What is this stranded silver ground wire in 40 amp circuit
Noting the irregularities in the way the strands are spiraled, that is certainly SE type cable, or &quot;Service Entrance&quot; cable.  Service entrances (weatherhead to main panel) are run hot-hot-neutral with no ground, so naturally, SE cable provides exactly that.  The bare wire is neutral, not ground.
Use of SE cable for ranges was legal in the 1970s, and as such, it is &quot;grandfathered&quot; today.  It is neutral, not ground, which means your range has a 3-wire ungrounded connection, also legal in the 1970s.
While it's grandfathered to the inspector, it is not grandfathered to the reaper.  3-wire connections have a fatal flaw: in this setup, the chassis of the range is bonded to the neutral wire.  If it  has a simple and common contact problem, it energizes the chassis of the range with lethal voltage when the oven light is on (i.e. door is opened).
When fatalities happen this way, it is reported by the press as miswiring which is untrue: it was wired correctly but neutral had poor contact. Which happens.
The new doctrine is to provide a separate ground wire; or; fit GFCI protection at the breaker.  Both of these solutions require removing the bad-news bonding strap inside the range that ties the chassis to neutral.
Merely removing the bad-news bonding strap is not enough; now the chassis will be energized by any ground fault (which grounding or GFCI would have detected).