Fire and Earth-Creating Combustion

Parts of lecture adapted from Fire, Stephen J. Pyne (2001)

Lecture Objectives:

1). Understand when and how the 3 main components of the fire triangle emerged on Earth

2). Understand how fire came to be on early earth

3). Understand lightning and its role in fire

According to many myths, we became truly human only when we acquired

fire (Stephen Pyne, 2001)

Fire Triangle

Fuel

Oxygen Heat

Earth formed ~4.5 billion years ago

*Cyanobacteria, split water and produced oxygen as byproduct via photosynthesis

*2.3 bya major shift from reducing to oxidizing environment

Cyanobacteria

Without oxygen the atmosphere would be fire neutral or fire retardant

*500 mya

Fire began around 450-400

mya

-once oxygen stabilized, it has remained relatively uniform-oxygen is a combustion constant Fuel

Oxygen Heat

-life's surge onto land injected burnable biomass into a previously empty combustion chamber

Early fires most likely burned amid ferns, within swamps of rotting debris

Carboniferous Forest (290-360 mya)

Bracken fern

Horsetail

Equisetum

Conifers

Fire frees carbon from plants and buries it as charcoal

Cretaceous/Tertiary boundary- period of mass extinction and mass

combustion

How fires came to be

-fire (combustion) needs a spark=a jolt of energy to unpack photosynthesized material to release enough surplus energy through oxidation to continue combustion early Earth offered several sources

Only Lightning

is sufficientl

y consistent

and universal

to account for the natural

history of fire

Source: USA TODAY research by Chris Cappella, Graphic by Kevin A. Kepple

Source: USA TODAY research by Chris Cappella, Graphic by Kevin A. Kepple

Source: USA TODAY research by Chris Cappella, Graphic by Kevin A. Kepple

http://thunderstorm.vaisala.com/explorer.html

The channel of every lightning flash, at a temperature of 30,000 to 50,000 degrees Fahrenheit, is extremely bright white. The apparent colors of lightning, then, are caused by intervening dust, moisture, and other particles in the air between the photographer and the lightning. (NOAA Photo Library, NOAA Central Library)

thunderstorm is about 10-20 miles away. Lightning can be seen up to 75 miles away at night when the intervening sky is clear and dark. Thunder, however, may be heard only a few miles away in a noisy location, 10 miles away in the open, and up to 15 miles away in quiet locations. (NOAA Photo Library, NOAA Central Library)

How lightning creates thunder:

-Lightning heats the air to more than 43,000 degrees, causing the air to quickly expand,

-the air then quickly cools after the flash, which causes it contract

-quick expansion and contraction of air around the lightning starts air molecules moving back and forth, making sound waves, which we hear as thunder

Lecture Objectives:

1). Understand when and how the 3 main components of the fire triangle emerged on Earth

2). Understand how fire came to be on early earth

3). Understand lightning and its role in fire