1. 22.4 – Early Life on Earth

2. Origin of Life
Bombardment from outer space prevented life from developing on Earth until at least 3.9 billion years ago (BYA)
Where and how the first life-form developed, however, remains an active area of research

3. Origins of Life
Earliest atmosphere contained hydrogen, methane and ammonia
This atmosphere + energy supplied by lightning would give rise to organic matter in shallow oceans

4. Primordial Soup
Miller & Urey devised an apparatus to test this hypothesis in 1953
Within one week their apparatus had produced organic molecules
Organic molecules included amino acids, the building blocks of proteins (& life)

5. http://www. centauri-dreams
Other Scenarios
Amino acids organized somewhere else in the universe and were brought to earth by asteroids or comets
Chemical synthesis of organic molecules is possible in interstellar clouds
Amino acids have been found in meteorites

6. Other Scenarios Amino acids originated deep in Earth or its oceans
Other Scenarios
Amino acids originated deep in Earth or its oceans
Conditions there are favorable for chemical synthesis
Organisms have been found at depths exceeding 3 km

7. Other Scenarios
Possibility that life emerged deep in the ocean at hydrothermal vents

9. Essential Characteristic of Life
Ability to reproduce
All cells require RNA and DNA to reproduce
Recent experiments suggest that RNA molecules might have been the first replicating molecules on Earth

12. Proterozoic Life
Nuclei are separate compartments that contain RNA and DNA
Prokaryotes = Organisms that do not contain nuclei
Eukaryotes = Organisms whose cells contain RNA and DNA in nuclei

13. Simple Eukaryotes Can be unicellular or multicellular
Because they contain nuclei and other internal structures, they are larger than prokaryotes
Extinction came from a widespread glaciation event 750 million years ago (mya)

14. http://io. uwinnipeg. ca/~simmons/16cm05/1116/28-04-EukaryoteOrigin-L

15. Multicellular Organisms
About 630 mya, the climate warmed dramatically and the first multicellular organisms appeared in the oceans
Fossils first discovered in 1947 in Australia
Collectively called the Ediacaran biota, these fossils show the impressions of large, soft-bodied eukaryotes.

16. Edicaran biota
Seemed to answer the question of why there are no fossils of organisms that existed during the first period of the Paleozoic era

17. Edicaran Fossils
In recent years, geologists have found Ediacaran fossils in all parts of the world.
Flourished between 630 mya and 540 mya.
Mass extinction = most of them disappeared
More likely related to present-day organisms began to inhabit the oceans

18. In-Class Assignment/Homework
WKT 22.4
AND pg #1-23
Answer on the back of WKT 22.4