LEC 20

Question 1

Earth’s Environmental History

Answer 1

Conditions on earth over the last 4.6 billion years have changed repeatedly

These changes have impacted the creation, evolution and extinction (where applicable) of all the organisms that have lived here

Question 2

Earth started out as:

Answer 2

An inhospitable place:
Very hot - no oceans or fresh water
Cracks in surface released molten rock & hot gases
Early atmosphere - mostly CO2, water vapor, H2, N2, CH4 and NH3
There was no O2
Constantly bombarded with radiation (no ozone layer to protect)

Question 3

Overtime, earth’s:

Answer 3

atmosphere cooled
Water vapor condensed and rain started to fall
Surface rocks were still hot, so most vaporized again
Cycle continued for millions of years
Eventually the rain remained liquid and pooled

Question 4

The first living organisms appeared approx. _______ billion years ago

Answer 4

3.8

Question 5

Organic molecules

Answer 5

Extreme environment = high amounts of energy

This energy led to the formation of simple organic compounds (amino acids, simple sugars & fatty acids) in the absence of enzymes

The organic molecules dissolved into the seas

Question 6

Scientists think RNA formed:

Answer 6

In clay mudflats along edge of oceans

From there, RNA and other organic molecules became enclosed in cell membranes

First self-replicating cells where then formed

It is believed DNA formed from RNA very early in evolution

Question 7

prokaryotes

Answer 7

Simple, single celled organisms without a nucleus or other organelles
Created energy via anaerobic metabolism
Had limited abilities to synthesize molecules
Relied on immediate environment to meet their raw material needs
If it was not available, the cells died

Question 8

Photosynthesis

Answer 8

developed the ability to produce some of the molecules required

Drew on the CO2, water and sunlight to create complex organic molecules containing carbon (photosynthesis)

Question 9

By-product of photosynthesis is O2 led to

Answer 9

an accumulation of oxygen in atmosphere

Question 10

Approximately 1.8 billion years ago

Answer 10

DNA becomes enclosed in nucleus forming eukaryotic cells
Believed more complex eukaryotic cells formed when cells engulfed other small prokaryotic cells (Endosymbiont Theory)
Eukaryotic cells become dominant cell type

Question 11

Approximately 1.4 billion years ago

Answer 11

first multi-cellular organisms appear

Question 12

Approximately 600 million years ago

Answer 12

Large number and diversification of animals and plants appear

Question 13

Approximately 65 million years ago

Answer 13

Dinosaurs disappear

Question 14

Approximately 6.5 million years ago

Answer 14

Our first distinctly human ancestors appear