24 - Evolution + the Fossil Record

What are the main topics in evolution & fossil record?

History of life, fossils & dating, time periods, Cambrian explosion, mass extinctions.

What are the essential characteristics of life?

Cellular, water-based, CHONPS elements, macromolecules, DNA/RNA, metabolism, reproduction, evolution.

What are the four macromolecules of life?

Proteins, carbohydrates, lipids, nucleic acids.

What is the Oparin-Haldane hypothesis?

Life arose from nonliving chemicals on early Earth.

What experiment supported early life chemistry?

Miller-Urey experiment.

What did the Miller experiment produce?

Amino acids.

What conditions were simulated in Miller experiment?

Reducing atmosphere, heat, electrical sparks.

Concept: What does this suggest about life’s origin?

Organic molecules can form naturally.

When did Earth form?

~4.5 billion years ago.

When did the universe begin?

~13.8 billion years ago.

When did life first appear?

~3.7–3.85 billion years ago.

What is evidence for early life?

Carbon isotope ratios (12C enrichment).

What is significance of 12C?

Biological processes favor lighter carbon.

What was the first major biological revolution?

Photosynthesis.

When did photosynthesis evolve?

~2.5 billion years ago.

What organisms performed early photosynthesis?

Cyanobacteria-like bacteria.

Concept: What did photosynthesis change?

Oxygenated atmosphere.

What is the oxygen revolution?

Increase in atmospheric oxygen.

Concept: Why was oxygen important?

Enabled complex life.

What is the Precambrian era?

90% of Earth’s history, mostly single-celled life.

What evolved during Precambrian?

Prokaryotes, oxygen, eukaryotes, first animals.

What is the “Age of Single Cells”?

Precambrian.

What are the major eras?

Precambrian, Paleozoic, Mesozoic, Cenozoic.

What is the Paleozoic era?

Age of invertebrates.

What is the Mesozoic era?

Age of reptiles.

What is the Cenozoic era?

Age of mammals.

What is a fossil?

Preserved remains or traces of organisms.

What are the 4 types of fossils?

Compression, casts/molds, permineralized, trace fossils.

What is a compression fossil?

Flattened remains preserved in rock.

What are casts and molds?

Impressions and fills of organisms.

What is permineralization?

Minerals replace organic material.

What is a trace fossil?

Evidence of activity (footprints, burrows).

Concept: Why is fossil record incomplete?

Soft bodies rarely fossilize.

What is radiometric dating?

Determining age using radioactive decay.

What is half-life?

Time for half of isotope to decay.

Concept: Why is half-life important?

It allows age calculation.

Example: What isotope is used for recent fossils?

Carbon-14.

Example: What isotopes date older rocks?

Uranium, potassium.

What is molecular clock?

Estimating divergence using mutation rates.

Concept: What assumption does molecular clock make?

Constant mutation rate.

Example: Mitochondrial mutation rate?

~2.2% per million years.

Concept: Why are fossil record and molecular clock different?

Incomplete fossils and variable mutation rates.

Concept: How are they complementary?

Fossils show extinct species; DNA shows relationships.

What is adaptive radiation?

Rapid diversification into new niches.

What causes adaptive radiation?

New environments, extinctions, innovations.

What is phylogenetic signature of radiation?

Bushy tree with rapid branching.

What is ecological opportunity?

Availability of new niches.

Example: What are Galápagos finches?

Adaptive radiation example.

Example: Hawaiian species?

Silverswords, honeycreepers.

What is morphological innovation?

New trait enabling new function.

Example: Plant innovations?

Seeds, flowers, cuticle.

Example: Animal innovations?

Feathers, limbs, jaws.

What is colonization of land?

Transition from aquatic to terrestrial life.

When did plants colonize land?

~420 million years ago.

When did tetrapods evolve?

~365 million years ago.

What are tetrapods?

Four-limbed vertebrates.

Concept: What enabled land colonization?

Adaptations to dryness and gravity.

What is Cambrian explosion?

Rapid appearance of diverse animal phyla.

When did Cambrian explosion occur?

~540 million years ago.

Where are key Cambrian fossils found?

Burgess Shale, China, Australia.

What organisms appeared in Cambrian?

Arthropods, mollusks, vertebrates.

Concept: Why is Cambrian explosion significant?

Origin of major animal body plans.

Concept: Was it truly sudden?

Fossil record suggests yes, genetics suggests gradual.

What preceded Cambrian explosion?

Ediacaran fauna.

What are Ediacaran organisms?

Soft-bodied early animals.

Concept: Why are Ediacaran fossils rare?

Lack hard parts.

What is homoplasy?

Similar traits evolving independently.

Concept: What causes gene tree conflict?

Horizontal gene transfer.

What is horizontal gene transfer?

Gene movement between organisms.

What is cenancestor?

Common ancestor with gene mixing.

What is a “living fossil”?

Species unchanged over long periods.

Example: Living fossils?

Ginkgo, horseshoe crab.

What is evolutionary trend?

Directional change over time.

Example: Trend in horses?

Increasing body size.

What are mass extinctions?

Rapid loss of many species globally.

What defines a mass extinction?

60% species lost in short time.

How many major mass extinctions?

Five.

What is background extinction?

Normal ongoing extinction.

Concept: What percent of species are extinct?

~99%.

What is ecological effect of mass extinction?

Creates new niches.

What follows mass extinctions?

Adaptive radiation.

What caused extinctions?

Climate change, volcanism, impacts.

Example: Permian extinction cause?

Global warming.

Example: Cretaceous extinction cause?

Asteroid impact.

What is Chicxulub crater?

Evidence of dinosaur-killing asteroid.

What evidence supports asteroid impact?

Shocked quartz, microtektites.

When did dinosaurs go extinct?

~65 million years ago.

What survived dinosaur extinction?

Birds.

Concept: Why did birds survive?

Likely smaller size, flexibility.

What is the 6th mass extinction?

Current human-driven extinction.

What causes modern extinction?

Habitat loss, climate change, invasives.

Concept: Why is current extinction unique?

Extremely rapid.

Concept: Why no radiation today?

Humans occupy niches.

What is background extinction rate?

Normal baseline extinction.

Concept: Are current rates above background?

Yes, much higher.

What is biodiversity hotspot?

Region with many species at risk.

Example: Tropical rainforest?

High biodiversity and threat.

Concept: Why is conservation important?

Prevent biodiversity loss.

What is fossil calibration?

Using fossils to set molecular clock.

Concept: Why calibrate molecular clock?

Improve accuracy.