CHAPTER 25

The History of Life on EarthBy:

Brian Vieyra

Vocab• Aboitic Synthesis-the preparation of a compound, often of biological relevance, without the use of

biological agents such as enzymes or nucleic acid• Protobionts- an aggregate of abiotically produced organic molecules, that has been demonstrated

to be formed by self assembly.

• Ribozyme-a molecule of RNA that acts as an enzyme, used in genetic research and gene therapy

• Stromatolite-A widely distributed sedimentary structure consisting of laminated carbonate or silicate rocks, produced over geologic time by the trapping, binding, or precipitating of sediment by groups of microorganisms, primarily cyanobacteria.

• Cambrian Explosion-The rapid diversification of multicellular animal life around the beginning of the Cambrian Period, resulting in the appearance of almost all modern animal phyla.

• Pangea-A hypothetical supercontinent that included all the landmasses of the earth before the Triassic Period. Pangaea broke apart during the Triassic and Jurassic Periods, separating into Laurasia and Gondwanaland.

• Adaptive radiation-Diversification of a species or single ancestral type into several forms that are each adaptively specialized to a specific environmental niche.

How might have life started on earth spontaneously?

• Conditions on earth allowed simple cells to live• 1)The abiotic (non-living) synthesis of small organic molecules (ex. Amino

acids)• 2)Joining of these small molecules into Macromolecules. (ex. Proteins) • 3)Packaging of molecules into “protobionts”, droplets w/ membranes that

maintained an internal chemistry diff that of surroundings• 4)The origin of self replicating-molecules that eventually made inheritance

possible.

How are the ages of fossils determined?

• There is a fossil record that is primarily based on the sequence in which fossils have accumulated in sedimentary rock layers called strata.

• The fossil record shows that there have been great changes in the kinds of organisms that dominated life on Earth at diff points in time.

• One of the most common techniques is Radiometric Dating.• Radiometric Dating is based on the Half-Life of isotopes.• Half-Life is the amount of time it takes for 50% of a sample of an isotope

to decay.

Major Mass Extinctions• Cretaceous extinction

-65 MillionYearsAgo-Probably caused by a several mile wide astroid-50% of marine life elimintaed -Many terrestrial plants and animals, including most of dinosaurs

• Permian extinction-251 MYA-Several enourmous volcanos errupted-an area of 1.2 million k^2 covered with a layer of lava several hundreds to thousends meters thick.-Oxygen deficit may have been major cause of marine life

• End Triassic extinction-199-214 MYA-Most likely caused by massive floods of lava-Led to deadly global warming

• Late Devonian extinction-364 MYA-Cause unknown

• Ordovician-Silurian extinction-439 MYA-Dropping sea lvls as glaciers formed, followed by rise of sea lvls by melting of glaciers