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b'This week let\'s find out a little something about the Cambrian explosion, where the relatively simple and tiny life on earth suddenly proliferated and grew much larger...and definitely stranger.\\n\\nThe Burgess shale area: beautiful AND full of fascinating fossils:\\n\\n\\n\\nAnomalocaris, pre-we-figured-out-what-these-things-are:\\n\\n\\n\\nWhat anomalocaris probably actually looked like, plus a couple of the "headless shrimp" fossils:\\n\\n\\n\\nMore "headless shrimp" fossils because for some reason I find them hilarious:\\n\\n\\n\\nMarrella. Tiny, weird, looks sort of like those creepy house centipedes that freak me out so much, but with horns:\\n\\n\\n\\nHallucigenia, long-time mystery fossil:\\n\\n\\n\\nWhat hallucingenia probably looked like, maybe:\\n\\n\\n\\nShow transcript:\\n\\nWelcome to Strange Animals Podcast. I\\u2019m your host, Kate Shaw.\\n\\nThis week\\u2019s topic is one I\\u2019ve been fascinated by for years but I\\u2019ve never read much about it: the Cambrian explosion. That refers to the explosion of life forms in the Cambrian period, which started about 540 million years ago. That was long before the dinosaurs, long before fish, basically long before almost all life on earth that wasn\\u2019t simple squidgy things living in warm, shallow seas.\\n\\nTo learn about the Cambrian explosion, let\\u2019s go back even farther first and learn about the first life on earth.\\n\\nObviously, the more recently an animal lived, the more likely we are to find fossils and other remains: footprints in fossilized mud, gastroliths and coproliths, and so forth. The farther back we go, the fewer remains we have. The earth is continually changing, with mountains rising up and continents moving around, volcanoes erupting, old mountains being worn down by wind and weather. That\\u2019s good for the earth and therefore for life in general, since nutrients are cycled through the ecosystem and habitats are continually renewed. But it\\u2019s bad when paleontologists are trying to find out what lived a billion years ago, because most of those rocks are gone, either weathered into sand long ago, melted into magma, or buried under the ocean or otherwise out of our reach.\\n\\nThe Earth formed about 4.5 billion years ago, oceans formed 4.4 billion years ago, and the oldest rocks we can find are about 4 billion years old. The first life on earth, single-celled organisms, dates back to about 3.8 billion years ago, maybe earlier. By 3.5 billion years ago, complex single-celled microorganisms had evolved\\u2014we know because we\\u2019ve found eleven microscopic fossils in rocks from western Australia. Researchers have concluded that the fossils belonged to five different taxonomical groups, which means that by 3.5 billion years ago, life was already well established and diverse.\\n\\nBy 2.5 billion years ago, the earth had continents roughly the same size as the ones today, although not anything like the same shapes or in the same places. Land also didn\\u2019t have dirt on it, just sand and bare rock, since dirt is largely decomposed organic matter and nothing was living or dying on the land yet. Not long after, 2.45 billion years ago, oxygen started to make up a large part of the earth\\u2019s atmosphere. That\\u2019s right, before then we literally could not have breathed the air. I mean, we could have, but we would die of suffocation because the air contained only trace amounts of oxygen. While having oxygen in the air sounds great to us now, the single-celled organisms living then couldn\\u2019t process it and died off\\u2014probably the greatest extinction event in the earth\\u2019s history. Only organisms that were able to evolve quickly enough to use oxygen survived and thrived.\\n\\nOne particular type of microorganism dating back 2.3 billion years, sulfur bacteria, again known from ancient rocks from western Australia, is still around. Modern sulfur bacteria live in the deep sea off the coast of Chile, and they literally have not needed to change at all in 2.3 billion years. That\\u2019s what you call success.\\n\\nThe earliest multicellular organisms date to around...'