8.Molybdenum

Question 1

What is molybdenum studied as a proxy for?

Answer 1

Oxygen

Question 2

What is Black shale studied as a proxy for? What relation does this have to the study of molybdenum?

Answer 2

A proxy for Seawater, molybdenum is often found in black shale and indicates oxygen levels in the ocean

Question 3

Molybdenum is an essential trace element for what?

Answer 3

Eukaryotes

Question 4

Molybdenum has poor solubility, what addition makes it soluble?

Answer 4

Adding oxygen gives the soluble MoO4^2- ion

Question 5

How does molybdenum end up in black shale?

Answer 5

Living creates take on small amounts of Mo, black shale is made up of broken down organic matter

Question 6

What inconsistency is there with the perceived jump in Mo in oceans?

Answer 6

Dramatic jump in Mo comes over a billion years past last BIF, which was thought to show an oxygenated ocean

Question 7

What other element could be to blame for end in BIFs? What does this mean?

Answer 7

Sulphide can also oxidise iron, so a sulphide rich ocean could have been likely instead of a fully oxygenated ocean

Question 8

What is the proposed process for sulphide ending up in the ocean?

Answer 8

Created by sulphide bacteria from sulphate in rocks and carried downstream from weathered rocks.

Question 9

What are 5 possible explanations for the steep rise in Molybdenum? How good is the evidence for each?

Answer 9

Oxygenation of the ocean - good evidence
Change in nutrient cycle - scant
Change in phosphorous cycle - fair
More chemical weathering on land - suggestive
‘Proto-lichens’ - None, just speculation

Question 10

When was the jump in Molybdenum?

Answer 10

About 500 Ma

Question 11

What event came just before the Mo Jump?

Answer 11

Cambrian Explosion

Question 12

From when is Molybdenum found in rocks?

Answer 12

2.7Bya