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Chapter 6 – Life on Earth: What Do Fossils Reveal?. Fossils are the remains or evidence of ancient organisms preserved in rock. Fossils: Surviving Records of Past Life. Preservation of ancient life is amazingly rare. Scavengers and bacteria destroy the deceased.

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chapter 6 life on earth what do fossils reveal
Chapter 6 – Life on Earth: What Do Fossils Reveal?

Fossils are the remains or evidence of ancient organisms preserved in rock.

fossils surviving records of past life
Fossils: Surviving Records of Past Life

Preservation of ancient life is amazingly rare.

Scavengers and bacteria destroy the deceased.

Weathering and erosion of rocks containing fossils eliminates evidence.

The best preserved fossils are those with “hard parts”.

Even hard parts require quick burial.

Soft parts are sometimes preserved.

how does past life become preserved
How Does Past Life Become Preserved?

Most preserved evidence of ancient life is marine.

Fossils are protected in rock.

Where most deposition of sediment occurs.

Little erosion.

Some terrestrial fossils preserved:

streams and lakes,

tar (pits),


tree sap,


lava flows,

or volcanic tephra (ash).

three common preservation processes
Three Common Preservation Processes

Rarely are the original “hard parts” preserved.

Permineralization - “to spread minerals throughout.

Silica, calcium carbonate, or iron dissolved in H2O percolates through sediment and is precipitated in openings.

Blood vessels


Bone pore space


Simultaneous exchange of original substance with minerals of a different composition.

Can be very precise.

Fossilized wood

Fossilized bone


Soft tissues are replaced by carbon as volatile components are driven off.

molds and casts
Molds and Casts

Mold - a void that the original material occupied.


Cast - molds that have been filled in by subsequent material.



soft tissue preservation
Soft Tissue Preservation

Occasionally soft tissues may be preserved. Mostly recent organisms.

Amber - Jurassic Park?

Frozen in ice

Preserved in “tar” (asphalt)

Preserved in peat bog


Amber is remarkably durable.


No dinosaurs

frozen in ice
Frozen in Ice

Pleistocene (or later) ice

frozen in ice13
Frozen in Ice

Pleistocene (or later) ice

preserved in asphalt
Preserved in Asphalt

La Brea Tar Pits

preserved in bog
Preserved in Bog

Lindow Man

trace fossils
Trace Fossils

Clues from trace fossils. Includes:

Fossil tracks




trace fossil behavior
Trace Fossil Behavior

Crawling traces Grazing trace

Resting traces Dwelling trace Feeding trace

trace fossils evidence
Trace Fossils Evidence

Tracks evidence

Bipedal or quadruped

Digitigrade-walked on toes (cat)

Plantigrade-walked on flats of feet (human) Weight

Size of depression in sediment

Aquatic or terrestrial

Webbed feet


Sharp claws

fossil abundance
Fossil Abundance

Why are some fossils common and others rare?

Better representation for organisms with hard parts.

Rapid burial

Little representation from organisms living in hilly or mountainous terrain.

figuring out how life is organized linnaeus leads the way
Figuring Out How Life is Organized- Linnaeus Leads the Way

Prior to Linnaeus organisms were classified in many different ways.

I.e., all flying organisms

Carl von Linné-Swedish naturalist

Organized organisms into groups with observable traits

Vertebrates, et cetera

Binary nomenclature

genus then species


Group of organisms for all cat-like organisms.

Felis domesticus-common house cat

Felis leo-African lion

Felis fatalis-saber-toothed cat

what is a species
What is a Species?

A species is a specific group of organisms

Structural, functional, and developmental similarities

Must be able to interbreed and produce fertile offspring

Generally similar but not necessarily identical, i.e., exhibit variation

biologists have the advantage
Biologists Have the Advantage

Biologists can work with many individuals and make many more comparisons than paleontologists.


Fertile offspring

Juvenile vs. adult variation

what is taxonomy
What is Taxonomy?

The naming and grouping of organisms.

Grouped in a hierarchy that defines levels of kinship.


The highest taxonomic level.

Three domains





A large group of related phyla.

Four kingdoms

Animalia-multicellular heterotrophic organisms

Plantae-multicellular autotrophic eukaryotes

Fungi-multicellular eukaryotes that absorb nutrients from dead organisms or are parasites

Protista-mostly single cell organisms

lamarck s flawed hypothesis
Lamarck’s Flawed Hypothesis

Organisms evolve through generations due to an “inner want”. Acquired characteristics could be inherited.


Stalin’s Lysenko Siberian wheat famine.

Weak evidence that some bacteria may be able to alter their DNA.

natural selection
Natural Selection

Charles Darwin and Alfred Wallace

More organisms are born than survive to become reproductive adults. (Darwin Award)

There is always variation among offspring.

Competition for food, shelter, living space, and sexual partners among species having individual variations and surplus reproductive capacity consistently results in survival of the more fit and elimination of the less fit.

only a theory
Only a Theory?

Is there evidence?

Dandelion height

Peppered Moth of London

Lungless Salamander


inheritance genes and dna
Inheritance, Genes, and DNA

Gregor Mendel and his garden peas.

Genes: divide in pollen and ovules are recombine in specific ways during fertilization

Chromosomes: formed of linked genes

Watson, Crick, and Franklin discovered the chemical structure of chromosomes as DNA

DNA: deoxyribonucleic acid