Unformatted text preview: today’s factoid • ‘Strange Antarc3c Microbes’ in Biology in the News on BB • at Blood Falls, Antarc3ca, researchers recently discovered new microbial species living in a highly inhospitable water environment underneath the glacier • photosynthesis is not possible there – microbes likely use iron and sulfur chemoautotrophy (more on this in a future lecture) • has interes3ng implica3ons for both the history of life on Earth and the possibility of life on other hEp://photolibrary.usap.gov/Antarc3caLibrary/ planets BLOOD_FALLS.JPG st mid term exam 1 • • • • • • • • Wed. September 30th in class covers material through 9/23 lecture (ﬁrst 10 lectures) prac3ce ques3ons are posted; review sessions TBA Be on 3me – >10 min late will not be allowed into room Bring only your ID and pencils – All other materials have to be le] on periphery of the room 35 mul3ple choice ques3ons + 3 bonus factoid ques3ons lowest of the three mid terms is dropped, avg. of other 2 = 60% of your grade Only documented medical/family/accident excuses accepted; we need to be NOTIFIED before end of the day on the day of the exam Reading phylogene.c trees Reading phylogene.c trees The goal of phylogene3c systema3cs is to designate taxonomic groups at all levels as the monophyle3c groups in the tree of life PARAPHYLETIC GROUP ‐ contains an ancestor and only some, not all of its descendants POLYPHYLETIC GROUP ‐ does not contain the common ancestor MONOPHYLETIC GROUP ‐ contains a common ancestor and all of its descendants Is this a monophyle.c group? Bryophytes Ferns Fungi Insecta Amphibia Aves Mammalia Which (if any) of these trees are iden.cal? Amphibia Aves Mammalia A B Amphibia Aves Mammalia Amphibia Amphibia Aves Mammalia C Mammalia D Aves a phylogene3c tree is a hypothesis a ‘phylogene.c hypothesis’ • it is always open to revision if new data or methods of analysis become available also: avoid this common mistake: • in the tree on the le], B is not more closely related to A than C and D are • B, C, and D are equally closely related to A A B C D Using phylogene3c trees The Evolu.onary History of HIV Origin and Evolu.on of Life on Earth • • • • • • How fossils are dated History of Life on Earth: beginnings Chemical Evolu.on (pre‐bio.c) Origin of Life Biological Evolu.on Evolu.on of Ecosystems Most evidence of this history of life comes from the fossil record Fossil cicada from the lower Cretaceous (~130‐145 mya) How do we date fossil evidence? • • Rela3ve: fossils occur in sedimentary rocks – Older rocks occur below younger rocks Geologic forma3ons of various ages are recognized, and o]en named, by the fossils they contain – Can use this to match geologic layers from diﬀerent parts of the world Absolute: – Radioisotope da3ng • E.g. carbon for fossils < 50,000 years old • 14C/12C ra3o in all living organisms is roughly constant – But when organisms die, they stop geong 14C from the environment and 14C/12C ra3o decreases » Half‐life = 5700 years • How do we date fossil evidence? Isotopes of other elements are used for longer 3meframes – Requires igneous rocks nearby (embedded) in the sedimentary rocks » 40K/40Ar ra3o used for most events in ancient evolu3on of life » [half life =~1.25 billion yrs] – Or if no igneous rocks nearby » Paleomagne3c da3ng » ‐record of known reversals of Earth’s magne3c ﬁeld preserved in sedimentary and igneous rocks • Table 21.2 – Good summary of major eras, periods, and events in Earth’s history » DO NOT have to memorize Gradual change in the fossil record (in posterior) hEp://www.zoology.ubc.ca/~bio336/Bio336/Lectures/Lecture23/Trilobites.jpg Macroevolu3onary paEerns: Mass ex3nc3ons Permian‐Triassic ex3nc3on ~ 96% of all marine species ~70% of all land species Meteor impact in Yucatan ‐ ex3nc3on of dinosaurs Causes of mass ex3nc3ons • S3ll largely unknown • 65 mya Cretaceous‐Ter3ary – much debated currently – Meteor impact – But also major volcanic ac3vity in Asia/India • Sea level drops/rises o]en implicated • Atmospheric changes (see ﬁg 21.5 in book) • Climate change (see ﬁg 21.6 in book) – e.g. “Flood Basalt events” • Major volcanic episodes on land masses or ocean ﬂoors • Send large amounts of par3culates into atmosphere for extended periods • Can cause major ex3nc3ons of plants and collapses of food chains Con.nental DriQ Alfred Wegener (1880‐1930) no3ced con3nental shapes seemed to ﬁt together looked for geological and fossil evience did not know the mechanism “The Origin of Con3nents and Oceans” (1912) coined the name “Pangaea” for a proposed ancient supercon3nent Precambrian Cambrian we now know the mechanism • plate tectonics, worked out in the 1960s Gondwanan Flora and Fauna Pangaea A far more ancient supercon3nent: Rodinia • ~1 billion to ~800 million years ago • Land masses were concentrated in the tropics • Hypothesis: this led to “Snowball Earth” Snowball Earth hypothesis • During Cryogenian period • (850‐630 million years ago) • Con3nents concentrated in tropics – Absorbed less heat from sun than open ocean – More rainfall ‐>more erosion -”Anti-Greenhouse effect” • Erosion removes CO2 from atmosphere • e.g. CaSiO3 + 2CO2 + H2O → Ca2+ + SiO2 + 2HCO3- • Glaciers covered virtually the en3re Earth • Only marine microorganisms survived The end of snowball Earth • Volcanic ac3vity eventually melted the ice and broke up Rodinia • Ice retreated • This set the stage for evolu3on of new life forms – Complexity, mul3cellularity – Cambrian Explosion Jumping back to the beginning: 4 billion years ago: Earth started to cool, crust started to solidify (but s3ll many volcanoes). Atmosphere: Very liEle oxygen No ozone layer, lots of UV radia3on Life arose ‐ how? ...
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- Fall '08
- Photosynthesis, • • , Insecta Amphibia Aves Mammalia, Amphibia Aves Mammalia, Insecta Amphibia Aves, • Sea level, largely unknown •