2. Three main types of fossils:
Actual remains Imprints
Petrification
3. Three main types of fossils:
Actual remains
•bones
•teeth
•shells
•amber
•frozen in ice
4. Three main types of fossils:
Actual remains
•bones
•teeth
•shells
•amber
•frozen in ice
5. Three main types of fossils:
Actual remains Imprints
•bones molds or casts
•teeth in mud, sand,
•shells etc. that turn
•amber to stone
•frozen in ice
6. Three main types of fossils:
Imprints
molds or casts
in mud, sand,
etc. that turn
to stone
7. Simulation of how imprint fossils are formed
http://www.classzone.com/books/earth_science/terc/content/visualizations/es2901/es2901page01.cfm
8. Three main types of fossils:
Actual remains Imprints
•bones molds or casts
•teeth in mud, sand,
•shells Petrification etc. that turn
•amber minerals to stone
•frozen in ice replace the
cellular
material and
harden to
stone
9.
10. This dragonfly was petrified by calcium carbonate (calcite) that covered its
surface. This type of petrification can occur in hot springs limestone caves.
11. Most fossils are preserved in sedimentary rock.
Sedimentary rock usually forms when small particles of sand, silt, clay,
or lime muds settle to the bottom of a body of water.
As sediments build up, they bury dead organisms that have sunk to the
bottom.
16. Most fossils are dated using a combination of
relative dating and radiometric techniques.
17. Relative Dating
Lower layers of sedimentary rock, and fossils they contain, are generally
older than upper layers.
Relative dating places rock layers and their fossils into a temporal
sequence.
18. To help establish the relative ages of rock layers and their fossils,
scientists use index fossils. Index fossils are distinctive fossils used to
establish and compare the relative ages of rock layers and the fossils
they contain.
If the same index fossil is found in two widely separated rock layers, the
rock layers are probably similar in age.
19. Radiometric Dating
Relative dating is important, but provides no information about a fossil’s
absolute age in years.
One way to date rocks and fossils is radiometric dating.
Radiometric dating relies on radioactive isotopes, which decay, or
break down, into nonradioactive isotopes at a steady rate.
Radiometric dating compares the amount of radioactive to nonreactive
isotopes in a sample to determine its age.
20. We detect these particles and the energy that
comes with it as radiation
21. The process of losing particles is called decay.
decay causes the atom to become something else:
potassium-40 argon-40
carbon-14 nitrogen-14
uranium-238 lead-206
22. the original material is called the parent isotope
the material it becomes
is called the daughter
product
23. Half-life : the length of time required for 50% of the
parent material to decay into the daughter product.
What’s the half-life of
What’s the half-life of
strontium-90?
strontium-90?
24. Half-life : the length of time required for 50% of the
parent material to decay into the daughter product.
What’s the half-life of
What’s the half-life of
strontium-90?
strontium-90?
Answer: 25 years
Answer: 25 years
25. Rates of decay are specific, constant, and
measureable.
•Which is why they can be used for
dating fossils once a standard has
been developed.
26. If a geochemical laboratory determines that the volcanic ash
in a sample of siltstone has a ratio of U-235 to Pb of 2:3, how
old is the ash?
27. 2+3 = 5 and 2/5 x 100 = 40% ANSWER: about 900 million years old
This dragonfly was petrified by calcium carbonate (calcite) that covered its surface. This type of example, called Calcareous sinter, is often occurred in hot springs or limestone region (limestone caves). As dragonflies are poikilotherm, they cannot move when their body temperature is low. So they raise body temperature by exposing themselves in the sunlight or by moving flight muscles. This dragonfly probably wandered off into a dark cave and became unable to move, and was soon covered with limy substance to be a stone like this.
