September 8, 2003
A: FROM MENTOR NORRIE ROBBINS IN CA
Good question, Sanna, because it is actually hard to answer. Paleontologists, who study fossils whatever the size, had to come together to make a decision because the answer isn’t simple. The decision was: “fossils are remains of life older than 10,000 years.” With this decision, kid footprints and leaf imprints in cement are therefore excluded from the classification “fossil.” So then, how do you know when something is older than 10,000 years? A whole slew of dating techniques using isotopes of elements such as C, Sr, U, Ar have been developed to tell this in the lab. But when a geologist, or anyone actually, goes up to an outcrop, there is no way to tell by just looking at the plant/animal/fungal/bacterial/algal remains/tracks/imprints unless the person is trained in those particular age rocks. The information you were given in Mongolia was probably correct—the palentologists there probably analyzed the remains and discovered that the silt at that location contained fossils. Silt absorbs moisture like that and is a size of particle which is larger than clay and smaller than sand. The technique you were told is for determination of silt and the person who taught you the technique was passing on information that some paleontologist had determined for that location. But you can go elsewhere on this Earth, and the remains in the silt there won’t be greater than 10,000 years old.
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A: FROM MENTOR SALLY RAMSDELLIN KY
This is a new one on me! Fossils are rocks. They are the remains or casts
of plants and/or animals that have been turned to stone by mineral
replacement. Maybe it is a difference in absorptivity that makes them
respond this way when wetted.