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.
Fossils are the remains or evidence of ancient organisms preserved in rock.
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.
Most preserved evidence of ancient life is marine.
Fossils are protected in rock.
Where most deposition of sediment occurs.
Some terrestrial fossils preserved:
streams and lakes,
or volcanic tephra (ash).
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.
Bone pore space
Simultaneous exchange of original substance with minerals of a different composition.
Can be very precise.
Soft tissues are replaced by carbon as volatile components are driven off.
Mold - a void that the original material occupied.
Cast - molds that have been filled in by subsequent material.
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.
La Brea Tar Pits
Clues from trace fossils. Includes:
Crawling traces Grazing trace
Resting traces Dwelling trace Feeding trace
Bipedal or quadruped
Digitigrade-walked on toes (cat)
Plantigrade-walked on flats of feet (human) Weight
Size of depression in sediment
Aquatic or terrestrial
Why are some fossils common and others rare?
Better representation for organisms with hard parts.
Little representation from organisms living in hilly or mountainous terrain.
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
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
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 can work with many individuals and make many more comparisons than paleontologists.
Juvenile vs. adult variation
The naming and grouping of organisms.
Grouped in a hierarchy that defines levels of kinship.
The highest taxonomic level.
A large group of related phyla.
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
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.
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.
Is there evidence?
Peppered Moth of London
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