The Population Reference Bureau says 107 billion.

It is an educated (wild) guess at best.  Records simply don’t exist for most of the world’s history.  We don’t know how fast people multiplied, what the birth and death rates were, and what effect unnamed wars and catastrophes had on population.  It is of interest, however, to note that in the human race’s earliest days, only 50% of babies survived.  Also that the Black Death regularly visited many areas of the world.  Black Death destroyed half of the Byzantine Empire in the 6th century—an estimated 100 million deaths.  Life expectancy at birth probably averaged only about 10 years for most of human history.

7.5 billion.  That says that only 6.5% of all people ever born are alive today.

Read Proverbs 8:22-31.  Among other things it says there that, “Before the    mountains were settled, before the hills was I brought forth.”  In other words, you’re older than the hills.  We were there when the Earth was created.  Additional Biblical scriptures showing our pre-earth existence include Rev. 12:7-9; Jeremiah 1:5; Hebrews 12:9; Acts 17:28-29; Eccl. 12:7; Romans 8:16-17; John 9:1-2; Job 38:3-7.  See also Moses 3:5.

The book of Moses in the Pearl of Great Price was translated in 1831.  The  Lord said in Moses 1:33-35, “And worlds without number have I created ... There are many worlds that have passed away by the word of my power.  And there are many that now stand, and innumerable are they unto man, but all things are numbered unto me, for they are mine and I know them.”

The first exoplanet (a planet outside our solar system) was first confirmed in 1992.

As of 1 August 2017, 3,639 have been confirmed.  Current thinking is that    every star probably has planets.  It is thought that 1 in 5 sun-like stars have an Earth-sized planet in its habitable zone.  That translates to perhaps 11 billion potentially habitable planets in our Milky Way Galaxy.  The nearest exoplanet is 4.2 light years away orbiting Proxima Centauri, the closest star to the Sun. Besides exoplanets there are also rogue planets known as sub-brown dwarfs not orbiting stars.  There are billions of sub-brown dwarfs in our Milky Way Galaxy.

Estimates are anywhere from 100 billion to 400 billion stars in our Milky     Way Galaxy.  There are perhaps 10 trillion galaxies.  If each galaxy contains      100 billion stars, the total number of stars in the universe would be a 1 with 24 zeroes behind it.

Most scientists are of the opinion that life on our planet came about by chance.  They’re not ready to accept the full import of the Lord’s simple statement in Moses 1:33-35.  What would intelligent life in those worlds look like?  Because of what we understand about the Plan of Salvation, we know that those worlds are inhabited by people who look just like us, and like their Father in Heaven.

The Earth rotates on its axis every 24 hours.  A person at the equator is       moving roughly 18.5 miles per second, or 1,000 MPH.

The Earth revolves around the sun every 365 days at a speed of 67,000 MPH.  Mercury and Venus, being closer to the sun, have to move considerably faster to maintain their distance from the sun.  Planets farther away from the Sun can go slower.  Some exoplanets are so near their stars that they complete an orbit in only a few hours.  Others are so far away that they take thousands of years to complete their orbits.

The Sun and the solar system are revolving around the center of the Milky Way Galaxy at a speed of 490,000 MPH.  A complete orbit takes about 200 million years.

The Milky Way Galaxy is hurtling through space at a speed of 1,350,000     MPH.

Church leaders thought that the Bible taught geocentrism, meaning that the Earth was the center of the universe, and that everything rotated around it.  Galileo realized that our solar system was heliocentric, meaning that everything rotated around the Sun.  They brought him before the Inquisition, and insisted that he recant his teachings.  That was in 1633.  He spent the rest of his life, 10 years, under house arrest for his rebellion.  Galileo was amazed at the stubbornness of church authorities who not only refused the evidences that he presented, but refused to even look through a telescope.  He said, “I wish that we might laugh at the remarkable stupidity of the common herd. What do you have to say about the principal philosophers of this academy who are filled with the stubbornness of an asp and do not want to look at either the planets, the moon or the telescope, even though I have freely and deliberately offered them the opportunity a thousand times? ... These philosophers shut their eyes to the light of truth.”

The peoples of the Book of Mormon had an understanding that surpassed that of the Europeans of the same time period.  They knew about planets (Alma 30:44), and they knew that the Earth moved (Helaman 12:14-15).  The Chinese were also far ahead in their understanding of astronomy.  And then there was Abraham.  The Lord showed him things that astronomers still don’t understand.  He was taught that everything revolves around Kolob, the star that is nearest to the throne of God.  He was shown these things so that he could teach the Egyptians.  (Abr. 3).

He was promised that if he was faithful, his posterity would be as numerous as the stars in the sky or as the sand.  “I will multiply thee, and thy seed after thee, like unto these (stars); and if thou canst count the number of sands, so shall be the number of thy seeds.”  (Abraham 3:14)  (Also Genesis 15:5; 22:17; D&C 132:30).

When Rebekah left home to become the wife of Isaac, “They blessed Rebekah, and said unto her, Thou art our sister, be thou the mother of thousands of millions, and let thy seed possess the gate of those which hate them.”  (Genesis 24:60).  One thousand million is one billion.  Thousands of millions would be equal to at least two billion.  She only had a set of twin sons.  But if you calculate when she lived, and allow that each descendant had five children, the total number of her posterity from then until now would be approximately two billion.  The promise given to Abraham was repeated to Isaac in Genesis 26:4.  “And I will make thy seed to multiply as the stars of heaven.”  Doctrine and Covenants 132:31 says that “This promise is yours also, because ye are of Abraham...”

“The Restoration’s revelations and translations accommodate a vast universe; thus it is no surprise to us that scientists’ latest estimate of the number of stars in the universe is approximately 70 sextillion—’more stars in the sky,’ scientists say, ‘than there are grains of sand in every beach and desert on Earth.’”  (General Conference, October 2003).  (His statement has since been updated by scientists who are quoted as saying “There are 5 to 10 more stars than there are grains of sand on all the world’s beaches.”)