3 origin of life edited3

Theories on the ORIGIN OF LIFE

Basic enigma of life: HOW DID LIFE ORIGINATE?

Nothing is directly known about the origin of life, the answer

to this question are exceedingly complex and at best only

tentative.

Theories of the origin of life: Still a

matter of speculation

Several intelligent explanations

account for the origin of life on earth

Religion

The origin of life must be attributed to an

agency outside nature called a creator.

Mythology Philosophy

1. THEORY OF SPECIAL CREATION

support or acceptance mostly due to faith rather than experimental or scientific evidences.

Supporters recently created a new discipline called “creation science”.

Proposed that universe started from a primeval fireball and had

been expanding and cooling since its inception 10-20 billion years

ago (bya).

Life originated from outer planets in the form of a resistant spore

(cosmozoa) propelled by radiation pressure, reached earth and

started the first form of life.

Idea was proposed by Richter in

1865. The theory did not gain any

support. Needs evidence for the

existence of ET life.

2. Cosmozoic or Interplanetary

The cosmozoic theory speculates that life

arrived on Earth as bacterial spores,

perhaps enclosed in a comet.

3. ABIOGENESIS (SPONTANEOUS GENERATION)

600 BC up to 2nd half of 19th century – believed that life could arise

spontaneously from nonliving substances.

Living organisms originated in sea lime under the influence of

factors in the environment s.a. heat, air, sun.

Thales (624-548 BC) ---“oceanic

water was the mother from which all

living forms originated”.

The origin of life without apparent cause

3. ABIOGENESIS (SPONTANEOUS GENERATION)

Aristotle‟s Hypothesis

Aristotle (384-322 BC)--- proposed

that living forms are animated forms of

non-living matter.

-Vital forces operate constantly and

improve the living world

Empedocles (540-433 BC) ---“life

originated by itself from non living matter

and imperfect forms were replaced by

perfect forms”

Biogenesis. Every living thing on earth is the offspring of other living things.

“Life comes from life” is referred to as the law of biogenesis, which asserts that

modern organisms do not spontaneously arise in nature from non-life.

Louis Pasteur

Working hypothesis: life arose from pre-existing life

Anton van Leeuwenhoek

Believed that microorganisms arose

from pre-existing organisms.

4. Biogenesis Theory

Francisco Redi

opposed abiogenesis

proposed that life could arise only

from pre-existing living things (thru

experiment) .

Louis Pasteur was the first to

be able to prove this theory

proposed that the organisms

that are not visible to the

naked eye are present in air.

Broth is boiled. Broth is free of

microorganisms

for a year.

Curved neck

is removed.

Broth is

teeming with

microorganisms

.

Pasteur’s Experiment

demonstrated that fermentation is caused by the growth

of micro-organisms, and that the emergent growth of bacteria in

nutrient broths is not due to spontaneous generation

OBSERVATIONS: Flies land on meat that is left uncovered. Later, maggots appear on the meat.

HYPOTHESIS: Flies produce maggots.

PROCEDURE

Controlled Variables: jars, type of meat, location, temperature, time

Manipulated Variables: gauze covering that keeps flies away from meat

Responding Variable: whether maggots appear

CONCLUSION: Maggots form only when flies come in contact with meat.

Spontaneous generation of maggots did not occur.

Redi’s Experiment

5. Natural or Marine (Primeval Soup)

Proposed that life did not originate in the surface of the earth but deep beneath the sea in or around hydrothermal vents.

In 1929 by J.B.S. Haldane; suggested that life was the result of UV radiation converting methane, ammonia and water into the first organic compounds in the early earth oceans.

6. Physico-chemical or coacervate droplet

theory (Oparin and Haldane) Chemical evolution:

1. Formation of simple organic compounds

the primitive inorganic molecules of earth interacted and combined

with one another to form simple organic compounds. These were in

the form of simple sugars, fatty acids, glycerol, amino acids and

nitrogen bases.

2. Formation of complex organic compounds

-Simple sugars combined, form complex polysaccharides (starch,

cellulose). Fatty acids and glycerol molecules combined to form

lipids. Amino acids combined forming polypeptides and proteins.

-Purines and pyrimidines combined with simple sugars and phosphates

to form nucleotides, which then formed nucleic acids.

Harold C. Urey and Stanley L. Miller

(1953) – conducted an experiment

simulating the primitive condition of the

Earth.

− discovered that a variety of amino

acids and organic acids were formed

Urey-Miller hypothesis

Proposed that amino acids can

be synthesized outside living

systems.

They conducted experiments

in which a gas mixture

containing hydrogen, ammonia,

methane and water vapor was

subjected to electric spark.

It yielded aldehydes, amino

acids and carboxylic acids.

3. Formation of molecular aggregates (Coacervates):

•Oparin and Fox proposed that the complex organic molecules synthesized

abiotically on the primitive earth formed large spherical aggregates as

cluster of complex organic molecules bound by fatty acids and divide.

•They remained suspended as droplets in sea water

•The coacervates had all the basic properties of living cells like,

metabolism, growth etc.

•However they lacked the complexity of the living cells like organelles.

•Thus these particles with proteins as enzymes and ATP as source of

energy were the first structures at the margin of non-living and living.

4. Formation of first primitive living cell:

Theories on the ORIGIN OF LIFE

Basic enigma of life:

Nothing is directly known about the origin of life, the answer

to this question are exceedingly complex and at best only

tentative.

Theories of the origin of life: Still a

matter of speculation

Several intelligent explanations

account for the origin of life on earth

HOW DID LIFE ORIGINATE?

Fossils as evidence of change

Features of Earliest Organisms

Extinction

• the earth is about 4.5 billion years old,

• the earliest known cells are found in 3.5 billion year old

rocks

• the earliest known eukaryotic cells date to 1.5 billion years

• the earliest multicellular animals date to 650 million years

• the earliest land animals date to about 450 million years

• the earliest mammals date to about 230 million years

• 65 m.y. ago there was a mass extinction of many living things

• the human family tree diverged from the other apes about

4.5 million years ago


Remains or traces of prehistoric life

preserved remains of animals, plants or their parts

Can be of entire organisms or a part which got

buried, a mould or cast, foot prints or imprints on a

stone.

• Physical evidence of organisms from the past

• Provides visible evidence that takes us back in time and shows organisms

have changed.

• The fossil record provides incomplete information about the history of life. • Paleontologists are scientists who collect and study fossils.

• Over 99% of all species that have lived on Earth have become extinct.

• Where are all these fossils??


Careful study of fossils

Opens a window into the lives of organisms that existed long ago and

provides information about the evolution of life over billions of years

The strata of one location can often be correlated with strata at

another location by the presence of index fossils

Index fossils (also known as guide fossils, indicator fossils or zone

fossils) are fossils used to define and identify geologic periods (or

faunal stages).

Example of Index fossils: Shelled animals called brachiopods were extremely abundant in ancient seas. Their fossils are useful indicators of the relative ages of rock strata in different locations

Methods of fossilization

Petrifaction- Turn into

stones.

This is due to formation

of sedimentary rocks

under water.

soft parts: disappear;

hard parts: preserved

due to mineralization.

muscles and other

soft organs: get

mineralized and form

rocky fossils.

Preservation of foot prints

prints, if left undisturbed: hardened and form rocky

fossils.

such imprints can provide clues regarding the

body form and characteristics of the extinct

animal.

A dinosaur footprint

Preservation in ice

Entire animals can get

frozen and may be

preserved

Body parts remain

intact without change.

E.g. woolly mammoth

from Siberia

Fossils: evidence of past life Types of fossils

• Carbonization – organic

matter becomes a thin

residue of carbon

• Preservation in amber

– hardened resin of

ancient trees surrounds an

organism

• Impression – replica of

the fossil's surface

preserved in fine-grained

sediment

Impressions: Moulds and cast

• Mold – a part/structure is buried and then dissolved by underground water • Fossilized moulds are found in volcanic ashes.

• Cast – hollow space of a mold that is filled with mineral matter

Natural casts of shelled

invertebrates

Natural mould of a trilobite

Types of fossils

• Petrified– cavities and pores are filled with precipitated mineral matter

• Permineralization– the pores of the organism are filled with minerals but some tissues of the plant or animal are still intact and are not replaced with minerals.

• Formed by replacement - cell material is removed and replaced with mineral matter

Fossils: evidence of past life

Trace – aka ichnofossils.

May be impressions made

on the substrate by an

organism. For ex: burrows,

footprints and feeding

marks, and root cavities.

Coprolites – fossil dung

and stomach contents

Gastroliths – stomach

stones used to grind food

by some extinct reptiles

Indirect fossil evidence includes:

The History of Life

Relative dating is a method used to

determine the age of rocks by

comparing them with those in other

layers.

Rock layers form in order by age—

the oldest on the bottom, with more

recent layers on top.

Dating Fossils

Radioactive dating (Absolute Dating)

• Uses the decay of radioactive isotopes to measure the age of a rock. the use of half-lives to determine the age of a sample. A half-life is the length of time required for half of the radioactive atoms (C, N) in a sample to decay.

Dating Fossils

Early members of the animal fossil record

◦ Include the Ediacaran fauna

Important fossils

(features of earliest organisms)

These animals were the precursors of organisms with

skeletons.

Ichthyostega - interconnecting link

between fishes and amphibians.

Important fossils


Seymouria - Interconnecting link

between Amphibians and Reptiles.

Important fossils


Dinosaurs - Extinct group of reptiles.

Important fossils


Archaeopteryx - Ancestral form of birds

Important fossils


Hyracotherium - Early ancestor of

horses.

Important fossils


Theropods

Allosaurus

Sinornis

Velociraptor

Archaeopteryx

Robin

Light bones

3-toed foot;

wishbone Down

feathers

Feathers with

shaft, veins,

and barbs

Flight feathers;

arms as long

as legs

Important fossils


Rodhocetus, an

ancient whale, lived

about 47 million

years ago.

Rodhocetus ankle bone

(left), a modern

artiodactyl, pronghorn

antelope ankle bone

(right).

Its distinctive ankle

bones point to a

close evolutionary

connection to

artiodactyls.

Important fossils


Dorudonatrox, an ancient whale that lived about

37 million years ago.

Important fossils


Extinction

The termination of a lineage without issue

or abrupt disappearance of specific groups

of organisms without leaving descendents.

The death of a species or group of taxa

Extinction Types: True Extinction and Pseudoextinction

1. True Extinctions -particular lineage totally disappears

without any progeny or evolutionary descendents.

E.g. extinction of dinosaurs as a group ; trilobites.

2. Pseudoextinction (phyletic extinction or phyletic

transformation) - a group may disappear leaving descendents

with evolutionary modifications.

Example:

Horse evolution while the earliest ancestor became extinct its

descendant survived to produce the modern „Equus‟.

Pattern of extinction

Major groups of herbivorous vertebrates are more susceptible than the carnivorous vertebrates

Larger organisms easily became extinct.

VanValen (1973) recorded a constancy in the rate of extinction in a number of groups.

Explained using „Mac Arthor‟s law‟ - “every new

adaptation encourages the survival of a possessor it also decreases a fitness of other species of that area”.

Causes of extinction

(1) A mass extinction: due to drastic changes in the environmental conditions.

(2) Any adaptive advance in one species decreases the fitness of all other species.

Red Queen‟s hypothesis : you have to keep running pretty fast, just in order to stay in the same place.

(3) Over specialization to a specific situation may cause extinction

(ex. Antlers)

(4) The spread of an epidemic disease without any control can cause extinction.

(5) An increase in the population strength of herbivorous animals cause rapid food shortage and cause extinction for several inter-related groups (Predation, competition)


(6) A sudden cosmic radiation can

cause the death of large organisms.

(7) A dust storm formed due to falling

of a meteorite is commonly

mentioned as a cause for the

disappearance of dinosaurs.

(8) Habitat degradation: The

degradation of a species' habitat may

alter the fitness landscape or such an

extent that the species is no longer

able to survive and becomes extinct.


(9) Coextinction: the loss of a species due to the extinction of another; for example, the extinction of parasitic insects following the loss of their hosts

(10) Genetic Pollution: uncontrolled hybridization, introgression genetic swamping which leads to homogenization or replacement of local genotypes as a result of a numerical and/or fitness advantage of the introduced plant or animal


In the recorded history of earth,

extinctions of major groups of organisms

were due to natural causes.

By end of Permian period of the Paleozoic

Era, nearly 60% of the varieties then

existed, became extinct.

Similar large scale extinctions have been

observed by the end of Mesozoic era


2006 IUCN Red List data.

2006 IUCN Red List data.

At present … mostly due to human interference.

The realization of such a cause lead to starting of several international voluntary agencies to monitor and control extinctions.

“The red-data book brought out regularly by W. W. F (World Wide Fund for nature, IUCN - international union for the conservation of nature and natural resources) provides a list of animals and plants that are endangered or have become extinct.


Education

3 origin of life edited3