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Tuesday, May 29, 2012

The Dating Game: Digging Up Fossils



Since ancient times, people had been digging up bones and other mineralized remains of creatures that lived and died a long, long time ago.
When dinosaur bones were unearthed in China about a thousand years ago, people wondered about the kinds of animals that had these bones. This was probably the start of dragon legends.

All over  the world, there are places that if one digs deep enough, one may find some ancient shells, bone fragments, a piece of petrified wood, or even a leaf print.
These relics are called fossils. They are usually found through digging. In fact, the term "fossil" comes from a Latin word that means, "to dig." Fossils are remains of ancient life; they give us clues about the distant past. Countless animals and plants that lived a long time ago were preserved in different ways. In hot and dry places, actual bones or teeth of an extinct creature are sometimes preserved; in moist places, the relic may be replaced by a rock-like copy of the original and thus fossilized. This process is called permineralization, and this takes place slowly over millions of years. This means that a fossil of a bone is no longer technically a bone; chemically, the fossil may be more like a rock. Also, if a once-living thing was a tree, the fossil may be a part of a tree trunk that underwent replacement of woody material with minerals. This is how the Petrified Forest came into being, which you might want to look up. 
Fossils range in age from 3.5 billion-year remains of algae to the 10,000-year-old actual remains of giant wooly mammoths preserved during the last ice age. Most fossils are excavated in sedimentary rock layers. Sedimentary rock is rock that has formed from sediment, like small pieces of rock, sand, or mud. These small pieces of debris are compressed and buried under more and more layers of sediment. After many, many years, they become sedimentary rock. Layers beneath are older than the layers near the surface. Paleontologists (scientists who study prehistoric life) use fossils to learn how life has changed and evolved throughout the planet's history.

 So, how do they know a fossil's age? Dating fossils is a relatively straightforward process. There are actually several methods. Here are some of them:
1.       Stratigraphy is the oldest method of fossil dating. This method involves the depth of a fossil's location. For example, dinosaur bones are usually found in sedimentary rocks; these rock layers are formed periodically over time. Newer layers are formed on top of older layers, compressing the older layers, turning them into rocks. Paleontologists can estimate the amount of time that has passed since the layer containing the fossil was formed.
2.       Scientists can also observe the fluctuations of the Earth's magnetic field. Rocks from different geological eras are affected by these magnetic field fluctuations, enabling scientists to study these, and provide an estimate of the rocks' age. This method is also called Paleomagnetic dating.
3.       Radioisotope dating of igneous rocks near the fossil can also be used. Unstable radioactive isotopes of elements, like Uranium-235, decay at constant rates. Examination of the remaining radioactive elements provides an accurate estimate of a rock's age. Radioisotope dating, however, is not used directly on fossils, since they do not contain radioisotopes used in the dating process. Instead, scientists date igneous layers of rock, found beneath and above the fossil (or fossils). These layers of rock are volcanic in origin; hence, some fossils, especially dinosaur fossils, are dated with respect to volcanic eruptions.
4.       There are fossils that are widely distributed in the planet but have a limited time span. These are the index fossils, and they are important in determining ancient biological history. Brachiopods (appeared during the Cambrian Period), trilobites (Pre-Cambrian, early Paleozoic, Paleozoic Period), ammonites (Triassic and Jurassic Period) are a few examples of these index fossils. The presence of index fossils helps scientists in making an educated estimate of other nearby fossils' age.

Excavating fossils is actually the tricky part. After locating the fossil, it must be carefully freed, without damaging it, from the rocky environment that served as its home for probably millions of years. First, the fossil (or fossils) should be labeled and photographed while still encased in rock. Its position should be noted carefully and meticulously. Using tools like picks and shovels, most of the overlying rock is removed. The rocks closest to the fossil, however, are removed with smaller hand tools like trowels, hammers, whisks, and dental tools. The exposed fossil is again labeled and photographed. Sometimes, not all of the overlying rock is removed at the dig site. The rest is carefully removed at the laboratory. Large fossils, in contrast to small fossils that are excavated with small hand tools, require more effort and bigger tools to expose-tools like shovels, picks, jackhammers, and even explosives.

Although excavated differently, both large and small fossils have to be treated very, very carefully to avoid damaging them. Fragile fossils, before removing them, are applied with a quick-setting glue using a brush or a sprayer. The fossils are packed very carefully before moving them to the laboratory. Large fossils are wrapped in paper or burlap, and applied with a layer of plaster (similar to those used in setting broken bones). Smaller ones can be packed in bags or boxes.
After being located, dug up, exposed, packed, and sent to the laboratory, it is now time to put the pieces together, much like piecing together a jigsaw puzzle. It is very rare for a whole skeleton—of any animal—to be found; sometimes, there are even pieces of different animals at the same site, which can add to the confusion. Knowledge of anatomy is therefore important to piece the fossils together, and to guess what the missing pieces are.
Paleontology is the science of fossils. The term comes from the Greek words logia (science), palaios (very old), and onta (existing things). Paleozoology is the science of extinct animals; the science of extinct plants is paleobotany.
Through the study of fossils, scientists have been able to put together a "picture" of what the world was like many ages ago. They have found evidence that the Himalayas, the Alps, the Rocky Mountains and other mountains were once under water.
How did the scientists know that? For one thing, they found fossils of sea animals high up on the slopes of these mountains. Obviously, these sea creatures did not climb up there. Scientists also found out through fossils that Europe and the United States were once covered with tropical forests; and that camels once roamed the plains of North America; that elephants and rhinoceros once lived in the Philippines.

Fossils also provided the clues that enabled scientists to trace the planet's animal life back to the earliest worms and shellfish, and that the great deposits of coal and chalk were the remains of living things that died millions of years ago. Of course, through fossils, we now know that giant reptiles (the dinosaurs) once roamed the earth; that these dragon-like monsters, at least some of them, stood more than a hundred feet long—the largest land animals that ever lived. We also know that when it comes to survivability, size doesn't matter—hundreds of giant species died out and made way for creatures with more brains and less bulk.
Fossils also tell us that modern humans have existed on this planet for "only" about half a million years. Compare that to the cockroach, which has been on this planet for hundreds of millions of years. Being the planet's Johnny-come-lately, it is no coincidence that among the latest fossils are those of early humans, which are found mostly in the Great Rift Valley, East Africa.
Humans were indeed "created" last.

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