Transcript Pre-activity reading/presentation

Unlocking Puzzles of the Past
Core Samples
What is a Sediment Core?
• A sediment core is a long piece of sediment
collected from the bottom of a body of water.
• The core is analyzed to reveal evidence of
organisms that lived during sediment formation.
How is a Core Collected?
Pushing the empty tube into the mud
Tube containing sediment core is
carried out of the pond
Researchers push an empty tube into the pond
bottom and use suction to pull out a core of
sediment
How is a Core Collected?
Removing a core from the tube
The sediment core is removed from the empty
tube in one continuous piece
How is a Core Collected?
Measuring and describing a core
Wrapping a core
The sediment core is described, carefully wrapped
up, and taken back to the lab for study
What Can We Find In Cores?
• Plant macrofossils are preserved seeds, leaves or
other plant segments useful in identifying plants.
• Plant microfossils are tiny pollen grains and spores
that are also useful, but can only be identified with a
very strong microscope.
Seed
Pollen grains
Leaf fragment
What Can We Find In Cores?
• We also can find signs of human activity such as
charcoal from fires or metal from industrial activities
Industrial particle
Relative Dating
← Top of Core
← Older
macrofossils
are found at
deeper levels
← Bottom of
Core
Since shallow
layers settled later,
macrofossils found
higher are younger
than those found
in deeper levels.
Relative Dating
Relative dating of fossils doesn’t give
information about actual age of
the fossils but it does allow
researchers to understand how
the ecological community
changed over time.
Relative Dating
By identifying plant macrofossils throughout the
core, it’s possible to tell which plants were
present when each sediment layer was formed.
Compression
The correlation between fossil depth and age is
difficult to determine due to several factors
including compression.
Compression
As sediment layers settle one atop another, top
layers create pressure on lower layers. The
excess weight presses the lower layers tightly
together.
Sediment compression
is exaggerated when the
core is pressed into the
tube to be withdrawn.
Why study Miller Woods?
The Miller Woods are home to 150 ponds that are
the last remnants of a once extensive pond system.
Why study Miller Woods?
The ponds formed
in rows as glaciers,
and Lake Michigan,
retreated to the
North in a process
of melting, stalling
and melting 15,000
years ago.
Glaciers
covered
Michigan
20,000
years ago
Why study Miller Woods?
• Henry Cowles, for which Cowles
bog is named, reported upwards
of 50 rows of ponds in the area
in the early 1900s. Today only a
few remain with the rest having
been taken over by industry and
housing.
Why study Miller Woods?
• These ponds contain
many unique groups of
plants and animals that
need to be protected.
• We need to understand
about how and why the
plant communities have
changed so we can
protect them for the
future
In this set of Activities…
• You will collect data from a sediment core to better
understand how relative dating is used to track
ecological changes.
• You’ll compare the species that lived there through
time and explore a connection to these changes and
the spread of human development.
• Finally you will collect a core from a local pond to
appreciate the methods involved.