General Biology 2: Geologic Time Scale (5th year, Grade 11 Senior High School)
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Biology
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This document contains lecture notes about Geologic Time Scale in the course General Biology 2. It includes information about different eons, eras, periods, and epochs, and its significant events. It has graphics and visuals to help you understand the topic.
GENERAL BIOLOGY 2 (Nery, 11E) - Water formation
Lesson 2: Geologic Time Scale - Bacteria microfossils called stromatolites
Stromatolites - layered sedimentary formations
● EON - ERA - PERIOD - EPOCH caused by formation of microbial mats
● Main event Cyanobacteria - possibly the earliest life forms
Proterozoic Eon
● The Earth is estimated to be 4.5 Billion years - 2.5 bya – 541 mya
old - Formation of the supercontinent Rodinia
● Scientists were able to estimate how old the - Atmosphere and oceans changed
Earth was through radiometric dating significantly
Radiometric dating - comparing the amount of - The great oxygenation event caused the
radioactive and nonradioactive isotopes to find out first ice age
rock age - Oldest fossil of eukaryotic cells
How a single-celled organism almost wiped out
Geologic Time Scale - record of life forms and life on Earth; The Great Oxygenation Event or
geological events in the history of Earth The Oxygen Catastrophe
- Scientists developed the time scale by Cyanobacteria - have no nuclei or other organelles
studying rock layers and fossils worldwide ● 3.5 billion years ago, the atmosphere was
mostly Nitrogen (N2), Carbon Dioxide
EON - ERA - PERIOD - EPOCH (CO2), and Methane (CH4).
Billions - Hundreds of millions - Tens of millions - ● Almost all oxygen was locked up in molecules
Millions of years like water, not floating around in the air.
● At the present we are in the holocene epoch ● The oceans were populated by anaerobic
of the quaternary microbes
period of Cenozoic era of the Phanerozoic Eon. Anaerobic microbes - unicellular life forms that
● “Anthropocene: Age thrive without oxygen and get energy by scavenging
of Man” what molecules they find.
The Precambrian Time ● Somewhere between 2.5 and 3.5 billion
- Started more than 550 million years ago years ago, one of these microbial species,
- Composed of Hadean, Archean, Protozoic probably floating on the surface of the ocean,
Eon evolved a new ability: photosynthesis.
- Comprise almost 88% of the Earth’s life ● Structures in their cell membrane could
history harness the energy from sunlight to turn
- Time before there were diverse organism on carbon dioxide and water into oxygen gas
earth and sugars, which they could use for
- The earliest life comprising Precambrian energy.
(Ediacaran) biota was long believed to ● Those organisms were the ancestors of what
include only tiny, sessile, soft-bodied we now call cyanobacteria. Their bluish
creatures. color comes from blue-green pigments that
● Sessile - stationary capture the sunlight they need.
Hadean Eon ● Photosynthesis gave them a huge advantage
- 4-6 – 4.0 bya over other species. They can now produce
- Earth forms their own energy from an almost endless
- From the word Hades - “God of the supply of raw ingredients so their populations
Underworld” exploded and they started polluting the
- Hellish conditions and cosmic collisions atmosphere with a new waste product:
Archean Eon oxygen.
- 4.0 – 2.5 bya ● The trickle of extra oxygen was soaked up by
- Oldest known rocks chemical reactions with iron or decomposing
- Cooling of the Earth cells, but after a few hundred million years,
, the cyanobacteria were producing oxygen 2. Charnia
faster than it could be absorbed, and the gas
started building up in the atmosphere.
● Oxygen-rich air was toxic for the rest of
Earth’s inhabitants.
Result: About 2.5 billion years ago was a mass
extinction of virtually all life on Earth which barely
spared the cyanobacteria.
● Methane had been acting as a potent
greenhouse gas that kept the Earth warm, but
now, the extra oxygen reacted with methane
to form carbon dioxide and water which don’t
trap as much heat. The thinner atmospheric 3. Cyclomedusa
blanket caused Earth’s first, and possibly
longest ice age, the Huronian Glaciation
(2.4 to 2.1 billion years ago).
Eventually, life adjusted. Aerobic organisms, which
can use oxygen for energy, started sopping up some
of the excess gas in the atmosphere. The oxygen
concentration rose and fell until eventually, it reached
the approximate 21% we have today.
Being able to use the chemical energy in oxygen
gave organisms the boost they needed to diversify.
● Hundreds of millions of years ago, some
other prehistoric microbe swallowed a Recent discovery:
cyanobacterium whole in a process called Coronacollina acula - Sessile
endosymbiosis. - South Australia
● The microbe acquired its own internal
photosynthesis factory. This was the
ancestor of plant cells.
● Cyanobacteria became chloroplasts, the
organelles that carry out photosynthesis
today.
Ediacaran Biota
1. Dickinsonia - same appearance as jellyfish
Phanerozoic Eon - “Visible Life”
Paleozoic Era - “Old Life”
- 541 – 252 million years ago
- Began with the breakup of the supercontinent
Rodinia into continents Gondwana and
Laurentia
- Sea levels were very high
- As the Paleozoic progressed, glaciations
created a global climate (first part), but
conditions warmed at the end of the first half
of the Paleozoic, the landmasses began
moving together (middle part).
- Pangaea was formed (latter third part of the
Paleozoic).
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