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Geologic Time
Geologic Time
Huge sections of time are broken down into smaller
groups of time:
Eons, Eras, Periods, and Epochs
Eon is the largest time block (kind of like what we would think of as years).
Era is a little less time (like months)
Period would be shorter time (like weeks)
Epochs are even shorter (like days)
(**No different then when we take years and divide them into months, weeks, and days.)
(the beginning)
(next after the 1st period)
(later – this is the time of the dinosaur)
Lesson 2
Absolute Time
“Fossils are rocks that formed from the remnants (what’s left) of onceliving things. All living organisms, under the right conditions, can be
When something is filled with
sediment (rocks) and makes it
look 3-D.
An imprint of something that was
once living.
When something is filled with atoms of rock material; this makes
them very hard (rock).
*Commonly found with wood.
When a living organism gets stuck in
something sticky (like sap) the sap and the
organism harden and get preserved.
An organism gets frozen and
the super cold temps prevent
it from decaying; therefore
preserving it.
The remains of an organism's
activities but not of the organism
-broken eggshells from a dinosaur's nest are trace fossils. footprints from an organism
-chewed section of a plant
-”coprolites” fossilized dung or feces (meaning: poop)
There are two types of dating which
geologists can use to make the timelines:
relative dating and absolute dating.
Relative dating does not give an exact
age (in years) to rocks or geologic events…
Instead, relative dating puts the events in
sequential order; the oldest comes first, and all
the rest of the events follow after, on the
“relative dating timeline”.
Example of relative dating (putting events in sequential order):
Since there weren’t scientists around during the formation of the Earth
(or for any of the geologic history of Earth) they (scientists) need to rely
on carefully recorded observations, so they can make assumptions
about these things.
These types of assumptions are called principles, and in these cases,
observations made by the scientific community, over time, have
repeatedly supported the assumptions.
Geologic Assumptions:
1. Uniformitarianism
2. The Principle of Superposition
3. The Principle of Original Horizontality
4. The Principle of Faunal Succession
By studying the rocks on Earth,
geologists (people who study
rocks) can make a chart that
outlines the geologic periods of
time when rocks were formed.
What is it?
The belief that all of the processes (things) that are shaping the Earth
today were the same processes (things) at work in the past; (also that
these processes occurred at the same rate and in the same way as they do
What can they assume with this?
Geologists can study how fast a process is occurring today, (like
formation of sedimentary rock layers or erosion), and make then they
can make assumptions about how the processes occurred in the past.
Doing this can help them form relative time lines for past
The Principle of Superposition
What is this one?
In layers of rock that have been undisturbed, (or as geologists say, "un-deformed,“)
the lowest layers formed first, then the next, and the next, and so on up to the
top layer.
What can they assume with this?
That the oldest layer is on the bottom and the layers get younger and
younger as you go up.
The Principle of
Original Horizontality
This tells us that when sedimentary rock layers are first formed, the sediments fall
in horizontal layers.
Using this principle, (plus knowing that movements of the crust can bend, fold, twist, break,
and move rock layers) we can assume that if we see several layers of rocks that
are in any form other than horizontal, they must have been acted upon by a
disturbance of the crust of some kind.
The Principle of Faunal Succession
With this principle we focus on the fossils
found in rock layers. If we can estimate
the age of the fossils, we can make
assumptions about the age of the
sedimentary rock layer in which the fossil
is found.
The Law of Cross-Cutting Relationships:
An igneous rock intrusion is younger than the rocks into
which it has intruded.
The Law of Unconformity:
An unconformity is a place where some of the existing rock
layers have been eroded by water or wind or changed in
some way causing pieces to be missing.
The Law of Deformity:
A deformity may be a tilting, faulting, or folding of existing
rock layers. Therefore, for the rock layers to be deformed,
they must be older than the event that deformed them.
An unconformity is a place where some of the existing rock layers have
been eroded by water or wind (Hint: if wind is hitting it what layer would it be?)
An igneous intrusion is younger than the rocks into which it has
intruded (goes through).
More advanced dating techniques have allowed geologists to
get more exact dates.
Absolute dating is the:
The measurement of time in definite periods of
time and is measured with something that gives us
a definite (exact) time.
It assigns specific dates to
rocks and geologic events.
Radiometric dating:
All rocks contain radioactive material that decays over time. The rate of radioactive
decay allows scientists to establish the absolute age of a rock.
** the most common radioactive element is carbon-14 found in all living organisms.
Radioactive decay starts with only parent element (an unstable isotope). Because
it's unstable, it will decay into a stable daughter element. The time it takes for half
of the amount of parent element to decay is constant, (and known as half-life).
After one half-life, half of the material is the parent element and the other half is
more stable daughter element.
After another half life, one-fourth will be the parent element. As the
substance keeps decaying, the amount of parent element will shrink,
although it will never be completely gone. The substance would then mostly
consist of the daughter element.
Lesson 3
Origin and Evolution
of Life
Scientists learn about Earth’s geological (the Earth itself) and
biological (living things) history through evidence from rocks
and fossils.
A fossil record helps us to understand the
past and why things are the way they are
Theory of evolution
“Life on Earth did not always look the same as it does today. Life has evolved”
(changed / altered).
“Evolution explains how new species of organisms arise or how existing organisms
adapt to new conditions over time.”
Modern day bird
“An adaptation refers to a characteristic of an
organism that allows it to survive in a particular
environment. “
When an adaptation (a change) makes an organism more likely to
survive and reproduce, the organism may pass the new
adaptation on to its offspring (babies); organisms with the new
adaptation will produce more babies than organisms that don’t
have the new adaptation. This process called: natural selection is
why some organisms with certain adaptations survive and others
do not, depending on Earth's changing conditions.
Chemical evolution:
The idea that the appearance of living systems (stuff) on Earth from
non-living molecules.
Living fossils:
Creatures that are very similar to species that lived
long ago (without much change) are called “living fossils”.
Phylogeny is studying how
different organisms
(plants/animals/etc.) are
connected (related) through
evolution (change over time).
 We use something called a
“cladogram” to show (in an
image/diagram) how one
organism is related to another