1. History of Life on Earth
Chapter 14

2. Early History of Earth
*Earth is 4.5 to 4.6 billion years old
*Evidence of life appears in the fossil record 3.5 bya (billion years ago)
*Primitive Earth = inhospitable environment; very hot, numerous volcanoes, very little free oxygen, combination of methane, ammonia, water vapor, carbon dioxide and nitrogen.

3. Dating of Earth & Fossils
Relative Dating: the
oldest fossils are found
in the bottom layers, while
the youngest fossils are
found in top layers
Fossils form best in what
type of rock?

4. Dating of Earth & fossils
Radiometric dating or Carbon Dating: used to estimate how long ago rocks formed and the age of fossils contained within those rocks
Radioactive isotopes that are
unstable decay over time into
stable elements.

5. Dating Fossils: Radiometric Dating
Each radioactive isotope has what is called a “half- life” (the amount of time it takes for ½ of the original isotope to decay)
Example – C-14 has a half-life of 5, 730 years. (Carbon 14 to Carbon 12)
By measuring how many half-lives have passed since a rock was formed, scientists can estimate the rock’s/fossil’s age
Also Uranium decays to lead
Potassium

6. Let’s watch!

8. Relative vs Absolute time

9. The Geologic time scale!!!!
BF1F7DA180
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Time Scale

10. Need to know Geologic Time
The earliest era when life began is Precambrian
First Vertebrates appear in the Paleozoic Era
This is called the Cambrian Explosion
Stromatolites (the cyanobacteria) helpled put oxygen on earth

11. Spontaneous Generation
The thought that life arises from non life
Can a fly come from a desk or a frog literally from a pond: NO!!
Disproved first by Fransico Redi: Meat experiment

12. Biogenesis!!! Biogenesis: Life comes from pre-existing life.
Proved by Louis Pasteur

13. Origins of Organic Molecules
“Primordial Soup” – Oparin suggested life began in the seas – Miller & Urey tested:
* simulated early conditions on earth’s atmosphere: water, methane, ammonia, hydrogen
* circulate atmospheric gases by boiling and condensing the water
* sparked with electricity (lightning)
* end result = produced amino acids, fatty acids and other hydrocarbons

14. Bill and the Urey Theory!

15. Origins of Organic Molecules
Possible Reactions
2) “The Bubble Model “ – Louis Lerman (1986) suggested : *Gases from undersea volcanic eruptions were trapped in underwater bubbles
* chemical reactions occur inside bubble, formed organic molecules
* bubbles rose to the surface & burst, release simple organic molecules into the air – more energy from the environment ( UV radiation & lightning)
* end result = formed complex organic molecules that fell into ocean with rain

16. Origins of Life
3.5 bya in fossil record -PROKARYOTES appear (used organic molecules as “food”)
Competition for limited food led to the photosynthetic bacteria = cyanobacteria (that released oxygen into atmosphere)
Allowed the ozone (O3) to form – protective shield to allow life on land
EUKARYOTES arose next (1.5bya) BUT HOW???

17. Endosymbiont Theory (Origin of Organelles)
■Explains how eukaryotes may have arisen
■Aerobic bacteria were “engulfed” by larger bacteria (formed a symbiotic relationship)
■Over time, developed into the MITOCHONDRIA

18. Endosymbiont Theory
■Separately, photosynthetic bacteria were also “engulfed”
■Over time, became the CHLOROPLASTS

19. Evidence to support Endosymbiosis:
Mitochondria & chloroplasts have their own DNA – similar to bacteria machinery
Both can replicate independently of cell division
Both have ribosomes similar to bacteria
Size & structure of each is similar to bacteria

20. Endosymbiont Theory Founder
Founded by Lynn Margulis
Dr. Margulis was best known for demonstrating a theory of biological change, called the endosymbiotic theory, that appears to suggest a degree of cooperation between organisms.
Died 2011 founded theory in 1970 with book “Origin of Eukaryotic Cells”
Theory Animation

21. Geologic Trip through Time
4 eras in Earth’s history – Geologic Time Scale
Era
End Date
Calendar Year Analogy
Precambrian
544 mya
Jan - Mid-Oct (87% of
history)
Paleozoic
245 mya
Mid-Oct - Early Dec
Mesozoic
65 mya
Dec 10th – late Dec.
Cenozoic
present
Dec 26th - Dec 31st

22. Origin of Prokaryotic and Eukaryotic Cells
Use the terms and phrases below to complete the concept map.
Chloroplasts
Cyanobacteria
Endosymbiosis
Fossils
Life on land
Mitochondria
Ozone
Prokaryotes
3.5 bya
eubacteria

23. Origin of Prokaryotic and Eukaryotic Cells
Use the terms and phrases below to complete the concept map.
prokaryotes
Chloroplasts
Cyanobacteria
Endosymbiosis
Eubacteria
Fossils
Life on land
Mitochondria
Ozone
Prokaryotes
3.5 bya
cyanobacteria
eubacteria
fossils
chloroplasts
mitochondria
3.5 bya
ozone
endosymbiosis
Life on land

24. Now time for a webquest…
Visit the following website and complete the webquest!
Life Has a History – CLICK HERE!