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Fossil Evidence of Evolution

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Presentation on theme: "Fossil Evidence of Evolution"— Presentation transcript:

1 Fossil Evidence of Evolution

2 Biblical Reference From one man he made all the nations, that they should inhabit the whole earth; and he marked out their appointed times in history and the boundaries of their lands. Acts 17:26

3 Fossils Remains or traces of past life forms
Most common in sedimentary rocks and in some accumulations of ash Extremely useful for determining relative ages of strata, but geologists also use them to determine environments of deposition Provide some evidence for organic evolution The word, fossil, comes from the Latin word, fossilis, which means “to obtain by digging”

4 The Fossil Record Record of ancient life preserved as fossils in rocks
Repository of prehistoric organisms that provides our only knowledge of such extinct animals as trilobites and dinosaurs Demonstrates how species have evolved over time

5 The Fossil Record The fossil record is made up of all the fossils ever discovered on Earth. The fossil record provides evidence that species have changed over time. Based on fossil evidence, scientists can recreate the physical appearance of species that are no longer alive on Earth.

6 Fossil Formation After an animal dies, any soft tissues animals do not eat break down. Only the dead animal’s hard parts, such as bones, shells, and teeth, remain. Under rare conditions, these parts become fossils. Fossils form via two methods: Mineralization Carbonization

7 Fossil Formation

8 Original Preservation
Remains are considered Unaltered if: They retain their original composition and structure by freezing or mummification (usually in amber or tar)

9 Altered Hard Parts Soft parts of remains decay while hard parts (shells, bones, etc.) become fossils. May become altered by: Mineral Replacement Usually from Groundwater or Volcanic Ash Recrystalization Due to Changes in Pressure and Temperature over Time

10 Altered Hard Parts

11 Molds and Casts Molds form Casts form Shell is buried.
when buried remains dissolve and leave a cavity Casts form if minerals or sediments fill in the cavity Shell is buried. Shell dissolves, leaving a cavity (Mold). Cavity fills with sediment, creating a Cast.

12 Cast of a Turtle

13 Trilobite Mold and Cast

14 Trace Fossils Indications of organic activity including tracks, trails, burrows, and nests A coprolite is a type of trace fossil consisting of fossilized feces that may provide information about the size and diet of the animal that produced it

15 Determining a Fossil’s Age
Instead of dating fossils directly, scientists date the rocks the fossils are embedded inside. In relative-age dating, scientists determine the relative order in which rock layers were deposited. Relative-age dating helps scientists determine the relative order in which species have appeared on Earth over time.

16 Absolute Age Dating Scientists take advantage of radioactive decay, a natural clocklike process in rocks, to learn a rock’s absolute age, or its age in years. To measure the age of sedimentary rock layers, scientists calculate the ages of igneous layers above and below them.

17 Absolute Age Dating If the age of the igneous layers is known, it is possible to estimate the age of the sedimentary layers - and the fossils they contain - between them.

18 Relative vs. Absolute Age
Relative Time: This rock is older than that one. Absolute Time: This rock is 542 Million Years Old.

19 The Geologic Time Scale
The geologic time scale is a chart that divides Earth’s history into four different eons - the longest time units in the geologic time scale. Hadean Eon Archaen Eon Proterozoic Eon Phanerozoic Eon 4.6 Billion years of Earth’s History has been reconstructed.

20 The Geologic Time Scale

21 Dividing Time 19th Century:
Geologist began to organize a geologic column Ordered succession of known strata Because they did not have absolute age dating techniques yet, scientists create time boundaries based upon fossils or other evidence of relative age Often a type of fossil disappeared from the rock record after a few layers. These were called index fossils.

22 Index Fossils Fossils that are easily recognized and widely distributed geographically Represent species that lived for relatively short periods of time Geologists can date a particular rock layer based on their presence. Trilobites are very common Index Fossils.


24 Extinctions Extinction occurs when the last individual organism of a species dies. A mass extinction occurs when many species become extinct within a few million years or less. Extinctions can occur when environments change.

25 Mass Extinctions The fossil record contains evidence that five mass extinction events have occurred during the Phanerozoic eon.

26 Evolution The fossil record contains evidence of the appearance of many new species over time. Biological evolution is the change over time in populations of related organisms.

27 Evolution in Horses The fossil record is evidence that horses descended from organisms for which only fossils exist today.

28 Pop Quiz Which refers to a chart that divides Earth’s history into different time units? A. fossil record B. geologic time scale C. relative-age dating D. trace fossil

29 Pop Quiz Which is the preserved evidence of the activity of an organism? A. cast B. fossil record C. mold D. trace fossil

30 Pop Quiz Which refers to the impression of an organism in a rock?
A. cast B. fossil C. mold D. trace fossil

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