Here are some resources where you can deep delve into the history of life. These narratives are interchangeably and intricately connected with “history of animals”, “natural history” and more such foundational narratives. Smithsonian: https://naturalhistory.si.edu/education/teaching-resources/life-science/early-life-earth-animal-origins#:~:text=These%20clusters%20of%20specialized%2C%20cooperating,were%20among%20the%20earliest%20animals. https://www.newscientist.com/article/dn17453-timeline-the-evolution-of-life/ https://www.bbvaopenmind.com/en/science/bioscience/what-were-the-first-animals-on-earth/ https://www.science.org.au/curious/space-time/origins-life-earth From Oxford University: https://www.oum.ox.ac.uk/firstanimals/ Britannica: https://www.britannica.com/science/life/Evolution-and-the-history-of-life-on-Earth
The 6 Kingdoms define how living organisms are classified or organized for research and academic reasons. Earlier on, there were only 2 kingdoms, plants and animals. However as discoveries continued, it became imperitive to have more kingdoms to classify living organisms. Currently we classify living organisms into plants, animals, protists, fungi, archaebacteria and eubacteria.