The Fossil Record

• Provides evidence about the history of life on Earth.

• It also shows how different groups of organisms, including species, have changed over time.

Relative Dating

Can determine

Is performed by

Drawbacks

Absolute Dating

Comparing Relative and Absolute Dating of Fossils

Imprecision and limitations of age data

Difficulty of radioassay laboratory methods

Comparing depth of a fossil’s source stratum to the position of a reference fossil or rock

Determining the relative amounts of a radioactive isotope and nonradioactive isotope in a specimen

Age of fossil with respect to another rock or fossil (that is, older or younger)

Age of a fossil in years

Relative vs. Absolute Dating

Principle of Superposition• In an undisturbed sequence of

sedimentary rocks, the oldest rocks are on the bottom with the most recent on top.

How fossils are formed

Water carries small rock particles to lakes and seas.

Dead organisms are buried by layers of sediment, which forms new rock.

The preserved remains may later be discovered and studied.

Geological Time Scale

• After the Precambrian Time, the time scale is divided into eras, which are subdivided into periods.

Era Period TimePermian

Carboniferous

Devonian

Silurian

Ordovician

Cambrian

(millions of years ago)Era Period Time (millions of

years ago)Era Period Time(millions of years ago)

290 – 245

360–290

410–360

440–410

505–440

544–505

1.8–present

65–1.8

145–65

208–145

245–208

Quaternary

Tertiary

Cretaceous

Jurassic

Triassic

Vendian 650–544

Geological Time Scale

• The major eras are Paleozoic, Mesozoic, and Cenozoic.

Era Period TimePermian

Carboniferous

Devonian

Silurian

Ordovician

Cambrian

(millions of years ago)Era Period Time (millions of

years ago)Era Period Time(millions of years ago)

290 – 245

360–290

410–360

440–410

505–440

544–505

1.8–present

65–1.8

145–65

208–145

245–208

Quaternary

Tertiary

Cretaceous

Jurassic

Triassic

Vendian 650–544

Geologic Time Scale

• Each period hosts significant evolutionary changes to species diversity and extinction.

Era Period TimePermian

Carboniferous

Devonian

Silurian

Ordovician

Cambrian

(millions of years ago)Era Period Time (millions of

years ago)Era Period Time(millions of years ago)

290 – 245

360–290

410–360

440–410

505–440

544–505

1.8–present

65–1.8

145–65

208–145

245–208

Quaternary

Tertiary

Cretaceous

Jurassic

Triassic

Vendian 650–544

Glaciations; mammals increased; humansMammals diversified; grassesAquatic reptiles diversified; flowering plants; mass extinctionDinosaurs diversified; birdsDinosaurs; small mammals; cone-bearing plantsReptiles diversified; seed plants; mass extinctionReptiles; winged insects diversified; coal swampsFishes diversified; land vertebrates (primitive amphibians)Land plants; land animals (arthropods)Aquatic arthropods; mollusks; vertebrates (jawless fishes)Marine invertebrates diversified; most animal phyla evolvedAnaerobic, then photosynthetic prokaryotes; eukaryotes, then multicellular life

Cenozoic

Mesozoic

Paleozoic

PrecambrianTime

QuaternaryTertiaryCretaceousJurassicTriassicPermianCarboniferousDevonianSilurianOrdovicianCambrian

1.8–present65–1.8145–65208–145245–208290–245363–290410–363440–410505–440544–505650–544

Key EventsEra Period Time (millions of years ago)

Summary of major events (pg. 429-34)

Hypothesis of early Earth

• Very hot surface from colliding meteorites

• Very hot planet core from radioactive materials

• Volcanoes spewing lava and gases that helped to form the early atmosphere

Hypothesis of early Earth

• About 4.4 billion years ago, Earth might have cooled enough for the water in its atmosphere to condense.

• This might have led to millions of years of rainstorms with lightning, enough rain to fill depressions that became Earth’s oceans.

• The oldest rocks dated are 3.9 million years old.

Fossils: evidence of an organism that lived long ago that is preserved in

Earth’s rocks• Paleontologists

estimate that about 95% species are extinct from life’s origins.

• Climate and ancient geography can be determined from fossils.

Fossils Types Formation

Trace fossils

Casts

Molds

Petrified/Permineralized

fossilsAmber-Preserved orfrozen fossils

A trace fossil is any indirect evidenceleft by an animal and may include afootprint, a trail, or a burrow.

When minerals in rocks fill a space left by a decayed organism, they makea replica, or cast, of the organism.

A mold forms when an organism isburied in sediment and then decays,leaving an empty space.

Petrified-minerals sometimes penetrateand replace the hard parts of an organism. Permineralized-void spacesin original organism infilled byminerals.At times, an entire organism was quickly trapped in ice or tree sap thathardened into amber.

What has been learned from fossils

• several episodes of mass extinction that fall between time divisions– mass extinction: an event that occurs when

many organisms disappear from the fossil record almost at once

• The geologic time scale begins with the formation of Earth about 4.6 billion years ago.

Precambrian – 87% of history• Oldest fossils about 3.4 billion years old

resembling cyanobacteria stromatolites.• Stromatolites still form today in Australia

from mats of cyanobacteria. • The stromatolites are evidence of the

existence of photosynthetic organisms on Earth during the Precambrian.

• Only prokaryotic life found in fossil record

End of Precambrian – 543 MYA• multicellular eukaryotes,

such as sponges and jelly-fishes, diversified and filled the oceans

Paleozoic and Cambrian Period

• Paleozoic Era: more animals and plants– Early: fishes, aquatic vertebrates, ferns– Middle: amphibians– Late: reptiles and mass extinction

– Cambrian Period: oceans teemed with many types of animals, including worms, sea stars, and unusual arthropods

Mesozoic - 248 MYA• Triassic Period: mammals and dinosaurs• Jurassic Period: dinosaurs and birds• Cretaceous Period: more mammals,

flowering plants, but mass extinction of dinosaurs 65 MYA

Continental drift

• Earth’s continents have moved during Earth’s history and are still moving today at a rate of about six centimeters per year.

• The theory for how the continents move is called plate tectonics.

Miller-Urey experiment showed one possible way for inorganic molecules to form organic molecules. Mixture of gases

simulating atmospheres of early Earth

Spark simulating lightning storms

Condensation chamber

Cold water cools chamber, causing droplets to form

Water vapor

Liquid containing amino acids and other organic compounds

How eukaryotic cells evolved

• Lynn Margulis proposed the endosymbiotic theory.

Aerobic bacteria

Ancient Prokaryotes

Ancient Anaerobic Prokaryote

Primitive Aerobic Eukaryote

Primitive Photosynthetic Eukaryote

Chloroplast

Photosynthetic bacteria

Nuclear envelope evolving Mitochondrion

Plants and plantlike protists

Animals, fungi, and non-plantlike protists

Endosymbiotic theory• Heterotrophic bacteria have plasmids

(DNA loop) & simple ribosomes in their cytoplasm

• Mitochondria have circular DNA & bacteria-like ribosomes

• So…Eukaryotic cells may have engulfed prokaryotic cells & by mutualism created the “first mitochondria.”

• Autotrophic bacteria are Cyanobacteria with chlorophyll

• So, Eukaryotic cells may have engulfed prokaryotic cyanobacteria & by mutualism created the “first chloroplast.”

Macroevolution Large-scale evolutionary patterns and

processes that occur over long periods of time. Includes 6 topics:ExtinctionAdaptive radiationConvergent evolutionDivergent evolutionPunctuated equilibriumChanges in developmental genes

Patterns of evolution• Darwin believed that

organisms evolved gradually.

• Niles Eldredge and Stephen Jay Gould believed punctuated equilibrium is how organisms evolved, periods of rapid evolution followed by periods of stasis.

Adaptive Radiation

• Single species or small groups of species evolved into diverse forms living in different ways.

Convergent Evolution

• Adaptive radiation can produce unrelated organisms that look similar due to similar environments.

Coevolution • Example: “This butterfly acquires a cardiac glycoside from members of the genus Asclepias. Because of their milky sap, these are commonly referred to as milkweed plants. The plants produce this toxin as a defense against herbivory, but the Monarch has the ability to sequester the toxin in fatty tissues so that it makes the butterfly unpalatable while not poisoning the butterfly.”

http://ecology.botany.ufl.edu/ ecologyf02

The process by which two species evolve in response to changes in each, other over time.