Download Notes: Chapter 17 History of Life of Earth

Chapter 17 History of Life of Earth
I. The Fossil Record
A. Fossil – preserved remains or evidence of an ancient
organism
B. Fossil record
a. Provides evidence about the history of life on Earth
b. Shows how different organisms have changed over
time
C. How most fossils form in sedimentary rock:
a. An organism is buried by layers of sediment over
many centuries
b. The remains of the organism absorb minerals from
sediment and turn into rock
D. Paleontologist – scientists who study fossils
E. Over 99% of all organisms that have lived on Earth are extinct!
F. Methods to determine the age of fossils:
a. Relative Dating – estimate a fossil’s age by comparing it
to other fossils using the layers of rock as a guide
1. Index fossil – allows a scientist to determine the
age of a rock layer
b. Radioactive Dating – calculate age of fossil based on
the amount of radioactive isotopes it contains
1. Half – life - the length of time required for ½ of the
radioactive atoms in a sample to decay
II. Geologic Time Scale
A. Precambrian – from Earth’s formation – 544 million years ago
90% of Earth’s History
a. Sequence of Precambrian events:
1. organic molecules formed
2. formation of microspheres – not cells but have
similar characteristics
3. formation of RNA and proteins
4. formation of DNA
5. formation of bacteria cells (prokaryotes)
6. formation of photosynthetic bacteria – created
oxygen
7. formation of eukaryotic cells through the process
of endosymbiosis – bacteria cells enter a larger cell,
forming a more advanced type of cell
8. formation of multicellular organisms
B. Paleozoic Era: 544 – 245 million years ago
a. invertebrates develop (no backbone)
b. “Cambrian explosion” occurs causing development of
different types of living things
c. vertebrates, insects and land plants develop
d. vertebrates invade land – amphibians and reptiles
e. first mass extinction occurs causing 95% of life to
become extinct
C. Mesozoic Era: 245 – 65 million years ago
a. dinosaurs become dominant
b. flowering plants and trees develop
c. small mammals appear
d. birds appear
e. another mass extinction occurs causing dinosaurs to
become extinct along with about half of other types of life
D. Cenozoic Era: 65 million years ago - present
a. mammals develop further; whales and dolphins
develop
b. grasses evolved, causing grass–eating animals such as
cattle, deer and sheep to develop
c. ice ages occurred
d. humans evolve
III. Patterns of evolution
A. Extinctions – caused collapse of ecosystems; unknown cause possibly asteroids, shifting of continents, volcanic eruptions, etc
B. Adaptive Radiation – a single species has evolved into
diverse forms of life ex: Darwin’s finches
C. Convergent Evolution – unrelated organisms can resemble
each other
Ex: dolphin and penguin very different but look similar
D. Coevolution – 2 species evolve in response to changes in
each other
Ex: flowers and bees
E. Punctuated equilibrium – new species are produced by
periods of rapid change and periods of little change
F. Developmental genes – most organisms have same “master
control genes, called hox genes; any change to this genes will cause
a change in the body plan