Exam 17: The Origins of Life and Precambrian Evolution

Important molecular discoveries in the 1980s have led researchers to hypothesize that the original,vital organic molecule shaping living things was not what was first thought.What molecule is currently supported as the candidate for the vital molecule for early life?

In attempting to construct a universal phylogeny,researchers analyzed several different gene sets.The results of this analysis are not congruent (see accompanying figure).The most likely explanation for this,as proposed by Carl Woese and others,is ________ [three words] in early populations,which would account for these discrepancies.

The gene that encodes small-subunit ribosomal RNA is useful for reconstructing the phylogeny of all organisms,because ________.

Fossil evidence suggests that the latest possible date for root of the universal phylogeny predates the ________ billion-year mark.

It is now thought that the last common ancestor of the three domains was not a single lineage.Rather,it was ________.

The explanation linking viruses to the origin of the three domains,which includes the conversion of cellular genomes from RNA to DNA,is known as the ________.

Analysis of the sequences of the small subunit rRNA generated a shift in our current taxonomic scheme,with the addition of three levels called domains.What are the three domains?

The authors of your textbook suggest that,"for genes shared among all organisms…Animals,Plants,and Fungi appear to possess less than 10% of the nucleotide-level diversity observed on Earth." Given the relatively recently generated phylogenies such as those in the accompanying figures,along with what you know about the history of life on this planet,does this seem like a reasonable statement? Explain.

Could a varying,self-replicating population of RNA molecules be considered alive?

The minimum age of the LUCA (last unique common ancestor)is the age of the oldest fossils that can be identified with certainty as close relatives of present-day prokaryotes and eukaryotes.Such fossils are about ________.

The earliest fossil records of bacteria-like organisms,dated at over 3 billion years,________.