Earth's History and the Universe

Earth's History: A Summary

• Earth's history is characterized by constant change, documented through paleogeography (past landscapes), paleontology (past organisms), paleoecology (past ecosystems), and paleoclimatology (past environments)
• The universe is estimated to be 13.8 billion years old, expanding at an increasing rate.
• The Big Bang theory describes the universe's origin from an infinitely dense, hot core. This theory is supported by Einstein's general relativity and empirical observations.
• Spectroscopy, the measurement of spectra (wavelengths of electromagnetic radiation), is used to determine elemental composition of celestial bodies such as the Sun.

Origin of the Universe

• The universe, containing infinite galaxies and solar systems, is expanding constantly since the Big Bang.
• The Big Bang, an explosive outward expansion, created atoms, starting with hydrogen (74%).
• Spectroscopy allows measurements of light and the spectrum to determine element composition in objects since the elements leave specific absorption signatures.
• The Doppler effect, with changes in wavelengths of light of a moving object, enables the determination of speed and direction of stars and galaxies. Hubble's observation of redshift helped prove the universe is expanding.

Death of a Star

• Stars, formed from combining elements via gravitational attraction, start their lives by fusing hydrogen into helium.
• Stars spend most of their lives with consistent size and energy output via controlled hydrogen fusion.
• Larger stars fuse heavier elements, forming heavier elements and increasing their size and brightness.
• The death of a star depends on mass: smaller stars form planetary nebulae; more massive stars produce supernovae, releasing even heavier elements.

Origin of the Solar System

• The nebular hypothesis states that the solar system originated from a spinning nebula that flattened into a protoplanetary disk, forming the Sun and planets.
• Planetary arrangement varies with temperature: Inner planets are rocky, formed from higher-melting-point materials; outer planets are gaseous giants containing mostly hydrogen and helium. Jupiter's influence affected inner planet formation by accelerating collision and movement of materials in the solar system.

Origin of Earth

• Objects building planets and moons were dispersed throughout the solar system at the start.
• Evidence of a later period of major impacts, called the Late Heavy Bombardment, roughly 4.1 - 3.8 billion years ago, is present in samples from the Moon. The bombardment could be caused by gravitational resonances between Jupiter and Saturn
• Earth is heterogeneous with layers of crust (felsic and mafic), mantle, and core.

Origin of the Moon

• The prevailing hypothesis for the Moon's origin is a giant-impact event involving a Mars-sized body that collided with early Earth, ejecting material that formed the Moon.

Origin of Earth's Water

• Possible sources of Earth's water include volcanic outgassing, comets, and meteorites.
• Isotopic matching of Earth's water with water from meteorites suggests meteorites were a significant source of Earth's water, rather than comets

Hadean Eon

• A period in Earth's earliest history. (4.5-4.0 billion years ago)
• Characterized by a partially molten surface, volcanism, and asteroid impacts.
• Earth's initial heat was caused by gravitational compression, radioactive decay, and asteroid impacts.

Archean Eon

• (4.0 - 2.5 billion years ago).
• Start of the rock record.
• Formation of early continents.

Proterozoic Eon

• (2.5 - 0.541 billion years ago).
• Continents moved and merged into a supercontinent called Rodinia.

Phanerozoic Eon

• (0.541 billion years ago to present)
• "Visible life" due to extensive fossil records.
• Divided into Paleozoic, Mesozoic, and Cenozoic eras.

Paleozoic Era

• Dominated by marine organisms.
• Gradual evolution of life on land, including tetrapods and amniotes.
• Extensive sea-level fluctuations.
• Formation of the supercontinent Pangea.
• Tectonic activity led to major mountain-building events (e.g., Appalachian Mountains).
• Formation of extensive forests during the Carboniferous Period leading to the formation of vast coal reserves.

Mesozoic Era

• "Age of Reptiles".
• Dinosaurs become dominant.
• Pangea begins to break apart.
• Development of flowering plants and major tectonic shifts led to formation of Rocky Mountains; interior seaway.

Cenozoic Era

• "Age of Mammals".
• Mammals and birds become dominant after the extinction of dinosaurs.
• Extensive ice ages occur.
• Formation of the Himalayas, Alps, and other mountain ranges.
• Plate movement creates basins and ranges in western North America in association with the San Andreas Fault.
• Early hominids and human evolution occur toward the end of this era

Anthropocene Epoch

• Possibility of human activity having initiated a new geologic epoch, characterized by major environmental changes caused by human activity as indicated by presence of uniquely human created materials like plastics, and metals in the geologic record.
• There are discussions surrounding the beginning of this epoch.