Search for Life in the Universe - Midterm #2

Terrestrial Planets

• smaller rocky, denser, with solid surfaces and relatively few moons

• Mercury, Venus, Earth, Mars

Jovian Planets

• large outer planets

• Jupiter and Saturn (gas giants), Uranus and Neptune (Ice giants)

Asteroids

• rocky/metallic small bodies

Comets

ice-rich bodies that can form tails near the sun

Kuiper Belt

• lies beyond Neptune

Oort Cloud

• proposed distant comet reservoir

Inner nebula

• too hot for many ices to condense

Colder Nebula

• permitted more solid material and the growth of larger cores

Nebular Theory

• a gas and dust cloud collapsed gravitationally, spun faster as angular momentum was conserved, and flattened into a disk

• the sun formed in the center. cooling enabled condensation of solids; accretion formed planetesimals, embryos, and planets

Evidence of the Nebular Theory

• mostly aligned, same-direction planetary orbits; differences between inner and outer planets; disks around young stars

Condensation

• formation of solids from gas

Accretion

Growth by accumulation

Differentiation

• internal separation by density

Parts of the Earth

• crust, mantle, outer core, inner core

Crust

thin solid exterior

Mantle

• slowly deforming solid rock

Outer core

• liquid metal

Inner core

• solid metal

Plate Tectonics

• divergent boundaries separate, convergent boundaries collide/subduct, transform boundaries slide past

Hadean Earth

• the oldest geologic eon of Earth’s history.

Giant-impact hypothesis

debris from a collision between early Earth and a large impactor formed the Moon

Prokaryotes

lack a membrane-bound nucleus

Eukaryotes

has a membrane-bound nucleus

Definition of Life

a working definition of life is a self-sustaining chemical system capable for Darwinian evolution. Viruses are a boundary case because they depend on hosts to produce

Three domains

Bacteria, Archaea, Eukarya

Cell membrane

regulated exchange

DNA

stores hereditary information

Ribosomes

build proteins

Mitochondria

participate in aerobic ATP production

Metabolism

all cellular chemistry

Catabolism

breaks molecules down

Anabolism

build molecules

Phototrophs

use light for energy

Chemotrophs

use chemical reactions

Autotrophs

use inorganic carbon

Heterotrophs

use organic Carbon

Oxygenic Photosynthesis

6CO2 + 6H2O + light -> C6H12O6 + 6O2

• biological process where plants, algae and cyanobacteria use light energy to split water molecules, producing chemical energy (ATP and NADPH), organic carbon, and molecular oxygen (O2) as a byproduct

Aerobic Respiration

reverses the overall reactant/product relationship and releases usable energy

DNA Base pairs

A-T and C-G.

DNA Replication

copies DNA

DNA Transcription

makes RNA

DNA Translation

builds proteins

Mutation

creates heritable variation

Natural selection

changes trait frequencies through differences in reproductive success; genetic drift changes allele frequencies randomly

Thermofiles

thrive in heat

Psychrophiles

thrive in the cold

Halophiles

thrive in salt

Acidophiles

thrive in acidity

Piezophiles

thrive at high pressure

Extremophiles

expand our ideas about potentially habitable environments but do not prove alien life exists

Evidence for evolution:

fossils, DNA relationships, comparative anatomy, biogeography, and observed changes, Evolution explains diversification, not the initial origin of life

Abiogenesis

means life emerging from nonliving chemistry.

Biosignature

a possible sign of life, not necessarily definitive proof

Primordial soup:

organic molecules accumulate and react in water-rich environments,

Hydrothermal vents

chemical gradients and mineral surfaces may facilitate complex chemistry

RNA world

RNA may once have served both information and catalytic roles

Miller-Urey experiment

produced organic compounds from simple starting chemicals under simulated conditions; it did NOT produce living organisms

Protocells

are membrane-line chemical compartments that may have preceded modern cells

Great Oxidation Event

• 2.4 billion years ago

• major increase in atmospheric oxygen

Humans and chimpanzees

• humans and living chimpanzees share a common ancestry; human evolution was branching, not a single ladder. Artificial life models life-like systems but is not automatically biological life.

Accretion vs Differentiation

growing a plant vs separating its internal materials

Relative vs Radiometric dating

ordering events vs assigning numerical ages

Positive vs Negative feedback

amplifying vs opposing an initial change

Autotroph vs Phototroph

carbon source vs energy spruce

Evolution vs Abiogenesis

changes in existing life vs initial emergence of life

Miller-Urey vs RNA world

an experiment producing organics vs a hypothesis about early replicating/catalytic chemistry

Natural selection vs drift

differential reproduction vs random changes

Habitability

depends on suitable conditions for liquid water, energy sources, necessary elements, and environmental stability

Natural greenhouse gases

they abosrob/reemit infrared radiation and help keep Earth warm. More greenhouse gases can enhance warming.