Download
1 / 35
360 likes | 427 Views
FOSSIL FORMATION & TYPES OF FOSSILS.
E N D
FOSSIL FORMATION & TYPES OF FOSSILS • 8.E.6A.4 Construct and analyze scientific arguments to support claims that different types of fossils provide evidence of (1) the diversity of life that has been present on Earth, (2) relationships between past and existing life forms, and (3) environmental changes that have occurred during Earth’s history.
FOSSIL RECORD • Fossils are mineral replacements, preserved remains, or traces of organisms that lived in the past. The collection of fossils and their placement in chronological order is known as the fossil record.It documents the existence, diversity, extinction, and change of many life forms and environmental changes throughout the history of life on Earth.
Thousands of layers of sedimentary rock not only provide evidence of the history of Earth itself but also of changes in organismswhose fossil remains have been found in those layers.
Erosion and weatheringof sedimentary rock layers can cause the destruction of fossils and result in gaps in the fossil record. Certain environmental conditions favor certain fossil formations. Therefore, the type of fossilsfound in an area can explain the environmental changes that have occurred.
RAPID BURIAL • The rapid burial of organisms, which is more likely to occur in marineenvironments, results in a greater likelihood that the remains of marine organisms will be preserved. Flash floods and volcanic ash falls help preserve land organisms.
Certain fossilized organisms could only live in specific environments or under particular climate conditions. • Extinction of life forms as well as how and when new life forms appeared is part of the fossil record. • Fossils can show structural similarities and differences in organisms over time revealing the vast diversity of life forms that have and continue to exist on Earth.
Anatomical similarities and differences between various organisms living today and between them and organisms in the fossil record enable the understanding of the diversity of life that has been present on Earth. Comparisons between living organisms and fossils also allow scientists to make inferences about the lines of descent.
Fossil FormationIn the first step of fossil formation an animal or plant must die in or near water or near enough to fall in shortly after death. In the following example a trilobite has died of old age on the bottom of the sea. Bacteria consume the soft body parts but leave the hard exoskeleton intact.
2nd Step: Sedimentation • As time passes sediments bury the exoskeleton. The faster this happens the more likely fossilization will occur. Land and mud slides definitely help. River deltas are also good for quick accumulation of sediments. This further insulates our trilobite from decomposition. Now we have fossil formation in progress.
3rd Step Permineralization • .The sediment goes through compression and cementation. The exoskeleton is replaced and turned into minerals. • If mineral-rich water percolates down through the sediments, the fossil formation process has an even better chance of preserving our ancient animal. Some of the minerals stick to the particles of sediment, effectively gluing them together into a solid mass.. In time the entire shell is replaced leaving rock in the exact shape of the trilobite or animal. That is fossil formation at work.
4th Step: Uplift • As the continental plates move around the earth, crashing into each other, mountains are formed. Former sea floors are lifted up and become dry land. This is exactly what has happened to our trilobite in the picture below. Now fossil formation is complete but our trilobite is buried under hundreds or even thousands of feet of rock! Thanks to the movement of the plates, our trilobite or fossil will come closer to the surface and nearer to discovery by some fortunate fossil hunter. Luckily nothing stays the same.
5th Step: Erosion at work • Fossil formation is revealed by weathering and erosion. Wind, rain, freeze and thaw, even earthquakes will help force the trilobite out of its burial ground and out into the light. If he or she is lucky enough, the trilobite will reveal itself in time to be spotted by a rock-hunter or fossil-digger. Who knows? It could even be YOU!
Check Point • 1. What is a fossil record? • 2. How would you explain rapid burial? • 3. What helps preserve land organism in rapid burial? • 4. What are the steps to fossil formation (short form)?
TYPES OF FOSSILS • Mold fossil – forms when sediments bury an organism and the sediments change into rock; the organism decays leaving a cavity in the shape of the organism. (CAKE PAN) • Cast fossil – forms when a mold is filled with sand or mud that hardens into the shape of the organism. (THE CAKE)
Petrified fossil (permineralized fossil) – forms when minerals soak into the buried remains, replacing the remains, and changing them into rock. • Preserved fossil – forms when entire organisms or parts of organisms are prevented from decaying by being trapped in rock, ice, tar, or amber.
Carbonized fossil – forms when organisms or parts, like leaves, stems, flowers, fish, are pressed between layers of soft mud or clay that hardens squeezing almost all the decaying organism away leaving the carbon imprint in the rock. Trace fossil – forms when the mud or sand hardens to stone where a footprint, trail, or burrow of an organism was left behind.
THE SIX TYPES OF FOSSILS NAME THAT FOSSIL
Check Point • 1. How would you explain the 6 types of fossils? (use key words) • 2. Which type of rock are fossils are more likely to form in?
