DO NOWS

• what do most scientists agree in relation to the origin of earth?

  1. earth is billions of years old
  2. the conditions of the early planet were very different from conditions today
• Today, the most widely accepted hypothesis of

  Earth’s origins is that the solar system formed from a

  cloud of dust and gas called a nebula.
• Gravity pulled the material in the nebula together into a large disk that circled the sun. Over millions of years, this

  material became the planets.
• For the first 700 million years, Earth was most

  likely molten.
• free oxygen was not a big part of the atmo-

  sphere until after the first forms of life evolved
• Hypotheses about how life began focus on three things: the formation of

  early organic molecules, the formation of early cells, and the structure of

  early genetic material.
• organic molecules are:

  • Sugars
  • amino acids (building blocks of life, form proteins)
• what is the miller-Urey experiment?

  When 2 scientists in the 1950s reproduced the experiments of early earth and concluded that organic molecules came from inorganic molecules
• Earth is billions of years old
• The conditions of the early planet and its atmosphere were very different from conditions today
• The most widely accepted hypothesis of Earth's origins is that the solar system formed from a cloud of dust and gas called a nebula
• For the first 700 million years, Earth was most likely molten
• Gases released from the molten Earth formed an atmosphere of ammonia, water vapor, methane, and carbon dioxide
• Free oxygen was not a big part of the atmosphere until after the first forms of life evolved
• Between 4 and 3.8 million years ago, Earth began to cool, leading to the formation of liquid water and energy sources like lightning and the sun
• Hypotheses about how life began focus on the formation of early organic molecules, the formation of early cells, and the structure of early genetic material
• Organic molecules, like sugars and amino acids, are the building blocks of life
• Two main hypotheses about how organic compounds could have appeared on Earth are the Miller-Urey experiment and the Meteorite hypothesis
• One hypothesis about early cell structure focuses on how organic molecules could have been brought together, while another hypothesis focuses on how cell membranes could have formed
• RNA, rather than DNA, may have been the genetic material in early living things
• Short chains of RNA can form from inorganic molecules, and RNA molecules called ribozymes can catalyze chemical reactions
• Over time, proteins and DNA may have replaced some functions of RNA, leading to today's system of genetic material
• what is the hypothesis on how organic molecules could have been brought together?

  hot gas came out of a crack in the ocean floor and, when that hot gas mixed with the cold ocean water, it tuned into rock. This rock had small compartments with organic molecules; they formed into the first cells due to being together.
• what is the hypothesis on how cell membranes could have formed?

  lipid molecules formed into a double membrane (lipid bilayer) due to the properties of the molecules. these membranes then surrounded organic molecules and these cell-like structures gave rise to the first true cells.
• What is the meteorite hypothesis?

  a meteorite, containing organic molecules, fell in Australia in 1969. There were 90 new organic molecules and 19 that were already found on earth. This suggests that the first organic molecules arrived on earth OR that they were already here.
• what were the conditions of the Hadean Eon ?

  • Materials making up earth were melted
  • earth was frequently hit by asteroids and comets
• what are ribozymes?

  RNA molecules that can catalyze chemical reactions, similar to the function of enzymes.
• RNA is primitive and less complicated than DNA. It is a single stranded molecule that is used to make proteins. It is simple so it makes sense that it may have been the genetic material in early living things.
• RNA can copy itself.
• The earliest microbes were prokaryotes that did not need oxygen to survive
• Microbes that evolved the ability to photosynthesize changed the atmosphere by giving off oxygen
• The earliest fossils of photosynthetic life are 3.5 billion years old and are fossils of cyanobacteria, which are bacteria that conduct photosynthesis
• Eukaryotic cells may have evolved through endosymbiosis
• Eukaryotic cells had evolved by 1.5 billion years ago and have a nucleus and other membrane-bound organelles
• Endosymbiosis is a relationship in which one organism lives within the body of another, and both benefit
• Early mitochondria and chloroplasts may have been small prokaryotic cells that were taken up by larger prokaryotes
• Mitochondria and chloroplasts have their own DNA, can copy themselves within the cell, are about the same size as prokaryotes, have circular DNA, and have gene structures similar to prokaryotes
• The evolution of sexual reproduction led to increased diversity
• Sexual reproduction allows new combinations of genes to come together, increases genetic variation within the population, and may have resulted in an increase in the rate of natural selection
• Early eukaryotes may have evolved from cells living close to each other and cooperating, which may have been the first step in the evolution of multicellular life