Lecture 27

Question 1

The Cambrian explosion

Answer 1

An event that marked the beginning of the Phanerozoic Eon - when most major animal phyla appeared in the fossil record. It lasted for 30 million years and resulted in the rapid appearance of most modern phyla.

Question 2

When did the Cambrian explosion happen

Answer 2

542 million years ago

Question 3

Three accepted explanations for the Cambrian explosion

Answer 3

environmental, developmental, and ecological

Question 4

Environmental cause of Cambrian explosion

Answer 4

It is believed that only in the Cambrian did oxygen levels in the ocean reach a threshold allowing complex life forms to form. Additionally, calcium in seawater increased (due to increased continental erosion) allowing microscopic organisms to build shells.

Question 5

The great unconformity

Answer 5

The weathering of the continent was so great between the Precambrian and Cambrian ages, that entire mountain and sediment layers were weathered away from the rock record.

Question 6

Developmental cause of Cambrian explosion

Answer 6

• Finally, Hox genes occurred that allowed animals to evolve. Minor modifications to the animal’s development as they grow from embryo to adult may have been able to cause very large changes in the final adult form.
• Horizontal gene transfer aided in the acquisition of the biochemical capability of biomineralization.

Question 7

Ecological cause of Cambrian explosion

Answer 7

1. end-Ediacaran mass extinction
2. evolution of eyes
3. arms race between predators and prey
4. development of large zooplankton

Question 8

End-Ediacaran mass-extinction

Answer 8

Extinction explains why Ediacaran fauna disappeared. This was likely followed by adaptive radiations.

Question 9

Evolution of eyes

Answer 9

The evolution of eyes meant that prey needed new defences against predation, such as the evolution of armour and spines.

Question 10

The arms race between predators and prey

Answer 10

Each tried to grow bigger, and as prey became bigger they developed greater mobility or they biomineralized to prevent being eaten.

Question 11

Development of large zooplankton

Answer 11

Large zooplankton meant that fecal pellets were deposited on the seafloor, providing a new energy source. This opened the door for more burrowing animals.

Question 12

Lagerstatten

Answer 12

Cambrian fossil records include deposits that preserve soft tissue (fossil sites with a community berried together). They allow paleontologists to examine the internal anatomy of animals and a variety of different organisms.

Question 13

Most significant lagerstatten deposits.

Answer 13

Cambrian Maotianshan shale beds (China), Sirius Passet (Greenland), the middle Cambrian Burgess Shale (Canada) - Alberta Shell, and the late Cambrian Orsten (Sweden) fossil beds.

Question 14

Burgess Shale

Answer 14

Correlate to the Stephen Formation, a dark mudstone 508 million years old. They were deposited at the base of a submerged escapement composed of the limestone reefs of the Cathedral Formation.

Question 15

The great proliferation of life in the Cambrian Period was entirely confined to the oceans. However, by ____ animal life also became established on land.

Answer 15

400 Ma

Question 16

Order of evolution in terms of fish

Answer 16

FIsh (growing bigger) –> fish evolve fins and become inland (first amphibians) –> amphibians went back to water to reproduce –> soon reptiles and animals that live on land don’t need to go back to the water to reproduce –> these animals colonize land and are not stuck on land

Question 17

Non-amniotic vertebrates

Answer 17

fish and amphibians must be in the water to reproduce. Their eggs are exposed and lack a covering.

Question 18

Meiotic vertebrates

Answer 18

Vertebrates that have evolved internal fertilization and an amniotic egg (enclosed egg).

Question 19

Before plants, ___ and ___ covered most of earth’s surfaces.

Answer 19

algae and bacteria

Question 20

Plants likely began from the evolution of ____, which formed from _____, and later the next steps were: ____.

Answer 20

Stromatolites, cyanobacteria, Chlorophytes

Question 21

Chlorophytes

Answer 21

green algae

Question 22

The earliest fossil evidence consists of ____.

Answer 22

spores

Question 23

Spores

Answer 23

plant reproductive structures

Question 24

Three major advances occurred in plant history:

Answer 24

1. seedless plants
2. naked-seed producing, pollinating, but non-flowering plants
3. Plants with both seeds and flowers (angiosperms)

Question 25

seedless plants

Answer 25

Seedless (spore-bearing) plants evolved, such as ferns and mosses, and were so abundant that they formed world’s largest coal deposits.

Question 26

gymnosperms

Answer 26

Naked seed-producing, pollinating, but non-flowering plants

Question 27

Naked seed-producing, pollinating, but non-flowering plants

Answer 27

Evolved in non-moist environments allowing them to expand their habits, and had spread across the supercontinent Pangea.

Question 28

Angiosperms

Answer 28

Plants with both flowers and seeds

Question 29

Evolution of plants with flowers and seeds

Answer 29

Self-enclosed seed-producing plants evolved from gymnosperms that randomly spread their pollen. They evolved by having nectar that enticed insects to deliver pollen for them.

Question 30

Early paleozoic plants profoundly altered the environment because they:

Answer 30

facilitated soil formation, provided food and shelter for emerging land animals, and paved for the evolution of large trees

Question 31

The phanerozoic era was punctuated by ______, attributed due to:

Answer 31

major extinction events

meteorite impacts, massive volcanic eruptions

Question 32

Two major extinctions

Answer 32

Permian-Triassic (252 Ma ago) and Cretaceous-Tertiary (66 Ma ago)

Question 33

Permian Extinction

Answer 33

The worst extinction event occurred at the end of the Permian when more than 90% of marine species and 70% of animals on land perished. This is directly related to the large igneous province in Russia where large magma releases caused a rifting event and produced CO2 and SO2. Falling acid rain and chemical weathering produced plankton blooms making oceans anoxic and acidic. Dust falling blocked sunlight.

Question 34

Cretaceous extinction

Answer 34

Wiped out 1/4 of all known species, and is likely caused by the impact of a large meteorite, having crashed somewhere off the coast of Mexico.

Question 35

Why the cretaceous extinction was likely caused by

Answer 35

1. abrupt manner of extinctions (usually takes tens of millions of years)
2. A thin layer of clay found in many parts at the crustaceous-Tertiary boundary with high concentrations of iridium. Iridium on earth can only be found in the mantle and core. The source must have been extraterrestrial.

Question 36

Flood Basalts in India

Answer 36

During the Mesozoic, India moved steadily northward and moved over a fixed hotspot in the mantle which led to a massive outpouring of flood basalts known as the Deccan Traps. Some suggest this led to an environmental catastrophe and the stressed ecosystem from volcanism was further harmed by the meteorite impact.

Question 37

Two factors that caused the Cretaceous extinction

Answer 37

Meteorite and hot-spot volcanism in India