Origin of Life on Earth

Formation of Earth

Our knowledge of earth’s history

•Hypotheses about Earth’s early history are based on a relatively small amount of evidence.

•Gaps and uncertainties make it likely that scientific ideas about the origin of life will change.

Formation of our Planet

• Evidence shows that Earth was not “born” in a single event.

• Pieces of cosmic debris were probably attracted to one another over the course of 100 million years.

• While Earth was young, it was struck by one or more objects, producing enough heat to melt the entire globe.

Formation of Earth

• Once Earth melted, its elements rearranged themselves according to density.

• The most dense elements formed the planet’s core.

• Moderately dense elements floated to the surface, cooled, and formed a solid crust.

• The least dense elements formed the first atmosphere.

Elements/ molecules/ compounds of early Earth

– Earth's early atmosphere probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water.

– Notice the early atmosphere had NO oxygen.

– Had frequent storms with lightning

– High ultra-violet light (no ozone layer)

Big Events on Planet Earth

• Scientists infer that about four billion years ago, Earth cooled and solid rocks formed on its surface.

• Millions of years later, volcanic activity shook Earth’s crust.

• About 3.8 billion years ago, Earth’s surface cooled enough for water to remain a liquid, and oceans covered much of the surface.

IB LEARNING OBJECTIVE

• Describe four processes needed for the spontaneous origin of life on Earth.

Requirements for Life as we know it.

• The following steps would have to occur for life as we know it to evolve:

– The non-living synthesis of simple organic molecules

– The assembly of these molecules into polymers

– The development of self-replication molecules, such as nucleic acids (DNA, RNA)

– The packaging of these molecules within membrane sacs, so that an internal chemistry can develop, different from the surrounding environment.

IB Learning Objectives

• Outline the experiments of Miller and Urey into the origin of organic compounds.

The First Organic Molecules

• The First Organic Molecules

• Could organic molecules have evolved under conditions on early Earth?

• In the 1950s, Stanley Miller and Harold Urey tried to answer that question by simulating conditions on the early Earth in a laboratory setting.

The First Organic Molecules• Miller and Urey’s Experiment

Mixture of gases simulatingatmosphere of early Earth

Condensationchamber

Spark simulatinglightning storms

Watervapor

Liquid containing amino acids and other organiccompounds

Cold water cools chamber, causing droplets to form.

The First Organic Molecules

– Miller and Urey's experiments suggested how mixtures of the organic compounds necessary for life could have arisen from simpler compounds present on a primitive Earth.

– Although their simulations of early Earth were not accurate, experiments with current knowledge yielded similar results.

Miller & Urey’s Experiment

• In order to discover how organic molecules evolved on earth, they recreated the conditions of early Earth.

– In their apparatus they mixed the gases:

• Ammonia

• Methane

• Hydrogen

– To form a reducing atmosphere.

Miller Urey’s Experiment

• The ran electric charges and the boiling and condensing of water simulated lightening and rainfall .

Miller & Urey’s Experiment

• What they discovered:

– They ran the experiment for one week.

– After one week the water turned murky brown.

– Inside the water they found 15 amino acids.

• What they concluded:

– Organic compounds ( the building blocks of life) could have spontaneously formed in early earth before there were any living organisms

Miller & Urey Experiment Animations

• http://bcs.whfreeman.com/thelifewire/content/chp03/0301s.swf

• http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter26/animation_-_miller-urey_experiment.html

• http://bcs.whfreeman.com/thelifewire/content/chp03/0302001.html

IB Learning Objectives

• Discuss possible locations where conditions would have allowed the synthesis of organic compounds

About 3.5 billion years ago life evolved

Ideas of the origin of organic molecule

•Three ideas about where the first organism molecules came from

– Miller & Urey’s Experiment suggest they could have originated on Earth spontaneously.

– Hydrothermal Vents

– Extraterrestrial origin (comets, meteorites)

• Instead of forming in the atmosphere, the first organic compounds may have been synthesized near submerged volcanoes and deep-sea vents

Video: Hydrothermal VentVideo: Hydrothermal Vent Video: TubewormsVideo: Tubeworms

Submerged Volcanoes

http://exploringorigins.org/fattyacids.htmlVideo on Organic Molecules forming in Hydrothermal vents.

Extraterrestrial Sources of Organic Compounds

• Some organic compounds from which the first life on Earth arose may have come from space

• Carbon compounds have been found in some meteorites that landed on Earth

• This idea is called panspermia