History of Life

Question 1

How old is the Earth?

Answer 1

4.58 billion years old

Question 2

What the 4 largest divisions of geological time (eons)? In which order did they occur? What are the basic characteristics of each? Which was the longest?

Answer 2

Hadean (4.58-4 bya)- Earth was unstable, hot, constantly bombarded
Archaen eon (4-2.5 bya)- Earth stabilized, continents and oceans formed, life begins around 3.7 bya
Proterozoic eon (2.5 bya-541 mya)- life becomes more prevalent, photosynthetic microbes lead to "great oxygenation" as evidenced by banded iron formations, eukaryotes appear 1.8 bya with multicellular life 1.6 bya
Phanerozoic eon (541 mya-present)- "visible life," sponges >600 mya, motile animals 585 mya

Question 3

What the earliest signs of life and how far back do they date?

Answer 3

Carbon isotope ratios indicative of biological life appear about 3.7 bya

Question 4

What are stromatolites?

Answer 4

Microbial communities, structures built up by biofilms containing cyanobacteria

Question 5

What are some of the major events of the Proterozoic?

Answer 5

Prevalence of life increases, “great oxygenation,” rise of eukaryotes 1.8 bya, multicellular life 1.6 bya

Question 6

What are banded iron formations and what do they signify about major changes during the Proterozoic?

Answer 6

Iron that was suspended in water fell out of solution when it reacted with O2, forming “iron bands” in the sediment

Question 7

What major change was associated with the Phanerozoic when it was initially designated?

Answer 7

The dawn of metazoan diversity (multicellular animals)

Question 8

What are some of the earliest evidence for metazoan life?

Answer 8

Evidence of sponges >600 mya, fossilized tunnels and tracks show evidence of motile animals 585 mya

Question 9

How has the discovery of the Ediacaran fauna complicated our view of the history of animal life?

Answer 9

Edicarian fauna are difficult to connect to any modern day fauna as their body plans are very different

Question 10

Why are some of these creatures so hard to classify?

Answer 10

Their body plans are largely unlike any modern organims

Question 11

What is taphonomy?

Answer 11

Processes related to the fate of an organism’s remains

Question 12

What is the Cambrian Explosion? Why are Cambrian fossil assemblages different from the diverse communities of the Ediacaran fauna?

Answer 12

Rapid appearance of diversified animal morphology. The difference from Edicarian fauna is that all modern phyla are now present

Question 13

What is a Lagerstätte? Why have they been important is our understanding of the history of life?

Answer 13

A rich fossil deposit including organisms that don’t typically fossilize well. Important because they show a more complete fossil record

Question 14

What is a bauplan? What is a major macroevolutionary question about the diversity of bodyplans that came out of the Cambrian?

Answer 14

Basic body plans. A major question is why do organisms have the body plans that they do? Are they inevitable due to natural selection?

Question 15

What is the field of Evo-Devo? What does this field have to do with macroevolution?

Answer 15

The study of how developmental processes evolve to give rise to new morphological features.

Question 16

What does the earliest evidence of our own bauplan look like in the fossil record? How old is it?

Answer 16

Chordates, which date back to the Cambrian explosion

Question 17

What are some explanations for the Cambrian explosion?

Answer 17

One explanation is that oxygen reached a critical threshold

Question 18

What are some of the major events in our own lineage in the periods immediately following the Cambrian?

Answer 18

Placoderms (jawed fish) gave rise to jawed vertebrates, divergence of ray and lobe finned fish (humans are lobed), development of pectoral/pelvic girdles and limbs 385-365 mya

Question 19

What was a major evolutionary innovation in our own lineage during the Silurian?

Answer 19

Development of jawed vertebrates

Question 20

What kind of fish are we?

Answer 20

Scaropterygians, or lobe-finned fish

Question 21

What do transitional fossils tell us about the evolution of the tetrapod skeleton? In very broad terms, how and when did this take place?

Answer 21

The transition to tetrapods was very gradual and smooth, occurring between 365-385 mya

Question 22

What questions do things like the tetrapod hand skeleton and the post-Cambrian diversity of baupläne lead us to ask about the role of optimality and deterministic evolution in the history of life?

Answer 22

How much of the bauplan is driven by natural selection? Is there anything optimal about them?