1. Chapter 17.2:
Earth’s Early History

2. Age of the Earth It is estimated that the Earth
is 4.6 billion years old
Theories of how the Earth was “born” vary (IE – the Big Bang Theory)
Elements arranged themselves according to density
Least dense make up the atmosphere, most dense make up the core

3. Earth’s Early Atmosphere
Earth’s early atmosphere probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water
All toxic gases except the
water

4. The Early Earth
It wasn’t until 4 billion years ago that the first solid rocks formed
It wasn’t until 3.8 billion years ago that the Earth was cool enough to have liquid water
So this is when the first oceans formed

5. Formation of Organic Molecules
Early atmosphere allowed the formation of organic molecules
Did not have oxygen
Would not form in today’s atmosphere
Oxygen is too reactive
Bacteria would eat the molecules

6. Miller and Urey
Stanley Miller and Harold Urey attempted to answer what the
Earth’s early atmosphere and
how life began
Filled an enclosed flask with
hydrogen methane, ammonia,
and water to represent the
atmosphere
Passed electricity through
this mixture

7. The Results Amino acids began to form after a couple days
Extensions of their experiments have also shown to make nucleotides
Scientists think that these were the first steps to life

8. The First Cells
Thought to have originated million years after oceans formed
Earliest cells called proteinoid microspheres were created when organic molecules became trapped in bubbles
Not alive but have some
characteristics of living cells

9. Oxygen-Free Life Forms
The first life forms are thought to have evolved in oxygen free environments approximately 3.5 billion years ago
Photosynthetic organisms evolved
in the oceans approximately 2.2 billion
years ago
Started pumping oxygen into the
atmosphere

10. Rusty Oceans
When oxygen mixed with iron in the water, the oceans began to rust
The iron oxide sank to the bottom of the oceans giving us the iron ore deposits that we use today

11. The Ozone Layer
The ozone layer formed when oxygen began to accumulate in the atmosphere
Created a poisonous atmosphere where most of the organisms became extinct
Those that survived became the anaerobic organisms that we know today or they evolved to use oxygen

12. Endosymbiotic Theory
Belief is that eukaryotes formed approx. 2 billion years ago
Prokaryotes “moved into” prokaryotic cells
Created a symbiotic relationship
One group was able to use oxygen to make ATP
Mitochondria
One group was able to use light to make sugars
Chloroplasts

14. Evidence of the Endosymbiotic Theory
Membranes of mitochondria and chloroplasts are similar to that of free-living prokaryotes
Mitochondria and chloroplasts have
DNA similar to bacterial DNA
Ribosomes similar to those of bacteria
Reproduce by binary fission

15. Sexual Reproduction
The use of sexual reproduction by early organisms allowed evolution to occur at a much quicker rate
More gene shuffling