### What was the Earth's mean temperature 3,5 billion years ago (3,5 Bya ) ?

**Lets see:**

** Sun's irradiating intensity was weaker. **

**It was only 75 % of the present,**

** S = 0,75*So**

** And Earth rotated twice as fast then,**

** 1 rotation in 12 hours. **

**Lets calculate:**

** Earth’s Without-Atmosphere Effective Temperature calculation Te.earth.3,5 Bya**

** So = 1.362 W/m² ( "So" is the present Solar constant )**

** Earth’s albedo: a earth = 0,30**

** Φ earth = 0,47 **

**β = 150 days*gr*oC/rotation*cal – is a Rotating Planet Surface Solar Irradiation Absorbing-Emitting Universal Law constant**

** N = 2 rotations /per day, was Earth’s sidereal rotation spin at 3,5 Bya**

** cp.earth = 1 cal/gr*oC**

** σ = 5,67*10⁻⁸ W/m²K⁴, the Stefan-Boltzmann constant**

** Earth’s Without-Atmosphere Effective Temperature Complete Formula Te.earth is:**

** Te.earth = [ Φ (1-a) So (β*N*cp)¹∕ ⁴ /4σ ]¹∕ ⁴**

** Τe.earth.3,5 Bya = [ 0,47(1-0,30)*0,75*1.362 W/m²(150 days*gr*oC/rotation*cal *2rotations/day*1 cal/gr*oC)¹∕ ⁴ /4*5,67*10⁻⁸ W/m²K⁴ ]¹∕ ⁴ =**

** Τe.earth.3,5 Bya = [ 0,47(1-0,30)*0,75*1.362 W/m²(150*2*1)¹∕ ⁴ /4*5,67*10⁻⁸ W/m²K⁴ ]¹∕ ⁴ = **

**Τe.earth.3.5 Bya = ( 6.167.274.722,0 )¹∕ ⁴ = ****280,23 K**

** Te.earth.3.5 Bya = 280,23 Κ**

** or Tmean.earth.3,5 Bya = 7 oC. **

**Conclusion: **

**3,5 billion years ago planet Earth had a sustainable for life mean temperature of 7 oC.**

** From Wikipedia: " Among the earliest fossil evidence for life is microbial mat fossils found in 3.48 billion-year-old sandstone in Western Australia,[63]".**