Midterm 2 Study Guide Flashcards
When did Earth start to form?
4.6 billion years ago
When was the first evidence of photosynthetic cells?
3.2-2.5 billion years ago
During what period was there a reducing atmosphere?
Precambrian Period
What is a reducing atmosphere?
An atmosphere that contains compounds that remove oxygen from metals and other materials leaving little to no free oxygen
What produced the oxygen in a reducing atmosphere?
Photosynthetic bacteria
What are the two characteristics of the Precambrian Period?
1.) Life is mostly unicellular
2.) Reducing atmosphere where photosynthetic bacteria produced oxygen
What is the Heterotroph Hypothesis?
Life on earth developed through gradual chemical evolution of carbon-based molecules in a “primordial soup”
In this hypothesis, earth’s atmosphere was reducing, which allowed biochemically important compounds to be produced abiotically and to be concentrated. Early cells could then feed on these compounds
(The first cells were heterotrophic and fed on organic molecules that were not produced by cells)
Who proposed the Heterotroph HYpothesis?
Oparin
When was the atmosphere reducing?
4.2 billion years ago to 2.5 billion years ago
What did the rise of photosynthetic organisms do?
Change the atmosphere to oxidizing
This also ends the reducing atmosphere hypothesized to be suitable for the origin of life in the Heterotroph Hypothesis
What molecules tend to be mainly present in a reducing atmosphere?
H2, NH3, H2S, H2O, CH4
What molecules tend to be mainly present in an oxidizing atmosphere?
N2, O2, H2, CO2, NOx
In order to support the Heterotroph Hypothesis, who tested whether or not small organic molecules could be formed abiotically under specified conditions?
Miller and Urey (1935) and Joan Oro (1954)
What molecules were used in Miller and Urey’s experiment and what did they produce?
CH4 + NH3 + H2O + Energy
15% of the carbon in the system was used to produce organic materials and 5% of the materials produced are biochemically important
What molecules were produced in Oro’s experiment and what did they produce?
HCN + NH3 + Energy
Produced adenine