Many times in the geologic past, mass
extinction has been linked to drastic changes in climate. Global ice
ages for example are characterized as periods of extensive cooling and
advance of continental ice sheets and alpine glaciers. The last global
scale event happened during the late Pleistocene epoch.
Late Pleistocene Glaciation in Ohio
Evidence of Pleistocene Glaciation:
Moraine: poorly-sorted sediment deposited by a glacier. Note:
Deep lakes formed during this time left behind extensive beach deposits
and other forms of sediments. See Photos at the bottom of the page.
Grooves in Silurian Limestone on Kelley’s
Glacial sediments found in Ohio
How might an Ice Age begin?
- Plate Tectonics:
- Opening and closing of ocean
basins changes ocean circulation patterns.
- Mountain building and atmospheric
- Decreased Greenhouse gasses in the
- Short term changes due to changes in
Earth’s orbit reducing the amount of solar radiation at the surface
How do Scientists study Ice Age Climate?
All of these systems record extreme
changes in climate over Geologic Time.
- Marine Sediment cores - marine
skeletal remain containing carbonate minerals
- Lake sediment cores - trapped
- Tree Rings - thickness related to
amount of rain
- Ice Cores - O18/O16 of ice changes
during glacials - interglacial; bubbles contain CO2& Methane;
changes in dust and volcanic ash. See Below
Continental Ice Sheet and Valley
Glacier Ice Cores
Lighter O16 evaporates with
ocean water and accumulates in snow and ice. During times of glaciation,
ocean water becomes enriched in O18. Therefore, marine
organism will show a high O18/O16 ratio and the
ice sheet will have a lower ratio.
This process is temperature dependent
and therefore is used as a "paleothermometer"
Computer Models:Atmospheric Circulation
Computer Models Large with Grid Size
Our Local Climate Model better
Models tested using Geologic Evidence
for Past Large Lake Systems in the Great Basin, USA.