History of Life 17-1

Fossils and Ancient Life -paleontologists study fossils to infer past history. -organisms habitat, food source, behavior etc… -fossilized organisms classified into groups oldest to youngest; includes how they change. -known as fossil record. -Most organisms have become extinct. -fossils form in sedimentary rock, mostly from hard body parts. -bones, scales, shells -fossils also include casts, molds, imprints, etc…

                            -fossils are revealed through uplift, erosion, weathering.

Dating Fossils -in relative dating, age determined by placement of fossil. -may use index fossil. -common fossil, easily recognizable, existed for short time period. -in absolute dating, age determined by radioactive dating. -age calculated from half-life base on remaining amount of radioactive isotopes. -half-life is how long it takes

for half a sample to decay. -different elements have different half-lives. -ex. Carbon-14 = 5,730 years. Potassium-40 = 1.26 billion years.

Geologic Time Scale -evolutionary time represent by geologic time scale. -divided into eras, periods. -developed by studying rock layers and index fossils. -divisions vary in duration. -divisions are marked by significant events -ex. mass extinctions followed by adaptive radiation.

Early Earth 17-2

Formation of Earth -Earth estimated at 4.6 billion years old. -Earth formed in a course of ~ 100 million years. -dust and other particles coalesced. Earth’s Early Atmosphere -theorized to be composed of : hydrogen cyanide (HCN), carbon dioxide (CO2),water (H2O), hydrogen sulfide (H2S), methane (CH4), and carbon monoxide (CO). -energy derived from lightning, volcanic eruptions, UV radiation.                                                                         First organic molecules

-Miller and Urey conduct experiment simulate early atmosphere. -generate amino acids, nucleic acids.   -other modern, more accurate experiments also generate organic molecules. -proteinoid microspheres form. -selectively permeable membranes, Similar to cells. -formation of RNA, followed by DNA. -RNA’s can catalyze chemical reactions. First Cells -oldest microfossils form 3.5 billion years ago (bya). -photosynthetic bacteria 2.2 bya. -oxygen accumulates, methane and hydrogen sulfide decrease, ozone formed. -some prokaryotes evolve internal membranes. -formation of first eukaryotes 2 bya. -endosymbiotic theory proposes how eukaryotes acquired mitochondria and chloroplast. Patterns of Evolution -extinctions followed by adaptive radiation. -species adapt/evolve to “vacant” niche. -coevolution results in two species evolving in response to each other.   -ex. host and parasite, prey and predator. -convergent evolution results when two unrelated species resemble each other. -do to similar adaptations to similar environment.   Rate of evolution

Punctuated equilibrium= long periods of no change followed by quick changes. Gradualism = continues small changes through time.