GEOL 106 Lecture Notes - Lecture 42: Meteor Crater, James Ussher, James Hutton
26 May 2018
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UNIFORMITARIANISM, GRADUALISM, AND CATASTROPHISM
- idea that Earth could not be hit by large objects from space was not accepted for many hundreds of
years until 15th century when Galileo invented telescope
- young earth belief of Archbishop Ussher: forced to conclude that most of processes that formed our
planet were catastrophic in nature (catastrophism) → explained biblical events
- James Hutton 1785: concept of gradualism or uniformitarianism = present geological processes may
be studied to learn the history of the past (the present is key to the past)
o argued that Earth must be much older than 6000 to allow gradual processes of erosion,
depositio, uplift to for outai rages ad other features of Earth’s surfae
- Charles Lyell 1830: proclaimed that earth had long history that could be understood by studying
present day processes and rock record
- Charles Darwin: impressed with Lyell and applied ideas of ancient Earth and uniformitarianism to
biological evolution
- gradualism lasted into twentieth century and culminated with discover of plate tectonics
o theory of plate tectonics explains the present position and origin of continents based on
relatively slow processes of seafloor spreading and uplift and continental drift
- occasional evidence of catastrophic events
o large craters of surface resulting from asteroid impacts
o uer of relatiel rapid etitios durig earth’s histor i hih a large peretage of
species of plants and animals perished relatively suddenly
o 5 extinctions are in relatively distant geologic past; most recent mass extinction is ongoing
today as a result of human activity
- extinctions:
o 65 million years ago: at Cretaceous-Paleogene (K-Pg) boundary: impact of asteroid in Mexico
o Barringer Crater (meteor Crater) in Arizona was listed as a probably impact event probably
with airbursts in 1947
o led to punctuated uniformitarianism
- punctuated uniformitarianism: although uniformitarianism explains the long geologic process of
gradual mountain building, canyon erosion and landscape construction, periodic catastrophic events
can occur and can cause mass extinctions
14.3 Mass Extinctions
- mass extinction: sudden loss of large numbers of plants and animals relative to the number of new
species being added
o generally coincide with boundaries of geologic periods or epochs of time scale
o most involve relatively rapid climate changes → can be triggered by plate tectonics,
volcanic activity, extraterrestrial impact
- plate tectonics is slow process that moves position of continents and habitats to different locations
→ can create new patterns of ocean circulation which have major effect on climate
- extremely large volcanic eruptions can cause climate change
o large basaltic eruptions producing huge volumes of flood basalts can release large
quantities of CO2, greenhouse gas, into atmosphere and cause global warming
o large explosive volcanic eruptions of more silica-rich lava can inject tremendous
quantities of volcanic ash into upper atmosphere and cause global cooling
- climate change is one of several effects of extraterrestrial impacts or airbursts that can contribute to
extinctions
- ajor ass etitio eets durig past 0 illio ears of Earth’s histor
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