17. History of Life

Overview of the key events in the history of life in the last 4.5 billion years

1. orign of the solar system and earth

2. prokaryotes

3. armostheric oxygen

4. single celled eukaryotes

5. musticellar eukoraytoes

6. animals

7. colonization of alnds

8. Humans

The fossil reocrd documents the history of life

• radiometrei dating uses the decay or radiocatice isotpes as a “clock” to date them

Muletiple lines of eveidnece suggest that life arose on earth billions of years ago

• earliest fosil of singel-celled life on earth date to arround 3.5 biollion years ago

• eveoulitnary trees ingereed froom the DNA of living speices alsosuggests that all life shares a single celled ancestory that lived arround 3-4 billion years ago

CUrrently we hypothesize that four key processes lead to the orgin of life

• abiotic sythensis of small orgnaic moleuces (acids, bases)

• Abiotic sythenses of thsese small molcues into marcomolcues

• packing macrmolecules into protocells

• the orgin of self-replicating mocleues

Condtions on the early earth may have allowed simple organize molcules to from

• many places on the early earth may have been condutive to the formation of simple molecules

• Simple reactsion among ambien C O N H could have been fuled by lighting, hdrothermal vents, volcani eruptions

The miller-Urery expermient (1953) let great support to hypthesis

• created constions simmilar to the earlty earth in lab

• heate water, methane, ammonia, hydrogen, and applied and electral charge

• oberservted the formatio of 11 of the 21 essential amino acids

Oirgin of single -celled prokaryotes

• earth;s first orgnaims were single-celled prokaryotes that lived in the ocean

• the earliest evidence from 3.5 billion years ago are fossiled stromatlies structres that are formed exculcey by single celled organims (still today!)

• early prokaryotes were earth’s sole inhbaittnats for about 1.5 billion year

eveoultion of photosyntheseis lead to “oxygen reveoultion”

• most atmoshpereic ozygen gas coems from photosythensis

• when photsyhtneizing organmis similar to today’s cyanbavteria eveoled, they began to conver CO2 to O2

• Dramtic increase in oxygen contetn in the atmoshpere, and condtions for celluar respiration bcome dominant

Origin of eukarotyes

Endomysis

• a kinds of mcafrage didnt desotry the bacterim, used and provided portenction, stabitly coxeisted

Rise of mutleisccluar organismis

• Fossile evidence and DNA sequence data seuggest that mutleucellar eukarotes merged about 1.3 biollion years ago

• Mutielcelluarty allows indivudals cells to copperate and speicalize in thier functions, allow for more complez organsims

• Mulitcuellary eveolved muleitpe times indiedpently

• Volovciie alage most simple mulstcellar ogransims

Cmbarian eplozsion and the diverstifaction of animal life

• many present day animal groups appear suddenlty in fossil formed 535-535 miillion years ago in the cmabrain preriod

• this phenomen is reffered to as cmbrain explosion

• Many possible cuases: increases oxygen, increases genetic complexity of organsims, climate change

Colonization of land

• larger forms of life, such as fungi and plants, began to colonize land, about 500 million years ago

• Arthpods were the first animals to colonize land

• vertrebrated follwer later with air rbeathing and other adapations

Species extincitons

• Extinction: after athrouhg sear,, no member of the speices is found alive anywhere in the world = total dispperance

• Mass extienction: large number of speices, genera, and even familes become eztinct nearly simulatansely

• Extion rate: rate at which speices are lost

Extiontics in the mpast

Mass ecitons are common (5 in fosssil record), family diveristy over time

Mass extinction

• Paloezonic ended with thhe end=permian mass exintction

• Volcanoes erupted on gran scel realses gasses

• 52% gamiles, 96% of speices of marine invertbreates wetn extinct

• Meszozoic ended with another mass extionction

• Asteriod hit earth and drasticly changed climate

• mamals rose in diveristy to rpelace dinsouars