The History of Life

Chapter 12

The Fossil Record

Fossil Forming Perminerilization Natural Casts Trace Fossils Amber preserved

fossils Preserved remains

Most fossils form in sedimentary rock

The Fossil Record

The Fossil Record

Relative Dating Estimates the time

an organism was alive based upon it’s placement in rock layers

Allows for inferences of species origin

Does not provide actual age dating of fossil

The Fossil RecordRadiometric Dating

Estimates actual or absolute age

Calculation of the age of a sample based upon the amount of remaining radioactive isotopes

Half life The amount of time it

takes for half of the iostopes in a sample to decay into another element

Different items have different half lives

The Fossil Record

Carbon-14 Dating Good for recent remains Carbon-14-taken up by organisms while

they are alive C-14 begins to break down when organism

dies Researchers compare the amount of

Carbon-14 to Carbon-12 or Nitrogen-14• The larger the ratio of C-14 to C-12 (or N-14),

the older the organism

The Geologic Time Scale

Index Fossils Easily recognized and

the species must have existed for a short period, but have a wide geographic range

It will only be found in a few layers, but they will be specific and in different locations Trilobite

Geologic Time Scale

Evolutionary time is represented by the Geologic Time Scale This orders rock by

ageDivided into units

based on order rocks and fossils were formed

Geologic Time Scale

Time between the Precambrian period and now is divided by eras Paleozoic Mesozoic Cenozoic

These divisions are defined somewhat by the organisms present

Geologic Time Scale

To further define time, eras are divided into periods

The Cambrian period is important to biology due to the huge explosion of organisms

Epochs Smallest unit of time;

several million years

Origin of Life

Earth is about 4.6 billion year old

How did the earth get here?

Formed by a condensing nebula

Material pulled together Collisions caused the

formation of planets

Origin of Life

Earth was very hot, violent first 700 million years

Many objects struck Earth releasing heat – kept Earth in a molten state Objects eventually separated into layers

Hydrogen, carbon monoxide, water vapor, methane, and carbon dioxide released Oxygen not released until about 2 billion years ago

Origin of Life

Miller-Urey Experiment Lightning strikes

caused inorganic molecules to form organic molecules

Electricity applied to these inorganic molecules led to the production of amino acids

Origin of Life

Meteorite Hypothesis Amino acids have

been found in meteorites

Suggests that amino acids could have been present when Earth formed

Origin of LifeIron Sulfide

Hypothesis Iron sulfide from

deep sea vents form chimneys

Compartments in these chimneys acted as pockets for biological molecules

The walls of these compartments acted as the first cell membranes

Origin of Life

Lipid Membrane Hypothesis Lipids tend to form

spheres – liposomes

These spheres could enclose organic molecules

Give rise to cells

Origin of Life

RNA – Early Genetic Material Ribozymes – RNA

molecules that can catalyze chemical reactions

Can make enzymes that would cut itself, copy itself, and make more of itself

Short chains of RNA can form from inorganic molecules

Early Single-Celled Organisms

Early microbes changed the Earth Deposited minerals, gave

off oxygen Cyanobacteria –

bacteria that carry out photosynthesis

• Stromatolites – colonies of cyanobacteria

Release of oxygen allowed for aerobic organisms

Early Single-Celled Organisms

Early prokaryotes are considered the ancestors of eukaryotes

Early on some smaller prokaryotes began to enter into other prokaryotes

Endosymbiotic Theory Eukaryotic cells arose

from living communities formed by prokaryotic cells

Eukaryotic Origins

Evidence of the Endosymbiotic Theory Mitochondria and chloroplasts:

• Contain DNA similar to bacterial DNA• Have ribosomes whose structure and size

closely resemble bacterial ribosome• Reproduce by binary fission

These three key pieces of evidence are what give credence to the idea that eukaryotes formed from prokaryotes

Reproduction and Multicellularity

After arrival, eukaryotes reproduced sexually

This increased the speed of evolution

Sexual reproduction allowed for shuffling of genes

Offspring never resembled their parents exactly

This increased the gene combinations – So?

Early Single-Celled Organisms

Sexual Reproduction vs. Asexual reproduction Asexual – ease, rate

of reproduction, energy efficient

Sexual – genetic diversity, increase in evolution

Paleozoic EraFossil evidence shows a very

diverse life during this eraWas initially thought that much of

this life originated during this eraActually came about much earlier

Cambrian Period Cambrian Explosion The explosion and

diversification of life during this period

Organisms had shells and outer skeletons

Common organisms: Jellyfish, worms,

sponges Brachiopods,

trilobites

Ordovician and Silurian Periods

Ancestors of modern octopi and squid appeared

Arthropods became the first land animals

Jawless fishes became the first vertebrates

Plants evolved from aquatic ancestors

Devonian Period

Plants began to adapt to drier areas

This allowed for invasion of new habitats

“Age of Fishes” Many groups of fishes

present in the oceans

Vertebrates began to also invade land

Carbiniferous and Permian Period

Reptiles evolved from amphibians

Winged insects began to appear Dragonflies and

cockroaches

Plants became abundant and when they died, their remains are now coal

Mesozoic Era

Lasted approximately 180 million years

This era is marked by two main features Dinosaurs Flowering plants

Triassic Period

Fishes, insects, reptiles, and cone-bearing plants were prominent

“Age of the Reptiles” Coelophysis – meat

eater

Mammals first appeared – mouse or shrew style

Jurassic Period

Dinosaurs the prominent life form

Ruled the earth for about 150 million years

Many scientists think that birds are close relatives

Cretaceous Period

Dinosaurs still present New life came about:

Leafy tress Shrubs Small flowering plants

Another mass extinction brought this period to and end More than half the plant

and animal groups wiped out

Cenozoic Era

About 65 million years ago Mammals evolved

Could live on land, in water, and even the air

Tertiary Period Warm and mild climate Whales and dolphins

evolved Quaternary Period

Climate cooled – ice ages Earth warmed up about

20,000 years ago Homo sapiens – 200,000

years ago in Africa

Extinction

99% of all species that ever existed are extinct

Extinctions happen for reasons Resources Environments change

Each extinction brings an opportunity for other species to succeed

Primate Evolution

Common Ancestors Primates are

mammals with flexible hands and feet

Divided into two groups• Prosimians• Anthropoids

Primate Evolution

Promisians Oldest primate group Active at night Lemurs, tarsiers

Anthropoids Divided into old

and new world monkeys as wells as hominoids

Hominids can be even further divided• Lesser apes

(gibbons)• Greater apes

(gorillas)• Hominids

(humans)

Primate Evolution

Bipedalism Walking upright, on

two legs Came before larger

brains and tool manipulation

Allowed to reach higher into trees, freed the hands

Primate Evolution

Early Human Fossils Two important genus

• Homo• Australopithecus

Homo habilis Homo

neanderthalensis• Neanderthals

Homo sapiens• Modern humans

Primate Evolution

Human Evolution Modern humans

came about 100,000 years ago

Came out of Ethiopia Brain was key to

evolution• Enlarged skull and

brain

Primate Evolution

Australopithecus afarensis Homo erectus

Homo neanderthalensis Homo sapiens