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GSC 102 Study Guide - Midterm Guide: Phanerozoic, Cenozoic, Mesozoic

Geological Sciences
Course Code
GSC 102
Study Guide

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GSC102: Exam #2 Review Sheet
Geologic Time Scale
1. Correct order of the Eras of the Phanerozoic Eon
Paleozoic, Mesozoic, Cenozoic (oldest to youngest)
2. Know which Eon, Era and Period each key event discussed below falls
Origin of Life
1. Function of DNA, RNA, and amino acids
RNA is important for a lot of different functions but I will only
talk about messenger RNA here, which is used to synthesize
protein from. RNA (Ribonucleic Acid) is synthesized in the
nucleus and is very similar to DNA. The synthesis of RNA also
involves the use of bases, but in RNA synthesis no thymine (T) is
used but uracil (U) is used instead. The synthesis of RNA from
DNA is called transcription (the DNA is transcribed into RNA).
The RNA strand starts with the only base that can form a base
pair with this T, the A. This continues until the complete
sequence of RNA is synthesized.
The translation of RNA to protein is different than the synthesis
of RNA from DNA (transcription). When the DNA was transcribed
into RNA, one base of DNA corresponded to one base of RNA, this
1 to 1 relation is not used in the translation to protein. During
this translation, 1 amino acid is added to the protein strand for
every 3 bases in the RNA. So a RNA sequence of 48 bases codes
for a protein strand of 16 amino acids. A certain combination of 3
bases always gives the same amino acids. These proteins are
essential in all living organisms, proteins are involved in DNA
synthesis, RNA synthesis, the immune response, cell structure
and for a lot more! So proteins are important for almost
everything in living organisms.
2. How life (amino acids) formed?
A) Miller-Urey experiment
The Miller-Urey experiment was an experiment that simulated
hypothetical conditions present on the early Earth in order to test what
kind of environment would be needed to allow life to begin. The
experiment is considered to be the classic experiment on the origin of
life. It was conducted in 1953 by Stanley L. Miller and Harold C. Urey at
the University of Chicago.
The experiment used water (H2O), methane (CH4), ammonia (NH3) and
hydrogen (H2) - materials which were believed to represent the major
components of the early Earth's atmosphere.

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B) Panspermia: the theory that life on the earth originated from
microorganisms or chemical precursors of life present in outer space and able
to initiate life on reaching a suitable environment.
i) Meteorites
a meteor that survives its passage through the earth's
atmosphere such that part of it strikes the ground. More than
90 percent of meteorites are of rock, while the remainder
consist wholly or partly of iron and nickel.
ii) Comet
a celestial object consisting of a nucleus of ice and dust and,
when near the sun, a “tail” of gas and dust particles pointing
away from the sun.
3. How genetic material formed?
A) DNA vs. RNA
DNA: A nucleic acid that contains the genetic instructions
used in the development and functioning of all modern living
organisms. DNA's genes are expressed, or manifested,
through the proteins that its nucleotides produce with the
help of RNA.
Funtion: The blueprint of biological guidelines that a living
organism must follow to exist and remain functional. Medium
of long-term, stable storage and transmission of genetic
Structure: Double-stranded. It has two nucleotide strands
which consist of its phosphate group, five-carbon sugar (the
stable 2-deoxyribose), and four nitrogen-containing
nucleobases: adenine, thymine, cytosine, and guanine.
Base pairing: Adenine links to thymine (A-T) and cytosine
links to guanine (C-G).
RNA: The information found in DNA determines which traits
are to be created, activated, or deactivated, while the various
forms of RNA do the work.
Function: Helps carry out DNA's blueprint guidelines.
Transfers genetic code needed for the creation of proteins
from the nucleus to the ribosome.
Structure: Single-stranded. Like DNA, RNA is composed of its
phosphate group, five-carbon sugar (the less stable ribose),
and 4 nitrogen-containing nucleobases: adenine, uracil (not
thymine), guanine, and cytosine.
Base pairing: Adenine links to uracil (A-U) and cytosine links
to guanine (C-G).
B) RNA world and evidence
C) Ancient Virus World

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The existence of several genes that are central to virus
replication and structure, are shared by a broad variety of
viruses but are missing from cellular genomes (virus
hallmark genes) suggests the model of an ancient virus world,
a flow of virus-specific genes that went uninterrupted from
the precellular stage of life's evolution to this day. This
concept is tightly linked to two key conjectures on evolution
of cells: existence of a complex, precellular,
compartmentalized but extensively mixing and recombining
pool of genes, and origin of the eukaryotic cell by archaeo-
bacterial fusion. The virus world concept and these models of
major transitions in the evolution of cells provide
complementary pieces of an emerging coherent picture of
life's history.
1. Proterozoic Atmosphere
A) Role of cyanobacteria
Cyanobacteria are aquatic and photosynthetic, that is, they live in
the water, and can manufacture their own food. Because they are
bacteria, they are quite small and usually unicellular, though
they often grow in colonies large enough to see. They have the
distinction of being the oldest known fossils, more than 3.5
billion years old
Many Proterozoic oil deposits are attributed to the activity of
cyanobacteria. They are also important providers of nitrogen
fertilizer in the cultivation of rice and beans. The cyanobacteria
have also been tremendously important in shaping the course of
evolution and ecological change throughout earth's history. The
oxygen atmosphere that we depend on was generated by
numerous cyanobacteria during the Archaean and Proterozoic
Eras. Before that time, the atmosphere had a very different
chemistry, unsuitable for life as we know it today.
The other great contribution of the cyanobacteria is the origin of
plants. The chloroplast with which plants make food for
themselves is actually a cyanobacterium living within the plant's
cells. Sometime in the late Proterozoic, or in the early Cambrian,
cyanobacteria began to take up residence within certain
eukaryote cells, making food for the eukaryote host in return for
a home. This event is known as endosymbiosis, and is also the
origin of the eukaryotic mitochondrion.
Because they are photosynthetic and aquatic, cyanobacteria are
often called "blue-green algae". This name is convenient for
talking about organisms in the water that make their own food,
but does not reflect any relationship between the cyanobacteria
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