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 4 billion years ago the first solid rocks formed
3.8 billion years ago that the Earth was cool enough to have liquid water
So this is when the first oceans formed

5. Earth BEFORE oceans formed
Characteristics of Earth before oceans formed:
Comets and asteroids
Volcanic activity
Atmosphere of poisonous gas

6. Why do you think oceans did not exist on Earth 4 billion years ago?
Water was a gas! Because Earth was very hot!

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

8. Miller and Urey
Stanley Miller and Harold Urey attempted to answer whether
Organic molecules could have
formed before life was present.
Filled an enclosed flask with
a mixture of gases and water to
simulate the Earth’s Atmosphere!
Used electrodes to produce a
Spark that simulates lightning!

9. Miller and Urey made sure no microscopic life existed in this experiment. Why?
They had to make sure the original simple substances they were testing were the ONLY possible source for the creation of organic molecules.

10. The Results from Miller and Urey
Amino acids began to form after a couple days.
This mixture of amino acids and other organic compounds showed us that molecules necessary for life could have risen from simple compounds present on early Earth without life.

11. The First Cells
Thought to have originated million years after oceans formed.
Why? Because the presences of liquid water was necessary for first life.
Earliest cells called proteinoid microspheres were created when organic molecules became trapped in bubbles
Not alive but have some
characteristics of living cells
They had SELECTIVELY
PERMEABLE MEMBRANES.

12. Oxygen-Free Life Forms
The first life forms are thought to have evolved in oxygen free environments approximately 3.5 billion years ago
First organisms on Earth were most
like today’s BACTERIA
Photosynthetic organisms evolved
in the oceans approximately 2.2 billion
years ago
Started pumping oxygen into the
atmosphere

13. Endosymbiotic Theory
Belief is that eukaryotes formed approx. 2 billion years ago from COMMUNITIES of PROKARYOTES.
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

15. 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

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