Early Earth & the Origin of Life (Ch. 26)

*The history of living organisms and the history of Earth are inextricably linked:

   Formation and subsequent breakup

of Pangaea affected biotic diversity

 The first photosynthetic organism released oxygen into the air and altered Earth’s atmosphere

 

  Homo sapiens have changed the land, water, and air on a scale and at a rate unprecedented for a single species

Figure 2. Sea level is changing. Observing stations from around the world report year-to-year changes in sea level. The reports are combined to produce a global average time series. The year 1976 is arbitrarily chosen as zero for display purpose.

Figure 1. Global warming revealed. Air temperature measured at weather stations on continents and sea temperature measured along ship tracks on the oceans are combined to produce a global mean temperature each year. This 150-year time series constitutes the direct, instrumental record of global warming.

History of Life on Earth:  Life on Earth originated between 3.5 and 4.0

billion years ago

  Because of the relatively simple structure of prokaryotes, it is assumed that the earliest organism were prokaryotes

*this is supported by fossil evidence (spherical & filamentous prokaryotes recovered from 3.5 billion year old stromatolites in Australia and Africa)

 Major Episodes in the History of Life:

   first prokaryotes- 3.5 to 4.0 billion

years ago

  photosynthetic bacteria- 2.5 billion

years ago

  first eukaryotes- 2 billion years ago 

 

~The oldest unequivocal remains of a diversity of microorganisms occur in the 2.0 BYO Gunflint Chert of the Canadian Shield

~This fauna includes not only bacteria and cyanobacteria but also ammonia consuming Kakabekia and some things that ressemble green algae and

fungus-like organisms

  plants evolved from green algae

  fungi and animals arose from different groups of heterotrophic unicellular organisms

   first animals (soft-bodied invertebrates)- 700 million years ago

 

  first terrestrial colonization by plants and

fungi- 475 million years ago

plants transformed the landscape and created new opportunities for all

forms of life

Prebiotic Chemical Evolution:   Earth’s ancient environment was

different from today:-very little atmospheric oxygen

-lightning, volcanic activity, meteorite, bombardment, UV radiation all more intense

  Chemical evolution may have occurred in four stages:

1)   abiotic synthesis of monomers

2)  joining of monomers into polymers (e.g. proteins, nucleic acid)

3)  formation of protobionts (droplets

formed from clusters of molecules)

4)  origin of heredity (likely that RNA was first)

 

Oparin / Haldane hypothesis (1920s): the reducing atmosphere and greater UV radiation on primitive Earth favored reactions that built complex organic molecules from simple monomers as building blocks

Miller / Urey experiment:

Simulated conditions on early Earth by

constructing an apparatus containing H2O, H2,

CH4, and NH3.

Results:• They produced amino acids and other organic

molecules.• Additional follow-up experiments have produced all

20 amino acids, ATP, some sugars, lipids and purine and pyrimidine bases of RNA and DNA.

  Protobionts: collections of abiotically produced molecules able to maintain an internal environment different from their surroundings and exhibiting some life properties such as metabolism and excitability

(experimental evidence suggests spontaneous formation of protobionts)

 

possible formation

of protobionts;self-repliating RNA as early

“genes”

Origin of Life - Different Hypotheses:

 

*No one knows how life actually began on Earth; experiments indicate key steps that could have occurred.

  Panspermia: some organic compounds may have reached Earth by way of meteorites and comets

meteorite

  Sea floor / Deep-sea vents: hot water and minerals emitted from deep sea vents may have provided energy and chemicals needed for early protobionts

 

  Simpler hereditary systems (self-replicating molecules) may have preceded nucleic acid genes.

The Major Lineages of Life: the 5 Kingdom System

Living organisms  Prokaryotic Eukaryotic 

Simple/unicells Multicellular

Autotrophic Heterotrophic 

Absorptive Ingestivenutrition nutrition(Animalia) (Fungi)

(Plantae)

(Protista)

(Monera)

How was the atmosphere of the early earth different than it is today?

A. The early earth’s atmosphere contained mostly carbon monoxide

B. The early earth’s atmosphere had more oxygen than it has today

C. The early earth’s atmosphere contained more single celled organisms than it does today

D. The early earth’s atmosphere did not contain oxygen

In the 4-stage hypothesis for the chemical evolution of life,

which of the following is the correct sequence? A. Synthesize monomers; join monomers; form protobionts; system of

heredity

B. Form protobionts; synthesize monomers; join monomers; system of heredity

C. System of heredity; join monomers; synthesize monomers; form protobionts

D. Synthesize monomers; join monomers; system of heredity; form protobionts

What is a protobiont?A. A self-replicating early life form that uses RNA for heredity

B. A group of monomers that join/bond when temporarily bonded to materials such as clay or volcanic rock

C. Early enzymes that were able to join basic amino acids together

D. Collection of abiotically produced molecules that can maintain an internal environment and exhibit some life properties

What is the name of the alternate hypothesis for the “seeding” of organic compounds on earth by meteorites & comets?

A. Deep Sea Vent Hypothesis

B. Panspermia

C. Impact Hypothesis

D. Early Earth “Seeding” Hypothesis

In the 5 Kingdom system used to classify all life, what are the names of the Kingdoms?

A. Bacteria; Plantae; Animalia; Fungi; Protista

B. Bacteria; Plantae; Animalia; Fungi; Monera

C. Plantae; Animalia; Bacteria; Monera; Protista

D. Plantae; Animalia; Fungi; Monera; Protista