SCIN100 — Chapter 12

In the early history of the earth, the solid surface of the earth weathered more rapidly than now because ________.
the early rain was very acidic
Why is the molten metallic outer core and the magnetic field important to life on Earth?
If we did not have the molten core and the magnetic field, we would be bombarded by cosmic rays that would strip away our atmosphere.
The ________ era is known as the “age of flowering plants.”
The age of Earth is about ________.
4.6 billion years
Which of the following gases was NOT part of Earth’s original atmosphere?
Early Earth was hot because ________.
a combination of collisions and radioactive decay produced heat
The earth formed approximately ________ years ago.
The beginning of the Phanerozoic is marked by the ________.
development of hard body parts, such as shells and bones
During the ________ era, the westward-moving North American plate began to override the Pacific plate, eventually causing the tectonic activity that ultimately formed the mountains of western North America.
Which one of the following represents the greatest expanse of geological time?
During the early Paleozoic era, South America, Africa, Australia, Antarctica, India, and perhaps China comprised the vast southern continent of ________.
The ________ period was a time of major extinctions, including 75 percent of amphibian families.
Describe the conditions on Earth during the Hadean.
The crust would have been largely ultramafic magma and rock (which may have been
subject to remelting). The atmosphere lacked free oxygen and would have been dominated
by volcanically emitted gases (water vapor, nitrogen, and carbon dioxide). For at least part
of the Hadean, temperatures were likely too hot to sustain a liquid ocean.
Which of the following is not a scientific hypothesis for how life began?
Outgassing and related volcanic materials brought proto amino acids to the surface of the earth.
One group of reptiles, exemplified by the fossil Archaeopteryx, led to the evolution of ________.
Earth’s primitive atmosphere evolved from gases ________.
expelled from within the earth
Zircons found in continental rocks give evidence that continental crust was forming as long ago as ________.
4.4 billion years ago
Earth’s core, mantle, and crust formed during the ________.
One important reason we do not know much about the geologic history of the Precambrian is that ________.
there are very few fossils preserved in Precambrian rocks
Mammals became the dominant land animals during the ________ era.
Which type of bacteria thrive in environments that lack free oxygen?
Describe at least 2 possible scientific hypotheses on the origin of life on Earth.
Darwin – He suggested that the original spark of life may have begun in a “warm little pond, with all sorts of ammonia and phosphoric salts, lights, heat, electricity, etc. A protein compound was then chemically formed ready to undergo still more complex changes”. He went on to explain that “at the present day such matter would be instantly devoured or absorbed, which would not have been the case before living creatures were formed”.

Oparin – No real progress was made until 1924 when Alexander Oparin reasoned that atmospheric oxygen prevented the synthesis of the organic molecules. Organic molecules are the necessary building blocks for the evolution of life. In his The Origin of Life,Oparin argued that a “primeval soup” of organic molecules could be created in an oxygen-less atmosphere through the action of sunlight. These would combine in ever-more complex fashions until they formed droplets. These droplets would “grow” by fusion with other droplets, and “reproduce” through fission into daughter droplets, and so have a primitive metabolism in which those factors which promote “cell integrity” survive, those that do not become extinct. Many modern theories of the origin of life still take Oparin’s ideas as a starting point.

Haldane – Around the same time J.B.S. Haldane also suggested that the Earth’s pre-biotic oceans, which were very different from what oceans are now, would have formed a “hot dilute soup”. In this soup, organic compounds, the building blocks of life, could have formed. This idea was called biopoiesis, the process of living matter evolving from self-replicating but nonliving molecules.

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