How can fire start without humans?

What did isaaac Newton discover about the structure of the earth? What is the value of old copper pennies? 2.55 mmol to moles? How would your answer for the molar mass of CO2 change if you had not carefully scraped water frost from the Dry Ice before use and water droplets too small to see remained in the flask? Is it strong when it reaches storm wind of 50kph? What are the names of all of the colleges that are a part of the U.N.C. system? What was the first metal extracted? What is a decision made based on observations? How did Beadle and Tatum determine what biochemical pathways had mutated? What is the limiting reagent for the reaction 4Al plus 3O2-2Al2 O3 given that you start with 10.0 grams of Al and 19.0 grams of O2? Does Newton'a first law of motion have to be capitalized? Why can the classification of organism can be diagrammed? How and why is melting of permafrost dangerous? Meteorologist study changes in the air to try to forecast the weather? Is plasmodium vivax is eukaryotic or prokaryotic? Is an equipment ground required in PVC conduit? Oil glands in the skin secrete a substance that helps kill the bacteriawhat do you think will happen if you washed your skin too often? Is Alpha Beta or gamma made from electrons? What happens to most of the energy produced by burning gas? What is the cost of wildfire?

How can fire start without humans?