1. ORIGIN OF LIFE
UNIT 5 EVOLUTION

2. Macroevolution
Many centuries ago, explorers had discovered fossils and understood how it revealed information about the past
Fossils showed how past organisms were very different from present
These fossils demonstrated macroevolution
Macroevolution – the pattern of evolution above the species level

3. The Beginning of Earth
Earth was formed from a cloud of dust and rocks that surrounded the sun

4. The Beginning of Earth
Millions of years later, Earth became covered with rock and ice from the collisions of the solar system

5. The Beginning of Earth
These collisions generated lots of heat which vaporized the remaining water on Earth (preventing the formation of seas and lakes)
Millions of years later, life was introduced on planet Earth
Earth’s atmosphere was covered with very little oxygen, water vapor and compounds released from volcanic eruptions
As Earth cooled, the water vapor condensed into oceans and allowed for hydrogen to escape into space

6. A.I Oparin and J.B.S. Haldane Organic Compounds
Hypothesized that Earth’s atmosphere was a reducing environment
Believed that organic compounds were formed from simpler molecules through lightning and UV radiation
Believed that organic compounds were produced in vents
Hydrothermal vents – areas on the sea floor where hot water and minerals are produced (interior of Earth near volcanoes)
Alkaline vents – areas on the sea floor that release warm water (more suited for an environment)

7. Miller-Urey Experiment
Showed the origin of organic molecules

8. The Fossil Record
Shows how Earth was a long time ago and how it evolved over time
Shows how organisms have changed and become extinct over time
Shows how new species arose from previously existing species
The fossil record is NOT completely accurate
Many organisms might have died at the wrong time or place
Many fossils may have been lost and only a few might have been discovered

9. Determining The Age of a Fossil
Radiometric Dating – a method of determining the age of fossils by basing it off the decay of radioactive isotopes
A “parent” isotope decays to its “daughter” isotope at a given rate
Half-life – the time required for 50% of a parent isotope to decay
Example: Carbon-14 (decays fast) = half life of 5,000 years
Example: Uranium-238 (decays slowly) = half life of 5 billion years
One can determine the age of a fossil in sedimentary rocks through the ages of its surrounding rocks
Example – a fossil is located between two volcano rocks (490 – 500 million years old), therefore the fossil is roughly 495 million years old.

10. Fossils

11. Geologic Record
Geologic Record – a scale describing the timing and relationship of events that have occurred throughout Earth's history.
Divided into 4 eons and 3 eras
Eons – Hadean, Archean, Proterozoic, Phanerozoic
Eras – Paleozoic, Mesozoic and Cenozoic
Each era represent a distinct age in the history of earth and life
Boundaries between eras represent major extinction events

12. Protocells
May have formed from fluid-filled vesicles with membrane- like structure
Exhibited simple reproduction and metabolism and maintained an internal chemical environment
In water, lipids and other organic molecules can spontaneously formed vesicles with a lipid bilayer
Adding clay can increase the rate of vesicle formation

13. Origin of Self-Replicating Molecules
The first genetic material was probably RNA, not DNA
RNA s single-stranded and can form 3D shapes by folding over on itself
Because it can form 3D shapes, it can act as an enzyme  ribozymes
Ribozymes can catalyze self-replication of RNA

14. The First Single-Celled Organisms
Earliest forms of life on Earth were stromatolites and prokaryotes
Prokaryotes – single celled organisms without a nucleus
Example – bacteria and cyanobacteria
Stromatolites – a mound of layered rocks that form when certain prokaryotes bind thin pieces of sediment together
Found in present day marine bays

15. Photosynthesis and Oxygen
Most atmospheric oxygen (O2) is of biological origin (photosynthesis)
Prokaryote similar to today’s cyanobacteria were the first photosynthesizers
O2 began accumulating in the atmosphere
Oxygen revolution  killed off much of the life on Earth because the organisms could not deal with toxic oxygen
The organisms that could survive with oxygen began using to get energy  cellular respiration

16. The First Eukaryotes
Eukaryotes were formed hundreds of millions of years ago
Eukaryotes – organisms that contains a membrane-bound nucleus
Eukaryotes are much more complex than prokaryotes
Unlike prokaryotes, eukaryotes contain a cytoskeleton (a feature that allows cells to change their shape)
Endosymbiont Theory – a theory that states how mitochondria and plastids were once small prokaryotes that formed within larger cells
Endosymbiont – a cell that lives within another cell, the host cell
Can occur through undigested prey or internal parasites

17. Evidence That Supports the Endosymbiont Theory
Inner membranes of chloroplasts and mitochondria are similar to plasma membranes of prokaryotes
Chloroplasts and mitochondria divide in a process which looks similar to prokaryotic cell division
DNA is found in chloroplasts and mitochondria in a single circular chromosome like circular chromosomes found in prokaryotes
The ribosomes found in mitochondria and chloroplasts are more similar to prokaryotic ribosomes that eukaryotic ribosomes

18. The Origin Of Multicellular Organisms
The introduction of eukaryotic cells created a diversity in life
The first eukaryotes that had appeared were single-celled
Years later, single-celled eukaryotes gave rise to multicellular forms
Algae
Plants
Fungi
Animals

19. The Earliest Multicellular Eukaryotes
Small, red algae were the oldest eukaryotes
Larger eukaryotes started appearing 600 million years later
These fossils were referred as “Ediacaran Biota”
Ediacaran Biota – soft bodied organisms
Before the rise of large and multicellular eukaryotes, Earth was a microbial world

20. The Cambrian Explosion
Before the Cambrian Explosion, all large animals were soft-bodied
Showed organisms to be scavengers rather than predators
Cambrian Explosion – a brief, period of time in history when the first large, hard-bodied animals had started appearing
Showed how animals had characteristics of being predators
Claws
Sharp spines
Heavy body armor

21. The Colonization of Land
There is evidence that cyanobacteria and prokaryotes were the first to cover earth’s damp surfaces
Later, larger forms of life (fungi, plants and animals) started appearing
The ability to move from water to land required many adaptations
Ability to reproduce on land
Ability to prevent dehydration
Example – Many plants have waterproof coatings of wax on their leaves that help them prevent dehydration

22. The Colonization of Land
Plants and fungi would work together to survive on land
Plants used fungi in the absorption of water and minerals from soil
Fungi used plants to obtain their nutrients
The most common and diverse land animals were arthropods (insects and spiders) and tetrapods (humans)
Arthropods were the first animals to colonize land