Chapter 25- The History of Life and Phylogenies

BIO

How old is the earth?

4.6 billions years old.

When did life begin?

Between 3.8 and 3.5 years ago.

What are the 5 major steps in early evolution of life?

1. Cellular life

2. Oxygen revolution

3. Nucleated cells (eukaryotes)

4. Multicellularity

5. Cambrian Explosion

What were the earliest cells like?

Prokaryotic, anaerobic, heterotrophic

What is the Oxygen Revolution and when did it occur?

Oxygen started accumulating- 2.7 billion years ago due to photosynthesis.

When did eukaryotic cells evolve?

Around 2 billion years ago.

Why is multicellularity important?

It allowed for tissue specialization and more complex organisms.

What is the Cambrian Explosion?

A “sudden” appearance of most modern animal body plans.

How many major mass extinctions have there been?

Five, we are currently in the sixth.

What causes mass extinctions?

Sudden, extraordinary environmental changes.

What is the 6th extinction, and what cause it?

The current, human cause (anthropogenic) extinction. It’s caused by pollution, climate change, habitat loss, etc.

What is background extinction?

The normal, ongoing extinction of species due to natural causes like environmental change, disease, competition, or predation.

How do background extinction and mass extinction differ?

Background extinction is slow; it affects a few species and happens continuously.

Mass extinction is fast, global and wipes out many species at once.

What are the oldest fossils?

Stromatolites (blue- green algae) - 3.5 billion years old.

Name 4 biases in the fossil record

1. Habitat bias- Sedimentation is necessary for fossils to form

2. Taxonomic and tissue bias- Some animals body parts fossilize better than others.

3. Temporal bias- More recent animals are more abundant than others.

4. Abundance bias- More common organisms are more likely to fossilize

What does “extant” mean?

It means living on earth today.

Estimated number of extant species?

10-100 million but the best estimate is 30 million.

What is phylogeny?

A hypothesis of evolution relationships (often genetic).

Define: Node, Sister taxa, Clade, Outgroup, Synapomorphy

Node: Most recent common ancestor

Sister taxa: Closest relatives

Clade: A group including an ancestor and all its descendants.

Outgroup: Species used to help root the tree, diverged earlier.

Synapomorphy: Shared derived trait from a common ancestor

What is the difference between Homology and Homoplasy?

Homology: Shared traits from a common ancestor

Homoplasy: Similar traits, but not from a common ancestor (convergent evolution)

What is the difference between a phylogenetic tree and taxonomic tree?

Phylogenetic tree: Evolutionary relationships

Taxonomic tree: Naming/ classification (kingdom, phylum, etc)

Both are hierarchical and branching

Why are scientific names preferred over common names?

They’re standardized and universal.

What is adaptive radiation?

Rapid evolution of many species from a common ancestor- often on islands- to fill in different ecological niches.

Do all species share a common ancestor?

Yes, all life on earth is related through a common ancestor.

When was the Cambrian Explosian?

about 530 million years ago