Chapter 14: Life, Death, and Evolution (426-431) Flashcards
Define ‘Hadean Eon’.
The period in Earth’s history from the beginning at 4.56 billion years ago, to 3.8 billion years.
During the Hadean Eon there was no free oxygen in the atmosphere, a necessity for most forms of life on Earth today. It was too hot for water to exist as a liquid, and atmospheric pressure was much greater than it is today.
Define ‘Archean Eon’.
The period in Earth’s his tory from 3.8 to 2.5 billion years ago. Characterized by …
Define ‘Proterozoic Eon’.
The period in Earth’s history from 2.5 billion to 542 million years ago. Characterized by…
Define ‘Phanerozoic Eon’.
The period in Earth’s history from 542 million years ago to the present day. Characterized by…
Life originated as much as …?
3.9 billion years ago.
As the planet cooled, water vapor condensed, fell as rain, and collected as surface water. When did this happen?
Water condensed as early as 4.4 bil. years ago (Hadeon Eon).
What are the 3 steps that must have been accomplished on the way to the complex life forms we know today?
(1) chemosynthesis of small organic molecules from inorganic precursors
(2) biosynthesis, the polymerization of small organic molecules to form biopolymers, especially proteins
(3) the development of the complex chemical machinery needed for metabolism and replication.
How did life contribute to the chemical evolution of the Earth system?
Through the buildup of oxygen and sequestration of carbon (i.e. limestone).
Oxygenation happened over a very long time, but the onset of major oxygenation coincides roughly with the beginning of the ___ Eon.
Proterozoic Eon.
Once the ozone layer began to absorb harmful shortwave radiation, organisms would have been able to survive in shallow waters; this critical stage was reached around 600 million years ago, just before the onset of the ___ Eon.
Phanerozoic Eon.
The emerging biosphere had a profound impact on carbon cycling. What are some long-terms storage reservoirs for carbon?
Limestone and organic sediment provide long-term storage reservoirs for carbon, sequestering it from the atmosphere and hydrosphere.
The most ancient known fossils are ___ billion years old, found in rocks from the Archean Eon. Some early fossils are the remains of microscopic prokaryotes; others are stromatolites that precipitated as a result of bacteria influencing the chemistry of seawater.
3.55
The earliest life, which dominated Earth for about 2 billion years, was ___ and ___.
Prokaryotic and anaerobic.
The first photosynthetic prokaryotes were probably ___.
Cyanobacteria.
What is the Gaia hypothesis?
Proposes that life has altered the environment at a global scale throughout life’s history on Earth and continues to do so; that these alterations contribute to biogeochemical stability (homeostasis or steady state); and that these alterations benefit life by increasing the probability of the persistence of life.
