The Big Bang • Using the math of general relativity, one can find an infinite density and temperature at a finite past. • This singularity constitutes the birth of our Universe.
The Big Bang • Measurements of temperature fluctuations in cosmic radiation calculate the age of the universe at about 13.7 billion years. • Within 10-37 seconds of the big bang, the Universe grew exponentially and the temperature reached about a billion kelvins. • Neutrons combined with protons at about this time, forming Helium and deuterium.
Early Earth • The Earth formed 4.5 bya by accretion (growth by gravity attracting matter) from the solar nebula – cloud of gas and dust left over from Sun’s formation.
Early Earth • After impact with another proto-planet, the moon was formed from the Earth and the hot liquid metals of the Earth’s core began to cool. • Oceans did not exist because Earth was too hot • As the planet cooled, clouds formed. Rain then created the oceans. • The atmosphere was composed mostly of water vapor, carbon dioxide, and nitrogen. • Volcanic activity was intense.
Origin of Life - Abiogenesis • The early atmosphere was likely reducing (gaining electrons) • The Miller-Urey experiments showed that amino acids can be catalyzed by electrical activity (lightning) in this environment. • Other theories have been proposed
Origin of Life - Abiogenesis • Thermal vents deep in the ocean release hot gases where organic chemistry could occur. • Extraterrestrial sources: • Life could have arrived on earth from deep within a meteor, protected from radiation.
Early Life • All life forms from a common ancestor
Early Life • Rocks that are more than 3.5 bya, called stromatolites, contain unicellular prokaryotic organisms that evolved in the absence of O2. • These cyanobacteria went through photosynthesis and by 2.2 bya, O2 was accumulating in the atmosphere.
Eukaryotes • The rise of oxygen in the atmosphere changed the Earth’s environment forever, allowing oxygen-breathers to evolve. • Endosymbiotic theory proposes that eukaryotes evolved from communities of prokaryotes that entered other cells and stayed as organelles.
Multicellular Organisms • 90% of Earth’s history occurred in the Precambrian. • Life existed only in the sea.
Cambrian Explosion • Diversification of life during the early Cambrian Period. • Around 530 mya, the majority of major groups of animals appeared in the fossil record. • This was arguably the most important period in evolution.