Origin of water on Earth

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Origin of water on Earth

• By
• Brian Spall

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(No Transcript)
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Overview

• Some water facts
• Introduction to the two main theories of the
  origin of Earths water
• Describe theories
• Problems
• Future research

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Facts About the Water

• Earth has about 3 x 1024g of water. Thats 0.06
  by weight.
• Roughly half is in the crust and the rest in the
  mantle.
• Earths D/H ratio is 1.5 x 10-4
• Mars has a D/H ratio of 3.0 x 10-4
• Venus has a high D/H ratio of 2.5 x 10-2
• Carbonaceous chondrites have an average D/H ratio
  of around 1.5 x 10-4
• Comets have a D/H ratio of 3.0 x 10-4

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The Two Major Theories

• The Late Veneer
• Supported by A. Morbidelli and J. Chambers
• Delivers water and gases to the upper mantle and
  crust
• Water comes in stages
• Earth starts dry

• Wet Planetesimals
• Supported by M. Drake and K. Righter
• Water found near by forming Earth
• Allows water from the beginning
• Simple and precise

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How the Late Veneer Works

• The ignited sun dries out the material in the
  inner solar system as a run-away growth of
  planetesimals occurs
• As Jupiter accretes to its present size, the
  astroid belt is depleted of material
• Wet carbonaceous chondrites and other
  Jupiter-Saturn planetesimals are brought in by
  gas drag and fall on the proto-Earth bringing
  water with present day D/H ratios
• A late bombardment from material originally
  located at the Neptune region might supply Earth
  with high D/H water and other elements

Carbonaceous Chondrite
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The Wet Planetesimal Theory

• Wet material at about 1 AU accretes together to
  form Earth
• Has shown that some water can be present as core
  forms
• If the inner solar systems D/H levels are low
  there could have been at most 50 water input
  from comets, if the levels where that of the
  protosteller level there would only be 10-15
  cometary water
• Water would have been present all of Earths
  existence and just more would show up over time
• Explains the seen oxygen differentiation of the
  planets

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Problems

• Why just Earth, what about Venus and Mars?
• Current models for Earths core formation needed
  dry material to behave the way we see
• The late veneer theory requires the astroid belt
  to have been very large
• Like other solar system events, one building
  block for the process doesnt fit with the data
• There is no way of knowing the Earths original
  D/H ratio
• There has been no simulation that produces the
  system we see today
• Oxygen isotope differences infer changing solar
  composition over small areas

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What to do in the future

• More sampling of asteroids and comets for D/H
  ratios and other composition factors
• Better computes for simulations
• A better understanding of our mantle and core
  chemistry
• Knowing how the Earth formed!
• Invention of the time machine

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Thank you