unit 11

fossil record & the geological time scale

paleontology

paleontology

the study of fossils

fossil

preserved remains or evidence of extinct or ancient organisms

extinct

term used to refer to a species that has died out; 99% of all species that have lived are extinct

microfossil

fossils of microscopic organisms

trace fossils

fossil footprints, steinkerns, imprints of artifacts of life

coprolites

fossilized remains of feces; shows what a species may have fed on

sedimentation

process where small pieces of sediment bury a dead organism; how fossils are formed

other substances fossils form in

tree sap, amber, tar pits or ice

the fossil record

the fossils where they are found, what they show, and the layers (time) that the species lived

what gets fossilized

mostly bone, teeth, shell, wood and other hard structures, soft tissue can be fossilized but it is rarer

several inferences that can be made from the fossil record

1: different organisms

2: today’s organisms are different from the past

3: comparing fossils from around the world tells us when and where species lived

4: many species are no longer around; they have gone extinct

types of extinctions

background and mass

background extinction

when natural selection causes extinctions occurring one species at a time

mass extinction

when hundreds or thousands of species occur in a short period of time; occurs because of a changed environment, ecosystem collapse or food web collapse

3 facts of the fossil record

1: fossils are distributed consistently; there is “order”

2: more recent fossils more closely resemble modern species

3: the order of appearance suggests a gradual evolution

problems with the fossil record

1: fossil record is discontinuous; it has gaps and is incomplete

2: missing transitional species, the intermediate forms

reasons for the discontinuity of the fossil record

not everything becomes fossilized, haven’t found all fossils yet

gradualism

slow gradual modification to new species

punctuated equilibrium

species evolve in spurts then don’t change for long periods of time; the short “window of change” would explain why there are gaps

tiktaalik

shows how amphibians evolved from fish, one-two-many bone system in lobes, fins have primitive elbows and wrists, had a neck, flat amphibian-like skull

archaeropteryx

proof that birds evolved from dinosaurs, although not a direct link to birds

skeletal features of reptiles (archaeopteryx)

teeth, long vertebrate tail, three claws on wings

features similar to birds in archaeopteryx

opposable hallux (big toe) and feathers

who did whales evolve from

land walking mammals

dating of fossils

relative dating and absolute dating

relative dating

comparing fossils/layers to other fossils and the layer they were found to determine when they lived; problem is that it doesn’t give an exact time that the organism lived

characteristics of an index fossil

1: easily identified

2: lived for a short amount of time

3: wide geographic range

good example of index fossils

trilobites

absolute dating

determined by radiometric dating or radioactive dating, uses radioactive isotopes and their known half-lives

half-life

amount of time required for half of the radioactive isotopes in a sample to decay (1/2, 1/4, 1/8, 1/16)

carbon 14

half-life is 5730, decays into nitrogen, only good for samples up to 60,000 yrs old, used on actual fossils, living organisms contain carbon

potassium & uranium

used to date the layers of rock that fossils are found in

geological time scale

timeline of earth; based upon rock layers and the fossil record

precambrian time

4.6 bya

Paleozoic era

“ancient life” 542 mya

mesozoic era

“middle life” 251 mya

Cenozoic era

“recent life” 65 mya

4 things must have occurred for life to come from chemical reactions

-formation of monomers

-polymerization

-formation of membranes

-heredity/reproduction

from various chemical combinations and energy sources we have formed

all 20 biological amino acids and others, several simple sugars, several basic lipids, all 5 nucleotides , even ATP

micelles and proteinoid microspheres similar to cell membrane

selectively permeable, can store and release energy, and they can grow and divide

formation of Earth

takes about 100 million yrs to form, objects collided together to from earth, collisions melted the earth and the elements arranged themselves by density

most dense elements

formed the core where radioactivity keeps the core melted (inner core and mantle)

medium density elements

formed the earth’s outer layer, the crust of the earth ( 3 to 7 miles wide)

least dense elements

formed the first atmosphere (hydrogen, carbon, nitrogen, and oxygen)

early atmosphere contained little

Oxygen

oxygen accumulated over time by

photosynthetic organisms

Abiotic origin of life hypothesis

life originated from non-living chemical reactions; simple molecules could’ve formed in a “primordial soup” of element/ compounds found on the early earth

4 things must’ve occurred (for AOLH)

-formation of monomers -polymerization -formation of membranes -heredity/ reproduction

Urey and Miller’s simulation of the early environment

created similar conditions that they believed mirrored the early atmosphere, tested to see if they could form basic molecules, wound up forming all 20 biological amino acids and others, several simple sugars, several basic lipids, all 5 nucleotides, and even ATP

polymerization

dehydration synthesis of monomers, has been shown to occur in non-living ways, heat on clay or rock, electrical currents, and UV rays have been shown to cause polymerization

micelles

simple phospholipids spontaneously from micelles, bubbles that separate hydrophobic interior from outer aqueous environment

proteinoid microspheres

collections of phospholipids and proteins self assemble into “proteinoid microspheres” which are membrane-like structures

3 living characteristics of living membranes

1: selectively permeable (some things can pass while others are excluded) 2: can store and release energy (forms a membrane potential) 3: can grow and divide (will accumulate more material and, once large enough, divide in two)

RNA prob originated first

-has some enzymatic abilities, ribosomes -has been observed growing in length and reproducing itself outside of living cells -forms proteins -has hereditary capabilities as seen in some viruses

first prokaryotic cells

most likely anaerobic as there was little oxygen around, most likely chemosynthetic using inorganic molecules

origin of eukaryotic cells

endosymbiotic hypothesis, mitochondria came from aerobic bacteria, chloroplasts came from photosynthetic bacteria

origin of multicellular organisms

soft bodied multicellular animals show up at the of precambrian (not many fossils because they don’t really have any hard parts)

origin of sexual reproduction

sexually reproducing are different with every birth, increase in diversity gave natural selection something to work with, natural selection acts on natural variation which is caused by genetic variation, speeds up the pace of evolution

Paleozoic era

Cambrian, ordovician, silurian, Devonian, Carboniferous, and permian periods