A, more complex organisms developed over time. One, only multi-cellular organisms found in older rocks, such as fossils, woolly, roundness, and saber-tube tigers. Two, organisms became more complex as time went on. Example, prokaryotes, then multi-cellular, then organisms, life moved on from water to land. The Earth's history includes mass extinctions, extinction, lots of members of a species, like a woolly mammoth and a saber-tube tiger. And two, mass extinction, lots of large members of species. Permian extinction, which means it is about an extinction, but took place about 250 million years ago. And I've dealt about 95% of all population of animals. Two, Cotaceous extinction, which is about 65 million years ago, took out about 50% of the species, including dinosaurs, over a period of 2 million years. It's also in the evidence for climate cooling and warming. In strategic hypothesis, the theory that mass extinction were caused by reasons on Earth, such as volcanoes, tsunamis, and or play jatomic. It's intrinsic means inside, like inside the Earth, the stuff that happens on the planet. And for an example, Pangaea, how this continent, this continent, and this one, were separated at one time and married together. Extremistic hypothesis, the theory that asteroid impact caused a mass extinction, extrinsic means outside, like stuff that doesn't happen on the Earth and it comes from outer space that causes natural disasters. Living organisms went from being simple to complex, at move, and moved from water to land, at various times, there have been mass extinction causing 50 to 90% of all species that disappear, like dinosaurs and other creatures. Draw double-level comparing to hypothesis about that that creates this, pretacious, extinction. Hypothesis one, extrinsic, hypothesis two, extrinsic. That's the end of 6.1. That's the end of 6.1.