Which of these evolutionary processes is thought to have occurred first?

Question

Which of these evolutionary processes is thought to have occurred first?

A. Simple compounds existed in Earth's early oceans and hot springs.
B. Complex molecules were produced when the Sun provided enough energy.
C. Molecules like DNA and RNA formed and later reproduced themselves.
D. Protobionts formed, followed by prokaryotic cells.

I dont believe in evolution either, but i have to write all this crap for biology... and when you dont believe something its hard to study...lol

Answer 1

evolutino is bupkiss... dont believe it.




,

Answer 2

You don't believe of survival of the fittest? It's hard to Deny it when you do some research and really discover the beauty of evolution.

Even looking at viruses is proof evolution exists, viruses evolve and build immunities to medications in a phenomenal level. As a matter of fact, scientists fear that the HIV virus will become air born in the way it infects.

You can even see stumps on water animals that clearly show the digits of what was once feet-

Evolution does not disprove anything. It only reinforces the mastermind of what created us.

You may deny it if you'd like, but it most certainly isn't crap. the answer is A

Answer 3

Well out of those, A but many scientists now think complex molecules could have come from outerspace - its not as crazy as it sounds, rather complex organic compounds - like amino acids for example can be found in molecular clouds out in space.

Answer 4

B.
Stars were needed to create the more complicated elements before simple compounds (A) could exist.

Answer 5

First A
then B
then D and C simultaneously

Answer 6

You win the longest question award...
The question is moot. Evolution is only a tactic to explain away a creator.

Answer 7

A or D

Answer 8

I think that it is probably A, D, C, B.

Answer 9

A

Answer 10

Origin of Life and Cells – Themes

• Life is hypothesized to have resulted from chemical evolution that started sometime after the Earth formed 4.6 billion years ago

• The diversification of cellular life on Earth began about 3.6 - 3.8 billion years ago, and has produced a continuum of immense diversity since that time

• Life and Earth have co-evolved over this time



1. In the Beginning…

• Solar system formed ~4.6 billion years ago, so Earth is ~4.6 billion years old

• Earth is ~93 million miles from the sun

• Maintains surface temp ~20°C

• Allows water to be present as a liquid

• Allows for complex chemical reactions



Earth formed as semi-solid mass
Became denser and stratified into three layers after 600 - 800 million years
1) Core: molten metalic (~3800 km thick)

2) Mantle: dense silicate minerals (~3000 km thick)

· not solid - has convection currents

· rock heats in center, rises to surface, cools, falls down to center again

3) Crust: lighter solid covering (= lithosphere)

• crust floats on mantle (~ 100 km thick)

• made of several plates that move

• Plate techtonics = movement of plates and continents on them

c. Plate Tectonics: (aka “Continental Drift”)

• Movement caused by material from mantle pushing plates apart

• Primarily in deep oceans (e.g., mid Atlantic ridge)

• Areas of major volcanic activity

• Plates collide and become wrinkled or slide over or under one another (= subduction)

• Leads to mountain building, earthquakes

d. Three Major Physical Areas of Earth

1) Lithosphere: solid part (crust)

2) Hydrosphere: water – covers 2/3 Earth’s surface

• Life originated here (originally << 2/3 of surface)

3) Atmosphere: thin gas envelope (~25 km thick)

• Made of N2 = 79%, O2 = 20%, CO2 = 0.04%

• Early atmosphere very different!

• Little to no O2 or O3 - (a good thing)

e. Co-evolution of Earth & Life

• Geological events alter environments and change the course of biological evolution

• Conversely, life changes the planet that it inhabits









2. Life on Earth originated 3.5 to 3.8 billion years ago

• During the 1st half-billion years, Earth was very inhospitable -

• Very hot, little water and solid crust material, bombarded by rock bodies left over from the origin of the solar system

• It is unlikely that life originated before ~4 billionh years ago

• No clear fossils have been found in the oldest surviving Earth rocks, from 3.8 billion years ago

• The oldest fossils found so far, were in rocks from Australia that are 3.5 billion years old

• These fossils, called stromatolites, resemble bacteria

• The presence of these fossils implies that life originated earlier



a. The first cells may have originated by chemical evolution on a young Earth -
A hypothesis:

• Life on Earth developed from nonliving materials that became ordered into aggregates that were capable of self-replication and metabolism

• This is not the idea that life arises from nonliving matter (= spontaneous generation)

• Spontaneous generation was refuted by Louis Pasteur whose experiments showed that microorganisms in spoiled foods did not arise “spontaneously”

• All life today comes from pre-existing life (= biogenesis)



· One hypothetical scenario: Chemical evolution occurred in four stages:

(1) the abiotic synthesis of small organic molecules

(2) joining these small molecules into polymers

(3) origin of self-replicating molecules – RNA

(4) packaging of these molecules into “protobionts”



· This hypothesis leads to predictions that can be tested in the laboratory !



1) A.I. Oparin and J.B.S. Haldane postulated that conditions on the early Earth favored synthesis of organic compounds from inorganic precursors

• This cannot happen today because O2 in the atmosphere attacks chemical bonds

• The reducing environment in the early atmosphere would have promoted the joining of simple molecules to form more complex ones

• Energy sources to synthesize organic molecules - lightning, volcanic activity, and ultraviolet sunlight (no ozone layer) - were more intense than today



• In 1953, Stanley Miller and Harold Urey tested the Oparin-Haldane hypothesis by creating “Early Earth” conditions in the laboratory

• The Miller-Urey experiments produced a variety of amino acids and other organic molecules

• The “atmosphere” in the Miller-Urey model consisted of H2O, H2, CH4, and NH3 (probably more reducing than actually existed)

• The Miller-Urey experiments stimulated debate on the origin of organic matter -



• Other possible origins of organic matter:

• Submerged volcanoes and deep-sea vents where hot water and minerals gush into the deep ocean?

• From space via meteorites or comets containing organic molecules?





2) Laboratory simulations of early-Earth conditions have produced organic polymers

• Researchers have produced organic polymers abioitcally, by dripping solutions of monomers onto hot clay or rock

• Similar conditions likely existed on early Earth near fresh lava or at deep-sea vents



3) RNA – the first genetic material?

• Researchers have proposed that the first hereditary material was RNA – not DNA

• RNA molecules are important in modern cells as both heredity templates & as catalysts

• RNA catalysts, called ribozymes, remove introns from RNA

• Ribozymes also help catalyze the synthesis of new RNA polymers



• Short polymers of ribonucleotides can be synthesized abiotically in the laboratory

• Sequences up to 40 bases long can be copied from a template according to the base-pairing rules



• In the pre-biotic world, RNA molecules may have been fully capable of ribozyme-catalyzed replication

• Copying errors may have led to pre-biotic evolution
(as selection favors the best at replication and “survival”)

• Because RNA also functions as an enzyme, it helps to resolve the paradox:
Which came first, genes or enzymes?



4) Protobionts can form by self-assembly

• Protobionts are aggregates of molecules surrounded by membrane-like structures

• Protobionts form spontaneously and may have preceded living cells

• Protobionts do not reproduce precisely, but they do maintain an internal chemical environment and show some properties associated with life - metabolism and excitability



• In the laboratory, phospholipids spontaneously form droplets called liposomes —> membrane-like bilayers

· These droplets can undergo osmotic swelling or shrinking in different salt concentrations

· They also store energy as a membrane potential, a voltage cross the surface

· Liposomes behave dynamically, growing by engulfing smaller liposomes or “giving birth” to smaller liposomes

· If enzymes are included among ingredients, they are incorporated into the droplets

· These protobionts are then able to absorb substrates from their surroundings and release the products of their actions catalyzed by the enzymes

· Natural section could refine protobionts containing hereditary information

· Once primitive RNA genes and their polypeptide products were packaged within a membrane, the protobionts could have evolved as units

· Molecular cooperation could be refined because favorable components were concentrated together, rather than spread throughout the surroundings



b. Debate about the origin of cellular life continues

· From protobiont to the simplest prokaryotic cell required many smaller evolutionary steps

· Key step was the replacement of RNA by DNA
—> more stable repository of genetic information

· RNA takes on modern role as intermediates in translation of genetic info

· Earliest true organisms were prokaryotic

· These prokaryotes apparently gave rise to all other life



3. Prokaryotes dominated evolutionary history from 3.5 to 2.0 billion years ago

Two rich sources for early prokaryote fossils are stromatolites (fossilized layered microbial mats) and sediments from ancient hydrothermal vent habitats
Thus, prokaryotes were already diverse over 3 bya
Relatively early, prokaryotes diverged into two main evolutionary branches, the bacteria and the archaea
Representatives from both groups still thrive in various environments today


Oxygen began accumulating in the atmosphere about 2.7 billion years ago
· Photosynthesis probably evolved very early in prokaryotic history

§ Early versions of photosynthesis did not produce O2

· Cyanobacteria, which produce O2 as a byproduct of photosynthesis, evolved over 2.7 billion years ago

· O2 initially reacted with dissolved iron to form the precipitate iron oxide

· Later (<2.7 bya), the O2 began to accumulate in the atmosphere



· Oxygen accumulation was gradual between 2.7 and 2.2 billion years ago, but increased rapidly afterward

· This “corrosive” O2 had an enormous impact on life, dooming many prokaryote groups

· Some species survived in habitats that remained anaerobic

· Other species evolved mechanisms to use O2 in cellular respiration, to help harvest the energy stored in organic molecules



4. Eukaryotic life began >2 billion years ago

Oldest Eukaryotic fossils appear ~ 2.1 bya
· Eukaryotic cells are larger and more complex than prokaryotic cells

· Contain membrane-enclosed organelles
(Nucleus, chloroplast, mitochondria, etc.)

Key event in the emergence of eukaryotic life appears to be the “oxygen revolution”
· Chloroplast produces O2

· Mitochondrion uses O2 for cellular respiration



5. Multicellular eukaryotes evolved by 1.2 bya

By ~1.5 bya – a great diversity of unicellular eukaryotic forms had evolved in the oceans
Several of them gave rise to multicellular forms
Recent fossils from China show a diversity of algae and animals from 570 million years ago, including beautifully preserved embryos


6. Animal diversity exploded during the early Cambrian period (540 mya)

The first diversification of multicellular organisms corresponds to the time of thawing of “Snowball” Earth (~570 mya)
A second, bigger radiation of eukaryotic forms produced most of the major groups of animals during the early Cambrian period —> Life’s “Big Bang”
All appear suddenly in the fossil record during the first 20 million years of the Cambrian period


7. Plants, fungi, & animals colonized the land about 500 million years ago

· The gradual evolution from aquatic to terrestrial habitats required adaptations to prevent dehydration and to reproduce on land

• For example, plants evolved a waterproof coating of wax to slow the loss of water

• Plants colonized land in association with fungi

• Symbiotic mutualism

· Plants created new opportunities for all life, including herbivorous animals (esp. arthropods!)

· The first terrestrial vertebrates were tetrapod amphibians

· Followed much later by reptiles, which gave rise to mammals and birds

· Mammals, including primates, diversified 50-60 million years ago

· Humans diverged from other primates only 5 million years ago



8. Geologic history and biological history have been episodic – marked by revolutions that opened many new ways of life

· Episodes driven by rapid global environmental changes

· Producing a number of mass extinctions

· Followed by revolutions that opened many new ways of life



· The formation of the super-continent Pangaea during the late Paleozoic era and its breakup during the Mesozoic era explain many biogeographic puzzles



· Two major mass extinctions are documented in the fossil record:

· Permian extinction

· Claimed about 96% of marine animal species and 8 out of 27 orders of insects

· Causes??

· Enormous volcanic eruptions

· Meteorite impact

· Cretaceous extinction

· Doomed many marine and terrestrial organisms - notably the dinosaurs

· Apparently caused by large meteor impact