Fossils and Geologic Time Scale

Chapter 17

What’s It All About Essential Question:

Can relative dating and relative frequency be a trusted thing?

Objectives: Describe the fossil

record Sate the information

that relative dating and radioactive dating provide about fossils

Identify the divisions of the geological time scales

Fossil Formation Provides evidence about the history of life

on Earth Shows how different groups of organisms,

including species have changed over time The fossil record is incomplete because just

the right conditions must occur.

How Fossils Form

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.

See page 418!

Interpreting Fossil Evidence Relative Dating—Age of a fossil is

determined by comparing its placement with that of fossils in other layers of rock Estimate of the age

Radioactive Dating—Calculate the age of a sample based on the amount of remaining radioactive isotopes it contains Accurate Age

Geologic Time Scale Used by paleontologists Represents evolutionary time Mark major changes in fossils

Division of Time Era—One of several subdivions of time

between the Precambrian and present Period—Unit of time in which eras are

subdivided

Draw a big table that looks like this:

Glaciations; mammals increased; humans

Mammals diversified; grasses

Aquatic reptiles diversified; flowering plants; mass extinction

Dinosaurs diversified; birds

Dinosaurs; small mammals; cone-bearing plants

Reptiles diversified; seed plants; mass extinction

Reptiles; winged insects diversified; coal swamps

Fishes 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

Quaternary

Tertiary

Cretaceous

Jurassic

Triassic

Permian

Carboniferous

Devonian

Silurian

Ordovician

Cambrian

1.8–present

65–1.8

145–65

208–145

245–208

290–245

363–290

410–363

440–410

505–440

544–505

650–544

Key EventsEra Period Time(millions of years ago)

Cen

ozoi

c E

ra Quaternary Period 1.8-present Glaciations, mammals increased, humans

Tertiary Period 65-1.8 Mammals diversified, grasses

Mes

ozoi

c E

ra Cretaceous Period

145-65 Aquatic reptiles diversified, flowering plants,

mass extinction Jurassic Period

208-145 Dinosaurs diversified, birds

Triassic Period 245-208 Dinosaurs, small mammals, cone-bearing

plants

Pal

eozo

ic E

ra Permian Period

290-245 Reptiles diversified; seed plants; mass extinction

Carboniferous Period 360-290 Reptiles; winged insects diversified; coal swamps

Devonian Period 410-360 Fishes diversified; land vertebrates (prim amphibs)

Silurian Period 440-410 Land plants; land animals (arthropods)

Ordovician Period 505-440 Aquatic arthropods; mollusks; vertebrates (jawless

Cambrian Period fishes) 544-505 Marine inverts diversified; most animal phyla

evolved

Pre

cam

bria

n T

ime Vendian Period

650-544 Anaerobic, then photosynthetic prokaryotes;

eukaryotes, then multicellular life