III. FOSSIL AND BIOCHEMICAL EVIDENCE

TYPES 0F FOSSILS

MOLD

BONES

IMPRINTS

PETRIFIED WOOD

CAST

AMBER

PALEONTOLOGY -the study of fossils

Sedimentary rock

Figure 22.18

The Fossil Record• The succession of forms observed in the fossil

record is consistent with other inferences about the major branches of descent in the tree of life.

• The Darwinian view of life– Predicts that evolutionary

transitions should leave signs in the fossil record

• Paleontologists– Have discovered fossils of many

such transitional forms

A. Fossils-relative and absolute dating methods

How Rocks and Fossils Are Dated

• Sedimentary strata– Reveal the relative

ages of fossils

Relative Dating Methods

• Index fossils– Are similar fossils found in the same strata in

different locations– Allow strata at one location to be correlated with

strata at another location

Figure 26.6

• The absolute ages of fossils– Can be determined by radiometric dating

Figure 26.7

1 2 3 4

Accumulating “daughter”

isotope

Ratio

of p

aren

t iso

tope

to

dau

ghte

r iso

tope

Remaining “parent” isotope

1

1

11

Time (half-lives)

2

4

816

Absolute Dating Methods

Magnetism Dating• Magnetic reversals of the north and south

magnetic poles:– Have occurred repeatedly in the past– Leave their record on rocks throughout the world– These marks are used for dating

Another Absolute Dating Method

The GeologicRecord

• By studying rocks and fossils at many different sites– Geologists

have established a geologic record of Earth’s history

B. A Discussion of what can be inferred from patterns in the fossil

record• The fossil evidence Is consistent with the idea

that today’s organisms evolved from a common ancestor.

• There have been catastrophic events that have affected the creation of new species.

• Geological events that alter environments– Change the course of biological evolution

• Conversely, life changes the planet that it inhabits

Figure 26.1

C. Biochemical SimilaritiesBetween Current & Past Species

Molecular Homologies• Biologists also observe

homologies among organisms at the molecular level– Such as genes that are shared

among organisms inherited from a common ancestor

1 2.4 3.14 5.18 6 7.15

XX1913.1710.169.128.11

1 2.19 3.8 4.16 5.14 6.7

XX15.1813.1711.129.10Figure 23.10

• Anatomical resemblances among species– Are generally reflected in their molecules, their

genes, and their gene products

Figure 22.16

Species

Human

Rhesus monkey

Mouse

Chicken

Frog

Lamprey 14%

54%

69%

87%

95%

100%

Percent of Amino Acids That AreIdentical to the Amino Acids in aHuman Hemoglobin Polypeptide

D. Shared Anatomical Structures• Homology– Is similarity resulting from common ancestry

• Homologous structures between organisms– Are anatomical resemblances that represent variations on

a structural theme that was present in a common ancestor

GILL SLITS

TAIL

All VETEBRATES

Similar Embryonic Development

• Comparative embryology– Reveals additional anatomical homologies not

visible in adult organisms

Figure 22.15

Pharyngealpouches

Post-analtail

Chick embryo Human embryo

VESTIGIAL STRUCTURES

Appendix

Are remnants of structures that served important functions in the organism’s ancestors