1. Earth’s Past

2. Determining Relative age
Relative age – the age of the object in relation to the age of other objects
No actual age in years given
Law of superposition – undeformed rock is younger at the top and older at the bottom
Layers of the rock – called strata

4. Determining the Absolute Age
Absolute age – the numerical age determined by an absolute dating process
Some estimated ages can be found for features 10,000 – 20,000 years old
Rates of erosion, rates of deposition, and varve count (layers deposited in lakes)

5. Most accurate is radiometric dating
Radiometric dating – determine age using the percentages of parent isotope to daughter isotope
Based on half life – time needed for half the parent to decay into the daughter isotope
Each isotope has a different half-life
Most commonly used is carbon 14 – turns into nitrogen 14 in 5730 years

7. Fossil – the remains of a plant or animal
The Fossil Record
Fossil – the remains of a plant or animal
Study of fossils – called paleontology
Become fossils by:
Mummification, amber, tar seeps, freezing, petrification (minerals)
Types of fossils:
Trace fossils – tracks, footprints
Index fossils – fossils that only appear in a specific rock layer meeting specific conditions (used to absolute age)

8. Fossil Formation Example

9. 100 million years ago Scallops and other
invertebrates inhabit the
sea in this area. When
they die, they are
covered by sand that
settles on them.
75 million years ago Pressure compacts the
loose sandy sediments
into hard sandstone. Dinosaurs now live,
and die, in the locality.
Like the scallops before
them, their bodies are
covered by sand..

10. 50 million years ago There is a tremendous volcanic
eruption in the area. The ash
thickly covers the land, and for
a while the land cannot support
much life.
20 million years ago A Parahippus, a 3-toed horse
common at the time,
dies at the locality. Like the
other creatures before it,
its body is buried in sand
and sediments by wave action.

11. 3 million years ago The massive force
of an earthquake causes
layers of sediments to tilt
and push upward.
Today Forces of erosion, such
as water moving against
rock for millions of years,
gradually wears away the
land surface and a few of
the rock layers beneath it.
The fossilized bones of the
horse, hidden for millions
of years, are exposed above
the ground.

12. With this a Geologic Time Scale was created
Geologic column – ordered arrangement of rock layers that is based on relative ages of the rocks
Used to estimate the ages of rock that cannot be dated radiometrically
Find similarities in rock and fossils of the layers to determine where it fits in time
With this a Geologic Time Scale was created

13. Geologic Time Scale
Contains blocks of times
Given an age, a name, and organisms of that time frame

15. Evolution/Change in fossils
Records have shown that over time organisms have changed
Over the years many strategies have been used to determine how the various organisms are related to each other

16. Strategies to Determined Relatedness
Fossil record – organisms and their order of existence
Comparative anatomy – structures in common
Embryology – how long they look similar during development
Biogeography – common locations of the same fossils
Molecular biology – the similarities in genetics and chemistry
Observed evolutionary changes – similarities seen externally

17. Early Fossils in the Fossil Record

18. Comparative Anatomy

23. Embryology

24. Molecular Biology