the thermal decomposition of materials at elevated temperatures in an inert atmosphere.[1] It involves the change of chemical composition and is irreversible. The word is coined from the Greek-derived elements pyro "fire" and lysis "separating".

Pyrolysis is most commonly applied to the treatment of organic materials. It is one of the processes involved in charring wood, starting at 200–300 °C (390–570 °F).[2] In general, pyrolysis of organic substances produces volatile products and leaves a solid residue enriched in carbon, char. Extreme pyrolysis, which leaves mostly carbon as the residue, is called carbonization.

The process is used heavily in the chemical industry, for example, to produce ethylene, many forms of carbon, and other chemicals from petroleum, coal, and even wood, to produce coke from coal. Aspirational applications of pyrolysis would convert biomass into syngas and biochar, waste plastics back into usable oil, or waste into safely disposable substances.   https://en.wikipedia.org/wiki/Pyrolysis

[Moontanman]

3 hours ago, StringJunky said:

It seems coal came first and the coal, under heat and pressure, pyrolysed* into tars.

* Pyrolysis -

Pyrolysis is the thermal decomposition of materials at elevated temperatures in an inert atmosphere.[1] It involves the change of chemical composition and is irreversible. The word is coined from the Greek-derived elements pyro "fire" and lysis "separating".

Pyrolysis is most commonly applied to the treatment of organic materials. It is one of the processes involved in charring wood, starting at 200–300 °C (390–570 °F).[2] In general, pyrolysis of organic substances produces volatile products and leaves a solid residue enriched in carbon, char. Extreme pyrolysis, which leaves mostly carbon as the residue, is called carbonization.

The process is used heavily in the chemical industry, for example, to produce ethylene, many forms of carbon, and other chemicals from petroleum, coal, and even wood, to produce coke from coal. Aspirational applications of pyrolysis would convert biomass into syngas and biochar, waste plastics back into usable oil, or waste into safely disposable substances.   https://en.wikipedia.org/wiki/Pyrolysis

Interesting but what becomes of the tar after it hardens over the eons? 

Evidently the La Brea Tar Pits are thought to be the result of oil broken down.

https://en.wikipedia.org/wiki/La_Brea_Tar_Pits

Edited August 7, 2018 by Moontanman

[StringJunky]

1 hour ago, Moontanman said:

Interesting but what becomes of the tar after it hardens over the eons? 

Evidently the La Brea Tar Pits are thought to be the result of oil broken down.

https://en.wikipedia.org/wiki/La_Brea_Tar_Pits

If you notice in your link, the tar is the heavier fraction of the oil left after the lighter fraction has evaporated. The tar (asphalt) is now being subject to anaerobic processes by bacteria and the final products are not yet known.

Quote

Microbial Diversity in Natural Asphalts of the Rancho La Brea Tar Pits

Relatively little is known yet about anaerobic petroleum hydrocarbon degradation, although there has been steady progress in this field (1, 23, 30, 50). Tentative mechanisms that function for anaerobic degradation of alkylbenzenes and nonaromatic hydrocarbons are proposed to involve hydrolases and carboxylases and are coupled to sulfate or nitrate reduction (35, 46). In our survey, anaerobic bacteria that were identified included members of Gammaproteobacteria (60 clones of purple sulfur bacteria), Bacteroidetes, Clostridia, and Acidobacteria, none of which have been studied with respect to their possible contributions to anaerobic degradation of petroleum hydrocarbons. Homologous genes for the benzylsuccinate synthase (bss), which is the key enzyme for anaerobic toluene degradation, have been cloned (33) and may provide an entry point for future studies on the relevance of this pathway in the tar pit bacteria. In addition to direct catabolism of hydrocarbons, anaerobic bacteria may also contribute to hydrocarbon degradation by syntrophy, in which metabolically linked consortia function to consume fatty acids and degradation products of hydrocarbons to generate methane (46).  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1932828/

Edit: Those tar  pits are only about 38000 years old, so there's probably lots for them to do before they reach a final equilibrium.

Edited August 7, 2018 by StringJunky