22.4 – Early Life on Earth

Origin of Life Bombardment from outer space prevented life from developing on Earth until at least 3.9 billion years ago (BYA) Where and how the first life-form developed, however, remains an active area of research

Origins of Life Earliest atmosphere contained hydrogen, methane and ammonia This atmosphere + energy supplied by lightning would give rise to organic matter in shallow oceans

Primordial Soup Miller & Urey devised an apparatus to test this hypothesis in 1953 Within one week their apparatus had produced organic molecules Organic molecules included amino acids, the building blocks of proteins (& life) http://www.pas.rochester.edu/~afrank/A105/LectureXVII/FG28_002.PCT.jpg

http://www. centauri-dreams http://www.centauri-dreams.org/wp-content/uploads/2007/07/interstellar_chemistry.jpg Other Scenarios Amino acids organized somewhere else in the universe and were brought to earth by asteroids or comets Chemical synthesis of organic molecules is possible in interstellar clouds Amino acids have been found in meteorites

Other Scenarios Amino acids originated deep in Earth or its oceans http://www.rsc.org/images/b820577a-350-FOR-TRIDION_tcm18-145077.jpg Other Scenarios Amino acids originated deep in Earth or its oceans Conditions there are favorable for chemical synthesis Organisms have been found at depths exceeding 3 km

Other Scenarios Possibility that life emerged deep in the ocean at hydrothermal vents http://www.divediscover.whoi.edu/images/vent_chemistry.jpg

http://www.astrochem.org/endoexo.jpg

Essential Characteristic of Life Ability to reproduce All cells require RNA and DNA to reproduce Recent experiments suggest that RNA molecules might have been the first replicating molecules on Earth http://www.odec.ca/projects/2004/mcgo4s0/public_html/t3/DNA-RNA_strcture.gif

Proterozoic Life Nuclei are separate compartments that contain RNA and DNA Prokaryotes = Organisms that do not contain nuclei Eukaryotes = Organisms whose cells contain RNA and DNA in nuclei

Simple Eukaryotes Can be unicellular or multicellular Because they contain nuclei and other internal structures, they are larger than prokaryotes Extinction came from a widespread glaciation event 750 million years ago (mya)

http://io. uwinnipeg. ca/~simmons/16cm05/1116/28-04-EukaryoteOrigin-L http://io.uwinnipeg.ca/~simmons/16cm05/1116/28-04-EukaryoteOrigin-L.gif

Multicellular Organisms About 630 mya, the climate warmed dramatically and the first multicellular organisms appeared in the oceans Fossils first discovered in 1947 in Australia Collectively called the Ediacaran biota, these fossils show the impressions of large, soft-bodied eukaryotes.

Edicaran biota Seemed to answer the question of why there are no fossils of organisms that existed during the first period of the Paleozoic era https://www.nampost.com.na/shop/products_pictures/eriacaran-fosils-2008.jpg

Edicaran Fossils In recent years, geologists have found Ediacaran fossils in all parts of the world. Flourished between 630 mya and 540 mya. Mass extinction = most of them disappeared More likely related to present-day organisms began to inhabit the oceans

In-Class Assignment/Homework WKT 22.4 AND pg. 641-2 #1-23 Answer on the back of WKT 22.4