We know how oil and natural gas deposits were created; living organisms died, were compressed, and heated under heavy layers of sediments in the Earth's crust.
Scientists have debated for years whether some of these hydrocarbons could also have been created deeper in the Earth and formed without organic matter. Now scientists say they have found that ethane and heavier hydrocarbons can be synthesized under the pressure-temperature conditions of the upper mantle; the layer of Earth under the crust and on top of the core.
Methane (CH4) is the main constituent of natural gas, while ethane (C2H6) is used as a petrochemical feedstock. Both of these hydrocarbons, and others associated with fuel, are called saturated hydrocarbons because they have simple, single bonds and are saturated with hydrogen.
Using a diamond anvil cell and a laser heat source, the scientists from the Carnegie Institution's Geophysical Laboratory, with colleagues from Russia and Sweden, first subjected methane to pressures exceeding 20 thousand times the atmospheric pressure at sea level and temperatures ranging from 1,300 F° to over 2,240 F°. These conditions mimic those found 40 to 95 miles deep inside the Earth.
The methane reacted and formed ethane, propane, butane, molecular hydrogen, and graphite. The scientists then subjected ethane to the same conditions and it produced methane. The transformations suggest heavier hydrocarbons could exist deep down. The reversibility implies that the synthesis of saturated hydrocarbons is thermodynamically controlled and does not require organic matter.
Artistic view of the Earth's interior shows hydrocarbons forming in the upper mantle and transported through deep faults to shallower depths in the Earth's crust. The inset shows a snapshot of the methane dissociation reaction studied in this work. Credit: Image courtesy A. Kolesnikov and V. Kutcherov
The scientists ruled out the possibility that catalysts used as part of the experimental apparatus were at work, but they acknowledge that catalysts could be involved in the deep Earth with its mix of compounds.
"We were intrigued by previous experiments and theoretical predictions," remarked Carnegie's Alexander Goncharov a coauthor. "Experiments reported some years ago subjected methane to high pressures and temperatures and found that heavier hydrocarbons formed from methane under very similar pressure and temperature conditions. However, the molecules could not be identified and a distribution was likely. We overcame this problem with our improved laser-heating technique where we could cook larger volumes more uniformly. And we found that methane can be produced from ethane."
The hydrocarbon products did not change for many hours, but the tell-tale chemical signatures began to fade after a few days.
Professor Kutcherov, a coauthor, put the finding into context: "The notion that hydrocarbons generated in the mantle migrate into the Earth's crust and contribute to oil-and-gas reservoirs was promoted in Russia and Ukraine many years ago. The synthesis and stability of the compounds studied here as well as heavier hydrocarbons over the full range of conditions within the Earth's mantle now need to be explored. In addition, the extent to which this 'reduced' carbon survives migration into the crust needs to be established (e.g., without being oxidized to CO2). These and related questions demonstrate the need for a new experimental and theoretical program to study the fate of carbon in the deep Earth."
The research was published in the July 26, advanced on-line issue of Nature Geoscience.
- PHYSICAL SCIENCES
- EARTH SCIENCES
- LIFE SCIENCES
- SOCIAL SCIENCES
Subscribe to the newsletter
Stay in touch with the scientific world!
Know Science And Want To Write?
- The Genetic History Of Ice Age Europe
- Exodus 2100: Due To Climate Change
- What Lies Beneath West Antarctica?
- Professor Frenkel: Why Shouldn't We Drop Algebra From Our Education System?
- Matter Can Potentially Accelerate The Expansion Of The Universe
- Three Earth-sized Planets Found Orbiting A Tiny Nearby Star
- Scientists Discover Oral Sex In Spiders
- "actually I prefer something real, not paper printed by a private entity, backed by full faith and..."
- "Hello Peter:I presume my readers are busy. I presume they have a mild degree of experience about..."
- "So keep your cash an watch the world come to an end . Cheap and selfish is the right way ..."
- "There is a tendency to label some as Global Warming Alarmists I think the warnings have been conservative..."
- "The guardian? You're funny :-) The CESM models only prove accurate with post-hoc data input corrections..."
- 3 Reasons Aerial Pesticides Are Not Causing Autism
- Most Stores Refuse E-Cigarette Sales to Minors
- Vitamin C Conundrum for the Organic Crowd
- Newsweek Journalist Loses His Mind, Time-Traveling Radioactivity And More Media Links
- This Single-Celled Organism Is Capable Of Learning
- Study Says Bilingual Kids’ Brains Are Smarter & Faster
- UC San Diego bioengineers create first online search engine for functional genomics data
- UK Health Check has only modest impact on risk factors for cardiovascular disease
- Adult brain prunes branched connections of new neurons
- Five new breast cancer genes and range of mutations pave way for personalized treatment
- Quantum sensors for high-precision magnetometry of superconductors