Exam 2: Origins of Life and the Early Atmosphere Flashcards
T or F: Iron oxides (BIfs) show rising oxygen levels from the Mid-Archean to the early Proterozoic.
(Iron was more likely being used up than oxygen after mid proterozoic. That’s why oxygen levels didn’t keep increasing and oxygen became a dominant thing today)
True
Oxygen levels in the air over time are based on…
oxygen bearing minerals in rocks
when oxygen levels rose
Great Oxygenation Event
T or F: Life could not survive on a molten Earth.
True
Modern life is ________ and _________.
abundant and complex
What did studies like the Miller-Urey experiment reveal about the origins of life’s essential molecules?
They started to detect certain molecules in the experiment (like nucleic acids, amino acids, etc.) that we associate with life today; tells us that ingredients for life could have formed from the early atmosphere
What are two hypotheses for where did life begin?
- Shallow Pond Hypothesis (“primordial soup”)
- Volcanic Vent Hypothesis
T or F: It is still an unanswered question of where did life begin.
True
In the Archean to early Proterozoic, what was life like?
- Only bacteria: simple, small, single-celled life
- Most simplest form of life we see today (in a sense of size, even though they are still complex)
What are the body fossils and trace fossils like for Archean bacteria?
- Body fossils: the chances of bacteria becoming fossilized is very rare, because bacteria has no hard parts
- Trace fossils: more common
bacterial trace fossils; the trace fossil marked by the presence of the bacteria, not a type of bacteria;
stromatolites
What is the earliest fossil evidence for life on Earth (and a source for oxygen)? When on the geologic time scale does it date back to?
stromatolites; Archean
Do stromatolites still exist today?
Yes, but they are rare
How do stromatolites form (2 steps)?
- Layers of sand are stuck together by bacteria (not good because sand can be thrown on top of bacteria and stick to it, which isn’t good for survivability because they need sunlight)
- When sand piles on top of them, bacteria keep growing on top and keep getting taller and taller. (burial of sand is important for the existence of stromatolites)
What allowed stromatolites to form in the modern world?
shifting sand removed competition
What gas is produced from photosynthesis?
oxygen
Bacteria in stromatolites use ________. This means they are producing ________ in our environment today.
photosynthesis; oxygen
The first stromatolites could possibly be the origin of what?
photosynthesis
What is the first evidence of living things transforming their environment?
The earliest stromatolites line up with when we first start seeing BIFs as well (mid-Archean). Could be a sign that by the time we have bacteria, we see photosynthesis.
What type of fossil is a stromatolite?
trace fossil
What are the three steps of the oxygen and carbon cycle?
- Animals and Plants breathe in oxygen and release carbon dioxide
- Plants create oxygen with photosynthesis.
- Oxygen goes to the atmosphere, and the cycle continues.
What is carbon dioxide?
A greenhouse gas that holds heat in the atmosphere. The more CO2, the warmer the atmosphere. The less CO2, the colder the atmosphere.
Why is carbon dioxide one of the most important atmospheric gases?
Plants need it and it’s a greenhouse gas that holds heat in the atmosphere.
What are the three things that are essential to having a planet that can support life?
- CO2
- H2O
- CH4
T or F: Greenhouse gasses are famously very hot even in the winter.
True
In the simplest version of the oxygen/carbon cycle, in the MODERN system, how is oxygen, carbon dioxide, and temperature? This is only true if what?
- oxygen: stays the same
- carbon dioxide: stays the same
- temperature: stays the same
- only true if there is a balance of plants and animals
In the simplest version of the oxygen/carbon cycle, in the ARCHEAN system, how is oxygen, carbon dioxide, and temperature?
- oxygen: increases
- carbon dioxide: decreases
- temperature: decreases
How was the increase in atmospheric oxygen connected to the Snowball Earth event?
because during the Archean, the plants were pumping out more and more oxygen with nobody to take it up, therefore making it colder because there was less CO2.
More O2, less CO2= (warmer/cooler) temperatures
cooler
T or F: Glaciers will only form in places that are cold all year.
True
Why do glaciers move? What direction do they move? What do they transport?
Gravity; downhill; sediment
one of the most powerful sources of moving sediment because it’s a solid. Can move large sediments.
glaciers
How is sediment in glaciers?
Angular, poorly sorted, no separation or maturity
T or F: Proterozoic glacial sediments are found worldwide, not just at the poles.
True
T or F: Everywhere seems to have been warm towards the end of the proterozoic.
False; cold
Earth was mostly (completely?) covered in ice; based on evidence of glacial sediment and knowledge of the carbon and oxygen cycle.
The Snowball Earth Hypothesis
Could Life Survive on “Snowball Earth”? What is the only evidence of life from this time?
There was life before and life after, so life had to have survived, although we have no evidence from this time except for sponges.
The great oxygenation event happened when?
At the beginning of the Proterozoic
What does it mean to say that animal life is multicellular?
Multiple kinds of different cells working together
What is important about the Ediacara biota? When did it exist?
- Earliest known animals
- Near the end of the Proterozoic
means before animals, life became increasingly complex
proterozoic
In the proterozoic there was the development of _________, which are larger, more complex cells.
eukaryotes
Addition of new cells related to rise in _______ because animals require it to live.
oxygen
Why are animals more complex than bacteria?
Because they are multicellular
Do we have any evidence that the Ediacaran living things ate each other?
No, there were no signs of predators.
Ediacara biota is recognizably ________, contains ________, and is ______ fossils which shows _______.
- symmetrical
- cholesterol (only present in animals)
- trace
- movement
Animals appear near the end of __________.
proterozoic
