Tuesday, February 28, 2012

First Civilization Part 1 Chapter 8

 

One Planetary Survey Robot that was sent by the Gliesians came into our solar system during the Amazonian period  and surveyed  Mars and Earth. The Amazonian period-started 3.3 Gyr ago. The Mars that the Planetary Surveyor examined noted that there were not many regions with meteorite impact craters,  otherwise the terrain was quite varied. It looked like the right place to explore.  If we go by the mineral time scale we would be in the Siderikan era (named for iron in Greek, for the iron oxides that formed) it began about the same time the Amazonian period began. At the beginning of this era there was a decline of volcanism and water was still plentiful, the most notable thing on the planet’s surface was the weathering process that caused the slow oxidation of the iron-rich rocks by atmospheric peroxides producing the red iron oxides that gave the planet its reddish color.  But then it also looked more like a green and blue habitable planet.

A comparison: This tells you how little we know of this planet's history:

Crater Time Line:

CraterTimeline

Mineral Time Line:

mineral timeline

The  Earth time period equivalent to this time would be the late Archean era 3.8-3.5 billion years ago. Photosynthesis began at this time. At the end of the Achaean era around 2.5 billion years ago the Proterozoic era   began. The atmosphere on Earth  had not become oxygen rich yet there and there were other gases in the atmosphere that were not good for life as we know it.  The first simple life appears, after that first multicultural life appeared. Then the Paleozoic is when the first vertebrae animals appears followed by the dinosaurs from the Melezoic to the Cenozoic periods  It was a not a good time to migrate there so the Surveyor noted.

 

martian plant

A Martian Plant and grass

As the Surveyor came to Mars it flew into the atmosphere and began its orbit. It began to analyze the gases in the atmosphere.  Record pictures of the land below the land in the south and the ocean in the northern areas.  There was also plant life and animal life on the planet much of it resembling prehistoric Earth.

600px-TerraformedMars

Mars During the Early Amazonian and Siderikan Periods

The Mars that the Planetary Surveyor explored was not the Mars we see today.  It would have been a green and blue planet with life on it.  The enormous impact basins, like the Hellas Planitia in the southern hemisphere may not have existed yet. If it had it would have definitely been an inland sea.

paelazoci

A Prehistoric Martian Swamp


There would have probably been the ancient, low-relief volcanic construction at the Tharsis Bulge located along the northeastern and southwestern portions of the rim. There would also have been more volcanic activity than the Tharsis Bulge on the planet- maybe even on the other side of the planet.  The basin floor contains thick, structurally complex sedimentary deposits that appeared to have a long geologic history of deposition, erosion, and internal deformation.  The two other large impact structures on the planet are the Argyre and Isidis basins if they existed then, would have  become lakes. The Argyre lake was located in the southern highlands and would have been surrounded by a ring of mountains and lush greenery.

Valles Marineris 2

The Valles Marineris at Night

Near the equator, what the Planetary Surveyor saw was not the Valles Marineris as we see  today.  There was to be sure a canyon there but one that was growing steadily bigger and bigger over time. There was also a river going down this rift valley.  Since plate tectonics at the time was still working it would still be going through the process to be the huge long rift canyon we see today. It  would have been surrounded by greenery and forests.

north pole

The Early Planum Boreum (the Martian North Pole)

Both residual ice caps were covered with thick-layered deposits of inter-bedded ice  at the poles. In the north, the layered deposits formed a 300 km high mountain. . Both plana (the Latin plural of planum) are sometimes treated to be synonymous with the “polar ice caps”, but in those days, they were real ice caps going deep with permanent ice forming a thick mantle on top of  layered deposits. The layered deposits probably represented alternating cycles of dust and ice deposition caused by climate changes related to variations in the planet's orbital parameters over time.  With all this information, the Planetary Surveyor Robot was ready to return home make its report and recommendations.
End of Part 1

Sunday, February 26, 2012

First Civilization Part 1 Chapter 7

 

The Phoenix lander returned data showing Martian soil to be slightly alkaline and containing elements such as magnesium, sodium, potassium and chlorides such as Sodium Chloride or natural salt. These nutrients are found in gardens on Earth, and are necessary for growth of plants. Experiments performed by the Lander showed that the Martian soil has a basic pH of 8.3, and may contain traces of the salt perchlorate.  Perchlorates are found in dry arid regions or in deserts this does not mean these chemicals are detrimental to life like NASA would like us to think.

Silicon_Map_Mars

Silicon Map of Mars

Evidence suggests that the planet was once significantly more habitable than it is today, and in all probability, living organisms once lived there and still do. The Viking probes of the mid-1970s carried experiments designed to detect microorganisms in Martian soil at their respective landing sites and had positive results, including a temporary increase of Carbon Dioxide production on exposure to water and nutrients. This sign of life was later disputed by some scientists (as usual), resulting in a continuing debate, with NASA scientist Gilbert Levin asserting that, Viking may have found life. A NASA re-analysis of the Viking data, in light of modern knowledge of extremophile forms of life, has suggested that the Viking tests were not sophisticated enough to detect these forms of life (and that is debatable). The tests could, however, have killed a life form.
ALH84001  

Martian Meteorite ALH84001

At the Johnson space center lab, some fascinating shapes have been found in the Martian meteorite ALH84001. Some scientists propose that these familiar looking shapes could be fossilized microbes extant on Mars before the meteorite was blasted into space by a meteor strike and sent on a 15 million-year voyage to Earth.  But no one knows the meteorite’s point of origin on Mars.  Small quantities of methane and formaldehyde were recently detected by Mars orbiters, which indicates there is life on Mars.  In conclusion this  meteorite contains the fossilized remains of simple life forms that once lived on Mars.
 
Scientists think that the most abundant chemical elements in the Martian crust, besides silicon and oxygen, are iron, magnesium, aluminum, and calcium. These elements are major components of the minerals comprising igneous rocks.  Hydrogen is present as water  ice and in hydrated minerals. Carbon occurs as carbon dioxide in the atmosphere and sometimes as dry ice at the poles. An unknown amount of carbon is also stored in carbonates. Molecular nitrogen makes up 2.7 percent of the atmosphere. As far as we know today, organic compounds are present because of the methane detected in the atmosphere.  That living organisms that live there today have went underground because of the changes that have occurred to the planet's atmosphere (there also seems to be some evidence that a few of these life forms have been seen on the surface of Mars occasionally).

opportunity rover

Opportunity Rover

The elemental composition of Mars is different from Earth's in several significant ways. First, Martian meteorite analysis suggests that the planet’s mantle is about twice as rich in iron as the Earth’s mantle. Second, its core is richer in sulfur. Third, the Martian mantle is richer in potassium and phosphorus than Earth’s, and fourth, the Martian crust contains a higher percentage of volatile elements such as sulfur and chlorine than the Earth's crust does. Many of these conclusions are supported by in situ analyses of rocks and soils on the Martian surface performed by the Martian rover still in operation there.
MarsTopoMap

Mars Topographical Map

Mars Orbital Laser Altimeter (MOLA) colorized shaded-relief maps showing elevations in the western and eastern hemispheres of Mars. (Left): The western hemisphere is dominated by the Tharsis Bulge region (red and brown). Tall volcanoes appear white. Valles Marineris (blue) is the long gash-like feature to the right. (Right): Eastern hemisphere shows the cratered highlands (yellow to red) with the Hellas basin (deep blue/purple) at lower left. The Elysium province is at the upper right edge. Areas north of the dichotomy boundary appear as shades of blue on both maps.  This dichotomy boundary was the shores of a huge ocean in the northern hemisphere of Mars.

mars ocean

The Northern Ocean on Mars

The northern and southern hemispheres of Mars are strikingly different from each other in topography. This dichotomy (division) is a fundamental global geologic feature of the planet. Simply stated, the northern part of the planet is an enormous topographic depression that was once a huge ocean. About one-third of the planet’s surface (mostly in the northern hemisphere) lies 3–6 km lower in elevation than the southern two-thirds indicating it was the basin of this ocean. The dichotomy is also different in two other ways: as a difference in impact crater density and crustal thickness between the two hemispheres.

 

mars-geology-plate-tectonics

Mars Plate Tectonics

Besides the volcanoes in and around the Tharsis Bulge, there is other evidence of plate tectonics on Mars. The Mars Global Surveyor (MGS) discovered magnetic stripes in the crust of Mars, especially in the Phaethontis and Eridania quadrangles. The magnetometer on MGS discovered 100 km wide stripes of magnetized crust running roughly parallel for up to 2000 km. These stripes alternate in polarity with the north magnetic pole of one pointing up from the surface and the south magnetic pole of the next pointing down. When similar stripes were discovered on Earth in the 1960s, they were taken as evidence of plate tectonics. However, there are some differences, between the magnetic stripes on Earth and those on Mars. The Martian stripes are wider, much more strongly magnetized, and do not appear to spread out from a middle crustal spreading zone. Because the area with the magnetic stripes is about 4 billion years old, it is possible that the global magnetic field probably lasted for two or three billion years of Mars' life. At that time, the temperature of the molten iron in the planet's core should have been high enough to mix it into a magnetic dynamo that would have produced Mars’ magnetic field. This would have been necessary to protect the planet’s atmosphere from being ripped away by the stellar wind and prevent harmful radiation from reaching the planet’s surface.

Banded_Iron_Formation

A Banded Magnetic Rock

The Viking Orbiters caused a revolution in our ideas about water on Mars. Huge river valleys were found in many areas. They showed that floods of water broke through natural dams, carved deep valleys, eroded grooves into bedrock, and traveled thousands of kilometers. Areas of branched streams, in the southern hemisphere, suggests that rain once fell upon the planet.

Saturday, February 25, 2012

First Civilization Part 1 Chapter 6

 

We will call the ancient astronauts the Gliesians.   They lived in a six-planet solar system that was in orbit around a red dwarf star.  Their home planet of Gliese was about 1.5 times larger than Earth.  The planet they lived on had liquid water and was a rocky planet.  It was a terrestrial planet much like Earth in the habitable zone of its star.

Gliesehomeplanet

The Planet Gliese

The temperature on Gliese averaged from 0-40 Celsius under normal conditions.  There was a Neptune and Jupiter sized planet in the outer part of that solar system and a Venus type planet closer to the star and two other smaller sized planets.  However, all of Gliese’s oceans were beginning to get very cold as was the daily temperatures.
cygnus

Cygnus

The red dwarf star at the solar system’s center had the mass of one half of that of our  Sun.  This solar system was located 21 light years from Earth in the constellation Cygnus.

red dwarf star

The Red Dwarf Star of Gliese

The planet was beginning to suffer from bitter cold.  The Gliesians began to make preparations for a migration.  But where ? The planet next closest to its sun suffered from the greenhouse effect. The planets in the outer solar system were gas giants.  They decided to send robot spacecraft to neighboring stars to look for a new home.

Robot_Probe

Gleisian Planetary Surveyor Robot


An M-class dwarf star such as the Gliesean’s star had a much lower mass than the Sun, causing the core region of the star to fuse hydrogen at a significantly lower rate. It had an effective temperature of 3250 Kelvin and it was falling due to age. It had a visual luminosity of 0.3% of that of the Sun.


However, this red dwarf  radiated primarily in the near infrared, with peak emissions at a wavelength of roughly 900 nanometers, for the star's total luminosity. (For comparison, the peak emission of the Sun is roughly 530 nanometers, in the middle of the visible part of the spectrum). When radiation over the entire spectrum is taken into account (not just the part that humans are able to see), something known as the bolometric correction, this star had a bolometric luminosity 2.0% of the Sun's total luminosity.  It was very dim by our standards.


This planet needed to be situated much closer to this star in order to receive a comparable amount of energy to that of a planet like Earth, which is what was needed there. But that energy was steadily decreasing.  No one had any idea of how long the Planetary Surveyor Robot would take to find a suitable planet.  Naturally, they would rely on astronomy and astrophysics to send them to the most likely areas in the galaxy, preferably some place that would not take long to reach. This would require a spaceship technology to have a warp drive technology at the very least.  Then if the planet discovered already had intelligent life that would definitely complicate the picture.  But they would have to migrate - there was no doubt about that. Time would be to short to do otherwise.

gliesian city 3

A city on Gliese during the daytime

Red dwarfs are the smallest, coolest, and most common type of star. Estimates of their abundance range from 70% to more than 90% of all stars in the galaxy, an often-quoted median figure being 73%. Red dwarfs are either late K or M spectral type. Given their low energy output, red dwarfs are never visible by the unaided eye from Earth; neither the closest red dwarf star to the Sun when viewed individually, Proxima Centauri (which is also the closest star to the Sun), nor the closest solitary red dwarf, Barnard's star, is anywhere near visual magnitude.

proxima centauri

Proxima Centauri

Planets that are close to red dwarfs to receive a sufficient amount of radiation for liquid water are likely to have long been tidally locked to their respective stars so that the planet rotates only once for every time it completes an orbit: this means that one face always points at the star (creating perpetual day) and one face always points away (creating perpetual night). Potential life would be limited to a ring-like region, known as the terminator, where the sun would always appear on the horizon. But Gleise was in a perfect spot in the habitable zone and did not have that problem. 
Red dwarfs are far more variable and violent than than other stars. The light by them may be reduced down to 40% for months at a time and that can definitely effect the temperature on a planet. Often they are covered in star spots that can dim their emitted light. So this issue only made the problem worse for the Gleisians.

ig383-exoplanet-14-02rich in water size between E and Nep

The Gliesian Red Dwarf Star with Star spots

There is, however, one major advantage that red dwarfs have over other stars as abodes for life: they live a long time (if that is an advantage at all). It took a very long time before humanity appeared on Earth, and life as we know it will see suitable conditions for as little as half a billion years more. Red dwarfs, by contrast, can live for trillions of years, because their nuclear reactions are far slower than those of larger stars, meaning that life would have a longer time to evolve and longer time to survive.

Friday, February 24, 2012

First Civilization Part 1 Chapter 5

 

Based on orbital observations and the examination of the Martian meteorite collection, the surface of Mars appears to be composed primarily of basalt. Basaltic rock is a black volcanic rock containing 55%  silicon dioxide .  Minerals found in balsaltic andesite include olivine, augite, and plagioclase. 

basaltic-andesite

Basaltic andesite

Some evidence suggests that a portion of the Martian surface is more silica-rich than typical basalt, and may be similar to andesitic rocks (A gray, fine-grained volcanic rock. Andesite consists mainly of sodium-rich plagioclase and one or more mafic minerals such as biotite, hornblende, or pyroxene. Plagioclase is a member of the feldspar family. 

Basaltic andiosite plagioglase

Basaltic andesite plagioclase

It is a major mineral in the Earth's crust and the rocky highlands of the Earth's moon.   It often contains small, visible crystals (phenocrysts) of plagioclase in it, these observations may also be explained by silicon dioxide (sand).  These are igneous rocks and are the result of the cooling and solidification of magma or lava.
Crater density timescale:
Studies of impact crater densities on the Martian surface have delineated four broad periods in the planet's geologic history. The periods were named after places on Mars that have large-scale surface features, such as large craters or widespread lava flows that date back to these time periods. There is also a second method called the Mineral Time Scale. The Crater Density Timescale is as follows:

CraterTimeline

Pre-Noachian: Represents the interval from the accretion and differentiation of the planet about 4.5 billion years ago (Gya) to the formation of the Hellas impact basin, between 4.1 and 3.8 Gya. Most of the geologic record of this interval has been erased by subsequent erosion and high impact rates. The crustal dichotomy (or shore of the Northern Ocean) is thought to have formed during this time, along with the Argyre and Isidis basins.
Noachian Period:  (named after Noachis Terra): Formation of the oldest extant surfaces of Mars, 4.5 billion years ago to 3.5 billion years ago. Noachian age surfaces are scarred by many large impact craters. The Tharsis bulge, a volcanic upland, is thought to have formed during this period (which means volcano activity had begun), with extensive flooding by liquid water late in the period.

tharsis bulge area

Tharsis Bulge Area

Hesperian Period:  (named after Hesperia Plenum): 3.5 billion years ago to 2.9 billion years ago. The Hesperian period is marked by the formation of extensive lava plains on Mars.
Amazonian Period: (named after Amazonis Planitia): 3.3-2.9 billion years ago to present. Amazonian regions have few meteorite impact craters, but are otherwise quite varied. Olympus Mons formed during this period, along with lava flows elsewhere on Mars which means volcano activity had increased.  First life appears on Mars.

mars-sea2

Martian river leading to the Northern Ocean

 

Mineral Time scale:
In 2006, researchers using data from the OMEGA Visible and Infrared Mineralogical Mapping Spectrometer on board the Mars Express orbiter proposed an alternative Martian timescale based on the predominant type of mineral alteration that occurred on Mars due to different types of chemical weathering in the planets' past. They proposed dividing the history of the Mars into three eras- the Phyllocian, Theiikian and Siderikan:
mineral timeline
Phyllocian Period: (named after phyllosilicate or clay minerals that characterize the era) lasted from the formation of the planet until around the Early Noachian (about 4.0 Gya). OMEGA identified outcropping of phyllosilicates at numerous locations on Mars, all in rocks that were exclusively Pre-Noachian or Noachian in age (most notably in rock exposures in Nili Fossae and Mawrith Vallis):
clay minerals on Mars

Clay minerals on Mars suggest the presence of liquid water in large quantities.

Clay or Phyllosillicates require a water-rich, alkaline environment to form. The Phyllocian era correlates with the age of valley network formation on Mars, suggesting an early climate that was conducive to the presence of abundant surface water. It is thought that deposits from this era are the best candidates in which to search for evidence of past and present life on the planet.
Theiikian Period: (named after sulfurous in Greek, for the sulfate minerals that were formed) lasted until about 3.5 Gya. It was an era of extensive volcanism, which released large amounts of sulfur dioxide  into the atmosphere. The  sulfur dioxide combined with water to create a sulfuric acid-rich environment that allowed the formation of hydrated sulfates (notably kieserite and gypsum).
Siderikan Period:  (named for iron in Greek, for the iron oxides that formed) lasted from 3.5 Gya until the present. Simple life forms and animals appear and go underground with the decline of volcanism and lack of available water late in that period. The most notable surface weathering process has been the slow oxidation of the iron-rich rocks by atmospheric peroxides producing the red iron oxides that give the planet its familiar color.


Earth Equivalent: Almost all this latter time can be located in the Proterozoic era 2.5 billion years-512 Ma. The Atmosphere became oxygen and rich and simple life forms appear.  1.5 Gya-251 Ma. multicultural life and first animals appear.  In 380 Ma first vertebrae land animals appear. Melezoic-Cenozoic:  251-65 Ma Age of the dinosaurs:
trex-triceratops

 

 

Thursday, February 23, 2012

First Civilization Part 1 Chapter 4

 

The geologic record of the Proterozoic (2,500-570 Ma) is known much better than that for the preceding Archean. In contrast to the deep-water deposits of the Archean, the Proterozoic features many strata that were laid down in extensive shallow epicontinental seas; furthermore, many of these rocks are less metamorphisized than Archean-Eon ones, and plenty are unaltered. Study of these rocks show that the period featured massive, rapid continental accretion (unique to the Proterozoic), super continent cycles, and wholly modern organic activity. The first-known glaciations occurred during the Proterozoic, one began shortly after the beginning of the period, while there were at least four during the Neoproterozoic, climaxing with the Snowball Earth of the Varangian glaciation.

1st ice age

The Proterozoic Ice age Begins

During the Solar System's formation, Mars had been created out of the protoplanetary disk that orbited the Sun as the result of a stochastic process of run-away accretion. Mars has many distinctive chemical features caused by its position in the Solar System. Elements with comparatively low boiling points such as chlorine, phosphorus and sulfur are much more common on Mars than Earth.  It also had a healthy atmosphere that cloaked it with clouds.

early Mars atmophere

Early Atmosphere of Mars

At this time Mars was just inside the habitable zone but on its outer edge, while Earth was a little outside of the inner edge of the zone itself.

mars earth hab zone

Early Positions of Earth and Mars in the Habitable Zone

Much of a planet’s history can be deciphered by looking at its surface, asking what came first, and what came next. For example, a lava flow that spreads out and fills a large impact crater is clearly younger than the crater, and a small crater on top of the same lava flow is younger than both the lava and the larger crater. This principle, is called the law of superposition, and other principles of stratigraphy (the study of the strata found in rocks) are used in determining the age of rocks and their strata such as are seen in mountainsides and canyons.

super strata 

Since there is no overturning, the rock at the bottom is older than the rock on the top by the Principle of Superposition.

 

The same methodology was later applied to the Moon and then to Mars.  Another stratigraphic principle used on planets where impact craters are well preserved is that of crater number density. The number of craters greater than a given size per unit surface area (usually a million km2) provides a relative age for that surface. This latter principle was used to figure out the age of Mars, but some look upon this method with skepticism.

martian crators

Large Crater Density on Mars

Assigning absolute ages to rock units on Mars is much more problematic. Numerous attempts have been made over the years to determine an absolute Martian chronology (timeline) by comparing estimated impact cratering rates for Mars to those on the Moon. Martian meteorites have provided datable samples that are consistent with ages calculated thus far, but the locations on Mars where these meteorites originated are unknown, limiting their value as chronostratigraphic tools.

Wednesday, February 22, 2012

First Civilization Part 1 Chapter 3

 

4450 Ma: 100 million years after the Moon formed, the first lunar crust, formed of lunar anorthosite, differentiated from lower magmas. The earliest Earth crust probably forms similarly out of similar material. On Earth the pluvial period starts, in which the Earth's crust cools enough to allow water accumulate in pools and streams.

pluvial earth

Pluvial Earth

4400 Ma: First known mineral, found at Jack Hills in Western Australia. Detrital zircons show presence of a solid crust and water.

oldest zicron2

Oldest Zircon form Jack Hills area western Australia

This is Latest possible date for a secondary atmosphere to form, produced by the Earth's crust outgassing, reinforced by water and possibly organic molecules delivered by comet impacts and carbonaceous chondrites (including type CI shown to be high in a number of amino acids and polycyclic aromatic hydrocarbons.

allen3CC

A Carbonaceous Chondrite Comet

late-heavy-bombardment

Late Heavy Bombardment

 

During the Archean Eon the Late Heavy Bombardment occurred (approximately 4100 Ma to 3800 Ma) during which a large number of impact craters are believed to have formed on the Moon, and by inference on Earth, Mercury, Venus and Mars as well was produced by comets and asteroids. This was caused  by the planetary migration of Neptune into the Kuiper belt as a result of orbital resonances between Jupiter. Gravitational disruption from the outer planets' migration would have sent large numbers of asteroids into the inner Solar System, severely depleting the original belt until it reached today's extremely low mass. This event is what may have triggered the Late Heavy Bombardment. This period of heavy bombardment lasted several hundred million years and is evident in the cratering still visible on geologically nearly dead bodies of the inner Solar System such as the Moon and Mercury.

moon early

The Early Moon

The oldest known evidence for life on Earth dates to 3.8 billion years ago—almost immediately after the end of the Late Heavy Bombardment.  Mars's two small moons, Deimos and Phobos both thought to be originally asteroids, are believed to have been captured by this time.

marsmoon

Mars and its two Moons

The first signs of life were showing up on Mars too.

Ordovician_Land_Scene

The Mid Noachian or Early Theakian Period on Mars

The Earth of the early Archean Eon (3,800-2,500 Ma) may have had a different tectonic style. During this time, the Earth's crust cooled enough that rocks and continental plates began to form. Some scientists think because the Earth was hotter, that plate tectonic activity was more vigorous than it is today. In contrast to the Proterozoic, Archean rocks are often heavily metamorphized deep-water sediments, such as graywackes, mudstones, volcanic sediments and banded iron formations. Greenstone belts are typical Archean formations, consisting of alternating high- and low-grade metamorphic rocks. The high-grade rocks were derived from volcanic island arcs, while the low-grade metamorphic rocks represent deep-sea sediments eroded from the neighboring island arcs and deposited in a forearc basin. In short, greenstone belts represent sutured proto-continents. About 3.5 billion years ago, the magnetic fields of Earth and Mars were formed.

earths_field_

The Magnetic Field of Earth

original Mars Magnetosphere

Mars Early Magnetosphere

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Tuesday, February 21, 2012

First Civilization Part 1 Chapter 2

 

 

After the formation of the sun the Protoplanetary disk formed the planets of the Solar System out of a disk-shaped mass of dust and gas left over from the formation of the Sun.

Protoplanetary-disk

The early formation of the solar system- from the Protoplanetary disk

 

The inner Solar System, the region of the Solar System inside 4 AU, was too warm for molecules like water and methane to condense, so the planetesmals that formed there could only form from compounds with high melting points, such as metals like iron, nickel, aluminum, and rocky silicates. These rocky bodies would become the terrestrial planets (Mercury, Venus, Earth, and Mars).
Early-Solar-System

Formation of the Planets

These compounds are quite rare in the universe, comprising only 0.6% of the mass of the nebula, so the terrestrial planets could not grow very large. The terrestrial embryos grew to about 0.05 Earth masses and ceased accumulating matter about 100,000 years after the formation of the Sun; subsequent collisions and mergers between other planetesimals  also formed by Protoplanetary disk allowed terrestrial planets to grow to their
present sizes.

proto-planet2

Planets forming from and among the planetesimals in the inner solar system.

 

However, one question is why did Mars came out so small compared with Earth ? Earth's Equatorial radius is 6,378.1 km and Mars' Equatorial radius is 3,396.2 km or 0.533 Earths.
 early Mars

Proto Mars

A study proposes that Jupiter had migrated inward about 1.5AU when Saturn formed, which means it moved into the area that would become known as the asteroid belt.

asteroid belt early

The early Asteroid Belt

The early Asteroid Belt would contain dry asteroids and water-rich objects similar to comets.  This means that Jupiter must have accumulated mass there at the expense of Mars then later Jupiter migrated back to its present position. Jupiter thus would have consumed much of the material that would have created a bigger Mars.

ig383-exoplanet-7-02jupiter sized

Proto Jupiter

During the Solar System's formation, Mars was created out of the protoplanetary disk that orbited the Sun as the result of a random run-away accretion. Mars has many distinctive chemical features caused by its position in the Solar System. Elements with comparatively low boiling points such as chlorine, phosphorus and sulfur that are much more common on Mars than Earth; these elements were probably removed from areas closer to the Sun.

proto earth2

Proto Earth

At about 4600 million years, the Proto-Earth formed at the inner hotter edge of the habitable zone of the Solar System. At this stage the luminosity of the sun was very high yet the size of the sun was small. Liquid water may have existed on the surface of the Proto-earth, probably due to the greenhouse warming of high levels of methane and carbon dioxide present in the atmosphere making it similar to a cross between modern day Venus and Mars. After another 3750 million years  during the Archean Eon, the Precambrian Super eon and Cryptic era start as the Earth–Moon system forms, possibly as a result of a glancing collision between proto–Earth and the hypothetical proto-planet Theia.

earth-moon formation

The Formation of the Moon

 

(The Earth was considerably smaller than now, before this impact.) This impact vaporized a large amount of the crust, and sent material into orbit around Earth, which lingered as rings for a few million years, until these rings condensed into the Moon. The Moon geology Pre-Nectarian  period started at that time.