Earth 125 1st Edition Lecture 14 Outline of Last Lecture I. Proterozoic Eukaryotesa. CellsII. Cambrian ExplosionIII. Prelude to Cambrian ExplosionIV. Phanerozoic history of animalsOutline of Current Lecture II. Review of Darwin’s problemsIII. “Life’s Big Hits”IV. Phanerozoic history marine animals, evolutionary faunas, vertebratesV. Transitional formsCurrent LectureI. Darwin’s Problemsa. Blending Inheritancei. Solved by Mendel: particulate nature of heredityii. Remember the bean plants?b. Young Earth (Kelvin <100 million year old Earth)i. Solved by discover radioactivity: earth is greater than 4 billion years oldc. The Cambrian-PreCambrian Gapi. Not yet solved in what we’ve learnedII. Life’s Big Hitsa. LIFE – Prokaryotes, chemistry, stromatolites, prokaryotic microfossils i. In the Archean periodb. Eukaryotesc. Otavia (first animals)d. Cambrian Explosione. Timeline: f. Importance of Cambrian Explosion:i. Diversity vs. disparity1. Diversity: how many?2. Disparity: how differentii. Disparity: very different = phylaiii. Diversity: somewhat different = species, genera, or familiesiv. What caused the evolution of animals at that time? Was it more rapid andif so, why?1. Extrinsic physical factors (glaciations, change in composition of atmospheres/oceans)2. Intrinsic factors (hox/regulatory genes, developmental plasticity)3. Extrinsic ecological factors (empty barrel, escalation)v. Empty ecological barrel: as time goes by, environment fills, success of large steps decreases, thus large steps become less common1. Homesteader analogy: When farmers (primary producers) got settled into land, they began to need things – this need led to the creation of other businesses. So, soon an entire “ecosystem” was developed. At the primitive stage, new businesses were disparate. If there’s a general store but no bank within a town, it makes moresense to go into the banking business rather than create unnecessary competition. After a while, all “normal” businesses have been created and the only way to establish a new business is to get into a business that already exists (competition). This creates more intense competition but more fine-tuned, creating niche products.a. Is there evidence for this type of ecosystem in the Cambrian? Is it just primary producers?i. No! Evidence of predators: Anomalocaris, bite marksii. Consequences of predation is escalation1. Prey: Escape or die, strong selective pressure to develop strategies2. Predators must respond or be left without a meal.g. Does evolution stop after Cambrian? No.i. Major features of diversity curve for marine animals1. early phase of expansion, middle phase of stability, post Permo-Triassic Ext “expansion,” perturbations by 5 major extinction eventsIII. Darwin’s Theory, continued.a. Problem of Cambrian-PreCambrian Gap (lack of fossil record)i. Solution: simple life in oldest rx (prokaryotes), Eukaryotes, Animals by Late Proterozoic (“long fuse” prior to Cambrian Explosion)b. But now, there’s this problem of Transitional Forms!i. “But, as by this theory innumerable transitional forms must have existed, why do we not find them embedded in countless numbers in the crust of the earth?ii. Darwin’s explanation: “the imperfection of the record being chiefly due toorganic beings…being embedded and preserved to a future age only in masses of sediment sufficiently thick and extensive to withstand an enormous amount of future degradation…Whilst the bed of the sea is stationary or rising, or when very little sediment is being deposited, there will be blanks in our geological history. The crust of the earth is a vast museum; but the natural collections have been made only at intervals of time immensely remote.”IV. From Fish to tetrapods: From water to land – a seemingly unbridgeable gapa. Fish breathe through gills, tetrapods through lungs.b. Fish move through fins, tetrapods through limbs. i. The Move from water onto land: Fundamental Problems1. Aerobic respiration (need for oxygen)a. In water, gills (external) yet in air, gills don’t work. Lungs work because they’re internal and do not dry