A fossil is a remainder of something that lived a very, very long time ago. It can be the image of a plant, or an animal, or even just the trace of an animal, such as its dung or tracks.

Animal fossils are formed when an animal dies and slowly becomes covered with soil, mud or silt. Over thousands and thousands of years, the animal decomposes and the hard parts of their body become replaced with minerals; this process is called permineralization.

Fossils can often be found in sedimentary rock, which is formed by the layering of material over many years. When plants and animals die, they often sink to the bottom of a river or lake, where they are eventually covered over with soil and/or rock particles. Over time these soil and rock layers slowly become pressed together into hard rock, trapping the plant or animal remains between the layers, as fossils.

Potential fossils: What in our world today will be found as fossils in the future? click for copyright

Because sedimentary rocks form in layers, scientists believe that fossils also form in layers from the oldest fossil to the youngest fossils. So, the fossils at the bottom of a deep layer of rock are most likely the oldest; the fossils toward the top of a rock are most likely the youngest. Scientists call this the "Law of Superposition."

Just as it makes sense that the fossils at the bottom of a rock would be the oldest, it also makes sense that the sediment that covers up organisms (that later become fossils) would be laid down in horizontal layers. This is called the "Law of Original Horizontality." But, we know that over time, these horizontal layers can shift. Sometimes, sedimentary rock layers are not horizontal, but have been moved or shifted due to some change in the Earth.

Scientists describe the Earth's long history in time periods that compose a geologic time scale. Time periods are broken up into eons, which are further divided into eras, which are then divided into periods, which are then divided into epochs.

Geologic time scale. click for copyright

Engineers study fossils from all over the geologic time scale. They look closely at the processes and functions that are found in prehistoric nature and apply them to current technologies. By understanding how prehistoric creatures lived and what caused them to become extinct, engineers can get new ideas for how to design something. Engineers can also use this information to create models of global climate change over the life of the Earth, as well as learn more about species extinction.

Engineers design the tools that paleontologists use to discover fossils. Examples include:

• Magnetic resonance imaging (MRI): A noninvasive diagnostic technique that produces computerized images of internal body tissues and is based on nuclear magnetic resonance of atoms within the body induced by the application of radio waves.
• Computer-assisted tomography (CAT scan): A medical imaging method in which digital geometry processing generates a 3-D image of the internals of an object from a large series of 2-D x-ray images taken around a single axis of rotation; used in many fields for nondestructive materials testing, including detecting cracks in aircraft skins, industrial pipes, underground pipes, corroded reinforcing steel inside concrete, leaking welds, finding broken wires in suspension bridges, and forensics, etc.
• Mass spectrometry (or spectroscopy): An instrumental method for identifying the chemical constitution of a substance by means of the separation of gaseous ions according to their differing mass and charge, for identifying unknown compounds to determine physical, chemical or biological properties of compounds.

Discussion Question: Ask students the following question and discuss as a class. First see if students can provide a definition before explaining it to them.

• What is a fossil? (Answer: A remainder of something that lived a long time ago, such as a prehistoric plant or animal.)

Class Vote: Ask several true/false questions about the lesson material and have students vote by holding thumbs up for true and thumbs down for false. Tally the votes and write the totals on the board. Give the right answer. Example questions:

• True or False: A piece of animal droppings (poop) can be a fossil. (Answer: True. This type of fossil is called a trace fossil because it shows that an organism was there.)
• True or False: Fossils are formed when people place them into sand for other people to find later. (Answer: False. Fossils are formed by sedimentary rock being formed on top of and around a dead organism.)
• True or False: Paleontology is the study of fossils. (Answer: True)
• True or False: Engineers have no use for studying fossils. (Answer: False. Engineers can get ideas from studying fossils. They can use what they learn about fossils to design new technologies that mimic the prehistoric natural world.)

Creative Writing: Have each student write an essay or letter from the perspective of a plant or animal that becomes fossilized and then is discovered by an engineer. Have them describe in detail how the plant or animal becomes a fossil, and how they are re-discovered after many years. Then have them explain what they helped the engineer to learn and maybe even a new technology that they influenced the engineer in designing. Award extra points for creativity.