This document discusses ice ages and their causes. It begins by defining an ice age as a long period where the Earth's surface cools and large ice sheets form. Evidence for ice ages includes geological features from glaciation as well as chemical and paleontological records. There have been at least five major ice ages in Earth's history. Causes of ice ages include changes in the atmosphere, positions of continents, ocean currents, uplift of the Tibetan Plateau, and volcanic activity. Variations in Earth's orbit also influence ice ages through their impact on solar radiation received.

1. ICE
AGES
By Aryan Goswami
Bsc geoinformatics

2. INTRODUCTION
An ice age is a long period of reduction in the
temperature of the Earth's surface and atmosphere,
resulting in the presence or expansion of continental
and polar ice sheets and alpine glaciers. Earth's climate
alternates between ice ages and greenhouse periods,
during which there are no glaciers on the planet. Earth is
currently in the Quaternary glaciation. Individual pulses
of cold climate within an ice age are termed glacial
periods (or, alternatively, glacial, glaciations, glacial
stages, stadial, stades, or colloquially, ice ages), and
intermittent warm periods within an ice age are
called interglacial or interstadials.

3. EVIDENCE
There are three main types of evidence for ice ages
• GEOLOGICAL
• CHEMICAL
• PALEONTOLOGICAL

4. GEOLOGICAL
• Geological evidence for ice ages comes in various forms,
including rock scouring and scratching, glacial
moraines, drumlins, valley cutting, and the deposition of till or
tillites and glacial erratic. Successive glaciations tend to distort
and erase the geological evidence for earlier glaciations,
making it difficult to interpret. Furthermore, this evidence was
difficult to date exactly; early theories assumed that the glacial
were short compared to the long interglacial. The advent of
sediment and ice cores revealed the true situation: glacial are
long, interglacial short. It took some time for the current theory
to be worked out.

5. CHEMICAL
• The chemical evidence mainly consists of variations in the ratios
of isotopes in fossils present in sediments and sedimentary rocks
and ocean sediment cores. For the most recent glacial periods ice
cores provide climate proxies from their ice, and atmospheric
samples from included bubbles of their ice, and atmospheric
samples from included bubbles of air. Because water containing
heavier isotopes has a higher heat of evaporation, its proportion
decreases with colder conditions. This allows a temperature
record to be constructed. However, this evidence can be
confounded by other factors recorded by isotope ratios.

6. PALEONTOLOGICAL
• The paleontological evidence consists of changes in the
geographical distribution of fossils. During a glacial period cold
adapted organisms spread into lower latitudes, and organisms
that prefer warmer conditions become extinct or are squeezed
into lower latitudes. This evidence is also difficult to interpret
because lower latitudes. This evidence is also difficult to interpret
because it requires sequences of sediments covering a long
period of time, over a wide range of latitudes and which are easily
correlated; ancient organisms which survive for several million
years without change and whose temperature preferences are
easily diagnosed; and the finding of the relevant fossils.

7. MAJOR ICE AGES
• There have been at least five major ice ages in the Earth's
history (the Huronian, Cryogenian, Andean-Saharan, late
Paleozoic, and the latest Quaternary Ice Age). Outside
these ages, the Earth seems to have been ice free even in
high latitudes; such periods are known as greenhouse
periods.
• The first three ice ages are still rather poorly known, but
the rock records of the last two, and the last in particular,
are quite good.

8. THE PALEOZOIC ICE AGE
• Evidences of glaciation during at least some part of the
Paleozoic Era are found on all the continents of the
Southern Hemisphere. In Africa, for example Gouges are
found on rocks of Ordovician age in the Sahara Desert
(near the present equator). These Gouges are made by the
erosional action of pebbles and rocks dragged along the
bottom of the glacier. Definite ice-deposited rocks of a
somewhat later age are found all the way to the southern
tip of Africa.

9. THE LATE CENOZOIC ICE AGE
• The Ice Age we know best is the most recent. It appears
to have begun with the formation of an ice cap in
Antarctica about 20 million years ago, or in the early
part of the Miocene time division of the Cenozoic Era.
The evidence for this is the presence of rock fragments
of this age found in cores of sediment raised from the
Southern Ocean. The only explanation for these
fragments so far from land is their transportation by
icebergs that broke from a large, parent ice sheet in
Antarctica.

10. MAJOR CAUSES OF ICE AGES
• CHANGES IN EARTH’S ATMOSPHERE
• POSITION OF THE CONTINENTS
• FLUCTUATIONS IN OCEAN CURRENTS
• UPLIFT OF THE TIBETAN PLATEAU
• VARIATIONS IN EARTH’S ORBIT
• VOLCANISM

11. CHANGES IN EARTH’S
ATMOSPHERE
• There is evidence that greenhouse gas levels fell at the start of ice
ages and rose during the retreat of the ice sheets, but it is difficult
to establish cause and effect (see the notes above on the role of
weathering). Greenhouse gas levels may also have been affected
by other factors which have been proposed as causes of ice ages,
such as the movement of continents and volcanism.
• The Snowball Earth hypothesis maintains that the severe freezing
in the late Proterozoic was ended by an increase in CO2 levels in
the atmosphere, mainly from volcanoes, and some supporters of
Snowball Earth argue that it was caused in the first place by a
reduction in atmospheric CO2. The hypothesis also warns of
future Snowball Earths.

12. POSITION OF THE
CONTINENTS
The geological record appears to show that ice ages start when the
continents are in positions which block or reduce the flow of warm water
from the equator to the poles and thus allow ice sheets to form. The ice
sheets increase Earth's reflectivity and thus reduce the absorption of solar
radiation. With less radiation absorbed the atmosphere cools; the cooling
allows the ice sheets to grow, which further increases reflectivity in
a positive feedback loop. The ice age continues until the reduction in
weathering causes an increase in the greenhouse effect.
There are three main contributors from the layout of the continents that
obstruct the movement of warm water to the poles:
• A continent sits on top of a pole, as Antarctica does today.
• A polar sea is almost land-locked, as the Arctic Ocean is today.
• A supercontinent covers most of the equator, as Rodinia did during
the Cryogenian period.

13. FLUCTUATION IN OCEAN
CURRENTS
• Another important contribution to ancient climate regimes is the
variation of ocean currents, which are modified by continent
position, sea levels and salinity, as well as other factors. They
can cool (e.g., aiding the creation of Antarctic ice) and the ability
to warm (e.g., giving the British Isles a temperate as opposed to a
boreal climate). The closing of the Isthmus of Panama about 3
million years ago may have ushered in the present period of
strong glaciation over North America by ending the exchange of
water between the tropical Atlantic and Pacific Oceans.

14. VOLCANISM
• Volcanic eruptions may have contributed to the inception and/or
the end of ice age periods. At times during the paleoclimate,
carbon dioxide levels were two or three times greater than today.
Volcanoes and movements in continental plates contributed to
high amounts of CO2 in the atmosphere. Carbon dioxide from
volcanoes probably contributed to periods with highest overall
temperatures. One suggested explanation of the Paleocene-
Eocene Thermal Maximum is that undersea volcanoes
released methane from clathrates and thus caused a large and
rapid increase in the greenhouse effect. There appears to be no
geological evidence for such eruptions at the right time, but this
does not prove they did not happen.

15. REFERENCES
• Wikipedia.com
• History.com
• Geology.utah.gov
• Cdm.org

16. THANK YOU