1. Earth’s Early History and Evolution of Multicellular Life

2. What features can you see on Earth’s surface in the photograph and the drawing?

3. Formation of the Earth
Evidence shows that the Earth is about 4.6 Billion years old
Earth was not “born” in a single event, but over time (100 million years)
Large amounts of heat melted the particles that made up the Early Earth

4. Formation of the Earth
The elements rearranged themselves according to density
QUESTION: Where did the most dense elements go? Least dense?

5. Density Demo Material Density Rubbing Alcohol .79 Lamp Oil .80
Baby Oil
.83
Vegetable Oil
.92
Ice Cube
Water
1.00
Milk
1.03
Dawn Dish Soap
1.06
Light Corn Syrup
1.33
Maple Syrup
1.37
Honey
1.42

6. Formation of the Earth
The most dense elements formed the planet’s core
The least dense elements (gases) formed the first atmosphere
Hydrogen
Nitrogen
(no oxygen…yet!)

7. Formation of the Earth
Early Earth’s atmosphere consisted of hydrogen cyanide, carbon dioxide, carbon monoxyide, nitrogen, hydrogen sulfide, and water.

8. Formation of the Earth
Geologists infer that about 4 billion years ago, Earth cooled enough to form rocks
Oceans did not exist because it was still too hot! (evaporation)

9. Formation of the Earth
About 3.8 billion years ago, the Earth’s surface cooled enough for water to remain liquid (condensation)
Now oceans covered most of the Earth’s surface

10. First Organic Molecules
In the 1950s, chemists Miller and Urey tried to simulate conditions on the early Earth in a lab

11. The First Organic Molecules
Over a few days, several amino acids (building blocks for proteins) began to accumulate
Miller and Urey’s experiment showed that mixtures of organic compounds necessary for life could have arisen from simpler compounds found on primitive Earth!

12. The Puzzle of Life’s Origin
It took about million years after the Earth cooled to find cells that looked similar to modern bacteria
QUESTION: How might these cells have originated?

13. The Puzzle of Life’s Origin
Formation of Microspheres
Under certain conditions large organic molecules can form tiny bubbles called proteinoid microspheres

14. The Puzzle of Life’s Origins
Evolution of RNA and DNA
There is some evidence that RNA may have existed before DNA
Small sequences of RNA could have formed and replicated on their own

15. The RNA World Theory
The theory is catalytic RNA can self replicate without enzymes and code for proteins. Scientists hypothesize that one of these proteins allowed RNA to convert into DNA.

16. Free Oxygen
Microscopic fossils, or microfossils, of single-celled prokaryotic organisms have been found on rocks more than 3.5 billion years old
They must have evolved in the absence of oxygen because Earth’s first atmosphere contained very little O2

17. Free Oxygen Over time, photosynthetic bacteria became common
Oxygen combined with iron in the oceans and turned the oceans brown!
The iron oxide fell to the ocean floor, the oceans became blue-green

18. Free Oxygen Oxygen began to accumulate in the atmosphere
Ozone formed- O3
Created first “pollution” crisis!
The rise of oxygen in the atmosphere drove some life forms to extinction, while other life forms evolved new, more efficient metabolic pathways that used oxygen for respiration

19. Endosymbiotic Theory Origin of Eukaryotic cells (cells with nuclei)
Eukaryotic cells arose from living communities formed by prokaryotic organisms
Lynn Margulis
Mitochondria and Chloroplasts have similar DNA to bacteria
Both have ribosomes
Reproduce by binary fission

20. Endosymbiotic Theory