Origins of Life on Earth

• Evidence shows Earth is 4.6 billion years old. Earth cooled and solidified 4.2 billion years

ago. The oldest fossils indicating life are 3.5 billion

years old. These are stromatolites, rocks created by

prokaryotes binding layers of sediment together

Oldest Fossils

Dating Fossils1.radiometric dating - measures the decay of a

radioactive element in the fossil2.other methods - # of tree rings, amino acid

racemization

Radiometric Dating14C - decay of C14 to N14 over time.half-life of 5730 yearsevery 5730 years, 1/2 of the remaining amount is

converted to 14N.

235U - measures decay of Uranium-235 to Lead-207 (207Pb)

half-life (t1/2) for U-235 is 713 million years.

A sample of bone is found to contain 25% of its original 14C. How old is it?

Originally 100%-->50%-->25% t1/2 t1/2Thus, 2 half-lives x 5730 = 11460 years old

Primary Abiogenesis 1st life arose from non-living materialsformed spontaneously from 1st organic molecules (containing carbon) in 1950’s Miller-Urey’s experiment reproducing early Earth conditions resulted in formation of simple organic molecules100 Greatest Discoveries: Orig

in of Life : Video : Science Channel

How Did Life Begin?

• a four-stage process proposed:1.Small organic molecules, like amino acids,

form from simple molecules2.the simple organic molecules join together

into larger ones, like proteins and nucleic acids

3.Molecules could copy themselves and provide the basis for reproduction and inheritance.

4.These molecules are enveloped in membranes to form the first pre-cells.

Where Did Life Begin?3 hypothesis:

1. Ocean Surface shallow tidal pools or moist clay harsh atmosphere makes this

difficult

2. Deep Sea Vents heated inorganic molecules mixing

with water can find archaebacteria still living in

these vents

3. Panspermialife didn’t begin on earth but arrived on

meteors and comets from space‘seeded’ life on earthMurchison Meteorite crashed into Australia in

1969scientists found it contained amino acids,

including some not found on earthalso contained sugars

Eukarya DevelopmentEndosymbiosis prokaryotic cell membrane ‘folded in’ resulting

in organelles ancestral prokaryotes developed symbiotic

relationships with each other insideeventually formed eukaryotic cellsmitochondria and chloroplasts have own DNA

Sexual Reproduction & Meiosisallowed for more genetic diversityonce variation in alleles, natural selection

could occurchange could occur rapidly, resulting in

multicellular organismsex adaptive radiation

Geologic Time Scale & Erasdivide Earth’s history into blocks called erasend of each era marked with period of major

changePrecambrian: 4.6 billion – 542 mya

Paleozoic Era542 – 251 mya

Mesozoic Era261 – 65.5 mya

Cenozoic Era65.5 mya – modern day

Mass Extinctionsmost eras ended as a result of mass extinctionleft a niche for new organisms to evolve to fill

those nichesadaptive radiation5-6 major mass extinctions in Earth’s history