Lecture 9: Plants Cool the Planet

Question 1

What are the three eras in the Phanerozoic Eon?

Answer 1

Palaeozoic, Mesozoic, Cenozoic

Question 2

What are the 6 periods within the Palaeozoic era in chronological order?

Answer 2

Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian

Question 3

What are the three periods within the Mesozoic era in chronological order?

Answer 3

Triassic, Jurassic, Cretaceous

Question 4

What are the two periods within the Cenozoic era in chronological order?

Answer 4

Tertiary, Quaternary

Question 5

Which era in the Phanerozoic eon is the biggest?

Answer 5

Palaeozoic

Question 6

Give 6 characteristics of the earth before the presence of plants?

Answer 6

Less oxygen
15X more CO2
7 degrees warmer
Anoxic Ocean
Arthropod tracks 
Freshwater algae (ancestors of land plants)

Question 7

What was the process that led to the creation of eukaryotic algae?

Answer 7

Around 2.5Ga cyanobacteria were consumed by eukaryote cells to become photosynthesising algae

Question 8

What do the eukaryotic algae start to do in the Proterozoic eon?

Answer 8

Make multi-cellular sea weeds and freshwater algae

Question 9

What are bryophytes?

Answer 9

Earliest forms of land plants reliant upon moist habitats which are also not able to maintain their water pressure so were therefore quite floppy

Question 10

What is the significance of bryophytes?

Answer 10

They are the earliest forms of land plants even though they are still reliant upon very moist environments

Question 11

When were the earliest land plants discovered?

Answer 11

Ordovician period

Question 12

Because it is difficult to find fossils of the earliest land plants, how are they analysed?

Answer 12

Through the spores that they produced which are hard and therefore well preserved in the ground

Question 13

When and what are the first fragments of actual land plant discovered?

Answer 13

460Ma Bryophyte remains

Question 14

What are bryophytes?

Answer 14

Part of a plant that are responsible for releasing spores

Question 15

What are trilete spores and when were they found?

Answer 15

~445Ma. These are type of pollen spore which are resistant against dry conditions suggesting that they had evolved from initially being heavily reliant upon moist environments

Question 16

When were the first vascular plants uncovered?

Answer 16

~425Ma in the Silurian period.

Question 17

What are important characteristics of the first vascular plants?

Answer 17

They can maintain their internal water pressure which allows them to keep shape. No leaves or roots means the photosynthetic pigment would be in stem and branches

Question 18

How efficient was the photosynthesis process carried out by the first vascular plants? and why?

Answer 18

Not very - because the photosynthesis pigment is in the stem probably

Question 19

What discovery was made toward the end of the Silurian period?

Answer 19

Fossils of bigger plants such as clubmosses which had interesting leaf structures and roots that would have been more efficient when carrying out photosynthesis compared to the first vascular plants

Question 20

When were the first clubmosses discovered in the late Silurian?

Answer 20

~420Ma

Question 21

What are protaxites fossils?

Answer 21

Not sure exactly - probably giant fungi due to variance of carbon isotope composition

Question 22

When were the first protaxite fossils discovered?

Answer 22

420-370Ma

Question 23

What phenomenon was thought to be responsible for preserving a whole ecosystem in good condition during the early Devonian period and what date exactly?

Answer 23

A volcanic phenomenon ~410Ma

Question 24

What did the ecosystem that was preserved by the volcanic eruption in the early Devonian consist of?

Answer 24

Plants, fungi and insects. Interactions between these different forms of life were evident

Question 25

What were three interactions between the components of the early Devonian ecosystem?

Answer 25

Plant-mycorrihizal fungi symbiosis (plant combines with fungi to provide carbohydrates in return for nutrients and minerals)
Nutrient recycling by fungi and animals that feeds the plants
Fungi infecting plants promoting evolution

Question 26

Is the early Devonian preserved ecosystem important?

Answer 26

Yes

Question 27

What were the first tree types and when were they dated to?

Answer 27

Wattieza around 385ma (Mid Devonian)

Question 28

Where were the first Wattieza discovered and how was the picture completed?

Answer 28

First discovered in New York as stumps that were matched up with branches found elswhere

Question 29

How tall were Wattieza thought to be and why?

Answer 29

~8m high so they could spread spores

Question 30

What were the second tree types and when were they dated to?

Answer 30

Archaeopteris trees dated to ~~375Ma (late Devonian)

Question 31

What was important about archaeopteris trees?

Answer 31

They had characteristics of trees that are more present on earth today

Question 32

How tall and wide were archaeopteris trees?

Answer 32

~10m high and 1.5 trunk diameter

Question 33

What was an indication of the success these early tree types were enjoying? what did this mean for weathering rates?

Answer 33

Forests were discovered around the same time (late Devonian) - means a lot of organic carbon buried increasing weathering

Question 34

What are most continental rocks made of?

Answer 34

Silicates

Question 35

How do plants combine with rainwater to begin the weathering process? (Carbon dioxide balance)

Answer 35

They dissolve rocks with fungi which combined with the carbon in the rain (which acts as acid rain) weathers the rocks. the rainwater then runs off the surface of the earth

Question 36

What happens to the ions released by the weathering process and some of the carbon that was in the rainwater? (Carbon dioxide balance)

Answer 36

It gets washed to the oceans - here it can be released to the atmosphere or they can form new carbonate rocks or organisms shells where they then over time sink to form new rocks or get buried in the sea floor which prevents them from interacting with the atmosphere. Locking it up.

Question 37

What does the locking up of carbon in carbonates or organism shells mean for the temperature of the planet?

Answer 37

It prevents a GHG forming which means the temperature falls

Question 38

Why do plants and fungi want to weather rocks?

Answer 38

To get nutrients and minerals

Question 39

How do plants and fungi actually weather rocks?

Answer 39

They make acids that dissolve solid rock

Question 40

How is plants and fungi’s weathering process assisted? and how does it happen?

Answer 40

Organic matter in soill from decomposed plants and organisms later becomes organic carbon which is consumed later by living plants and fungi which convert it in to CO2. This is then all trapped in the soil which reacts with rainwater to increase the concentration of carbonic acid that helps weathering.

Question 41

What are two non-chemical weathering processes?

Answer 41

recycling of water that physically weathers as well as bioturbation of plant roots

Question 42

What can happen to some of the phosphorus molecules released by weathering?

Answer 42

They can find their way out of plant cycle in to new production cycles to increase production of oxygen

Question 43

How does the weathering out of ions contribute to the climate?

Answer 43

They cool the planet to the degree which plants are happy with

Question 44

What events are thought to have coincided with CO2 reductions?

Answer 44

Glacial periods

Question 45

What event happened between the transition between the Ordivician and Silurian periods?

Answer 45

A major glaciation

Question 46

What was the result of the glass moss experiment?

Answer 46

mosses were found to accelerate the weathering of rocks by a factor of 2 to 5 or even 9 depending on the rock type

Question 47

What degree of reduction in carbon dioxide levels is thought to be enough to trigger a glaciation period?

Answer 47

Halving