EPT - What are Fossils? Lesson

 

What are Fossils?

When viewed as stationary objects, the continents present some very interesting (and confusing) facts. The first has to do with fossils:

Fossils are the mineralized remains of organisms that once lived in an area. The term "fossil" includes a wide variety of artifacts, including actual skeletons, eggs, and wood that have been preserved through a process called petrification. Petrification is the gradual replacement of organic material with inorganic minerals; as organic remains decay underground, the spaces left behind are filled with minerals that are dissolved in water. Other types of fossils include footprints and other impressions that were made when objects fell into soft sediments (such as mud) that then hardened and eventually became sedimentary rock.

Fossils can tell scientists many things about the history of an area, including the kinds of plants and animals that were living there. Fossils can even provide clues about the climate of a region. For example, fossils of ferns and cycads, both tropical plants, have been found on islands in the Antarctic. Since the climate in Antarctica today would not support these types of plants, logic suggests that the island must have been much warmer - and experienced higher levels of precipitation - than it is today.

With few exceptions, plant and animal species today are generally confined to one or a few continents, and their ranges are usually contiguous (the ranges on different continents are connected together). Lions, rhinoceros, and zebras are found only in Africa, while bison, whitetail deer, and mountain lions are North American species. Some plants and animals (such as armadillos, wolves, and birds) do range across several continents, but their territory is continuous across the continents (plants and animals do not recognize geopolitical boundaries, so their range does not always match up with the boundaries of a country such as the United States).

However, the fossil record tells a different story. Fossils of plants and animals can be found on several different continents, with no connections indicating how they got there. Cynognathus was a 3 m (10 ft) long, land-dwelling reptile whose fossils can be found in the middle of South America as well as the southeastern portion of Africa; but how did it arrive at these two locations simultaneously? No reptile could swim across the Atlantic Ocean, nor survive the months it would take to drift across on a fallen log, etc. Even more confusing is Lystrosaurus, whose fossils are found in Africa, India and Antarctica. Not only are there vast distances between these locations, but the climates are so very different that it would be impossible for Lystrosaurus to live in all three areas today.

There is another very odd discontinuity between fossils found on land and fossils found on the ocean floor - while fossils found on land can be literally billions of years old, the oldest fossils found in sedimentary rock on the ocean floor date back to less than 200 million years ago.

 

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