Major Ice Age Periods• Fluctuating cool periods on Earth which lasted for

millions of years

2100-2400MM years ago “Huronian”

800-600MM years ago “Snowball Earth”

460-430MM “Andrean-Saharan”

350-250MM “Karoo Ice Age”

2.58MM “Pliocene-Quaternary Ice Age”

• Most caused primarily by plate tectonics and also albedo effect and decrease of greenhouse gases like CO2 & methane.

Plate Tectonics

Major Ice Ages Contain Many Glacial Advances

• We are still in the Pliocene-quaternary major ice age which began about 2.58 MM years ago.

• All the major ice ages contain many glacial advances called glaciations and glacial retreats called interglaciations.

• Glaciations every 40-100 M years

Glaciations

• 51 glaciations in last 2.58MM years.

• Last glaciation peaked 20M years ago

• We are now in a warming period called interglaciation.

Some Affecters of Glaciations

• Changes in Earth’s axis tilt.

• Eccentricity of Earth’s orbit

• Precession of vernal equinox

• Albedo and “greenhouse” gasses

• Variations in solar output

• Meteorites and volcanism Glaciations (periodic iceages)

Here’s a history of global climate change studies

Earth’s Seasons

• Earth’s axis tilt causes our seasons.

• Equinox occurs twice yearly. Marking the beginning of Spring and Autumn.

Precession of Equinox

• Because of the moon and Sun’s gravitational force on our equator the polar axis precesses 25,800 years per cycle.

• Vernal equinox is currently on 20 March.

• At dawn during vernal equinox the sun passes through a constellation, soon to be Aquarius.

Earth Axis Tilt

• Fluctuates between 21.6 to 24.5 degrees every 41M years.

• Higher angles provide less radiation on the northern hemisphere.

• We are currently at 23.4 degrees.

How Is Mean Global Temperature Measured?

• By comparing historical temperatures throughout N. Hemisphere. Problems with this include:

– Regional and historical differences in measurement methodology. Recent standardization of methods has helped but still getting an average is a daunting task.

• Using dendrothermology

– Tree rings thickness is affected by temperature and other things so giving another controversial measurement for mean temperature throughout N. Hemisphere.

• Some scientists agree the mean has risen 0.5 oC since 1980! Man made CO2 is a possible cause.

12M B.P.

• Interglaciation was well under way.

• Hunters and gatherers congregated for ritual and feasting.

• The fertile crescent is where the first farming and irrigation happened.

Gobekli Tepe

River Valley Communities

• N. India, Central American, Syria, Egypt and Peru.

• The Nile in Egypt was best suited for development of a unified community.

– The Nile was most rich in decayed vegetable matter and Potash leaving its flood plane fertilized annually.

Annual Flood & Calendar

• Annually in mid July the rivers would flood their banks bringing water, silt, compost and fertilizer to the region.

• Agricultural planning evolved around the flood and triggered the calendar.

6000 B.P.

• First evidence of irrigation methods in the Nile.

• As the population grew, haphazard methods of irrigation gave way to the scratch plow sometime around 6000-5000 B.P

Arguably the most fundamental invention in history of mankind and triggered modern civilization.

The Scratch Plow

• A tool of surplus

• Permitted specialized skills to thrive within a community. The surplus paid for:

• Potters, craftsmen, carpenters, weavers, bakers, musicians, leather-workers, metal workers and scribes.

Metal Tools

• 5000 BP Copper deposits in Sinai made first metal tools.

• 4200 BP Bronze, a natural copper alloy (mixture) was smelted and hammered for hardening.

Egyptian bronze was 90% Copper with Arsenic & Zinc

A Trigger of Change

Writing was invented to identify ownership

Taxes

Mathematics

Astronomy and a Calendar

Architecture

Engineering

Militia and weapons

Science & Technology

• Science is a work in progress to explain the world around us.

• Technology sometimes referred to as applied sciences. Improves our lives.

• Science begets technology and visa-versa.

Science/Technology cont.

• Science and technology work together synergistically.

• Science Technology• Electromagnetic induction electrical generator

• The pendulum pendulum clock

• Thermodynamics steam engines

Humans Before Farming

• Paleopathologists reveal average height of late Ice man (10M B.P.) was 5’9” and 5’5” for women.

• Average life expectancy was about 26 years.

Humans After Farming• 5000 B.P. the avg. man was 5’3”, about 6” shorter!

• 2x increase in tooth enamel defects, 4x iron-deficiency, 3x increase in bone lesions from infectious disease.

• Average life expectancy was only 19 years!

• Farming also brought deep class divisions.

The Plow

• Ancient scratch plow 6000 B.P.

– Plowshare

• Modern plow, ca. 1400 B.P.

– Coulter, plowshare, landside, moldboard, slip heel.

The Plow (600 AD)

Electromagnet

• Conductive wire wrapped around iron core.

• Adding current to the wire produces a magnetic field.

• Used in relay switches.

Electromagnetic Relay Switch

An electromagnetic relay is made using a moving armature like this one or with a spinning cup.

Both varieties switch circuits when current or magnetism gets great enough.

Questions

• Describe the operation of the electromagnet and the relay.

• What were the triggers for the development of the calendar.

• Explain the last glacial retreat’s effect on human civilization.

• Why do organizations become more complex

• Sides 22-23

• #11

• # 9-10

• Man #25-26

Questions

• Explain how writing, civil engineering, mathematics, metallurgy, etc. were triggered by farming & the scratch plow.

• What caused the major cooling periods? When did the last ice age begin? When did it end?

• What causes glaciations? When was the last one?

• #13-16

• #1 & 3

• #4-8

Questions• How is irrigation and the

plow connected to civil engineering, mathematics, metallurgy and writing?

• What sacrifices were endured in the beginning of modern agriculture?

• Why according to Jared Diamond are germs important to European takeover of native Americans? Why were European germs more potent than native germs?

• #13-15

• #18-19

• Yellow Book pages 104-111