Transcript A trip through geologic time Feb. 2012

March 2012
By award winning Mr. Huppert
1. What is a fossil?
 A fossil is the preserved remains or traces of
living things


Provides evidence of how life changed over time
Provides clues to what past environments were like
2. How does a fossil form?

An organism dies. Sediment covers the remains.
The sediment becomes rock.
2 a. What type of rock do fossils form in?

Sedimentary
3. What is a mold fossil and how does it form?
 A hollow area in sediment in the shape of an
organism. Forms when the hard part of the
organism is buried in sediment.
4. What is a cast fossil and how does it form?
 A cast fossil is a solid copy of the shape of an
organism. A cast is the opposite of a mold.
5. What is a petrified fossil?
 A fossil in which minerals have replaced all or
part of the organism.
6. What are carbon films?
 An extremely thin coating of carbon on rock
from the organism.
7. Describe trace fossils:
 Trace fossils can tell us about the organisms
size, behavior, number of feet, whether or not it
traveled in groups, etc…
8.What are some other ways organisms can be
preserved?
 Organisms can be preserved in tar, amber, and
ice.
9. What is the name of the type of scientist that
studies fossils?
 A Paleontologist
10. What is the fossil record?
 The fossil record provides evidence about the
history of life and past environments on Earth.
It shows how different groups of organisms
have changed over time.
11. What is the name of the theory that describes
and explains the change of organisms over time?
 Evolution
1. What is the difference between relative and
absolute age?
 Relative age is the age of a rock compared to
the ages of other rocks. Absolute is the exact
(within a few years) age of the rock.
2. What is the law of superposition?
 The oldest rock layers are on the bottom. Each
higher layer above is younger.
3. How do scientists determine the relative age of
rocks?
 They look at extrusions, intrusions, faults and
gaps in the geologic record.
Extrusions are always younger than the rocks below
it
 An intrusion is always younger then the rock layer
around or beneath it.

4. How can scientists use fossils to date rocks and
what is an index fossil?
 Fossils that are widely distributed and
represent an organism that lived only briefly
can tell the relative ages of the rock layer they
are in. The fossils are called index fossils.
Describe in detail radioactive decay:
 Radioactive decay occurs when certain
elements breakdown or decay into a different
version of the same element or into a new
element. The rate of decay is constant (called
half life). Half life is the amount of time it takes
half of the atoms to decay over time.
2. Does radioactive dating determine absolute or
relative age?
 Absolute
3. What are the two most common radioactive
elements used in radioactive dating?
 Potassium- argon and Carbon 14
1.What is the geologic time scale?
 A record of life forms and geologic events in
Earth’s history.
2.What criteria did scientists use to determine
how to divide up the units of geologic time?
 They used major changes in life forms at
certain times.
Era- one of the three long units of time between
Precambrian and present
Period- the unit that is used to divide era’s
1. How long ago do scientists believe the earth
formed?
 4.6 billion years ago
2. How do scientists know this?
 Through radioactive dating of rocks
3.How did the earth take shape? (how did it
form?)
 It began as a ball of dust and rock pulled
together by gravity. Denser material sank to
the core. The collisions made the planet very
hot.
4. How many atmospheres do we think the earth
had?
 Two
5.What happened to the first atmosphere?
 It was destroyed by the sun- solar storms. (Our
mortal enemy)
6.How do we believe the oceans formed?
 Water vapor in the atmosphere condensed and
accumulated forming the oceans.
7. Describe the first life on earth:
 Single celled similar to todays bacteria. (Very
simple)