22.4 – Early Life on Earth22.4 – Early Life on Earth

Origin of LifeOrigin of Life

• Bombardment from outer space Bombardment from outer space prevented life from developing on prevented life from developing on Earth until at least 3.9 billion years Earth until at least 3.9 billion years ago (BYA) ago (BYA)

• Where and how the first life-form Where and how the first life-form developed, however, remains an developed, however, remains an active area of researchactive area of research

Origins of LifeOrigins of Life

• Earliest atmosphere contained Earliest atmosphere contained hydrogen, methane and ammoniahydrogen, methane and ammonia

• This atmosphere + energy supplied This atmosphere + energy supplied by lightning would give rise to by lightning would give rise to organic matter in shallow oceansorganic matter in shallow oceans

Primordial SoupPrimordial Soup• Miller & Urey Miller & Urey

devised an devised an apparatus to test apparatus to test this hypothesis in this hypothesis in 19531953– Within one week their Within one week their

apparatus had apparatus had produced organic produced organic moleculesmolecules

– Organic molecules Organic molecules included amino acids, included amino acids, the building blocks of the building blocks of proteins (& life)proteins (& life) http://www.pas.rochester.edu/~afrank/A105/LectureXVII/FG28_002.PCT.jpg

Other ScenariosOther Scenarios1.1. Amino acids organized Amino acids organized

somewhere else in the somewhere else in the universe and were universe and were brought to earth by brought to earth by asteroids or cometsasteroids or comets

• Chemical synthesis of Chemical synthesis of organic molecules is organic molecules is possible in interstellar possible in interstellar cloudsclouds

• Amino acids have been Amino acids have been found in meteoritesfound in meteorites

http://www.centauri-dreams.org/wp-content/uploads/2007/07/interstellar_chemistry.jpg

Other ScenariosOther Scenarios

2.2.Amino acids originated deep in Earth Amino acids originated deep in Earth or its oceansor its oceans

• Conditions there are favorable for Conditions there are favorable for chemical synthesischemical synthesis

• Organisms have been found at Organisms have been found at depths exceeding 3 kmdepths exceeding 3 km

http://www.rsc.org/images/b820577a-350-FOR-TRIDION_tcm18-145077.jpg

Other ScenariosOther Scenarios

3.3. Possibility that life emerged deep in Possibility that life emerged deep in the ocean at hydrothermal ventsthe ocean at hydrothermal vents

http://www.divediscover.whoi.edu/images/vent_chemistry.jpg

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

Essential Characteristic of Essential Characteristic of LifeLife• Ability to reproduceAbility to reproduce

• All cells require RNA All cells require RNA and DNA to and DNA to reproducereproduce

• Recent experiments Recent experiments suggest that RNA suggest that RNA molecules might have molecules might have been the first been the first replicating molecules replicating molecules on Earthon Earth

http://www.odec.ca/projects/2004/mcgo4s0/public_html/t3/DNA-RNA_strcture.gif

Proterozoic LifeProterozoic Life

• Nuclei are separate compartments Nuclei are separate compartments that contain RNA and DNAthat contain RNA and DNA

• Prokaryotes = Organisms that do not Prokaryotes = Organisms that do not contain nucleicontain nuclei

• Eukaryotes = Organisms whose cells Eukaryotes = Organisms whose cells contain RNA and DNA in nucleicontain RNA and DNA in nuclei

Simple EukaryotesSimple Eukaryotes

• Can be unicellular or multicellularCan be unicellular or multicellular

• Because they contain nuclei and Because they contain nuclei and other internal structures, they are other internal structures, they are larger than prokaryoteslarger than prokaryotes

• Extinction came from a widespread Extinction came from a widespread glaciation event 750 million years glaciation event 750 million years ago (mya)ago (mya)

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

Multicellular OrganismsMulticellular Organisms

• About 630 mya, the climate warmed About 630 mya, the climate warmed dramatically and the first multicellular dramatically and the first multicellular organisms appeared in the oceansorganisms appeared in the oceans

• Fossils first discovered in 1947 in Fossils first discovered in 1947 in AustraliaAustralia– Collectively called the Ediacaran biota, Collectively called the Ediacaran biota,

these fossils show the impressions of these fossils show the impressions of large, soft-bodied eukaryotes.large, soft-bodied eukaryotes.

Edicaran biotaEdicaran biota

• Seemed to answer Seemed to answer the question of the question of why there are no why there are no fossils of fossils of organisms that organisms that existed during the existed during the first period of the first period of the Paleozoic eraPaleozoic era

https://www.nampost.com.na/shop/products_pictures/eriacaran-fosils-2008.jpg

Edicaran FossilsEdicaran Fossils

• In recent years, geologists have In recent years, geologists have found Ediacaran fossils in all parts of found Ediacaran fossils in all parts of the world. the world. – Flourished between 630 mya and 540 Flourished between 630 mya and 540

mya. mya.

• Mass extinction = most of them Mass extinction = most of them disappeareddisappeared– More likely related to present-day More likely related to present-day

organisms began to inhabit the oceansorganisms began to inhabit the oceans

In-Class In-Class Assignment/HomeworkAssignment/Homework

• WKT 22.4WKT 22.4

• AND pg. 641-2 #1-23AND pg. 641-2 #1-23– Answer on the back of WKT 22.4Answer on the back of WKT 22.4