Tualatin's Mastodon and Fossils EarthCache
Tualatin's Mastodon and Fossils
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The mastodon skeleton was unearthed in Tualatin near the Library in 1962 by two Portland State University students. John George grew up in Tualatin and remembered the town marshal telling about some enormous bones that he had seen in the swamp near Nyberg Creek (just south of the current Fred Meyer store parking lot). Along with Ron and George Sund, George spent a a month excavating the bones, recovering nearly half of a skeleton. The bones were originally displayed at Portland State University before being given to then Tualatin City Manager Yvonne Addington in the 1970s. After several years in storage (first in Tualatin, then at the Portland Zoo), the Tualatin Historical Society and community members raised funds to have the bones cleaned and restored, and the skeleton was put on display within the Library. The current display was created as part of the Library's renovation and expansion in 2008. The skeleton was carbon-dated and determined to have died about 14,000 years ago. Scientists estimate this mastodon was a female who died in her 20s. Around 14,000 years ago, (when the Tualatin mastodon was alive) the area was a land of small hills with open evergreen forests, meadows, and wetlands. Just north of Mt. Rainier in Washington, stretched a huge glacier, thousands of feet thick and thousands of miles wide. Although we don’t know for sure how she died, scientists speculate from where her bones were found that she may have drowned in a bog. In the 1870s, Tualatin pioneers discovered a huge jawbone while digging a drainage ditch. The curious settlers sent the jaw to the Smithsonian Institution, where scientists examined it and declared it came from a “prehistoric creature.” How do fossils form? There are several different ways fossils are formed. An animal dies, its skeleton settles on the sea floor and is buried by sediment. Skeleton buried by sediment The sediment surrounding the skeleton thickens and begins to turn to stone. The skeleton continues to be buried as sediment is added to the surface of the sea floor. As the sea floor sinks, pressure increases in the lower layers of sediment and it turns it into hard rock. The skeleton dissolves and a mould is formed. Now buried at depth and surrounded by stone, the skeleton is dissolved by ground water. This leaves a cavity (or hole) preserving the shape of the original skeleton. This cavity is known as a natural mould. Skeleton buried by sediment Minerals crystallise inside the mould and a cast is formed. Water rich in minerals enters the mould, and fills the cavity. The minerals deposited in the mould form a cast of the mould. This cast has the same shape as the original skeleton, but none of its internal features. Skeleton buried by sediment The fossil is exposed on the Earth's surface. Millions of years later, the rock surrounding the skeleton rises to the Earth's surface (this happens during mountain building, earthquakes and other earth processes). The rock is worn away by wind and rain, and the fossil is now exposed, waiting to be found! To claim this cache please send me the answers to these questions: #1. How many fossils do you find here? #2. What are they?
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