ASTRO 106 Lecture Notes - Lecture 3: Cambrian Explosion, Micropaleontology, Water Vapor

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Geological time scale: hadea(cid:374) (cid:894)(cid:862)hellish earth(cid:863)(cid:895) eo(cid:374): (cid:1008). (cid:1009)-3. 85 billion years ago. Volcanoes and impacts: ar(cid:272)hea(cid:374) (cid:894)(cid:862)a(cid:374)(cid:272)ie(cid:374)t life(cid:863)(cid:895) eo(cid:374): (cid:1007). 8(cid:1009)-2. 5 billion years ago. Single-cell organisms: first fossil microbes: proterozoic (cid:894)(cid:862)earlier life(cid:863)(cid:895) eo(cid:374): (cid:1006). (cid:1009)-0. 54 billion years ago. Oldest eukarya (cells with nucleus) still single-celled creatures. Development of oxygen: pha(cid:374)erozoi(cid:272) (cid:894)(cid:862)(cid:448)isi(cid:271)le life(cid:863)(cid:895) eo(cid:374): (cid:1004). (cid:1009)(cid:1008)-0 billion years ago. Beginning of this eon was marked by the cambrian period (cambrian. Multi-cell organisms: fossils visible to the naked eye. Impact sterilization: moon formed 4. 4 billion years ago from large collision of mars-sized body with. Impact sterilization by large asteroids for first 300-(cid:1010)(cid:1004)(cid:1004) (cid:373)illio(cid:374) (cid:455)ears(cid:863) 350-400 km: raise temperature to 2,000 c and vaporize oceans. 150-190 km: vaporize top few hundred meters of the oceans. ~100 asteroids of this big still exist, but not threatening earth now. Last sterilization: 3. 9-4. 2 gyr (billion years) ago: first indirect evidence for life: 13c/12c isotope ratio. Living tissue and fossils show less 13c: stronger evidence: fossils from stromatolites.

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