Fossil Review
What are Fossils?
Fossils are the remains or traces of ancient life that have been preserved by natural processes,
from spectacular skeletons to tiny sea shells. Some fossils are the preserved remains of whole
organisms or parts of organisms; these are called body fossils. Imprints, tracks, and trails can also
become fossilized, like dinosaur footprints or worm burrows; these are called trace fossils. Fossils are
not the remains of the organism itself! They are rocks.
A fossil can preserve an entire organism or just part of one. Bones, shells, feathers, and leaves
can all become fossils. Fossils can be very large or very small. Microfossils are only visible with a
microscope. Bacteria and pollen create microfossils. Macrofossils can be several meters long and
weigh several tons. Macrofossils can be petrified trees or dinosaur bones.
How do fossils form?
The way a fossil forms depends on a few things. The most important step is that the remains
or traces of life must be buried, the quicker the better. The longer they remain exposed the more
likely it is that they will be destroyed by scavengers or by the environment itself. Imagine a desert
versus the bottom of a deep sea… wind blasted sand dunes and hungry scavengers versus still,
murky waters where gloopy mud is laid down steadily… where do you think fossils are more likely
to form? Apart from burial the other key points are…
 Hard parts best. Got bones or shells? Then you are more likely to become a fossil because
soft bits rot away quickly.
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Where do you live? If there is sediment like mud or sand being laid down then you have a
chance to be buried by it and fossilized. Ice also works well.
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The recipe for success. Once buried there is a chance minerals can start to fill gaps in your
remains or even replace them, basically turning them into stone. This is when fossilization
really happens and depends a great deal on what natural minerals are in the sediment.
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And finally… with luck the rock layer you are preserved in will be eroded and your fossilized
remains become exposed and ready to be discovered.
Preserved remains become fossils if they reach an age of about 10,000 years. Fossils can come
from the Archaeaean Eon (which began almost 4 billion years ago) all the way up to the Holocene
Epoch (which continues today). The fossilized teeth of wooly mammoths are some of our most
"recent" fossils. Some of the oldest fossils are those of ancient algae that lived in the ocean more than
3 billion years ago.
What Can We Learn from Fossils?
By studying the remains of life and the traces it left behind we can learn a lot about how
animals and plants lived and behaved millions of years ago. We can also learn about animals and
plants that are alive today by studying their ancestors.
Fossils of ancient marine animals called ammonites have been unearthed in the highest
mountain range in the world, the Himalayas in Nepal. This tells scientists that millions of years ago,
the rocks that became the Himalayas were at the bottom of the ocean. Fossils of an ancient giant
shark, a megalodon, have been found in the landlocked U.S. state of Utah. This tells scientists that
millions of years ago, the middle of North America was probably entirely underwater.
Finally, we can also learn a great deal about how life has evolved on Earth through the study
of fossils.
Answer the following IN YOUR
the words from the passage.
OWN WORDS. You will not receive credit for using
1. What is a fossil? __________________________________________________________________
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2. What is the difference between body fossils and trace fossils? ______________________________
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3. What is the ideal scenario for a fossil to be created? (hint: there is more than one factor) ________
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4. What is one organism that can create a microfossil and one organism that can create a macrofossil?
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5. Why is the study of fossils important? _________________________________________________
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