History of Life Chapter 26

What you need to know! The age of the Earth and when prokaryotic and eukaryotic life emerged. Characteristics of the early planet and its atmosphere. How Miller and Urey tested the Oparin-Haldane hypothesis and what they learned. Methods used to date fossils and rocks. Evidence for endosymbiosis How continental drift can explain the current distribution of species.

Earth Earth was created 4.6 billion years ago (bya) Inhospitable conditions made life impossible

Earth 3.8 bya the Earth’s surface cooled enough for water to exist in liquid form It rained for millions of years The oceans were born Life emerges 3.8 bya – 3.7 bya

Theory for How Life Arose 1. Small organic molecules were synthesized. 2. These small molecules joined into macromolecules, such as proteins and nucleic acids. 3. All these molecules were packaged into protobionts whose internal chemistry differed from that of the external environment 4. Self-replicating molecules emerged that made inheritance possible.

Oparin & Haldane Hypothesized early atmosphere energized by lightning and UV radiation formed organic compounds (primitive soup) Miller & Urey modeled the hypothesis and successful created amino acids

Protobionts: First life-like Structures Lipid bubbles surround self-replicating RNA (the first genetic material) Ribozymes are RNA catalysts that replicate RNA Some of these bubbles had semipermeable membranes w/ rudimentary metabolisms (protobionts)

Key Events Prokaryotes are the earliest living organisms (3.8 bya – 3.7 bya) Oxygen begins to accumulate (evolution of photosynthesis) 2.7 bya Eukaryotes 2.1 bya (endosymbiotic hypothesis) Multicellular eukaryotes 1.2bya Colonization of Land.5 bya (evolution of plants, fungi, and animals)

Endosymbiotic Hypothesis Mitochondria and plastids (chloroplasts) were small prokaryotes that symbiotically evolved to survive within larger archaea bacteria Evidence: 1. Both organelles have enzymes and transport systems just like bacteria 2. Both replicate just like prokaryotes 3. Both contain a single, circular DNA w/ no histones 4. Both have independent ribosomes

Precambrian Time All of this time, from the beginning of the earth to the evolution of prokaryotes, eukaryotes, and multicellular organisms is called Precambrian Time Precambrian Time lasts from 4.6 bya to 544 mya (.544 bya) A mass extinction ends Precambrian Time (snowball Earth?)

Continental Drift Giant plates of rock floating on a sea of molten rock Alters habitats (promoting allopatric speciation) Accounts for biogeographical phenomenon (trilobites, marsupials) Causes Mass Extinctions Adaptive radiation on a global scale

Paleozoic 225mya – 544mya Cambrian (Cambrian Explosion) Ordovician Silurian Devonian Carboniferous Permian (Permian Extinction 95% of all life)

Paleozoic

Mesozoic Age of Reptiles, 65mya – 225mya Triassic Jurassic Cretaceous (mass extinction 50% of all life)

Mesozoic

Cenozoic Age of Mammals, Today – 65mya Tertiary Quaternary

Cenozoic

Relative Dating Comparison of fossil age to strata age (age of the layer of rock the fossil is found in) Index fossils existed for a short period of time over a wide geographic range Used to help date fossils found in the same strata

Radiometric Dating Analysis of radioactive isotopes in fossils Radioactive isotopes have distinctive half-lives Half-life (t 1/2 ) = time period when half the radioactive sample decays into other elements

Radiometric Dating Reasoning Living organisms take up small amounts of isotopes with food, air, and water Living organisms always have the same % of isotopes as present in the environment (0.1% of C14) When organisms die, they stop replenishing their isotopes Isotopes slowly degrade over time Measured using half-lives to determine how long ago the organism died

Example Carbon 14 degrades into Nitrogen 14 Half-Life = 5,600 years OrganismC14N14 Alive100%0% 5,600 years dead50%50% 11,200 years25%75% A fossil has 1/8 of the normal ratio of C14. Estimate the age of this fossil