EVIDENCE OF EVOLUTION

THE FOSSIL RECORD Our best proof of the history of life on Earth Preserved remains of life buried in sediment may be preserved bodies, bones, footprints, impressions, etc. Bones/Wood/Calcium is slowly replaced by harder minerals over time from surrounding rock. Skin, feathers, soft tissues only fossilize if no O 2 is present or if the sediment is very fine (limestone)

Interpreting Fossil Prints

How do we know how old a fossil is? Relative age dating –approximation of dating by comparing rock layers Absolute age dating –Precision of dating by measuring radioactive decay of elements

Relative Age Dating Relative age dating follows the Law of Superposition –Law of Superposition – older rocks are found under younger rocks Exception to the rule – unconformities (break in the rock record) Index Fossil – an organism that lived during a specific period of time and is abundant.

Unconformity Brain Teaser

Absolute Age Dating Radioactive Elements: an unstable atom that gives off radiation (energy) from its nucleus (protons & neutrons) to become stable. Ex: C 14,U 238, K 40 Radioactive dating: Radioactive decay (going from unstable to stable) occurs at a constant rate represented by a half life. Each radioactive element has its own rate of decay (half life). EX: U 238 takes 4.5 billion yrs for HALF of it to decay to Pb 206 EX: C 14 takes 5730 yrs for HALF to decay to C 12 Half life: the amount of time that it takes for half of the radioactive atoms in a specimen to become stable. 100 C 14 atoms 5730yrs. 50 C 14 atoms 5730yrs. ? atoms

Example of Radioactive Decay

Why study fossils? Ancient organisms are examined and compared to modern organisms Evolutionists attempt to find TRANSITIONAL SPECIES that show the change of form over time- the “missing links”

Transitional Species

Archaeopteryx- Transitional Species?

Completeness of the Fossil Record?

Comparative Anatomy Analogous Structures Homologous Structures Vestigial Structures

Analogous Structures structures that have the same function, but have no evolutionary connection no common ancestor wings- bees, birds, bats Why do these similar functions exist? (NOT SEEN AS EVOLUTIONARY EVIDENCE)

Homologous Structures body parts that have the same structures, but might have different functions share a common ancestor vertebrate forelimb bones- bat wing, mouse forelimb, and human arm

Vestigial Structures structures that are found in an organism but appear to serve no function (reduced in size) They are a remnant of an organism’s evolutionary past –Ex: Whales and snakes have pelvic bones; manatees “sea cows” have finger nails on their fins –Humans? ear muscles canine teeth tailbone appendix goose bumps

Comparative Embryology Evolutionists believe that similarities in the developmental pattern of organisms exist because of a common ancestor –vestigial gill slits/pouches –bony tail –covered in a fine hair Human embryo Pig embryo Chicken embryo

Comparative Embryology in Vertebrates All vertebrates are similar in early stages of development. Differences accumulate in later stages of development. New development instructions are added to old instructions inherited from ancestors.

Comparing Genetics An organism’s evolutionary history is in their DNA sequence (genetic code) If a species changes, their genetic code changes Modern genetic testing is used to compare the similarity of the genetic code of organisms Closely related species will share more similarities in their genetic code Ex. Chimpanzees & Humans have over 98% the same D.N.A.

What is DNA? DNA stores information DNA = Deoxyribonucleic acid Subunit = nucleotides Nucleotides contain a nitrogen base 4 different nitrogen bases adenine (A) guanine (G) thymine (T) cytosine (C) Complimentary Strands (A-T) (G-C) Double Strands (Double Helix) Chromosomes – long strands of DNA 46 chromosomes in humans