History of the Earth Guided Notes pg.
176 in Life Science Book
1. Fossils- traces or imprints of living
things, such as animals, plants,
bacteria, and fungi that are
preserved in rock.
2. How do paleontologists figure out
the age of a fossil? Relative dating or
absolute dating
3. Principle of Superposition- This
principle states that in a sequence of
undisturbed sedimentary layers or
lava flows, the oldest layers are at
the bottom.
4. Relative dating- look at a cross
section of sedimentary rock
- Oldest layer is on the bottom
- Examine the sequence of fossils
starting at the bottom
5. Absolute dating- Force holds atoms together; if
there isn’t enough force to hold
them together, the atom is
considered unstable
- Unstable atoms decay by releasing
energy, particles or both
- Each kind of unstable atom decays
at its own rate.
6. Half-life- time it takes half of the
unstable atom in a sample to decay.
- Half-life range from fractions of a
second to billions of years
7. How do you find the half life of a
fossil? Measuring the ratio of
unstable atoms to stable atoms,
scientist determine the approximate
age
8. Geologic Time Scale- scientist use
to outline the history of life on earth
- Scientists used fossils and absolute
dating to make this scale
- Paleontologists divided the scale
up into big categories called eras
9. Era- characterized by the type of
animal that dominated the earth at
that time
- Examples: Mesozoic Era: dinosaurs
reptiles (Age of the Reptile)
10. Mass extinction- large number of
species died out at the same time
- Scientists aren’t sure what causes a
mass extinction
11. How do scientists believe mass
extinction can happen? Major
changes in Earth’s climate or
atmosphere
- Climate could have changed
because of movement of
continents or all dinosaurs died out
because a meteorite could have
collided with Earth causing major
climate changes.
12. Pangaea- “supercontinent”
- All the continents were together at
one time
13. What do plate tectonics cause
animals to do? Causes animals to
adapt or they will not survive.
Eras
1. Precambrian Time- 4.6 billion
years ago-540 million years ago
-life began and transformed the
planet
2. What was the atmosphere made
of during this time period?
Atmosphere lacked oxygen, rich in
other gases like carbon monoxide,
carbon dioxide, hydrogen, and
nitrogen
3. If I was to picture what earth look
like at that time, what would I see?
Pictured as a place of great turmoil
- Meteorites crashing, violent
thunderstorms and volcanic
eruptions were constant
- Intense radiation from the sun
4. How did the first forms of life
develop during the Precambrian era?
Scientists think life developed from
nonliving matter
-chemicals that already existed in
the environment (water, clay,
dissolved material, gases present)
-energy was present on Earth;
chemicals reacted with one another
and formed complex molecules
making life possible
-time passed and prokaryotes
formed (they have no nucleus)
-these prokaryotes were anaerobic
(they did not require oxygen to
survive)
-these prokaryotes made their own
food through photosynthesis
-through the process of
photosynthesis, oxygen was
released
-this changed Earth’s atmosphere
forever
5. What is a radiation shield and how
does it make a huge impact on how
our earth is today? As the
atmosphere filled with oxygen, this
helped to form the radiation shield
(this is also known as the ozone
layer)
-the ozone layers purpose is to
absorb UV radiation
-before the ozone layer,
underground and under the ocean
was the only way for survival
-ozone layer allowed thing the
ability to live on land
6. By the end of the Precambrian
era, what has developed on earth?
-at the 1 billion years mark,
eukaryotes formed (they have a
nucleus, more complex structure and
bigger organism)
-over the next 2.5 billion years,
scientists think they kept evolving to
form more complexed organisms
7. Paleozoic Era- 540 million years
ago-248 million years ago
8. What has developed during this
era? Plants, fungi, air-breathing
animals on dry land
- Huge forests covered earth by the
end of this era
- All major plant groups besides
flowering plants appeared during
this era
9. By the end of this era, how has life
on earth changed? Crawling insects
were the first animals followed by
salamander like animals
-near the end of this era, reptiles,
winged insects and dragonflies
appeared
- Largest mass extinction happened
during this period where 90% of
marine species died out
10. Mesozoic Era- 248 million years
ago-183 million years ago
11. What has developed during this
era?
-Age of the Reptile because of the
burst of evolution from surviving
reptiles
12. This era is known as the Age of the
__Reptile_________. Why?
Dinosaurs dominated Earth for 150
million years
13. What made their appearances
during this period?
- Large marine lizards appeared
- First birds appeared during this
time
- Most important plant was the
cone-bearing seed plant formed
large forests
- Flowering plants made their
appearance
14. What happened at the end of this
era? The dinosaurs and others
became extinct
15. What is the dinosaur theory?
Meteorite hit Earth; this generated a
giant dust cloud with enough heat to
cause worldwide fires
- When this happened, the dust
cloud block out the sunlight from
getting to the plants so they died.
- After the plants died, the plant
eating dinosaurs died
- After the plant eating dinosaurs
died, the meat eating dinosaurs
died
- Only species able to survive were
small mammals that were able to
burrow underground
16. Cenozoic era- 65 million years
ago-present
17. What has developed during this
era?
- Fossils are embedded in rock layers
so we know the most about this
era
- Many mammals, birds, insects, and
flowering plants appeared
18. This era is considered the Age of
_____Mammal_____.
- Mammals came to dominate
- Mastodons, saber-tooth cats, giant
sloths and small horses are some
examples