Theories of the Origins of Life

Theories of the

Origins of Life

● Began as a concentrated single point, containing all known matter and energy.

● Approximately 13.7 billion years ago this single point began to expand –known as the Big Bang.

● The universe has been expanding ever since.

● Matter is not distributed uniformly throughout the universe.

● Gravity began attracting helium and hydrogen atoms together.

● As the density increased, matter collapsed and compacted under its own weight, causing a warm, dense core called a protostar.

Origin of the Universe

● The theorized “life cycle” of a star:

● The nuclear fusion reaction from protostars creates stars.

● The star burns for millions of years, consuming it’s hydrogen.

● Heavy elements form as hydrogen

atoms fuse during the “life-cycle” of a star.

● The core becomes denser and

eventually collapses under the extreme gravity forces generated by the density.

● The star may explode causing a supernova.

● Supernova explosions account for the

distribution of heavy elements through-

out the universe.

Origin of the Solar System

● The sun, Earth, and other planets in the solar system are only one of the millions of such systems that make up the Milky Way Galaxy.

● The current theory (Solar Nebular Theory) of how our solar system began with a large cloud of hydrogen and helium called a nebula.

● A shock wave from a supernova caused the cloud to condense, which caused it to spin.

● As the cloud collapsed and became denser, it flattened in a disk due to the rotation. At the center a protostar developed and began the nuclear fusion process, becoming the sun.

● Some gas continued to revolve around the

sun, eventually condensing into masses too small to

become stars – they became the planets.

Origin of the Earth…

● According to nebular theory, Earth (and other solar

system planets) formed through accretion – the process by which small particles clump together because of gravity.

● As a mass grows the more gravity it has, the more

additional mass it attracts.

● The Earth’s growing mass caused its core to compress causing the core to heat and become molten liquid. The outer core is still molten.

● With this molten liquid, heavy matter, iron and nickel, sank toward the center, while light matter, oxygen and silicon, moved toward the surface.

This process of density

stratification formed the

layers of the Earth.

● The most widely accepted theory for the moon’s origin is the Orpheus theory.

● Orpheus theory says that a planet-sized body struck Earth during its early

development and sent some of its material into orbit, forming the moon.

Origin of the Moon…

Origin of the Atmosphere and Oceans

● When the Earth cooled enough for the surface to form a crust, gases from volcanic activity escaped accumulating as an early atmosphere.

● Gas included chlorine, nitrogen, sulfur, methane, water vapor, but NO OXYGEN.

● The surface was still so hot that when water vapor formed clouds,

then rain, the rain

boiled off again

when it hit the

ground.

● Finally, the Earth cooled enough to allow the rainwater to accumulate and the oceans formed as water vapor

condensed.

● Scientists also believed that comets (made up of

frozen gases) and meteorites brought water to Earth

during formation

The process that allowed life to form began with development of the oceans.

● Carbon dioxide dissolved into young oceans, leaving a nitrogen-rich atmosphere. Scientists think these were the conditions required for life.

● There was NO OXYGEN in the early atmospere as it was not needed.

● The first organisms were probably anaerobic

bacteria (did not use oxygen).

● Stromatolites have

been around for over 3 billion years and are believed to be first photosynthetic

organisms.

● Oxygen, essential to life today, entered the

atmosphere about 1.5 billion years ago when photosynthesizing

organisms (cyanobacteria) began using carbon

dioxide and releasing

oxygen.

● The oxygen combined with the available iron on Earth (oxidized) and substantial quantities of

oxygen accumulated in the atmosphere.

● Ozone, an oxygen molecule found high in the

atmosphere, is also important because it protects life from ultraviolet radiation.

● This allowed life to move from the ocean to

land

Why the Seas Are Salty

● One source of sea salts is minerals and chemicals eroding and dissolving into fresh water flowing into the ocean - Waves and surf also contribute by eroding coastal rock.

● Hydrothermal vents change seawater by adding some materials while removing others.

● Scientists believe these processes all

counterbalance so the average salinity of

seawater remains constant.

● The ocean is said to be in chemical

equilibrium.

Abiogenesis

● There is fossil evidence that life began in the ocean.

Scientists have found that marine life fossils are significantly older than fossils of terrestrial life.

● Cyanobacteria, some of the oldest marine fossils, are dated 3.5 billion years old – this suggests that life began in the sea.

● It is not clear how the first molecules that comprise the building blocks of life originated.

● The Urey-Miller experiment (1953) did not produce life, but did prove that basic

molecules used by living

systems readily form under

certain conditions.

● Regardless of the exact environment that allowed life to happen, biologists propose that simple molecules randomly combined and separated. Eventually larger, more stable

molecules formed by chance.

● When one of these combinations became capable of reproducing itself, life was

born.

● This origination of life from nonliving matter

is called abiogenesis, sometimes referred to

as spontaneous generation.

Oxygen and Evolution

● Heterotrophs are organisms that rely on consuming compounds to obtain chemical energy.

● Autotrophs can create organic chemical energy compounds from inorganic compounds and an external energy source.

● The appearance of autotrophs was significant because they break down carbon dioxide into oxygen.

● Oxygen is important to life because oxygen reactions allow organisms to use chemical energy more

effectively.

● The theory of evolution, originally proposed by Charles Darwin, is based on the principle that in nature,

various characteristics affect survival. Those with favorable characteristics are more likely than those with less favorable characteristics to survive and reproduce.

● The theory of evolution says that over millions of years natural selection and mutation caused the development of all the different life forms and their characteristics.

● In other words, organisms became more varied and complex over the millions

of years.