Oil From The Sky EarthCache
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About 450 million years ago – the Middle Ordovician period, during which life on Earth was still primarily confined to the sea – our world was pounded by a hail of L-chondrite meteors, probably as the result of the breakup of a large parent body. L-chondrite meteors still fall to Earth from this ancient parent to this day. That ancient catastrophe may have triggered the Great Ordovician Biodiversification Event, during which simple Cambrian sea life gave way to Palaeozoic fauna, including the first vertebrates and the first land-dwelling arthropods.
One of those ancient meteors sliced through the atmosphere and struck the shallow sea, gouging out a ten-mile-wide crater in the sea bed. Over eons of time layers of silt and sediment were deposited over the crater. The sea eventually receded, leaving the crater buried deep beneath the land surface. It remained hidden until 1991 when oil geologist Rex Olson discovered anomalies in seismic data. He and oilman Howard Hamm agreed that Olson had discovered an ancient underground crater or “astrobleme,” a term meaning star wound. Geologists studied the data and have concluded that the age and nature of the crater are consistent with the Ordovician meteor event described above.
So what does an ancient asteroid impact have to do with oil?
On impact, millions of tons of bedrock were vaporized, shattered, and expelled from the impact site in all directions. The underlying granite was compressed and fractured, then rebounded to form an uplifted crater floor surrounded by a rim of bedrock, 1400 feet higher than the surrounding land. Within the crater, infalling material and rubble were deposited atop the melted rock on the crater floor. It is this infalling material, held within the crater walls, that became the primary reservoir rocks that hold the oil that is produced today. Oil reservoirs are often formed when permeable or fractured rock is contained within surrounding formations of solid (or at least less permeable) rock, and the formation of the crater created just such a structure.
Before the discovery of oil here, geologists were skeptical that concealed impact sites such as this could produce commercially-viable quantities of oil and gas. However, about sixty wells were sunk into the Ames Astrobleme and half of these are still producing today, making this site the most productive of the six known oil-producing astroblemes.
Hamm later financed the construction of the Ames Astrobleme Museum, a unique, unstaffed museum which is open 24 hours a day. Videos and other displays at the museum describe the crater and its geological and commercial significance.
To log this Earth Cache, visit the museum and email your answer to the following question:
- What physical evidence of the ancient asteroid strike can be seen from this location?
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