Ch 25: History of life …as we understand it

• Conditions on early Earth made the origin of life possible– Chemical and physical processes on early Earth may have

produced very simple cells through a sequence of stages:• Abiotic synthesis of small organic molecules• Joining of these small molecules into macromolecules• Packaging of molecules into protocells

– Membraneous packets of chemicals

Synthesis of Organic Compounds…

• Earth formed about 4.6 billion years ago, along with the rest of the solar system

• Bombardment of Earth by rocks and ice likely vaporized water and prevented seas from forming before 4.2 to 3.9 billion years ago

• Earth’s early atmosphere likely contained water vapor and chemicals released by volcanic eruptions (nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, hydrogen, hydrogen sulfide)

Are the key building blocks of life hard to come by?

• Amino acids have been found in meteorites• RNA monomers have been produced spontaneously from

simple molecules• In water, lipids and other organic molecules can

spontaneously form vesicles with a lipid bilayer• Adding clay can increase the rate of vesicle formation• Vesicles exhibit simple reproduction and metabolism and

maintain an internal chemical environment– Resultprotocells

The fossil record documents this history of life in geologic time

Dimetrodon

Stromatolites

Fossilizedstromatolite

Coccosteuscuspidatus

4.5 cm

0.5 m

2.5 cm

Present

Rhomaleosaurus victor

Tiktaalik

Hallucigenia

Dickinsonia costata

Tappania

1 cm

1 m

100 mya

175200

300

375400

5005255656001,500

3,500

270

Figure 25.4

How Rocks and Fossils Are Dated

• Sedimentary strata reveal the relative ages of fossils

• The absolute ages of fossils can be determined by radiometric dating– A “parent” isotope decays to a “daughter”

isotope at a constant rate– Each isotope has a known half-life, the time

required for half the parent isotope to decay

Refer to: Keeping Time handout

Limitations of Carbon dating

• Radiocarbon dating can be used to date fossils up to 75,000 years old

• For older fossils, some isotopes can be used to date sedimentary rock layers above and below the fossil

Geologic record is divided into the Archaean, the Proterozoic, and the Phanerozoic eons

The Phanerozoic encompasses multicellular eukaryotic life and is divided into three eras: Paleozoic, Mesozoic, and Cenozoic

The Cambrian explosion refers to the sudden appearance of a multitude of modern body designs (530 million years ago)first evidence of predator-prey interactions

Appearance of selected animal groups in the fossil recordAnd, the colonization of land…

Fungi, plants, and animals began to colonize land about 500 million years ago

Vascular tissue in plants transports materials internally and appeared by about 420 million years ago

Plants and fungi today form mutually beneficial associations and likely colonized land together

Arthropods and tetrapods are the most widespread and diverse land animals

Tetrapods evolved from lobe-finned fishes around 365 million years ago

Sponges

Cnidarians

Echinoderms

Chordates

Brachiopods

Annelids

Molluscs

Arthropods

Ediacaran CambrianPROTEROZOIC PALEOZOIC

Time (millions of years ago)635 605 575 545 515 485 0

Figure 25.10

The fossil record shows that most species that have ever lived are now extinct…

Further reading: the last parts of Ch 25 that includes Mass extinctions

Ch 26: Phylogeny and Systematics

• What is meant by phylogeny?

• Evolutionary history of a species…– Based on common ancestry– Supported by shared

characteristics and genetics– Documented by fossils and

genetics

Eon > Era > Periods > Epochs

Systematics?

= study of the organismal diversity of life

How do we make sense of all this diversity?

Organize it… using fossil, molecular, and genetic data to infer evolutionary relationships

Taxonomy & classification

Phylogenies show evolutionaryrelationships --Diversity of Life

Taxonomy is the ordered division and naming of organisms

Domain Kingdom Phylum Class Order

Family Genus

Species

Each group is nested within the level above

Broad or less specific

More specific

Closely related species belong to the same genus, similar genera are included in a family, etc…Species that share the same structures, behaviors, etc, can interbreed and produce fertile offspring.

• Grouped by shared characters (Evolutionary relationships)– Embryology– Reproduction strategies– Symmetry (body plan)– Morphology– Feeding mode– Interspecific interactions

(e.g. symbiosis)– Etc…

Systematists depict evolutionary relationships in branching phylogenetic trees

• A phylogenetic tree represents a hypothesis about evolutionary relationships• Each branch point represents the divergence of two species• Sister taxa are groups that share an immediate common ancestor

Branch point:where lineages diverge

ANCESTRALLINEAGE

This branch pointrepresents thecommon ancestor oftaxa A–G.

This branch point forms apolytomy: an unresolvedpattern of divergence.

Sistertaxa

Basaltaxon

Taxon A

Taxon B

Taxon C

Taxon D

Taxon E

Taxon F

Taxon G

• Cladistics groups organisms by common descent• A clade is a group of species that includes an

ancestral species and all its descendants

– Clades can be nested in larger clades, but not all groupings of organisms qualify as clades

Figure 26.11

TAXA Lancelet(outgroup)

Lamprey

Bass

Frog

Turtle

Leopard

Vertebralcolumn

(backbone)

Four walkinglegs

Hinged jaws

Amnion

Hair

Vertebralcolumn

Hinged jaws

Four walking legs

Amnion

Hair

(a) Character table (b) Phylogenetic tree

CHAR

ACT

ERS

Lanc

elet

(out

grou

p)

Lam

prey

Bass

Frog

Turt

le

Leop

ard

0

0

0

0

0

1

0

0

0

0

1

1

0

0

0

1

1

1

0

0

1

1

1

1

0

1

1

1

1

1

• Historical 5 Kingdom system… until about 1970

3 domains, many kingdoms