The conventional idea is the oil and gas that fuels our homes and cars started out as living organisms that died, were compressed, and heated under heavy layers of sediments in the Earth’s crust. It’s a sound idea that can be replicated and observed. The new idea, which has a been around for decades particularly in the former Soviet Union is that some of the oil and much of the gas deposits have another geophysical source.
For years scientists have debated whether some of these hydrocarbons could also have been created deeper in the Earth and formed without organic matter. Now for the first time, scientists at the Carnegie Institution’s Geophysical Laboratory with colleagues from Russia and Sweden 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. The research was published in the July 26, advanced on-line issue of Nature Geoscience.
The two smallest hydrocarbons methane (CH4) the main constituent of natural gas and ethane (C2H6) is used as a petrochemical feedstock and others associated with natural gas, are called saturated hydrocarbons because they have simple, single bonds and are blessed being fully saturated with hydrogen in the molecule.
The research group using a diamond anvil cell and a laser heat source 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.
The research group also 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.
Carnegie’s Alexander Goncharov a coauthor of the paper says, “We were intrigued by previous experiments and theoretical predictions. 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.”
That reaction observation puts the deep hydrocarbon formation idea into the realm of observable possibilities. That also leaves a huge hydrogen matter to resolve. At those temperatures and pressures with only speculative other conditions the idea is able to gain some credible traction.
Professor Kutcherov, another 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 offers a new take on the planetary carbon cycle. The research does need supported as understanding the cycle in a more full way would help make humanity a better steward of the planet’s resources of carbon which is a prime element of all life. The carbon cycle is one measured in millions if not hundreds of millions of years which is an important factor in managing the carbon available.
Even suppositional understanding would need research support from fields such as cosmochemistry, mineral physics, theoretical geochemistry, petroleum geology, organic chemistry, microbial ecology, high-pressure technology, diamond synthesis, geodynamics, evolutionary biology among many others.
That research got a major boost when on July 1st 2009 the Alfred P. Sloan Foundation, well known for its basic science support, awarded the Carnegie Institution a $4 million grant over three years to initiate the Deep Carbon Observatory – an international, decade-long project to investigate the nature of carbon in Earth’s deep interior. Headquartered at the institution’s Geophysical Laboratory, the Deep Carbon Observatory will coordinate the efforts of hundreds of researchers from more than two dozen countries. Their multi-disciplinary research will focus on Earth’s poorly understood deep carbon cycle, including the largely unknown role of deep biology and the possible influences of this cycle on critical societal concerns related to energy, environment and climate.
The planet’s carbon cycle seems to be well understood as a process, but much more depth of understanding will make a big difference. Carbon is critical and the planet’s cycle needs firm, high quality science applied before the types seen muckraking with the climate cycle kidnap it.