14-2: EARTH’S HISTORY

The Formation of Earth About 5 billion years ago, our solar system was a swirling mass of gas and dust Over time, these materials collapsed inward forming the sun

Formation (cont.) The planets are thought to have been made from 400 million years of constant collisions of dust and debris Earth grew from these collisions Thermal energy was released each time debris hit the Earth

Earth’s Age Earth is more than 4 billion years old (~4.6 b.y.) How do we know? Scientists have drilled holes down into Earth’s layers More modern techniques established in the 20th century

Radiometric Dating A radioactive isotope is used to date material The isotope is chemically unstable Nucleus will release particles/radiant energy Known as radioactive decay Scientists will measure the half-life of a radioactive isotope Length of time it takes for ½ of the isotope to decay Half-lives vary from fraction of a second to billions of years

Half-live Graph

Example: C-14 Dating Organic materials can be dated by comparing the amount of C-14:C-12 Living things take carbon into their bodies constantly, most of it in the form of C-12; a very small proportion of it is C-14, which undergoes decay

Example: C-14 Dating When an organism dies, its uptake of carbon STOPS, and decay of the existing C-14 continues Thus over time, the amount of C-14 declines with respect to the original amount of stable C-12 The half-life of C-14 is 5,730 years C-14 is limited to organic remains less than 60,000 years old

Radiometric Dating (cont.) The two isotopes that were used to date the Earth were: Thorium-230 (75,000 years) Uranium-238 (4.5 billion yrs) Scientists found rocks + zircon crystals that are 4.2 billion years old - - so Earth must be older than that

The First Organic Compounds All of the elements in organic compounds were thought to have existed on Earth and in the solar system when Earth formed How did all these elements assemble into life forms?

Alexander I. Oparin In 1923, Oparin + Haldane “Primordial Soup” model Spontaneous origin from inorganic gases They believed the atmosphere contained: Ammonia – NH3 Hydrogen gas – H2 Water vapor – H2O Methane gas – CH4

Oparin (cont.) At high temps, these gases might have formed org. comps such as amino acids When the Earth cooled, water condensed to form lakes and seas compounds collected in water over time, entered chemical reactions = fueled by lightning + UV radiation These rxns could have ultimately resulted in macromolecules essential to life such as PROTEINS; building blocks for the 1st cells

Synthesis of Org. Compounds Oparin never tested his hypothesis In 1953, Miller + Urey tested Oparin’s hypothesis Set-up this apparatus

Miller-Urey (cont.) Experiment: Chamber with gases Oparin thought were on early Earth Simulated lightning (spark from electrode) Chemical reactions Produced a variety of organic compounds, including AA

Miller-Urey (cont.) Since the 1950s, scientists have continued to explore this idea of spontaneous origin Have been able to produce AA, ATP, and DNA nucleotides Suggests that there were many ways these compounds could have formed on young Earth

Miller-Urey (cont.) The gases included: In more recent years, new hypotheses were proposed as to the atmosphere on early Earth The gases included: Carbon dioxide – CO2 Nitrogen – N2 Water vapor – H2O Lab simulations showed the CO2 + O2 interfere with production of organic compounds Organic compounds might have only been able to be produced in protected areas from the atmosphere… Under WATER???

Org. Compounds beyond Earth Another Hypothesis… The organic compounds could have been carried to Earth by debris from space (meteorite) Scientists hypothesized that these compounds were formed in space and could have accumulated on Earth’s surface

From Molecules to Cell-like Structures Scientists (Sidney Fox) have tried to create the physical structures that may have given rise to the first cells These cell-like structures were created in a lab from simple organic compounds Microspheres Spherical in shape Composed of many protein molecules organized in a membrane Coacervates Collection of droplets from dissimilar substances (AA + sugars)

From Molecules to Cell-like Structures For many years, it had been assumed that all cell structures and the chemical reactions of life required ENZYMES that were specified by the genetic information of the cell Both microspheres and coacervates were spontaneously created in a lab and have several life-like properties, such as growth, reproduction, + taking in substances from their environment Microspheres + coacervates do not have hereditary characteristics and thus aren’t LIVING!