Fossils are the remains and/or traces of prehistoric life. The critical factor is age. Fossils have to be older than 10,000 years, the generally accepted temporal boundary marking the end of the last Pleistocene glacial event. Fossil remains include bones, teeth, shells, and wood. Fossil traces include footprints, burrows, impressions, molds, casts, and coprolites.
Fossils are found in the sedimentary rock layers in which they were originally buried. So, the question really is, where do these layers occur? The sea cliffs at Torrey Pines State Reserve provide excellent exposures of 48-50 million year old fossil-bearing sedimentary rocks. The fossils in these rocks occur right at the surface because erosion has done the "digging" for us.
Since fossils occur in sedimentary rock layers, wherever sedimentary rocks are found there is a potential for fossil discovery. As mentioned above, the sea cliffs at Torrey Pines State Reserve offer good opportunities to observe fossils. These fossils generally consist of Eocene-aged (48-50 million years old) shells of estuarine snails and oysters. Because the fossils are in a state reserve there is no collecting allowed. However, this protection ensures that we and future generations will continue to be able to discover and enjoy these paleontological remains.
Yes. Dinosaur remains have been found in Cretaceous-aged (70-75 million years old) sedimentary rocks as exposed at Sunset Cliffs, La Jolla Bay, and Carlsbad. The types of dinosaurs represented by these local fossils include hadrosaur (duck-billed dinosaur) and nodosaur (armored dinosaur).
The age of a fossil can be determined by several means. One method, called superposition, is based on the position of a fossil in a stacked sequence of sedimentary rock layers. The fossils in the lowest layers are older than the fossils in the upper layers. This method does not give an absolute age for the fossil, only a relative age (older or younger). Absolute age of a fossil is determined by radiometric dating -- a method that relies on the natural radioactivity of certain elemental isotopes. Different isotopes have different rates of radioactive decay and these rates are constant. This constancy of decay rates serves as a "radiometric clock" that allows geochronologists to analyze samples and measure the relative quantities (ratios) of "parent" to "daughter" isotopes. These ratios provide a means for determining when the "radiometric clock" started and therefore the age of the rock layers associated with the fossil.
In the movies "Jurassic Park" and "The Lost World," scientists cloned dinosaurs from DNA found in prehistoric blood-sucking insects preserved in amber. How real is this premise?
With today's technology it is impossible to recreate extinct dinosaurs. It is extremely unlikely that scientists will ever be able to bring them back to life. Only with a quantum leap in scientific understanding could such a project be successful.
In the movie, researchers find fossilized blood-sucking insects that had bitten living dinosaurs. Soon afterward, these insects were caught in oozing tree sap that fossilized into amber. The scientists in the film extracted dinosaur blood from the fossilized insects and used the DNA in the blood to recreate dinosaurs.
Scientists really do study ancient insects fossilized in amber, but none have ever been found with blood inside them. Most of the amber found with insects trapped inside is not old enough to have been around when the dinosaurs lived between 65 and about 210 million years ago.
DNA is very fragile and deteriorates over time. Even if a blood-engorged insect was found, the blood would have to have been perfectly preserved over millions of years so the cells could be extracted in good condition. Finally, for the DNA to be viable, the insect must have died before it got a chance to digest the blood.
If a good piece of amber were found containing an insect full of dinosaur blood, the blood cells would have to be separated from the insect's cells -- a difficult process. (Also, there is no guarantee that the insect's last meal was from a dinosaur). If this were accomplished, scientists could use a new technique called polymerase chain reaction (PCR) to replicate the DNA enough times to work with it. Such technology, developed in the last decade, is now used in laboratories around the world.
Even if it could be determined that the DNA recovered was from a dinosaur, there would still be problems. Since DNA deteriorates over time, very little of a creature's complete genetic materials, call the genome, would be likely to be left after more than 65 million years. The genome of such a complex creature as a dinosaur is made up of billions of pairs of building blocks called nucleic acids -- the primary form of which is deoxyribonucleic acid (DNA). These acids are grouped into genes, which in turn are strung together into chromosomes. If you imagine the genome as a book, the chromosomes are chapters, genes are sentences and the nucleic acids are the alphabet. At present, the most that could be hoped for would be to find perhaps two or three hundred nucleic acid pairs, or less than one millionth of the genome -- not nearly enough to "read" the genome as one would a book.
Even if the entire genome of a dinosaur were somehow discovered, it would be found out of order, in tiny pieces. Literally, billions of nucleic acids would have to be combined correctly, like putting together an enormous jigsaw puzzle where each piece was shaped exactly alike. The genetic code is only one of many crucial factors that go into creating a living creature. Without interactions between the DNA and products supplied by the mother, a creature would not develop and you would merely have chemicals in a test tube.
New technology has made research on fossil DNA possible, but no dinosaur DNA has ever been found. At the American Museum of Natural History, researchers have extracted the sequenced DNA from a termite that lived 25 to 40 million years ago, long after the end of the age of dinosaurs. Other scientists have found fossil DNA from other insects and plants.