View Full Version : Dumb guy asks Geologist dumb questions

11-28-2005, 05:30 PM
Can't believe how dumb this guy is...even used my email address

Dear John,

I'm happy to try to answer your questions sent to USGS Ask-a-Geologist,

#1 Is it not possible that most of the earth's oil supply is
That oil well in Texas, and the one in Saudi Arabia, are pumping from
the same source?

No, this is not so, this is not the way oil in the earth is distributed. In each oil field, oil is present in one or more particular oil-bearing, permeable rock formations. The geologic situation is different in each area, the oil-bearing rocks are of different types, depths, and ages and are separated by faults, folds, continental boundaries and many other geologic structures, so that the oil-bearing strata in each region are totally different and not connected.

You can find some good, basic information about petroleum geology on these websites:

#2 I it posssible that the oil acts as a heat shield, protecting the
planet's surface from the core's heat?...
something like oil in a transformer?...and would this bode badly for our
delicate climate?

Also, this isn't really the case. Oil-bearing rocks (usually, sedimentary rocks such as sandstone and limestone) are only present "here and there" within the Earth's crust, and they are only one of the many, many different kinds of rocks present in the crust. When oil is present, it occurs as a film around mineral grains, in the pore spaces of the rock formation, and it only makes up a small fraction of the total rock formation. And, there is a great deal more water pres
ent, as "groundwater" similarly occupying the pore spaces in rocks, than there is oil.

It is true that the overall thickness of the rock layers of the Earth's crust, insulates the surface from the higher temperatures of the mantle and core of the Earth. Subsurface water plays a minor role in this (the temperatures near the surface can be higher, if there are channels for water movement that bring extra geothermal heat to the surface--such as where there are hot springs and geysers), but oil, would play a very insignificant role in this.

#3 Are we changing the weight of the planet, by burning off all this
oil....and would that affect it's orbit?

That's an interesting question, about changing the Earth's weight, or its orbit. The first and simplest answer is, no, there is no overall change in the planet's mass (= weight) from burning oil, because both the reactants and the products of burning oil or natural gas, are all present on Earth to begin with, and remain on Earth, in the ground or in the atmosphere. The simplest chemical equation for burning a hydrocarbon (methane, CH4), would be:

CH4 + 3 O2 = CO2 + 2 H2O

The CO2 and H2O produced all remain in the atmosphere, so there is no overall change in the weight of the Earth.

There are, however, a few processes that slowly change the total mass of the Earth with time. One is the escape of small amounts of light gases (such as hydrogen, helium, or water vapor) from the Earth's outer atmosphere. The other is the infall of meteorites, or meteoritic and comet dust, into the atmosphere. The total change in the Earth's mass due to either of these processes, however, is very small.

There is an effect, however, on the speed of the Earth's rotation, whenever any material is redistributed from its original location, to any new location either further from, or closer to, the center of the earth. This is an angular momentum effect, and the analogy commonly given for it, is the way a spinning ice skater will spin faster, if he folds his arms in closer to his body, and will spin slower if he spreads his arms out. Any process on our planet that takes material further from the surface (such as taking it from within the crust, into the atmosphere) will slightly decrease the planet's rotation speed, plus the opposite. These processes are taking place all the time, naturally, and human activities can also produce this effect. For example, eruption of volcanoes or emission of volcanic gases, condensation or evaporation of water, melting of glaciers, uplift or erosion of mountains, and settling of sediment to the sea floor, all slightly change the angular momentum of the earth, and hence it's rotation speed. These changes can be measured (or, more likely, they can be calculated, because they are usually too small to actually measure). A human activity such as building a large dam, can be one of the things that very slightly changes the earth's rotation, because the water held behind a dam is now being kept at a higher elevation (= greater distance from the earth's center) than it would otherwise be.

In actual fact, however, all these changes are very, very small. I saw figures given, for example, for the amount the earth's rotation was changed by the redistribution of mass from the fault movement that caused the December, 2004 earthquake and tsunami. The reported figure (calculated; this is too small to actually measure) is a shortening of the length of the day, by 2.64 microseconds (2.64 x 10-6 seconds). This effect, and other similar ones, are very small compared to a more measurable, and continually occurring, process; the tidal interaction between the Earth and Moon, which continually increases the length of the day by about 15 microseconds per year. (I'm quoting these numbers from,


So to go back to your question, pumping oil (or water) from within the earth's crust to the surface, or burning the oil, would have a very slight effect on the earth's rotation, but probably too small to measure. Also, the pumping of oil or water to the surface, would be partly or largely compensated for, by the slight downward settling of the rock strata, as the fluids are pumped out.

#4 What replaces the oil mass? just voids?...and wouldn't this affect
the tectonic plates?

My very last sentence in answering your #3, above, relates to the answer to this question too. As the oil (or water) that occupies the pore spaces in the rock is pumped out, the rock settles slightly; the sediment grains in it shift slightly closer together, and the entire thickness of the sedimentary strata, and the surface, will sink slightly. This effect is, in fact, noticed, in places like the Texas Gulf Coast, where a lot of both oil, and groundwater, have been pumped to the surface. It causes land subsidence, which can sometimes be gradual and widespread, or sometimes form localized cracks or fissures, or even cause mild earthquakes. So, to that degree, it can slightly effect the behavior of the tectonic plates of the Earth.

I hope these comments will have helped answer your questions.

Best regards,

Pete Modreski, USGS, Denver CO
Ask-a-Geologist for Nov. 25-26, 2005

Peter J. Modreski
U.S. Geological Survey, Denver, Colorado
Central Region Office of Communications
Events and Community Relations - Geologic Outreach & Education
Geochemist and Geologic Specialist for Abrasives, Gemstones,
Quartz, Beryllium, Cesium, and Rubidium

Isn't this internet great.....where you can ask things you should have learned in 6th grade Geology....and get good answers?????