Fossil record of fire
The fossil record of fire first appears with the establishment of a land-based flora in the Middle Ordovician period, 470 million years ago,[1] permitting the accumulation of oxygen in the atmosphere as never before, as the new hordes of land plants pumped it out as a waste product.
[10] Wildfires are natural events that burn wildlands - forests, grasslands, and prairie - leading to the destruction of ecosystems and can be traced through charcoal records.
Charcoal is the largest product of fire by size and often deposited in layers of sedimentary rocks and lakes.
Charcoal is formed from incomplete combustion of terrestrial ecosystems (vegetation) [11][12] and its evidence describes fire disturbance regimes - frequency and intensity (magnitude) - and the rate of accumulation through time.
Stage 1: Measurement of sediment samples and treating with 25 ml of 6% hydrogen peroxide to oxidize the organic matter, and heating for 24 hours.
This process leaves the charcoal intact but breaks down any organic matter present; Stage 2: Sieving, washing, and rinsing the samples with deionized water, and drying onto a petri dish for 12 – 48 hours.
[15] When counting the charcoal, identifying them into different morphotypes is sometimes done because it helps to understand the vegetation type and plant habit (for instance woody or grassy) present at a given geologic time.
The amount of oxygen in the atmosphere is the major control on the abundance of fire; this can be approximated by a number of proxies.
[8] Fires really took off in the high-oxygen, high-biomass period of the Carboniferous, where the coal-forming forests frequently burned; the coal that is the fossilised remains of those trees may contain as much as 10-20% charcoal by volume.
[8] Contrary to popular perception, there is no evidence of a global inferno at the end of the Cretaceous, when many lineages were driven to extinction, most notably all non-avian dinosaurs; the record of fire after this point is somewhat sparse until the advent of human intervention around half a million years ago, although this may be biased by a lack of investigations from this period.
This activity destroys the vegetation structure (species composition) and consequently decreases ecosystem functions and services.
Similarly, the destruction of a grassland by fire activity facilitates the washing of the topsoil by erosion and a loss of plant community and ecosystem services.
On the other hand, wildfire activities can cause the destruction of forest canopies which opens a window for understory vegetation to flourish given the amount of direct sunlight received.
