Lecture 26

Question 1

When did the great oxidation event occur

Answer 1

2.5 billion YA

Question 2

What is the oxidation event

Answer 2

When we know oxygen started existing in the atmosphere

Question 3

What piece of evidence do we have for the great oxidation event?

Answer 3

Fractionation of sulfur by bacteria (there was a MIF signature before oxygen in the atmosphere), red-coloration of red beds popping up (iron turning red after it is oxidized by oxygen in the atmosphere), reduced minerals (pyrite and uranite got preserved where they usually shouldn’t) that were preserved while traveling long distances proving that they didn’t get oxidized, manganese deposits showing they reacted with oxygen at some point, and enrichment in chromium and uranium which needed oxygen.

Question 4

GOE Proxies

Answer 4

Contain rounded grains of pyrite - shows as rivers were carrying pyrite for a long period of time, they got preserved in the GEO Proxies as they didn’t have any oxygen to react with.

Question 5

Manganese ore (Mn Oxide) layer in South Africa

Answer 5

This proves that at a certain time, Oxygen entered the atmosphere and oxidized the ore-forming bands of Manganese ore in sedimentary rocks.

Question 6

Branded-iron formations

Answer 6

chemically precipitated sediment (iron and silica), typically laminated, consisting of 20% iron (1.8-3.8) billion years old. This formation required bacteria to oxidize dissolved Fe(II) in seawater to form ferric hydroxide minerals. This shows what the ocean consisted of and shows that seawater contained bacteria.

Question 7

Two types of reactions that may have formed banded iron formations

Answer 7

1. photosynthesis

2. anoxygenic photosynthesis (need cyanobacteria)

Question 8

How do Cr formations relate to oxidation event

Answer 8

Bacteria oxidize pyrite (using oxygen) which acidifies the soil. This eventually causes acidity to be high enough to form a beak Cr. After pyrite peaked on land, it is continuously used up and acidity levels dropped reducing the amount of Cr. The Cr and Iron get formed into banded iron formations in the ocean.

Question 9

Ozone screen ramifications

Answer 9

1. allows for the increased occupation of the photic zone in the oceans by plankton
2. bacteria could form biofilms on land which can accelerate biological weathering
3. started the formation of Eukaryotes

Question 10

What are the indicators of life in the Proterozoic era

Answer 10

Stromatolites (microbial mats that eventually were eaten by predation once animals evolved) and thrombolites (eaten stromatolites ended up popping up), Gunflint Chert (contains fossils of cyanobacteria on earth), Grypania (eukaryotic algae size of 2 cm), Huntington formation (remnants of red algae), acritarchs (Organic thin-walled microorganisms likely eukaryotes),

Question 11

Rodinia

Answer 11

Supercontinent lasting 250 million years (formed about 1 billion years ago)

Question 12

Snowball earth events

Answer 12

The entire earth is covered in thick snow (due to glaciation)

Question 13

Sturtian glaciation age

Answer 13

760-950 Myr

Question 14

Marionan glaciation age

Answer 14

620-590 Myr

Question 15

Deglaciation and rise of animals hypothesis

Answer 15

As glaciers melted, fine powder of phosphate washed into the ocean and formed cyanobacteria and plankton blooms which increased O2 levels. This produced enough oxygen in the atmosphere to allow animals to evolve.

Question 16

Ediacaran Fauna

Answer 16

This shows that Neoprotezoic seas were populated largely by soft-bodied organisms. However, some tiny shell-bearing organisms have also been found such as Cloudinia (a tubular form of precipitated calcium carbonate) used to protect from predators. Additionally, trace fossils of simple burros exist.