Origins of Life and Precambrian Explosion

Cambrian Explosion

1% of Earth's history, but relatively rapid appearance of many large and complex animals. One of the great events in the history of current life!!

Which of the following is a problem for reconstructing the tree of life from living organisms?

1)Finding a homologous gene. 2)Finding a gene under strong stabilizing selection. 3)Finding a gene that has the same function across all species. 4)Running an analysis with that many taxa. 5)All of the above (CORRECT)

Which of the following is a crucial piece of information missing so far from the evidence supporting the RNA world hypothesis?

1)Genetic variation in RNA. 2)Evidence that RNA can work with DNA. 3)Evidence that RNA can self replicate. (CORRECT) 4)Evidence that RNA can do several different functions of a living organism.

Which of the following is true about the geological time scale?

1)Intervals are based on a suite of diagnostic fossils. (CORRECT) 2)We know the more about the mesozoic era than the cenozoic. 3)It is a hierarchy divided into equal time scales. 4)All of the above are true.

Which of the following is true about protostomes and deuterostomes?

1)Protostomes are bilaterally symmetrical and deuterostomes are radially symmetrical. 2)Only protostomes are diploblastic. 3)Humans are protostomes. 4)Only protostomes are found in the burgess shale. 5)None of the above are true. (CORRECT)

Which of the following is now considered to be true about "living" fossils??

1)They often lack genetic variation, which is necessary for evolutionary change. 2)They really have changed, but as they often change back, over time it looks like stasis. (CORRECT) 3)They are very simple organisms that had very few morphological traits to change in the first place. 4)They haven't had sufficient time to change. ***Genetic variation present even if morphological variation is not

Why was the discovery of enzymes made of RNA so exciting that the scientists who discovered them won the Nobel Prize??

1)They solved the problem of which evolved first, DNA or proteins (CORRECT) 2)They proved that life could not have evolved on earth. 3)They solved the problem of how to define living things. 4)They demonstrated that any molecule can act as an enzyme. **The Ribozyme from Tetrahymena thermophilia

Which of the following is the best definition of a fossil??

1. Any trace left by an organism that lived in the past. (CORRECT) 2. The unaltered remains of an organism 3. Molds left in rock of a living organism. 4. When a living organism becomes mineralized.

Deep evolutionary history a web

A universal phylogeny based on concatenated sequences of 31 universal genes, most ribosomal proteins (2006).

Which of the following is a characteristic found in the organisms that were common of Cambrian fauna but NOT common in the Precambrian fauna?

A)Radial body plans. B)Hard shells. C)Mostly left trace fossils. D)Bilateral symmetry. E)Both b and d (CORRECT)

Macroevolutionary Patterns

Adaptive Radiations Triggered by many different factors (i.e. colonization of new habitats, evolution of novel morphologies)

Burgess Shale Fauna cont.

Diploblasts and triploblasts --Cnidaria and Ctenohora have two embryonic tissues, radially symmetrical body plan (or asymmetrical) --Remaining animals have three embryonic tissues, one plane of symmetry (bilaterally symmetric - Bilaterians) Protostomes and deuterostomes --Differences in gastrulation within the Bilaterians (mouth first or second) --Both occur in Burgess Shale Lophotrochozoans and ecdysozoans --Ecdysozonas are molting Protosomes, while the lophotrochozoans have a lophophore

The Burgess Shale Fauna

Discovered in 1900s in Field, BC Also, Chengjiang Biota, Yunnan province, China Little overlap with Ediacaran fauna Amazing diversity --all kinds of arthropods (i.e. trilobites) --Segmented worms --Chordates (including jawless vertebrates)

The Ediacaran ("eddy a ca rin") Fauna -end of Proterozoic

First specimens found in Ediacara Hills of south Australia Compressed and impression fossils No shells or hard parts Asymmetrical or radial bodies (many planes of symmetry) Doushantuo rock formation allowed some soft body information to be preserved (minerals replaced soft tissue) Kimberella- one of few bilaterally symmetrical, mollusc-like

Phylogeny of all living things

Five kingdom scheme is misleading Analysis of nucloetide sequences of small subunit rRNAs reveal three clades 1)Bacteria 2)Archaea 3)Eucarya **estimate of tree were not all the same

Cosmic Calendar

For the first 3.2 billion years, all life was unicellular. 560 million years ago, first animals appear. These same animals dominate for 20 million (jellyfish and sponges). And then.....543 million years ago, over a period of 40 million years most living phyla appeared.

Fossil Record

Fossil = any trace left by an organism that lived in the past How do we get fossils? --Compression and impression fossils --Permineralized fossils --Casts and molds --Unaltered remains

The cenancestor (sin ancestor) was not a single species, but a community

Gene swapping!! Latest possible date for root of tree - most definitive information comes from fossils Oldest fossils of single celled eukaryotes 1.85-2.1 billion years old

Was the Cambrian Explosion really an explosion??

Genetic differences in sequence, calibrated by comparing those groups with known fossil ages, concludes changes present long before Cambrian fossils show up. 1) Split of Bilatera estimated to be much earlier than Cambrian (900 Ma) 2) Another data set estimated chordates and echinoderms diverged 1000 Ma and protosomes and deuterostomes diverged 1200 Ma Deep Homologies - structures can arise by the modification of pre-existing genetic regulatory circuits.

What caused the explosion?

Note that the explosion occurred at the same time in geographically distant parts of the globe - suggests world wide change. Key to evolution of multicellularity and larger size during Proterozoic was increase in oxygen concentrations in seawater. Key to evolution of animals in Cambrian may have been --increase in atmospheric oxygen - making large size and rapid movement possible --Mass extinction of Ediacaran fauna - opportunity for small deuterosomes and protosomes to evolve.

Fossils

Oldest fossils are probaby eukaryoes 1.85-2.1 billion years old Fossil cynobacteria look a lot like extant relatives

What is life?

One definition: If it forms populations capable of evolving by natural selection, then it is alive. --The ability to store and transmit information (genotype) and the ability to express that information (phenotype) --How does one exclude a salt crystal or a computer virus?

RNA World Hypothesis

RNA World Hypothesis - catalytic RNA molecules were a transitional form between nonliving matter and the earliest cells.

Types

Radiation of bilateral symmetric animals driven by how the organisms made a living! Ediacaran - absorbed nutrients across a membrane, grazed on organic debris Burgess Shale - filter feeders, scavengers, predators and more!

Possibly find fossils of earliest life here? Driest, oldest desert on the planet

The Atacama in Chile. Less than 1 millimeter (0.04 inch) of rain a year! 50 times drier than Death Valley in California. Dry for 20-40 million years. Great place for fossils....like these human sized penguins.

Phanerozoic Eon (541 million years to present)

The Paleozoic "ancient life" era The Mesozoic "age of reptiles" era The Cenozoic "age of mammals" era

Early life forms- Fossils on the moon??

The first life on earth would have left traces in our planet's infant rocks. Early layers have since been squeezed and heated out of all recognition. Some researchers say we should look for evidence of the earliest life on earth in rocks on the moon.

Origin of Organelles

The last common ancestor was a bacteria - lacking nucleus and organelles. Evolution of Mitochondria and Chloroplasts --Have their own chromosomes (small circular DNA molecules similar to bacteria's) --Lynn Margulis's idea that they are simbionts has been supported by phylogenetic evidence.

RNA as an Early Life Form

Until 1982, RNA was just the relay molecule for DNA Evidence that RNA is ancient --Catalytic RNA --Basic currency for biological energy is ribonucleoside triphospates (ATP and GTP) --Therefore has a genotype (primary sequence of nucleotides) AND a phenotype (a catalyst)

Where did the first living cell come from??

We do not know much about the earth's environment during this time (first fossil is 3.7 billion years old) Panspermia Hypothesis - life did not necessarily originate here on earth (astrobiology) --Did microbes exist on other planets? --Could they survive a trip here? This hypothesis pushes problem elsewhere. Murchison meterorite (4.6 billion years old), landed in 1969, contained organic compounds. Most researchers still assume primordial form arose on Earth.

Fossil Record

What are the weaknesses of the fossil record? Sampling biases --Geographic --Taxonomic --Temporal

Antonio Lazcano

What we know: 1) CHONSP to monomers to Proteins to cells 2) Origin early (as soon as earth was habitable), microbial, unicellular 3) RNA world to DNA world What we don't know: 1) Environments 2) Chemistry 3) Pre-RNA world - can't study RNA world today What we don't know we don't know ( pull of the present - what we see today as a representative of the past) 1) environment of early earth quite different 2) biotic diversity winnowed over time (99.9% extinct) 3) biochemistry, metabolism - highly derived