Chapter 19: The History Of Life Ridgewood High School

Chapter 19.1 Fossil Record  Paleontologist: scientists who study fossils.  Fossil Record: preserved remains of organisms from past life that is maintained and recorded. **The fossil record provides evidence about the history of life on Earth. It also shows how different organisms have changed over time.

Ex: Of Fossil Record

The Fossil Record  Extinct: Organisms that have died out. Usually a species becomes extinct at a time.  Fossils can appear in different age rocks depending on how old the rock is will help determine the age of the fossils.

How Do Fossils Form?  Not all organisms will form into a fossil, certain conditions need to take place: They form in sedimentary rocks Sedimentary rock is formed from exposure to rain, heat, and wind.  Why is the fossil record described as an incomplete record of life’s history?

How Fossils Form

Relative Dating  Relative Dating: the age of a fossil is determined by comparing its placement with that of fossils in other layers of rock.  Index Fossils: similar to an index for a book, these fossils are specific. a species must be easily recognized and must have existed for a short period but have had a wide geographic range.

Relative Dating  Relative dating allows paleontologists to estimate a fossil’s age compared with that of other fossils. Relative dating DOES NOT give the actual age in years.

Relative Dating and Age of Fossils

Radioactive Dating and Half-Life  Half-life is the length of time required for half of the radioactive atoms in a sample to decay.  Radioactive dating is the use of half-lives to determine the age of a sample.

Radioactive Dating and Half-Life  In radioactive dating, scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains.

Carbon-14 vs. Uranium- 238 Dating  Carbon-14 is used to estimate the age of organic materials, such as wood and leather, up to about 58,000 to 62,000 years. Carbon- 14 half-life is 5770 years.  Uranium-238 has an estimated half life of 4.47 million years. It is used to date things that are many million years old such as dinosaur bones.  The half-life for Uranium-235 is 713 million years.

Radioactive Dating and Half-Life

Geologic Time Scale  Geologic Time Scale: represents evolutionary time It is used by paleontologists and broken into divisions of time.  Era: The time after Precambrian is broken into 3 eras or 3 time periods. Each era is then broken into periods.

Geologic Time Scale

Geologic Time As a Clock

Section 19.4 Patterns of Evolution  Macroevolution: refers to the large scale evolutionary changes that take place over long periods of time. Six important patterns of macroevolution are:  Mass extinctions  Adaptive radiation  Convergent evolution  Coevolution  Punctuated equilibrium  Changes in developmental genes

Mass Extinction  Extinction occurs all the time…Over 99% of the organisms that ever lived are NOW extinct.  Paleontologists used believe one factor created the mass extinction, and today many believe it was multiple factors that contributed to the mass extinctions.

Adaptive Radiation  Adaptive Radiation: a single species or a small group of species has evolved into several different forms that live in different ways. Ex: Darwin’s Finches Ex: (Large scale) Dinosaurs were products of a large adaptive radiation among ancient reptiles.

Convergent Evolution  Convergent Evolution: a process in which unrelated organisms come to resemble one another. Ex: all animals found in the water…dolphin, shark, fish.

Coevolution  Coevoltuion: the process by which two species evolve in response to changes in each other over time. Ex: plants and plant-eating insects evolve together because if the plant has an adaptation then the insect will need one too.

Punctuated Equilibrium  Punctuated Equilibrium: a term used to describe a period of long, stable periods interrupted by brief periods of more rapid changes. VS.  Gradualism: a slow steady change in a particular line of decent.