3. Are the preserved remnants or impressions left by
organisms that lived in the past
best places to find them are in lake, swamp and river
In essence, they are the historical documents of
4. The fossil record is the ordered array
in which fossils appear within
These rocks record the passing of
5. Sedimentary rocks are the richest
source of fossils
Sedimentary rocks are form from layers of sand
and silt that settle to the bottom of seas and
As deposits pile up, they compress older sediment
below them into rock
The bodies of dead organisms settle along with
the sediments, but only a tiny fraction are preserved
Rates of sedimentation vary depending on a
variety of processes, leading to the formation of
10. Index fossils are another tool to determine
the age of rock layers.
• Index fossils can provide
the relative age of a
– existed only during
specific spans of time
– occurred in large
• Index fossils include
fusulinids and trilobites.
11. Fossils can form in several ways:
by water are
a hard structure.
12. A natural cast forms
when flowing water
removes all of the
original tissue, leaving
16. • Radiometric dating uses decay of unstable
Radiometric dating provides an accurate way to
estimate the age of fossils.
– Isotopes are atoms of an element that differ in their
number of neutrons.
17. Radiometric dating uses decay of
– Isotopes are atoms of an element that differ in their number of
– A half-life is the amount of time it takes for half of
the isotope to decay.
26. Fossil evidence shows that marsupials evolved in the Jurassic
but after the continents started to break-up, the marsupials must have
got separated into two populations, one in the Americas and the other
in Australasia. In fact fossil marsupials have even been found in
Antarctica and South Africa as well, providing evidence that that these
continents acted as a land bridge connecting the two populations for a
28. KEY CONCEPT
The geologic time scale divides Earth’s history based on
major past events.
29. • The history of Earth is
represented in the geologic 100
time scale. 250
• Cumulative findings from 550
morphology, and geology
led to new ways of thinking
about the natural world
This time span makes up the
vast majority of Earth’s history.
It includes the oldest known
rocks and fossils, the origin of
eukaryotes, and the oldest
30. • Eras last tens to hundreds of millions of years.
– consist of two or more periods
– three eras: Cenozoic, Mesozoic, Paleozoic
31. • Periods last tens of millions of years.
– most commonly used units of time on time scale
– associated with rock systems.
• Epochs last several million years.