Origins of Life

TOPIC 6

THEORIES OF THE ORIGIN OF LIFE

WHAT ARE WE LEARNING TODAY?WHAT ARE WE LEARNING TODAY?BenchmarksSC.912.L.15.8 – Describe the

scientific explanations of the origin of life on Earth.

Learning Objectives I will describe scientific

explanations of the origin of life on Earth.

I will identify situations or conditions contributing to the origin of life on Earth.

Scientists explain that that life arose from nonlife billions of years ago through the theory of abiogenesis. Could life arise from nonlife today? Explain.

WHAT IS THE ESSENTIAL QUESTION?WHAT IS THE ESSENTIAL QUESTION?

WHAT CONDITIONS MAKE EARTH UNIQUE? Only planet known to sustain life. Several conditions make

Earth able to sustain life aswe know it. presence of liquid water moderate temperature

range free oxygen in the

atmosphere adequate sunlight no toxic substances in the atmosphere absence of lethal radiation

WHAT WAS EARTH LIKE? Earth’s early atmosphere probably contained hydrogen cyanide, carbon

dioxide, carbon monoxide, nitrogen,hydrogen sulfide, and water.

Volcanic activity probably formed it. Released great amounts of water vapor

that later condensed to form oceans. Released CO2 that warms the

atmosphere by absorbing outgoing heat. How did that affect the temperature?

This early atmosphere lackedoxygen, so it could not support life as we know it today. WHERE DID LIFE BEGIN? HOW DID LIFE BEGIN? WHAT DID IT LOOK LIKE? SO MANY QUESTIONS!!!

Proposed by Alexander Oparin and John Haldane. Early atmosphere contain

NH3, CO2, H2O, H2, and CH4

At high temperatures, these gases may have formed single organic compounds.

When Earth cooled and water vapor condensed, these simple organic compounds would have collected in lakes and oceans.

Overtime. these compounds could have entered complex chemical reactions, fueled by energy from ultraviolet radiation, volcanic eruptions, and lighting.

Fossil evidence indicates that life on Earth appeared about 3.5 billion years ago in the oceans Provided protection

from UV radiation Allowed

multidirectional movement

Served as a medium for essential chemical reactions.

Anaerobic prokaryotes

WHERE DID LIFE BEGIN?Fossil Evidence Primordial Soup Theory

Abiogenesis or spontaneous generation states that life can arise from nonliving things Oparin reasoned that O2 prevents the

synthesis of certain organic compounds that are necessary building blocks for the evolution of life

Oparin proposed that the "spontaneous generation of life" did in fact occur once, but was now impossible because the conditions found on the early Earth had changed

Oparin argued that a "primeval soup" of organic molecules could be created in an oxygen-less atmosphere.

Biogenesis states that every living thing came from a pre-existing living thing. In 1668 Francesco Redi, proved

that no maggots appeared in meat when flies were prevented from laying eggs.

In 1768, Lazzaro Spallanzani demonstrated that microbes were present in the air, and could be killed by boiling.

In 1861, Louis Pasteur performed a series of experiments which demonstrated that organisms such as bacteria and fungi do not spontaneously appear in sterile, nutrient-rich media.

ABIOGENESIS VS. BIOGENESIS

Can generate amino acids and sugars from an atmosphere loaded with water, methane, ammonia and hydrogen

Demonstrated in the famous Miller-Urey experiment reported in 1953

New evidence suggestthat it may haveoccurred in volcanicclouds

These vents release important hydrogen-rich molecules

Mineral catalysts could have made critical reactions occurs faster

HOW DID LIFE BEGIN?Hydrothermal Vents Electric Spark

Experiment conducted in 1953 by Staley L. Miller and Harold C. Urey

Their apparatus, illustrated inthe figure included a: Gas chamber containing gases present in Earth early atmosphereElectrodes supply electricity to provide energy to drive chemical reactionsWater chamber substituted for the oceans and lakes.

The Miller-Urey experiment produced a variety of organic compounds, including amino acids.

HOW DID THE FIRST ORGANIC COMPOUNDS FORM?

Clay may have provided the foundation for first organic compounds.

Mineral crystals in clay could have arranged organic compounds into organized patterns.

Life could have come from outer space in a comet or meteorite.

HOW DID LIFE BEGIN?Panspermia Community Clay

3 billion years ago ice might have covered the oceans.

Protected from UV light, organic compounds may have formed and reacted with one another.

Ice Earth

Sidney Fox and other scientists have done extensive research on the physical structures that may have given rise to the first cells.

Cell like structures, including microspheres and coacervates, form spontaneously in certain kinds of solutions. Coacervates and microspheres like cells can take up certain

substances from their surroundings. Coacervates can grow Microspheres can bud to from smaller microspheres. However,

microspheres and coacervates do not have all of the properties of life. Unlike cells, microspheres and coacervates do not have hereditary

material.

HOW DID CELLS FORM?

About 2.7 b.y.a., cyanobacteria or blue-green algae began photosynthetic reactions

About 1.8 b.y.a, the atmosphere contained abundant free oxygen.Allowed for the development of

more complex, oxygen-breathing life forms

Caused the first mass extinction of organism that had evolved in an oxygen-less planet

Ended the process of chemical evolution

WHEN DID ATMOSPHERIC OXYGEN APPEARED?

Spirulina

According to the endosymbiotic theory, eukaryotic cells formed from a symbiosis among several different prokaryotic organisms. Eukaryote provided a beneficial

environment Prokaryote provided a method of

energy synthesis. Did not receive much support until

the 1960s, when it was championed by Lynn Margulis of Boston University.

HOW DID THE FIRST EUKARYOTES FORMS?Aerobic

prokaryote

Anaerobic eukaryote

WHAT EVIDENCE SUPPORTS THE ENDOSYMBIOTIC THEORY? Mitochondria and chloroplasts contain DNA similar to bacterial

DNA. Mitochondria and

chloroplasts have ribosomes whose sizeand structure closelyresemble those of bacteria.

Mitochondria and chloroplasts, like bacteria, reproduce by binary fission.

Mitochondria and chloroplast replicate independently from the replication cycle of the cells that contains them.

Scientists explain that life arose from nonlife billions of years ago through the theory of abiogenesis.Could life arise from nonlife today? Explain.

WHAT IS THE ESSENTIAL QUESTION?WHAT IS THE ESSENTIAL QUESTION?